Home

Acoustic Triangulation Device - Department of Electrical

1. Signal reconstruction from a series of sampled values The reason why we want to reconstruct the signal out of the microphones is that we want to obtain the max amplitude max frequency min amplitude and min frequency that come out of the band pass filters MatLab will be programmed to do these tasks Also with the reconstructed signal we can then proceed to use more signal analysis m order to distinguish of which type of event has passed through our band pass filters Before we begin to explain the method we will be using for our type of gun detection it is important that we first explain what a sound wave actually is A sound wave is a traveling wave with an oscillation of pressure through air of frequencies within range and level of hearing The speed of sound depends on the medium temperature and elevation of which the wave is traveling not by the frequency or amplitude of the sound In air the speed of sound at sea level is approximately 343 m s Sound propagates through air as a longitudinal wave Longitudinal sound waves are waves of alternating pressure from the equilibrium pressure which cause regions of reduction in volume and density Type of gun detection In order to tell which type of gun was fired we must be able to compare the event gunshot s sound wave with a database of gunshots that we have previously recorded and stored We are not trying to reconstruct the original gunshot characteristics we would just be compa
2. To make certain that all of our wavelet transforms are comparable to each other all of our scales of our wavelet functions must be normalized to have unit energy The equation we will be implementing to do the normalization is as follows 1 2 7 yr sa UR Ur se Then after normalization each scale s has 25 with N being the number of points By using the convolution formula normalization of our functions to have unit energy can be done by n n t r Y n n t Wl W aL 5 5 5 Since in our design we have chosen to use the Daubechies wavelet function which is an orthogonal wavelet function reconstruction of the original time signal can be determined using deconvolution The very first step in process of different type of gunshot recognition by using the discrete wavelet transform will be to take our recordings of the various types of guns that we have shot eliminate all noises that do not pertain to the exact gunshot and then to normalize the gunshot signatures The reason that we will be normalizing these recordings is so that the volume of each type of gunshot does not affect our results After we do the normalizing process we will then proceed to do the discrete wavelet transform to each of the gunshot recordings The next step will then be to take each of the gunshot recordings and get the average of the coefficients We will then being the storing process on these discrete wa
3. 2D Hyperbolic Multilateration a hyperbola of possible locations b intersection of 3 hyperbolas B M di The point that is found after solving all the required equations is the relative location of the sound source with respect to the array In order to find the exact location a compass is still required Since we will know the locations of each microphone relative to the GPS unit in the array the orientation of the array given by the compass will give us the exact coordinates of each microphone The relative location of the source and the exact locations of the microphones can be used to calculate the exact location of the sound source The multilateration equations involved in finding the exact location of the source start with the distance rate time formula in the same manner as the triangulation equations The speed of sound C is the same formula as above relating to the temperature T C 331 5 606 x T The distance D in the distance rate time formula now represents the distance from a particular microphone to the sound source The time t now represents the time it takes for the sound wave produced by the sonic event to reach the particular microphone D C Xt The distance can be represented by the distance formula which uses the coordinate location of two points For the two dimensional case there are three microphones located at points A B and C which each have an x coordinate and a y coordinate The sound source al
4. 7 NSVn Satellite ID number ield N or S Direction of latitude 5 7 67 A typical NMEA 0183 string might look like lt CR gt lt LF gt MRK 0 lt CR gt lt LF gt ZDA 123336 8069 17 06 2001 13 0 lt CR gt lt LF gt GLL 4916 45 N 12311 12 W 225444 A DXCR LF VTG 218 7 T 2 38 H 0 18 V lt CR gt lt LF gt SGD 1 0 G 1 0 M lt CR gt lt LF gt SYS 3T 9 lt CR gt lt LF gt ZEY 0 28745E 006 lt CR gt lt LF gt NSV 2 00 000 00 0 0 00 0 00 00 D lt CR gt lt LF gt NSV 7 00 000 00 0 0 00 0 00 00 D lt CR gt lt LF gt NSV 28 00 000 00 0 0 00 0 00 00 N lt CR gt lt LF gt NSV 1 00 000 00 0 0 00 0 00 00 D lt CR gt lt LF gt NSV 13 00 000 00 0 0 00 0 00 00 D lt CR gt lt LF gt NSV 4 00 000 00 0 0 00 0 00 00 N lt CR gt lt LF gt NSV 25 00 000 00 0 0 00 0 00 00 N lt CR gt lt LF gt NSV 0 00 000 00 0 0 00 0 00 00 N lt CR gt lt LF gt NSV 11 00 000 00 0 0 00 0 00 00 D lt CR gt lt LF gt NSV 0 00 000 00 0 0 00 0 00 00 N lt CR gt lt LF gt amp For a complete description of NMEA codes see the appendix Shown below is a portion of the block diagram for the ATD that displays the interconnections between the EM 408 and the Arduino Mega Figure 5 3 1 VCC Arduino Mega EM 408 GND 3V3 TX RXO The EM 408 can transmit an entire NMEA message every second which is more than adequate for a stationary device such as the ATD Additionally it is accurate to within 5 meters which closely matches the ATD s specific
5. string types may include gunshot explosion or being more specific such Position position as the caliber or decibel and frequency level of the signal An getPosition int event who s mother wave cannot be found in the wave database getType string will be termed unclassified This may be changed later by the user The position variable contains the origin at which the event occurred This will be a pair of GPS coordinates that have been i multilaterated by the ATD Each GPS coordinate is stored as an integer named either latitude or longitude in the position class longitude int The class Event will have two functions as well getPosition getLatitude int and getType which return the respective position and type of getLongitude int the wave Note the position class has similar functions to retrieve the latitude and longitude of the event The Wave class contains digital information about the analog wave that was received by each of the speakers and can be thought of as a three dimensional version of the wave The analog to digital voltage int 6000 converter on board the Arduino mega will provide ime int 6000 information about the wave in samples and this information must be store in one variable to be useful The wave class has six sub variables voltage frequency amplitude type and timeofArrival The variable 1s an integer array that contains each voltage received per sample and as the ATD mus
6. The software will be designed to install and run in a Microsoft Windows environment The ATD is designed to be scalable Additions that can be incorporated may include but are not limited to a video surveillance unit that vectors to the source location a Digital Signal Processing DSP unit to analyze and distinguish between types of events simultaneous multiple shot recognition and solar charging capabilities The video surveillance will consist of a linear control system that actuates towards the source GPS location and zooms in to a proper magnification based on the source distance The DSP will be used as described in Chapter 4 Sound Detection to compare an event to a database of event wavelets and provide information about the source to the user such as gunshot type or signal attenuation Simultaneous shot recognition would use the DSP to allow the ATD to separate multiple sources from multiple directions and relay all of the source locations simultaneously to the user Solar power would allow the unit to be rapidly deployed in obscure locations It would eliminate the need for an infrastructure to run the unit making it a convenient choice for military applications It will require further investigation to successfully integrate all of these additions Section 2 Motivation Our combined knowledge of microcontroller programming signal analysis and software design proved the ATD to be the perfect project for our group Our main motivat
7. The sensors may detect a new value from a sensor for example a new temperature If there is a new temperature detected by the thermometer the screen will be updated with the new value and the new speed of sound will be calculated and stored The sensors may also detect a sonic event which will trigger the multilateration process Based on the user s chosen preferences the resulting calculated location will be displayed and or sent appropriately Figure 6 1 c shows a data flow diagram of the ATD This diagram shows the storage and transmission of data throughout the ATD The sound data is initially received by the microphones It is then sent through the pre amp to be amplified After being amplified the sound is then sent to the filter to eliminate any sounds with a frequency outside of the frequency range of a gunshot This filtered sound is then used by functions that find its amplitude frequency and time of arrival The amplitude and frequency are then used by the wavelet analysis functions which will then send gunshot type information to the connected computer The temperature data will be received by the thermometer and the used by a function that calculates the speed of sound The coordinate data from the GPS and the directional data from the compass will be used by functions that locate the individual microphones The time of arrival information along with the calculated speed of sound and the microphone locations will be used by the multilat
8. increased significantly if we do not get the exact temperature reading of the environment that the ATD is in The DS18B20 has an incredibly high accuracy in temperature measurement in the environments that we will be designing it for We will be programming the Arduino microcontroller to be taking a temperature measurement every ten seconds The reason for taking so many measurements 1s that we need this to be as accurate as possible 71 Chapter 6 Software Section 1 Overview The software for the ATD will have several main functions including functions to get the amplitude frequency and time of arrival of the sound wave Determining the event type and using triangulation to obtain the signals GPS coordinates will also be integral parts of the ATD software The purpose of the software is to receive the event sound wave signal convert it from analog to digital and then process the digital signal to determine what type of wave it 1s what the source might be and where it is coming from The Arduino Mega provides a large supply of software support from the manufacturer and can easily be programmed in C or C The class libraries for accessing the analog digital and UART ports are all provided from the Arduino website and information can be transmitted and received with no more than one or two lines of code on average The analog signal coming into the Arduino Mega from the microphones break out board will be sampled at 1 MHz and in each of th
9. P Cm Cu Cn I 0 5 0 05 LU 005 51 O15 02 025 O38 U 35 UA O46 Normalized Frequency Below is a figure of the Bode Plot of the 223 caliber round This figure is a visual representation of the 223 caliber sound wave s Bode Plot using the Audacity software As you can see in the Bode Plot figure the peak frequency is at 630 Hertz and its magnitude at this specific frequency is 3 dB Also it is to be noted from this figure that the max amplitudes of the of the 223 caliber sound wave occur in the frequency range of approximately 350 Hertz to around KHz Bode Plot of 223 caliber 36 Figure 4b 7 B Frequency Analysis 10 dB 0 dB 10 dB 20 dB 30 dB 40 dB 50 dB 0 dB T0 dB BD0 dB 86Hz 1r4Hz 47Hz 691Hz 1KHz aKHz BKH Z 11KHz Cursor 623 Hz D 5 30B Peak 630 Hz D5 Spectrum T Epot Hanning window Loa frequency Close Figure 4b 8 Time domain representation of the 223 caliber round 3 wt E LE x dile Lee Yew Pret Gererste Ereg Anseye yie Set T S E K 5 P b pw wp 0 Sey 210 S H lri DPA A 7 70 f E 7 50 3 00 3 10 La E53 8 40 50 bo 8 76 E d c A med Chick anc drag ts sete ct ack Teowmci uam 44122 Curse O87 800644 in aec Dup Te Of 37 9 mm Kel Tec PF 9 Spectrum of the 9mm Kel Tec The figure below is the waveform of the 9 mm caliber round of the Kel Tec PF 9 This figure is a visual representation of our recorded
10. accuracy without a higher price or degree of complexity The Atmel SAMO is easy to use and allows for USB or RS232 connections to the PC The JTAG connector would allow for easier testing and provide for a smoother design process overall but provides no extra benefit to the end user It is an excellent example of the variety of development boards on the market and provides a good data point for our design Other than this the SAMO is not especially useful for any type of acoustic triangulation device 66 Section 3 GPS The Global Positions System GPS will be used to determine the exact coordinates of the ATD in order to provide a reference frame for calculation There are many varieties of GPS available with a range of strengths and weaknesses but only one that fits the requirements for the ATD and has the combined advantage of compatibility with and support for the Arduino Mega development board The EM 408 is a relatively inexpensive GPS unit based on the Sirf Star III chipset a chipset used in most commercial GPS products Some of the features of the EM 408 which make it an excellent choice for the ATD include e Extremely high sensitivity 159dBm e 5m Positional Accuracy e Cold Start 42s e 75mA at 3 3V We will be using the 3V3 output on the Arduino Mega e 20gram weight e Outputs NMEA 0183 binary protocol The NMEA 0183 binary protocol is an ASCII serial communications protocol that will be used to define how data will be tr
11. based on its relationship with 0 as shown in figure 3 2 below 0 oe 52 Q4 0 30 These equations again should work regardless of the orientation of the array There are still two locations that the source could come from one on each side of the line which connects the first and second microphones The third microphone again tells us that the source came from the opposite side that it is located The top view and the side both use the same equations with the exception of the value for the speed of sound This allows for the simultaneous solving of the two equations which gives the values for the angle a and the angle a2 The angle a2 which is based on the top view must be normalized based on the reading from the compass The angle a which is based on the side view must be normalized to find the vertical angle with respect to the eround These angles for each array can then be used to find a distance and direction and therefore an exact location in a similar way as in the two dimensional case This exact location however will also take into account the elevation of the source of the sonic event 16 Figure 3 5 3D Triangulation a Side view single array b Top view single array Q ND eel ree c View with both arrays 17 Chapter 4 Sound Detection Section 1 Signal Analysis We reconstructed the signal out of a separate microphone attached to the computer using MatLab The sampling theorem states t
12. long term stability low noise and flatter frequency response Directional characteristics of Microphones For our design we will be implementing an Omni directional microphone The Omni directional microphone captures the sound in 59 all directions which is ideal for our project There are many types of directional properties but four our design we need to pick up the sound in all direction Figure 5 1 2 Directions of microphones Omni directional Cardioid Hypercardioid Figure 5 1 3 Typical Microphone Frequency Response for a vocal microphone i H T SE E Le IC dB s 6 5680558 582888355 1 ar Frequency Cycles per Second Note A higher response means that the frequency will be exaggerated and a lower response means that the frequency will be attenuated A frequency response curve that 1s uniformly sensitive in all frequencies will be a flat response curve ideal The reasons why we chose the condenser microphone for our design is as follows 1 Hlatter frequency response 2 High sensitivity 3 Excellent transient response 4 Stronger signal 5 Lightweight 60 Microphones researched The following microphones were among the top choices for the ATD Characteristics of Knowles MD9745APZ F e Lightweight Very small E High Sensitivity Excellent S N ratio Affordable The reason why we were interested in this microphone during our research phase was because for
13. of 44 Magnum The figure below is of the frequency spectrum of the 44 Magnum round This figure is a visual representation of the frequency spectrum of our recorded sound wave using the Matlab spec function in DSP tools library Notice from this figure at around 0 normalized frequencies the magnitude is at around 2 6 At around 0 015 normalized frequencies the magnitude 1s around 2 4 magnitude At around 0 0266 normalized frequency as you can see from the plot the magnitude is maximum and is approximately 4 47 Higher normalized frequencies than 04 begin to decrease in the plot and become minimum of approximately 0 magnitude at around 0 15 normalized frequency These are the most important characteristics of the spectrum of the 44 Magnum 50 Figure 4b 26 Figure 1 el ES File Edit View Insert Tools Desktop Window Help E DSR RIS SI lED EMIS G spectrum 44mag wav 4 5 35 r L in La Magnitude Cn 0 5 0 05 O05 mi Di 02 025 OS O55 04 Normalized Frequency Bode of 44 Magnum Below is a figure of the Bode Plot of the 44 Magnum round This figure is a visual representation of the 44 Magnum sound wave s Bode Plot using the Audacity software As you can see in the Bode Plot figure the peak frequency is at 1148 Hertz and its magnitude at this specific frequency is 3 dB Also it is to be noted from this figure that the max amplitudes of the of the 44 Magnum s sound wave occur in the frequency range
14. of the ATD fun and exciting and while working on the ATD we have learned quite a lot We have learned about things such as triangulation multilateration signal analysis filtering and how each of the different components needed for the ATD to work I believe that this semester the designing processes overall went very well and that we worked incredibly hard to get this design completed We believe that with our vast research and time spent towards during this semester that the ATD was a successful project One of the things that we wish we could have done with our ATD design 1s to be able to have it be wireless If we had more than one semester to build our prototype we would have implemented wireless capabilities If time was not an issue we also would have designed the ATD to be able to work while moving We would have liked to be able to add a camera to our prototype to video the location that the ATD has detected for a gunshot event The version of the ATD presented in this paper is best suited for high profile events such as political speeches The unit is portable and easy to calibrate and set up quickly It 1s durable enough to withstand the packing and unpacking from storage but 1s not suited for extended outdoor use It can locate targets accurately at a limited distance of 400 meters and as such is suited for the speech setting It must be powered by and used from a computer or a laptop which will be readily available at such events T
15. off will be important to balance The ATD is intrinsically less accurate than the GPS it uses to determine its own position This is due to two main factors First the GPS satellites surround the source which in our case is the GPS unit itself This makes the GPS triangulation calculations simpler and more accurate than the ATD which is at a single location outside of the source This is discussed in further detail in Ch 3 Triangulation Theory The second is that the GPS satellites are thousands of kilometers apart yet the ATD unit s satellites microphones are within a meter of each other Cost The ATD must be low cost in order to be effective This would allow many ATD units to be spread across large areas such as cities or military encampments at a reasonable price Additionally singular units should be affordable to private owners who may only need small areas of coverage A good metric for the affordability of a unit may be its price per cubic foot of coverage The cost of production will be largely determined by the GPS and Microcontroller As shown above the ATD is intrinsically less accurate than the GPS and as such the error due to using a less expensive GPS is negligible in comparison to the error in the ATD unit However we would like to minimize the ATD error and so where we will use an inexpensive GPS we must use relatively expensive microphones and a high frequency processor to take samples The higher sample rate will let us pu
16. our design we require the microphone to be able to have an operating voltage of 3 3 Volts We will be powering the microphones from the microcontrollers 3 3 or 5 Volt power supply The Knowles MD9745 also met our specifications for being able to operate in our temperature environment Since our goal of the project is to detect a sound wave in the 300 to 3 KHz frequency range this specific microphone met the requirement Below is a table showing the specifications of the Knowles MD9745APZ F with test condition Vs 2 0 V RL 2 2 k ohm Ta 20 C RH 65 This microphone has a high sensitivity it has a minimum sensitivity of 46 and a maximum of 42 It has an operation temperature of 25 to 55 Celsius The frequency range for this microphone 19 in the 100 to 10 KHz frequency range This frequency range is perfect for what the ATD requires Table 5 1 4 Specifications of Knowles MD9745 APZ F Item Symbol ELM Minimum Maximum Units ELM Sensitivity S Operation Tope EV lemperature Range Max Operating Voltage SINRatio SIN L Emme R Consumption E Range m OMNI DIRECTIONAL 61 Below is a Bode plot of the frequency and sensitivity of the Knowles microphone As you can see at higher frequencies the response becomes curved which means that the microphone is not equally sensitive to all frequencies Figure 5 1 5 Frequency Response of Knowles MD9745APZ F Characteristics of Panason
17. s sound wave occur in the frequency range of approximately 350 Hertz to around 800 Hertz All of the data we have taken will allow us to be able to distinguish between types of gunshot events We will be taking these signals that we have obtained and use our designed wavelet transform on them We will then be storing the information we have received from the wavelet characteristics With this wavelet information we will then be able to compare our event wavelet to our stored data in order to best compare the type of event that the ATD has detected 57 Figure 4b 35 e 8 Frequency Analysis Cu reor 562 Hz C5 3 dB Peak 566 Hz C 5 Spectrum 512 I Export Hanning window ka Log frequency Close EN ange Ede Echt Ven prave lararabs Effect Anaise Hdp L ILI lt R R 47 re M m 3i 0 ai WM IB ds 1 00 1 30 1 06 Lick wed Zrag iz ket muds Prec aee diih D eg 0 571 ER mp aa Te CTR 58 Chapter 5 Component Specifications Section 1 Microphones A microphone is a transducer that converts sound into electrical signals Microphones are described by their transducer principle directional characteristic and diaphragm size The microphones diaphragm is the thin disk that vibrates from incoming sound waves and produces an electric signal This current from the microphone is very small and requires amplification to be used in appli
18. some of the fabrication options the Arduino Mega lends itself to In the Arduino Mega Block Diagram in the appendix you can clearly see all USART inputs on the right side as well as the ADC inputs on the top Each input will correspond to a register in the device making data from the peripherals easy to access As a short example the output of the GPS connects to the input of USART 0 The 8N1 signal from the GPS is transmitted at 4800 baud into a register discussed later Inside the register we will find an 8 bit ASCII string as NMEA dictates from which we will be able to ascertain the latitude and longitude of the device The number of rising edges of the clock between when the first and second analog signals are processed through the ADC Port K above will be used to determine the angle of attack of the sound wave and the clock difference between the first and third analog signals will complete the calculation by providing us with a distance as described in Chapter 3 Triangulation Theory The ATmegal280 will then compute the absolute position of the acoustic event and transmit that location via USB Not shown above to the user s computer where a software that fits the philosophy of use of the ATD will take over BeagleBoard Listed Features e 600MHz superscalar ARM Cortex A8 processor Over 1 200 Dhrystone MIPS Up to 10 million polygons per second graphics output HD video capable C64x DSP core 128MB LPDDR RAM 256MB NAND Flash I2C DS SPI M
19. the battlefield is a constantly changing environment In a situation like Washington DC s beltway sniper in 2002 we might want the unit to be small enough to be concealable Where you would want a criminal like this to know the ATD exists you wouldn t want him to know where they are and therefore be able to avoid or disable the unit A similar unit could be used to prevent gang violence and unlawful gunfire within city limits Durability The ATD must also be durable enough for its philosophy of use Returning to the speech scenario the unit should be able to survive constant handling and the abuse of travel Packing and unpacking the unit should not change its dimensions in the slightest way Any dimensional change in the unit will cause it to be increasingly inaccurate For the battlefield scenario the need for durability is apparent Even in an armored vehicle the unit may be subject to vibration and shock If the vehicle is jarred or turned over suddenly the unit should still be able to function The unit must be water resistant and heat resistant to cope with extreme outdoor environments This applies to all scenarios where the weather will be unknown including the urban scenario described above Ease of Use The ATD must be easy to set up and use It might seem that a preliminary set up would include leveling the units to the millimeter aiming them in the correct orientation also to the millimeter spacing each array to an exact spec
20. these components will be combined to produce the acoustic source s GPS coordinates which will then be displayed on screen Each microphone will hear the event at a different time The event will trigger the microphones to produce a current which will be amplified by a breakout board to a voltage described in Chapter 5 Section 1 Microphones The microcontroller must be able to accept at least four of these analog inputs and convert them into a digital signal This will require the microcontroller to have multiple independent analog to digital converters ADC The digital signal may then be processed to provide event information such as frequency and decibel range as well as the time of arrival The GPS unit described in Chapter 5 Section 4 uses a standard called NMEA 0183 National Marine Electronics Association This standard outputs an 8N1 8 bits no parity 1 stop bit serial signal at 4800 Baud This signal is described in further detail in Section 4 and for now it is sufficient to know the Microcontroller needs at least one 8 bit serial input The USART input on most microcontrollers seems to satisfy this requirement Once calculated the microcontroller must upload the GPS coordinates to the host PC and then continue listening Preferably the microcontroller would send and receive data via USB It is an added bonus if the microcontroller can power itself through USB as well We will avoid the RS232 standard as most modern PC s do not have this inpu
21. 0 04 0 0 Magnitude 0 02 0 005 0 0 005 0 01 0 015 0 02 mms 0 03 0 035 0 04 0 045 Time s 12 Gauge Shotgun Spectrum The figure below is of the frequency spectrum of the 12 gauge shotgun This figure is a visual representation of the frequency spectrum of our recorded sound wave using the Matlab spec function in DSP tools library As you can see from this figure the frequency axis has been normalized Notice from this figure at around 0 normalized frequencies the magnitude is max at around 5 At around 0 013 normalized frequencies the magnitude has another maximum at around 4 15 magnitude At around 0 05 56 normalized frequency as you can see from the plot the magnitude 1s approximately 0 77 In the region of 0 05 normalized frequencies the signal begins to decrease Figure 4b 34 Figure 1 ID x File Edit view Insert Tools Desktop window Help d D hel SS amS E 0 TUS S spectrum shotgun waw Magnitude 0 05 U 00s 0 1 BE we RES O25 O35 0 35 0 4 Mormalized Frequency Bode Plot of 12 Gauge Shotgun Below is a figure of the Bode Plot of the 12 gauge shotgun This figure is a visual representation of the 12 gauge shotgun sound wave s Bode Plot using the Audacity software As you can see in the Bode Plot figure the peak frequency 1s at 566 Hertz and its magnitude at this specific frequency is 3 dB Also it is to be noted from this figure that the max amplitudes of the of the 12 gauge shotgun
22. Chapter 1 Executive Summary Section 1 Brief Project Description The Acoustic Triangulation Device ATD is an electronic system designed to detect the location of a sonic event specifically gunshots or explosions and relay that location in real time to the user Its main subsystems include but are not limited to a microphone array GPS locator and real time triangulation software These systems will work together to determine the origin of any sonic event within a predetermined frequency range This relative location will be translated into GPS coordinates and relayed a desired remote device As will be shown the philosophy of use is broad and the device will prove useful in a variety of applications Each microphone array consists of four microphones in a pyramid configuration The spacing and relative position of each microphone will be discussed in further detail in Chapter 3 Triangulation Theory The microphones will be connected to a central timing unit that will measure the exact time that each microphone detects a valid event The accuracy of the unit highly depends on the speed of our clock and the geometry of the array Both the geometry of the pyramid and the arrival time of the events will be used by the triangulation software to calculate a unit vector in the direction of the event s origin A second array will simultaneously time the event and the two calculated unit vectors will intersect at the acoustic source A Global Posi
23. Equations for the discrete wavelet transform W j k 2 V V x 27 y 27 n k In the above equation V is the mother wavelet This mother wavelet is a representation of a function in time with a finite energy This mother wavelet also has a fast decay time The discrete wavelet transform can be computed using an extremely quick pyramidal algorithm This pyramidal algorithm allows the signal to be analyzed in different octave frequency bands and it allows different resolutions by decomposing the signal in coarse approximations and detail information This decomposition as mentioned above is done by using the high pass and low pass filtering of the time domain signal Yuan Lk gt x n e 2k n Vin k 5 x n h 2k n Where Y k are the outputs of the high and low pass filters after the down sampling of a factor of two The wavelet coefficients represent the energy of the signal in the time and frequency These coefficients can be represented by using different techniques such as by taking the ratios of the mean values between adjacent sub bands in order to provide information on the frequency distribution Other techniques such as by taking the mean value of the coefficients in each sub band can also provide information on the frequency distribution In order to get the change in frequency distribution we must take the standard deviation in each sub band For our design purposes we will be comparing the coefficients of the wavelet transforms
24. GPS AM FM radio Background One of the main functions of the ATD is its ability to discriminate between acoustic events and ambient sound as well as determine and classify the type of event it heard The ATD will use wavelet analysis to analyze the gunshot and find the best match to a mother wavelet in a gunshot database Wavelet analysis is described in further detail in Chapter 4 sound detection Preparation Use Matlab to calculate the wavelet function for each of the eight gunshots Observe the frequency response plots in Chapter 4 sound detection and answer each of the following A Which guns have the most similar wavelets Which have the most dissimilar B What effect do you think this will have on the ATD signal classification C Which wavelets do you think will be the easiest for the ATD to triangulate Why D Which wavelets will be the hardest to triangulate Why E What effect if any do you think ambient sound will have on the ATD accuracy Why Experiment 1 Set up the Remington 870 and external GPS at a distance of 100 meters due north of the ATD Make sure the ATD and shotgun are at the same elevation Orient the ATD so the digital compass arrow faces due north Fire three shots from the shotgun Compare and record the external GPS and ATD results 2 Repeat part one for the Remington 870 Taurus PT1911 Bushmaster AR 15 AK 47 44 Magnum Berretta M9 Ruger Blackhawk 38 Ruger 22 and Kel Tec PF9 3 Pick one
25. MC SD capabilities DVI D and S video video output JTAG SD MMC socket 3 5mm stereo in out 65 The BeagleBoard is by far the most powerful and versatile of the three boards It has a 600Mhz processor which would allow for pinpoint accuracy almost regardless of microphone spacing Both USB and RS232 input output are available making it useable with practically any PC The TMS320 C54x DSP would allow for expandability if the ATD was to be modified to allow for event classification and discrimination Sufficient digital signal processing could literally allow the ATD to tell what round was fired and in what direction Additionally the beagle board has a DVI video output which would allow the ATD to be entirely standalone A touch screen display could be connected to the microcontroller allowing the user to triangulate sonic events independent of an external computer Atmel SAM9 L9260 Listed Features e MCU ATIISAM9260 16 32 bit ARM9TM 180MHz operation standard JTAG connector with ARM 2x10 pin layout 64MB SDRAM 512MB NAND Flash seen in Linux as silicon drive Ethernet 100Mbit connector USB host and USB device connectors RS232 interface and drivers SD MMC card connector One user button and one reset button One power and two status LEDs On board voltage regulator 3 3V with up to 800mA current single power supply 5V DC required 18 432MHz crystal on socket The Atmel SAMO is supported by an ARM9 180MHz processor giving the ATD a high degree of
26. act location of a sound source Each array will give us an angle which tells us the direction of the source Using these two directions and the known distance between the two arrays we can determine the sound source s location If the microphones are close enough together and the sound source is sufficiently far away we can assume the sound wave approaches as a straight line perpendicular to the line originating from the source We can then find the distance Ax in figure 3 4 below using the distance rate time formula where the distance is Ax the rate is the speed of sound C and the time is the difference between the time of first detection and the time of second detection tg ta AX S x tp t4 The speed of sound C changes in relation to the temperature of the air Other factors can affect the speed of sound such as the barometric pressure and humidity however 12 these factors are insignificant in comparison to the temperature The temperature T 19 measured in C C 331 3 606 x T Knowing the distance Ax and the side of the array S we can find the angle 0 using trigonometry Then we can find the angle a based on its relationship with 0 as shown in figure 3 4 AX1 0 cos 2 Q1 0 30 These equations will work regardless of the orientation of the array therefore the times ta and tg will always be the time that the first and second microphones detect a sonic event respectively Based on the
27. airly simple to design a graphical user interface Below is a picture of the Processing IDE Figure 6 2 a Processing IDE sketch aprz8a There are several menu options in the ATD gui The first option is Train New Event Type This option puts the ATD in a mode that will record the next event it detects and add it to the database with a name of the users choosing The second option is to arm the ATD for normal use This will allow the ATD to start detecting events and display them to the screen when they are found The map that is shown is the location of the event displayed with Google Earth The Get Map function will save the displayed map for archival purposes Below is a picture of the user interface after having found an event 76 Figure 6 1 b User Interface IS Ballistic Event A oustic So File Action Train New Event Type Arm Q Get Map T a S IS A gt l aa i i 2010 Europa Technologies gt 281360 1 33 An Si OW eler 64ft l Eve alt GO Section 3 GPS The EM 408 GPS uses the NMEA standard output string to output data In order to read this data a C program can be written to extract that output and make sense of it The data is then transmitted from the Arduino board through the serial port to the computer This GPS data will also be used internally along with the compass data to store the exact location of each microphone This data about each microphone s position will be
28. ally converted signal will be divided by the signal time duration and this solution will be stored in the wave class as the waves frequency Once the frequency of the digital wave is calculated and stored in the appropriate wave class variable all waves outside a threshold frequency will be dumped again saving memory Each time an event makes it passed the main filter the amplitude of the signal and time of arrival is stored into the same wave class variable described in Chapter 6 Software These amplitudes are sent to the event determining subroutine where the audio signal will be processed to provide valuable feedback for the user Each of the arrival times and the corresponding analog inputs are then sent to the triangulation subroutine for analysis In addition to the main filter the final design may include pre filters designed to lighten the load of the Arduinos analog sampling If a signal is outside of a certain plausible range for an event there is no point in the Arduino wasting a sample on that event As such we would like to filter the signal before it gets to the Arduino but after the signal has been amplified by the preamps on the breakout board Note the breakout board s internal capacitance does not significantly generate signal cutoff in the ranges the ATD 1s designed for These filters will be physical bandpass RC filters and the allowable band will be 200 3100 Hz allowing some room for physical error To the right is the current p
29. ansmitted from the GPS talker to the Arduino Mega listener It transmits eight data bits no parity bit and one stop bit 8N1 at 4800 baud Each message s starting character is a dollar sign The next two characters identify the talker followed by three characters for the type of message The remaining data fields are delimited by a comma Two commas in succession denote that data is missing The first character following the last data field character is an asterisk The asterisk is immediately followed by a two digit checksum representing a hex number The checksum is the XOR of all characters from The stream ends with lt CR gt lt LF gt Shown below is a chart displaying the various fields of a NMEA 0183 string Note fields two and four provide the ATD with its reference locations in latitude and longitude The ATD software must be able to translate these into the appropriate coordinate system for the intended philosophy of use Additionally the EM 408 doesn t provide any information about orientation unless the unit is moving As the primary use of the ATD is as a stationary unit the GPS will have to be augmented with a digital compass to provide a complete sonic event coordinate set Table 5 3 1 o Start Character ZDA hhmmss ssss dd mm yyyy UTC of position fix yyyyy yy Latitude in degrees minutes 4 3 4 lyyyyyyy Longitude in degrees minutes 5 orW Direction of longitude 6 NSV
30. ations It s low cost 1s well within the budget for the ATD Finally there is almost limitless support for the EM 408 including the Arduino Mega development board interconnect shown above as well as some open source subroutines that may serve useful when coding the ATD s multilateration algorithms 68 The EM 408 can start up in three modes cold warm and hot If the GPS is being turned on for the first time or has moved more than 60 miles since its last satellite feed the unit will start cold This means the EM 408 cannot predict which satellites are overhead and must reestablish connections with them at random The EM 408 has a 42 second cold startup time much faster than other units which lends itself to the fast setup time needed on the ATD For setup times it is assumed the unit will start cold and this 42 second specification is the one that will be used throughout the remainder of the paper Section 4 Compass To properly identify the acoustic events location we must be able to reference the direction the ATD 19 facing Without a compass the device could tell you it s postion and how many degrees off of each microphone line the even was but not the direction of the microphone line and thus not the true direction of the event A compass must be used to relay to the ATD which direction is north and the ATD can then combine this with its GPS coordinates to establish a reference frame for the multilateration calculations The HMC 6352 i
31. be detecting from the 223 caliber round As you can notice from the above figure of the 45 caliber round s sound wave and that of the 223 caliber round the sound waves are completely different This will be an important characteristic in event discrimination Figure 4b 5 Figure 1 II XJ File Edit View Insert Tools Desktop Window Help N D c Mell Em IDIi s oo Binary Data arl15 wav 1 Afs 0 6 0 4 0 2 i Magnitude 0 2 0 4 0 6 08 1 S 1 J S 4 5 E 7 x 10 Time ei Spectrum of the 223 caliber The figure below is of the frequency spectrum of the 223 caliber round This figure is a visual representation of the frequency spectrum of our recorded sound wave using the 35 Matlab spec function in DSP tools library Notice from this figure at around 0 01 normalized frequencies the magnitude is max at around 4 6 At around 0 02 normalized frequencies the magnitude is around 1 4 magnitude At around 0 3 normalized frequency as you can see from the plot the magnitude was approximately 1 These characteristics of the 223 caliber in our plots are extremely important because we will be comparing these characteristics of each gunshot recording to an event gunshot in order to best compare which type of gunshot has been fired Figure 4b 6 Fiqure 1 OO File Edit View Insert Tools Desktop Window Help d Deh R amp AE uw mE s n spectrum ar15 waw 4 5 Magnitude bi DJ Cn
32. cation There are many different types of transducer principles for microphones however for our project the only types of microphones we are interested in are the two most common dynamic and condenser Figure 5 1 1 Diaphragm Waves V s ixl B e unn CP Audio Signal Dynamic Microphone Dynamic Microphones function by using the electromagnetic principle When there is relative motion between a magnet and a coil of wire current is produced along the wire The diaphragm is connected to the coil when it vibrates due to the sound waves the coil moves which creates current along the wire Dynamic Microphones are very basic and have very few parts to them They are very sturdy resistant to moisture and do not break easily which would be ideal for our project Dynamic microphones require no external power which also would benefit our design since we need multiple microphones per array Condenser Microphone Condenser microphones operate by using a capacitor to convert acoustical energy into electrical energy The front plate of the capacitor Diaphragm 19 a very light material and when vibration occurs the capacitance changes which creates a charge or discharge current depending on the distance apart from the plates Condenser microphones require an external power source Because of this power source condenser microphones have a much stronger signal than the dynamic microphones Condenser microphones have high sensitivity
33. correct position on the said map The wave sound will also be provided to the user in wav format so that they may intuitively be able to verify the information the ATD is providing them with and reclassify the acoustic event as necessary Note reclassifying wave events will effect the functionality of the ATD and must be presented only as an advanced option for the user Once the process is complete the user will be given the option to save the event which will save the map image wave file longitude and latitude into a single folder or send the event via email or other medium to the correct authorities The user may also view all events stored of the current area on one map to reveal event patterns There will be search options which would allow the user to search by area event type or event frequency allowing the user pull up information such as which locations have the most gunfire When the processing is complete the ATD returns to listening mode once again Additional options for scalability will include and LCD display on the unit which will display the latitude and longitude of the event as well as the type Also the unit may have a keypad as indicated in the additional parts section of the budget This coupled with a power source solar battery other will allow the unit to be standalone and only raise the price by a little under 100 The current version of the ATD is a prototype which most likely will not be standalone and as such the ab
34. crophone we will be building up to eight filters We want each filter to be as close to an exact match as possible and be as simple as possible to build The filter design that we will be implementing is as follows The figure below is of a second order band pass multi loop filter with no positive feedback In the figure V1 corresponds to the microphone The values for the capacitors and resistors were computed by using a design process with the Center frequency at 1350 Hz Quality Factor of 0 5 and Mid Band Gain of 0 4 For our band pass filter we will be using the LM 358 operational amplifier The design process for the values of the resistors and capacitors are as follows Figure 4 3 4 Second Order Band Pass Multi Loop filter with no positive feedback Multisim Circuit2 L File Edit View Place Simulate Transfer Tools Options Hel D el el 22 afm spen bz a C2 R5 1 18kOhm 196 U1 R4 c1 x 5900hm_1 R6 5 90kOhm 196 7111 5 as mg ofl Ready Tran 0 024 s NUM 2 With Capacitors equal to 0 1 uF and Wo in radians per second The figure below shows the typical response of a band pass filter For our design f1 and f2 corresponds to 300 Hz and 3000 Hz respectively The 3 dB bandwidth for our design therefore 1s equal to the difference between these frequencies 2700 Hz If we do not get an accurate measure using this band pass design we will have the freedom in ou
35. e board and most likely the best choice of the three It s 16 analog inputs each with ADC capability as well as the 54 digital inputs including UART and USART give the board more than enough room for all of the microphones as well as the central GPS unit The low operating voltage would give the ATD the scalability to be solar powered if need be and the form factor is small and lightweight enough to fit all of our specifications Additionally the programming interface is simple and easy to use because it links compiles and assembles all from one interface This 64 interface is a standard C programming environment and can be installed on any Linux or Windows based operating system There is a downfall of the Arduino Mega and that is it s 16Mhz ATmega 1280 processor which will inadvertently increase the microphone spacing and the size the ATD The slow sample rate will force the ATD microphones to be spaced far apart and there will be a large tradeoff between size and accuracy because of this however we predict all specifications will remain within threshold values The following pages will be dedicated to the Arduino Mega ATmegal280 microcontroller and its role in the development of the ATD Block diagrams will be presented along with a brief overview of the complete ATD design from the perspective of the ATmegal280 Sample inputs and code will provide the building blocks for the final triangulation software and we will take a first look at
36. e case in our philosophy of use where the ATD will be attached to a moving vehicle we will need the information from the RMC section of the output stream of the GPS For that information we will need to read the incoming characters until the GPRMC label is read in Once that label is read the following 80 characters will be stored in a variable and split into each piece of information that the message contains For the other philosophies of use that pertain to a stationary ATD unit the GGA data will be sufficient The same process of scanning the incoming stream for the label applies only this time the label will be GPGGA Again the following 80 characters will be stored and then split into the appropriate pieces of data After the input stream from the GPS is parsed and split the data will be used to calculate the locations of the microphones based on their location relative to the GPS unit These relative locations will be hard coded into the software because they will be predetermined If the user has chosen the option to receive the raw GPS data it will also be transmitted through the serial port to the computer 78 Section 4 UML Class Diagram The event class is designed to store acoustic events in digital wave form It contains two variables a string called type and position called position The position class is explained further in the next section The string type defines the type of event that the ATD heard Examples of type
37. e occur in the frequency range of approximately 350 Hertz to around 1 1 KHz This frequency range must be noted and it must be compared to all other types of gunshot characteristics 42 Figure 4b 15 CR Frequency Analysis 1ra4Hz 3SATHz Cursor 1251 Hz DX8 2 dB Peak 1249 Hz D 5 Spectrum i Export Hanning window Log frequency Close Figure 4b 16 Time domain representation of the 9mm Beretta Below is the time domain representation of the 9mm Beretta So far we can tell just by the data that we have recovered from the above firearms that every type of gun has its own distinguishable characteristics The frequency range of the sound waves max magnitudes and attenuation factors are all types of characteristics that our data varies from Below is more data that we have gathered for further investigation into the different types of firearms bet px L LI am or een i 43 22 caliber The figure below is the waveform of the 22 caliber round This figure is a visual representation of our recorded sound wave using the Matlab dis function in DSP tools library Notice as you can see in the wave at around 5 milliseconds there is a small sharp fall followed by small slight sharp rise This is the representation of the bullet noise ground reflection of our recorded gunshot from the 22 caliber As you can see right after the bullet noise ground reflection the signal ju
38. e of 100 meters due north of the ATD Make sure the ATD and shotgun are at the same elevation Orient the ATD so the digital compass arrow faces due north Fire three shots from the shotgun Compare and record the external GPS and ATD results 2 Drop the ATD from a distance of one meter Repeat part one of the experiment Record any noticeable changes in accuracy Repeat this for three meters 3 Run the ATD casing over with the truck Not kidding Run it over with a truck 4 Repeat part one of the experiment in light rain Does the rain affect the Accuracy of the ATD Record all results 88 Experiment 5 Ease of Use Objectives To verify the intuitiveness and ease of use of the ATD and to compare the results of an experienced user with those of an inexperienced user To determine the amount of time it takes for an inexperienced user to setup and retrieve results from the ATD Equipment Remington 870 Acoustic Triangulation Device External GPS One Professional Engineer One Non Professional Business Management Student One stopwatch Background The ATD must be intuitive and easy to use The average person must be able to set up the device in less than five minutes and retrieve and interpret results almost instantaneously A soldier on the battlefield or an officer on patrol doesn t need to know how to multilaterate a three dimensional sound wave but the same soldier does need to know what is shooting at him and where it
39. e sent to our Arduino microcontroller The Arduino microcontroller can then analyze these signals and determine the times of arrival using 24 the microcontroller s clock from when the sound waves approach our array of microphones The amplification of one hundred from the Breakout Boards should be enough for our microcontroller to be able to pick up a gunshot from a reasonable distance If the gunshots from distances in our specifications are not received out of the Breakout Board more amplification will be needed From the knowledge and experience we have in amplifiers this will not be a difficult task to solve Figure 4 3 1 The figure below is a schematic of the Breakout Board U1 in this figure is an OPA344 Operation Amplifier This Breakout Board has an operating voltage ranging from 2 7V up to 5 5V This is perfect for our design and we will be using the Arduino microcontroller to power these units The OPA344 is a series rail to rail CMOS operational amplifier designed for precision low power applications It operates in a temperature range from 55 to 125 degrees Celsius This operational amplifier has a voltage output swing from rail of ImV Figure 4 3 2 25 Section 4 Filtering A gunshot s maximum sound level for a typical rifle 1s in the 130 Hz to 3 kHz Frequency range The frequency range of an adult male voice is in the frequency range of 85 Hz to 155 Hz and for an adult female 165 Hz to 255 Hz Because of t
40. e will be implemented in Since the speed of sound is calculated by the equation C 331 3 0 606 x T with T measured in degrees Celsius it is imperative to get the exact temperature of the environment in order to get the speed of sound equation to be as accurate as possible due to it depending on the temperature of the medium of which it is traveling The DS18B20 is a perfect digital temperature sensor for our prototype The features that make this the ideal temperature sensor are as follows e Unique I wire interface requires only one port pin for communication Requires no external components Can be powered from our Arduino Microcontrollers 3 3V power supply D e Measures temperatures from 55 C to 125 C e 0 5 C accuracy from 10 C to 85 C e Converts temperature to 12 bit digital word in a max of 750ms e Temperature alarm condition Shown below is a portion of the block diagram for the ATD that displays the interconnections between the DS18B20 and the Arduino Mega Figure 5 5 1 WVCC 33 THERM D515B20 70 The DS18B20 designed by Maxim IC provides 9 bit to 12 bit Celsius temperature measurements We will be using this temperature measurement to adjust our sound calculations in order to get an accurate speed measurement This is very important for our calculations because we are computing our multilateration algorithm in an extremely small time scale The error in locating the position of the gunshot or event would be
41. ems 3 12 10 Debugging mostly done and interface programmed Functioning 3 26 10 Start writing prototype presentation 4 9 10 Calibration and tweaking Finish Review and presentation evaluation 82 Chapter 8 Fabrication and Testing Section 1 Fabrication A Printed Circuit board PCB will be designed and fabricated to house the Microcontroller DSP GPS compass each of the four speakers as well as the power supply thermometer and any additional peripherals PCB123 is a company that creates PCBs with the traces and holes pre fitted to the board based on a design the user submits through proprietary CAD software provided on their website A microcontroller to PCB board attachment called a shield will be used to fit the Arduino mega to the PCB This attachment converts the breadboard style pin outs on the Arduino into metal pins which can be soldered onto the PCB As shown in the Eagle schematic below there are four traces etched for the Vcc Gnd TX and RX pins on the GPS and adequate space to mount this unit These traces run along the board to the 3V3 Gnd R XU and again Gnd pin holes respectively making sure to provide enough space for the Arduinos PCB shield in the middle Figure 8 1 1 HSG E K T D m A M e U 3 File Edt Drew Yew bok Ubay Options Window Hep Raas ESS BAQAG OB Dop setz P ce Ai ZE e Je GO Ox ANG ROA ei NAG Sg es Located at the four corners of the PCB there a
42. eration function to calculate the location of the sonic event This location will be sent to the connected computer 73 Figure 6 1 b ATD Activity Diagram Initialize all values including GPS coordinates compass bearing and temperature and make calculations including microphone positions and speed of sound Wait for input data sample each input as well as amplify and filter sound input New non event data received Sonic event detected User selects menu option Appropriate Store arrival menu option times for each Update executed detection appropriate data on screen Use triangulation process to calculate sound source location Yes Send location data through serial port to computer 74 Figure 6 1 c Data Flow Diagram Computer interface Wavelet analysis Microphone interfaces Analog to Digital Converter Get frequency Get amplitude Time of arrival Ken wm e vm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm lees Amplify sound Triangulation Find mic locations Find speed of sound GPS Compass Thermometer interface interface interface 75 Section 2 User Interface The user interface was written using a program called Processing This program was designed to interface easily with any Arduino development board It uses java as its base language and therefore was f
43. ese samples the time and amplitude of the signal will be saved In reality the ATD should only need to save about 3000 of the 19000 sample it will get within any given second because the sound waves that will count as events are in the 300 3000 Hz range as the Nyquist Shannon sampling theorem states a complete wave can be constructing by sampling at merely twice the frequency of the source This does not account for however the fact that the ATD has multiple microphones trying to find the time of arrival of the sound which has little to do with the actually sound frequency As such we would like to sample as often as possible to produce the most accurate times of arrival and thus the most accurate GPS even coordinates Once the digitized version of the wave is created the ATD can then compare the corresponding times of arrival and relay the GPS coordinates to an outside source The triangulation algorithm will initialize its variable values based on information from the EM 408 GPS unit the HMC 6352 Digital Compass the Microphones as well as the DS18B20 thermometer Information from the thermometer will be used to calculate more accurately the speed of sound in the present environment This will be used as c in the calculations described in Chapter 3 Triangulation Theory and a relative location of the event will be the result The triangulation algorithm will then couple this result with information from the GPS and compass to produce and abs
44. frequency axis has been normalized At around 0 normalized frequencies the magnitude is around 0 25 At around 0 01 normalized frequencies the magnitude is around 0 7 magnitude At around 0 027 normalized frequency as you can see from the plot the magnitude was maximum and approximately 1 5 As the frequency increases after 005 the signals magnitude begins to decrease These characteristics in our plots are extremely important because we will be comparing these characteristics of each gunshot recording to an event gunshot in order to best compare which type of gunshot has been fired Figure 4b 22 Figure 1 Cg gt File Edit View Insert Tools Desktop Window Help Dp ck GNE eR mE DE n Spectrum 38 wawv 1 5 Magnitude 0 5 t 05 d Bde Ee de of css BE Be Mormalzed Frequency Bode Plot of 38 caliber Below is a figure of the Bode Plot of the 38 caliber This figure is a visual representation of the 38 caliber sound wave s Bode Plot using the Audacity software As you can see in the Bode Plot figure the peak frequency is at 1187 Hertz and its magnitude at this specific frequency is 6 dB This peak frequency is very close to the value of the peak frequency of the 22 caliber Also it is to be noted from this figure that the max amplitudes of the of the 38 calibers sound wave occur in the frequency range of approximately 600 Hertz to around 1 KHz This is also extremely similar to that of the 22 caliber character
45. frequency range of approximately 500 Hertz to around 1 5 KHz This frequency range must be noted and it must be compared to all other types of gunshot characteristics This frequency range of the max amplitudes will most likely be different for all other types of guns Figure 4b 3 B Frequency Analysi Cursor 1251 Hz D 6 2 dB Peak 1249 Hz D 6 Spectrum lt 512 Hanning window Loa frequency a T La eech l ad pe 219 Zeen 21 8 Mm Ewer BP PAS 4 9 4 75 4 80 125 223 caliber AR 15 The figure below is the waveform of the 223 caliber round This figure is a visual representation of our recorded sound wave using the Matlab dis function in DSP tools library This visualization is the equivalent to what a digital oscilloscope would show of the 223 caliber wave Notice as you can see from this figure at approximately three milliseconds there is a sharp fall and then following a slight rise of the waveform This characteristic of the waveform is the representation of the 223 caliber bullet noise ground reflection of our recorded gunshot As you can see right after the bullet noise ground reflection the signal increases in size and begins to attenuate This is the visual representation of the AR 15 gunshots muzzle blast This attenuation in the AR 15 s muzzle blast is not as high as the other gunshot characteristics This muzzle blast 1s what our ATD prototype will
46. gnum s sound wave occur in the frequency range of approximately 300 Hertz to around 800 Hertz This frequency range must be noted and it must be compared to all other types of gunshot characteristics 54 Figure 4b 31 Cu reor 4 8 Hz A 4 3 dB Peak 475 Hz LPA Hanning window Log frequency Figure 4b 32 Time domain representation of the AK 47 Yu na om file n Tee Pec neen ieg Are He NM L n h Ze SIP Le 8 b j a j v b ET E CET EE Pe 4 7 9 Jg 718 TRANH ZS SP D 1 56 te 3 8 1 56 t 206 Lich aed 34 HW ecto Pupae n Career 9311740 mmaa joar OF 55 12 Gauge Shotgun The figure below is the waveform of the 12 gauge shotgun This figure is a visual representation of our recorded sound wave using the Matlab dis function in DSP tools library Notice as you can see in the wave at around 0 014 seconds there is a small sharp fall followed by an extremely slight sharp rise This is the representation of the bullet noise ground reflection of our recorded gunshot As you can see right after the bullet noise ground reflection the signal jumps extremely high and attenuates This is the visual representation of the gunshots muzzle blast This muzzle blast is what our ATD prototype will be detecting from 12 gauge shotgun Figure 4b 33 Figure 1 PII W File Edit View Insert Tools Desktop Window Help Helk Rana alna wary Data shotgun waw Zoom OUE UU
47. hat if a continuous function contains only frequencies within a bandwidth B Hertz it is completely determined by its value at a series of points spaced less than 1 2 B seconds apart This means that a signal of finite length T can be restricted to the bandwidth B fmax fmin therefore we only need to specify A and B to define the signal From this the sampling rate now depends on the bandwidth of the signal not the maximum frequency The figure below shows the spectrum of a band limited signal of finite length This is important for us to use since a gunshot is not an infinite long signal Using the below equations will simplify our analysis in obtaining the reconstructed signal Figure 4 1 a f IER Y CRX Spectrum of a band limited signal of finite length mls K K A As Cos Qn fot B 2 x Sin Qn fot i 0 i 0 MI x t A Cos 2znfst B Sin 22nfot ma O Combining these equations and manipulating using algebra the signal can be reconstructed by the following equation x t dx Sinc 759 T 24 Dec At K of samples 1 And it follows K 2N with N pude of ae and m F gt 2B X sample values t 18 Shown below is a figure of signal reconstruction from a series of sampled values using the sinc function from above to do the reconstruction Figure 4 1 b sam ples GE Input signal and samples taken Sine function interpolation from samples
48. hat we used to record our data of the sound waves for all the firearms We also would like to give a special thanks to Helen and Cliff Johnson for allowing us to use their property in Leesburg Florida to go out and shoot these firearms As you can see in the pictures the weather outside was not ideal However with limited time we had to obtain our data so a little rain did not ruin our plans In order to obtain the sound waves one member of our group sat inside a car so the rain would not ruin our laptop and recorded the sound waves of the guns using the microphones we purchased The software we used to gather our data is Audacity We recorded our sound waves using an audio sampling rate of 44 KHz and with a 16 bit audio sample size Initially we thought that the rain might affect our readings in a negative way We first believed that the rain would cause interference in our sound waves and that we would be unable to distinguish the noise apart from the actual gunshots We also believed that since we were taking our recordings from inside a car and the microphone being inside the car that possibly we would have interference in our data due to sound reverberation from the walls of the car Fortunately for us these factors did not affect our data however since we were recording our gunshots from a short distance 5 meters clipping of the sound waves were obtained because of this 31 After receiving the sound wave from Audacit
49. he two angles that make up the 15 direction Figure 3 5 a below shows a side view which is rotated 30 above being parallel with the ground This means that the side view is perpendicular to the plane made by the front face that is shown and that the dot in the center represents the rear microphone that would be recessed into the page The top view is perpendicular to the plane that is the ground and the dot in the center represents the top microphone which would be protruding out of the page This top view is rotated from the side view such that the line connecting the two lower microphones is fixed and the upper microphone 19 rotated down and out of the page by 60 The same formula is then used as in the two dimensional case to determine the length Ax this formula works for both the side view and the top view AX X tp t4 The speed of sound C is different in the three dimensional case In each view only a portion of the vector that represents the speed of sound is traveling in the same direction as the vector that points along Ax This portion is dependent on the angle of the opposing viewpoint In this way the two separate equations are solved simultaneously which results in finding the correct direction towards the sonic event Lomp C x sin CQ Crop C xsin Q1 Knowing the distance Ax and the side of the array S we can find the angle 0 in the same way as two dimensional triangulation Then we can find the angle o
50. his for our design purpose we decided to use a band pass filter with a pass band frequency range of 300 Hz to 3 KHz If we decide not to distinguish between types of gunshots and other sounds analyzing the signals 1s unnecessary and we would just be focusing on triggering when an event happens in the pass band range and then sending those signals from the microphones to the clock However if we do decide to distinguish between the different types of sounds it would require the use of in depth signal analysis There are many different types of band pass filters One of the main types that we decided to do research on is the Butterworth Band Pass filter The reason why we chose to do research on the Butterworth approach is as follows 1 We have the most experience using them 2 Good frequency roll off 3 No ripples in either pass or stop bands The figure below is of a typical Butterworth band pass filter magnitude response This is a fifth order Butterworth filter response with the Low pass cutoff frequency at 9 rad s and High Pass of 0 1 rad s The red and pink show the Magnitude response Phase delay is the green curve and group delay is the cyan curve response Figure 4 3 3 Order lt 5 LP 8 Dragis HP 0 1rad s Butterworth WBP Response C A N 26 After doing more research into band pass filters we came across an approach that we think is best suited for our design Since we are going to have to build a filter for each mi
51. his is a first prototype and all tests were completed in an open field The cost of our ATD design was extremely impressive In the beginning we believed that this project would cost around a total of one thousand dollars From our research we have learned that the total cost of the ATD will be approximately three hundred dollars This is extremely nice because all of the current gunshot detectors are very expensive to purchase The ATD design we believe has surpassed our initial design expectations There are very few parts of our prototype that will require more research needed in order to get everything for our prototype to work The ATD will be challenging to build and we know that we must start working on our prototype as soon as possible so we know we will have enough time to complete the building process In conclusion we believe that we will be able to get the ATD to work and function extremely well and meet all of our specifications 95 WORKS CITED Rob Maher 2007 April Acoustical Characterization of Gunshots Online HYPERLINK http www microflown com data SSA maher ieeesafe 0407 109 113 pdf http www microflown com data SSA_maher_ieeesafe_0407_109 113 pdf J Hartikka 1992 308 Measured Online HYPERLINK http guns connect fi rs 308measured html http guns connect fi rs 308measured html How Do Microphones Work Online HYPERLINK www mediacollege com http www mediacollege com audio mic
52. ic WM 63GNT335 e Lightweight e Expensive e Higher Frequency Range Below is a table showing the specifications of the Panasonic WM 63GNT335 For this microphone the frequency range is from 20Hz to 16 KHz This is considerably more than the range from what we need for our ATD prototype The operating voltage is 10 Volts maximum and the sensitivity is 44 dB The signal to noise ratio is 58 dB which is very high The Panasonic WM 63GNT335 meets all our specifications for our prototype Table 5 1 6 Item Symbol Test Minimum Maximum Units Condition Sensitivity E 1 3 Max p Operating Voltage SIN Ratio SIN 38 T Current Consumption Impedance Zout ee s um Range Directivity OMNI DIRECTIONAL 62 For our prototype we decided to use the Knowles MD9745APZ F The reason why we decided to use this microphone is that it is extremely cheap has a high sensitivity and signal to noise ratio and it is extremely small and lightweight Section 2 Microcontroller DSP The ATD s microcontroller is the central nervous system for the entire unit As such it must be able to deal with a vast array of analog and digital signals It must be able to process these signals quickly and relay an output to the user or the user s computer The five most important input and output signals the microcontroller will be dealing with are the microphones the GPS the digital compass digital thermometer and the user s PC Each of
53. iew Insert Tools Desktop Window Help N Dee RIR S xIDEI ec Binary Data ak4 way Magnitude 0 02 0 04 0 01 0 005 U 0 005 O01 0 015 0 02 0 025 0 03 0 035 0 04 Time te 53 AK 47 Spectrum The figure below is of the frequency spectrum of the 7 62 mm round This figure is a visual representation of the frequency spectrum of our recorded sound wave using the Matlab spec function in DSP tools library As you can see from this figure the frequency axis has been normalized Notice from this figure at around O normalized frequencies the magnitude is max at around 5 At around 0 012 normalized frequencies the magnitude has another maximum point at around 3 37 magnitude At around 0 025 normalized frequency as you can see from the plot the magnitude 1s approximately 1 34 Figure 4b 30 Figure 1 Iof x Fie Edit Wiew Insert Tools Desktop Window Help W D c BE 5 x e Rm ev uI TD Em ri spectrum akdz way S 45 4 29 3 25 Magnitude 0 05 U 0 05 0 1 0 15 0 2 0 25 0 3 0 35 Mormalized Frequency Bode Plot of AK 47 Below is a figure of the Bode Plot of the AK 47 s 7 62 mm round This figure is a visual representation of the AK 47 sound wave s Bode Plot using the Audacity software As you can see in the Bode Plot figure the peak frequency is at 475 Hertz and its magnitude at this specific frequency is 3 dB Also it is to be noted from this figure that the max amplitudes of the of the 44 Ma
54. ified distance calibrating the unit with sensitive equipment all while in the heat of battle or in the frenzy of a public event The average user simply isn t capable of this nor should they have to be The ATD must be able to accurately triangulate an event from any orientation Each ATD array must be able to be placed an arbitrary distance from each other The ATD must never need calibration as setup time 1s critical in many of the scenarios described above The user interface must be clean and simple The feedback from the system must not be ambiguous and should have immediate meaning to the user For example different scenarios require different coordinate systems and this must be apparent upon display Section 2 Specifications The ATD must be capable of determining even coordinates within the following specifications The ATD must e Be under 500 We will accomplish this by minimizing our GPS costs as described above Additionally we will use a low cost microcontroller and write the software on a free compiler Chapter 7 Section 1 Budget shows that we are well under 500 and this allows for some margin of error as well as extra funding for additional components e Be under 10 lbs We will accomplish this by using light weight composite materials Furthermore we will minimize the number of sensors and equipment to only what is necessary for the triangulation of the source e Be under cubic meter We will accomplish this by using a
55. ion was to find a project to which we could all contribute equally and stay interested in through the entirety of our Senior Design experience Additionally we were looking for a project that was applicable to real world events and would prepare us for our real world careers With crime on the rise as well as recent world events the ability to accurately detect gunfire has become increasingly important Our first priority of course is to save lives by eiving law enforcement their most advanced tool yet in the apprehension of armed criminals If the location of a gunshot is known in real time and the authorities can be notified instantly the criminal has a greater chance of being caught and 1s therefore less likely to commit the crime in the first place We all have vast experience with both firearms and electronics which makes this an exciting endeavor for everyone in the group Learning more about topics we already love and are knowledgeable about makes this more of a hobby for us than a school project Being passionate about what we re doing will keep us interested and a high level of interest will yield excellent results in the final product Passion and interest were important deciding factors for the ATD project Section 3 Philosophy of Use We envision the ATD being used in four main situations including VIP protection inner city law enforcement military personnel protection and civilian property protection Clearly there are other app
56. ire the soldiers would be able to order an airstrike or mortar attack on the enemy position Additionally the coordinates could be relayed to a drone to survey the area and send back reconnaissance data increasing our troops survivability and lowering the chance of friendly fire Owners of civilian properties or national parks could use the ATD to detect if there is gunfire in an unauthorized location Owners of hunting grounds would be able to tell if there was out of season hunting or hunting in restricted or protected areas The DSP addition would allow the property or park owners to determine if an unauthorized type of weapon was being fired on the premises thus helping with the conservation of wildlife As you can see the ATD is extremely versatile and benefits everyone everywhere every time real time Figure 1 3 b Chapter 2 Requirements and Specifications Section Requirements The ATD must be able to demonstrate the following requirements Range and accuracy The ATD must be accurate at long distances The farther away the source is the less accurate the triangulation becomes yet snipers can easily hit their targets from well outside 1000 meters In order to be accurate at long distances our signal resolution must have a high signal resolution and in turn a high sample rate This will require a fast clock Additionally the farther apart each microphone is the more accurate the ATD will be This size accuracy trade
57. is a block diagram for the ATD showing only the Arduino Mega input and output lines necessary for the ATDs application Not shown is the power source for the Arduino which will vary depending on its application In an outdoors environment the ATD will be standalone most likely solar powered with its own LCD display and keypad These components have been omitted as they are not design critical Also not shown is the ATD to computer connection that will be present if the unit is not standalone This connection however is design critical and will use the same USB connection the power comes from The Arduino s USB connection will be a two way communication network between the user and ATD as well as a convenient power supply Figure 9 1 Acoustic Triangulation Device Block Diagram Wee GAL MIC b L n UK S 3 Arduino Mega AN O 7 Ier HN DAN CHD Digital Compass SUA StL Vee CHI SB n Thermometer Each of the six microphones and their corresponding break out boards will be connected to the Arduinos 3V3 voltage output to supply power The ATD will by default be in listening mode and the microphones will be sampled at IMHz The analog signal representative of the sound source is taken in through each of eight microphones This signal 1s then amplified to a useable voltage by each microphone s corresponding break out board The amplified signal is processed through six of the Arduino s sixteen analog inputs and converted thro
58. is coming from The ATD must be intuitive to use According to Pearson in Senior Design for Electrical and Computer Engineering Management is not a profession and Engineering 1s so in this experiment we will be using a Business Management student as our test group and the control group will be an electrical or computer engineer involved in the development of the ATD Preparation A Create an instruction set for the average user Make sure the set is under one page and contains no terms that need to be defined to anyone outside of the ATD development B Interview the Business Management student and record what they expect the ATD setup and results to look like Record the time they expect it will take to set up the unit Modify the instruction page C Record the Engineers setup and result interpretation times Do you expect the business major setup time to be larger smaller the same Experiment 1 Let the test group read over the instruction page Provide them no other external feedback Set up the Remington 870 and external GPS at a location outside of the test group s site radius 2 Tell the test group to begin the ATD setup and start the timer Record the setup time Compare the results to the Engineer s setup time 3 Fire one shot from the shotgun and start the timer Record the time it takes the test group to determine the location of the event Compare the results to the Engineer 89 Chapter 9 Design Summary Below
59. istance Should the drop be the drop linear exponential Why B What distance related parameter do you expect to affect accuracy the most temperature variance reverberation signal attenuation What parameter should affect accuracy the least At what distance do you expect the ATD to stop yielding useful results Why C How can the ATD be made more accurate over a longer distance Experiment 1 Set up the Remington 870 and external GPS at a distance of 500 meters due north of the ATD Make sure the ATD and shotgun are at the same elevation Orient the ATD so the digital compass arrow faces due north Fire three shots from the shotgun Compare and record the external GPS and ATD results 2 Repeat part one for 600 700 800 900 and 1000 meters Use linear regression to interpolate an accuracy drop of graph from the results 3 Compare the results of the experiment with parts A and B of the preparation Taking these results into account if you had to make one modification to the ATD to improve it what would it be 86 Experiment 3 Signal Discrimination and Classification Objectives To determine the extent to which the ATD and classify acoustic events and to test the capability of the ATD to discriminate between and acoustic event and ambient sound Equipment Remington 870 Taurus PT1911 Bushmaster AR 15 AK 47 44 Magnum Berretta M9 Ruger Blackhawk 38 Ruger 22 Kel Tec PF9 Acoustic Triangulation Device External
60. istics From observing this data we believe that it will be a very 48 difficult task for us to determine between the 38 caliber and the 22 caliber Maybe there is some way with the ratio of coefficients using the wavelet transform that we will be able to distinguish from extremely close data Figure 4b 23 ee M E Duet X YE PETIT ot Fier te Ore 44 Magnum The figure below is the waveform of the 44 Magnum round This figure is a visual representation of our recorded sound wave using the Matlab dis function in DSP tools library Notice as you can see in the wave at around 0 015 seconds there is a small sharp fall followed by small slight sharp rise This is the representation of the bullet noise ground reflection of our recorded gunshot of the 44 Magnum This bullet noise 49 ground reflection is much attenuated As you can see right after the bullet noise ground reflection the signal jumps extremely high This is the visual representation of the gunshots muzzle blast This muzzle blast is what our ATD prototype will be detecting and comparing the coefficients from the 44 Magnum round to that of other types of events Figure 4b 25 File Edit Wiew Insert Tools Desktop Window Help N Del RI m SI IDE c Binary Data 44mag wav 0 02 0 015 0 01 0 005 U 0 005 Magnitude 0 01 0 015 0 02 0 025 0 008 0 01 0 012 0 014 0 016 0 018 0 02 0 022 0 024 0 026 Time ei Spectrum
61. l detection scheme of the ATD prototype This scheme is how we will be wiring an individual microphone and band pass filter to the Arduino Microcontroller As you can see the signal detection scheme is composed of a microphone band pass filter and the Arduino Mega microcontroller Figure 4 3 10 Ardumo Meza ANALOG IN 0 POWER SV RC COMPONETS LM 358 Aud Mic 1 Gnd T VCC From our research we have found that it would most likely be the easiest and best way to design and build our own filters We also determined that a passive low pass filter was sufficient for our design 30 Chapter 4b Gunshot Theory Section Sound detection overview There are many different types of guns however the most conventional use an explosive charge to propel the bullet out of the barrel The sound that comes out of the barrel travels in all directions but the majority of the acoustic energy travels in the direction that the barrel is pointed The shock wave that is emitted is called the muzzle blast and this is what the ATD will be detecting and using to locate the origin of the blast For our Sound Detection chapter we were required to go out and shoot different types of guns This was the fun part of our design project To the right are pictures of our group and Louis shooting the AR 15 assault rifle We would like to give a special thanks to Louis Schieferdecker top for supplying us with the firearms and ammunition t
62. l portions of the distance to the sound source based on figure 3 4 below the case in which the positive vertical direction is North and the positive horizontal direction 1s East are the following Dvert D x sin 180 54 Dhoriz D x cos 180 f Combining these equations we can get a single equation for the angle that each array produces with only the variables t4 tg the temperature T and a 1 331 34 606 XT X tp4 tA41 S 1 331 34 606 XT X tp2 tA42 S 4 COS 30 a cos 30 We can also combine the previous equations to get a single equation for the distance between the sound source and the first array D with only the variables o oo the distance between the two arrays L and D Fe sin 90 a2 XL sin 180 90 a4 90 2 14 Figure 3 4 2D Triangulation 5 o o2 i Bi po 4C S S L S 0 AX CUR 5 F Ay L Section 5 3D Triangulation For three dimensional triangulation the equations are similar to the two dimensional case When in three dimensions there are two angles represented by each array instead of just one Each array will then consist of an equilateral triangular pyramid The two directions produced by these arrays will again allow us to determine the exact location of the sonic event In the three dimensional triangulation case we approximate the sound wave as a plane instead of a line Also two perspectives are needed to get t
63. le below is for our prototype being powered from USB The stand alone total is the total cost that it would cost to implement a standalone power supply if we decide to implement this with the time that we have Fortunately for us our actual project will have a total cost of around three hundred dollars which will be divided equally among the group Expected Budget Johnathan Sanders 300 Ben Noble 300 Jeremy Hopfinger 300 Actual Budget Mics Preamps 31 80 note prices do not include tax 80 Section 3 Milestone Chart Date 9 15 09 10 2 09 10 9 09 10 16 09 10 23 09 10 30 09 11 6 09 11 20 09 11 27 09 Rough idea of goals and specs Research for specs mostly done Research components that satisfy specs all dal Activities Begin research Start documenting research data Paper Paper outline complete Begin writing Complete Goals and objectives Draft of explicit summary Finish detailed block diagram Draft of build plan Draft of evaluation plan Draft of Paper with all sections Complete Senior Design 1 Paper 81 Dates Activities Start testing 1 4 10 physical parts Determine if parts are acceptable 1 15 10 and buy more as needed start coding Start assembl 1 29 10 software of esit 2 12 10 x Start integration Algorithms mostly of subsystems programmed 2 26 10 Start testing integrated syst
64. lications but the ATD will be most effective in these areas An example of a VIP protection scenario would be a large speech by an important public figure History has shown these speeches to be among the most vulnerable times for public figures and with the large numbers of people attending it s easy for a gunman to escape in the crowd If once the shot was fired the gunman s exact GPS location and a surveillance video of the area were sent to the secret service for example the gunman would be apprehended immediately or better yet knowing this would never have fired in the first place Inner city law enforcement would find the ATD useful against gang violence and long distance fire such as Washington DC s beltway sniper situation in 2002 In situations like these often there is no one left to alert the authorities once the crime has been committed This results in slow response times by the authorities and emergency services and little if any evidence is left on scene by the time they arrive If however the ATD was used to alert law enforcement and paramedics they could be on scene within minutes after the first shot was fired The faster response time would lead to the apprehension of the criminal and an increased chance of saving the victims life Military personnel would find the ATD especially useful as they are under fire for much of their career Knowing the GPS coordinates of an ambush by guerilla fighters snipers or even tank f
65. mation will be determined using a compass on each array Based on figure 3 4 below the case 1n which both arrays are in the same orientation and their bases are parallel to the line that connects them to each other the correct equations to use would be the following equations p 90 a p 90 a Da 180 6 fz Then using the Law of Sines we can determine the distance from the first array to the sound source 13 Sinp xL sin D In order to find the exact location we then need to know the exact location of each array This information is given to us by the GPS Since the size of each array is small in comparison to the distance from the sound source to the arrays the GPS can be located at any point inside the array and still give a good enough approximation of the array s location This means that we can say that each microphone is at approximately the same location as the GPS unit The coordinates for the sound source are found by adding the vertical portion of the distance to the vertical coordinate of the GPS and the horizontal portion of the distance to the horizontal coordinate of the GPS for the first array The vertical and horizontal directions will have to be normalized to North South and East West directions to find the proper coordinates This will be accomplished by using the compass values for each array and will adjust the a and D angles accordingly The equations for finding the vertical and horizonta
66. microcontroller with a high speed clock This will provide for increased accuracy with smaller microphone spacing This is described in further detail in Chapter 3 Triangulation Theory e Be accurate to within 4 meters at a range of 400 meters We will accomplish this by sampling the source wave at a high rate thus increasing resolution and decreasing error Each array will have its own independent GPS giving the user the ability to place them anywhere they like minimum allowable distance is at least 5 meters apart e Be able to be set up in less than 5 minutes We will accomplish this by programming the user interface to startup quickly and letting the arrays be placed at arbitrary distances Also the arrays can be in any orientation at any height and still provide accurate results as described in Chapter 3 Triangulation Theory This will allow the user to place the units quickly anywhere and in any orientation they like e Software should install on any Windows XP or later computer We will accomplish this by programming the software in Microsoft Visual Studio and packaging the install file in a Microsoft Windows executable format using the Visual Studio packaging tool e Triangulate targets at multiple altitudes We will accomplish this as described by the equations shown in detail in Chapter 3 Triangulation Theory e Respond in less than second We will accomplish this by programming a fast interface as well as making sure that the Microco
67. mps extremely high showing the representation of the gunshots muzzle blast This characteristic of the 22 caliber round s muzzle blast is the signal that the ATD will be detecting and analyzing to distinguish itself from other types of sound Figure 4b 17 File Edit view Insert Tools Desktop Window Help E Dee KIS are DEM Q a Binary Data 22 wavy 0 06 UU Magnitude 0 02 0 04 5 i 5 10 15 Time sj TES 44 Spectrum of the 22 caliber The figure below is of the frequency spectrum of the 22 caliber round This figure is a visual representation of the frequency spectrum of our recorded sound wave using the Matlab spec function in DSP tools library As you can see from this figure the frequency axis has been normalized Notice from this figure at around 0 normalized frequencies the magnitude is max at around 6 At around 0 025 normalized frequencies the magnitude then has another spike maximum magnitude of around 2 At around 0 03 normalized frequency as you can see from the plot the magnitude was minimum of approximately 0 2 These characteristics in our plots are extremely important because we will be comparing these characteristics of each gunshot recording to an event gunshot in order to best compare which type of gunshot has been fired So far out of all of the data that we have received the data for the 22 1s the weakest This spectrum signal of the 22 is extremely small compared to that of all the o
68. nformation A n is the coarse approximations associated with the scaling function As you can see from this figure down sampling is used which means that only one out of two data is used in this process At each level in the above figure the signal is decomposed into low and high frequencies The input signal must be a multiple of 2 n with n equal to the number of levels Figure 4 2 2 X n Down sampling is used in DWT because for every time you filter you are incrementing by a large amount of data so it is necessary for down sampling to occur It should also be noticed that when half of the frequencies of the signal are removed half the samples can be discarded according to Nyquist s rule After this entire process 1s completed there will be numerous signals that represent the same signal but each signal will correspond to a specific frequency range This process can be repeated multiple times and the number of times it 1s repeated corresponds to what the application calls for For our design we will have to test this to see how many processes we need for our analysis There are many different types of wavelet shapes to choose from Using Matlab we have come across the Daubechies wavelet This wavelet is most similar in shape to that of a gunshot The following figure is an example of the Daubechies wavelet in Matlab 21 The figure below shows a Daubechies wavelet in Matlab with a decomposition level of four As you can see fr
69. ng that the upper microphone heard the sound first we can eliminate half of the hyperbola The points along the hyperbola are the only places such that the difference in time for the sound wave to reach the second microphone after having reached the first microphone is the same As the sound source approaches a point that is equidistant from the two microphones the hyperbola flattens out At this point where the source is equidistant from the two microphones the sound wave will reach the two microphones at the same time and thus a straight line will represent the possible locations of the source When a third microphone is added there are three different parings of microphones which will produce three different hyperbolas of possible locations based on their respective time differences of arrival There is only one location where all three hyperbolas intersect as shown in Figure 3 1 b and this location is the location of the event source Figure 3 1 b also demonstrates the fact that the microphones can be at any location Each pair of microphones will produce a possible location hyperbola regardless of their location with respect to the other microphones in the array as long as the three microphones are not in a single line If the microphones are all in a single line there are still two points at which all hyperbolas intersect Any additional microphones located in the same line beyond the first two will not give any new information Figure 3 1
70. ntralized components of the ATD Notice the volume dimensions are within specifications and the unit is not awkwardly shaped making it easy to transport Notice also the closed unit will be monolithic which will mean durability as no parts will get caught or break off during transport or setup Both the USB and external microphone unit connections from the Arduino extend to just the outer edge of the PCB enclosure and are the only two connections to the unit fulfilling the simplicity requirement The GPS compass and temperature sensors are still within the enclosure however the casing in these areas consists of a clear Lexan to allow sound and light in The bulk of the PCB enclosure will be Lexan Predrilled screw holes will enable ease of disassembly and repair of the ATD Figure 8 1 2 84 Section 2 Testing The ATD will be tested through a series of five experiments providing data about the accuracy range signal discrimination and classification durability and ease of use of the unit Experiment 1 Event Location Accuracy Objectives To determine if the ATD can locate a singular target event 400 meters away to within an accuracy of four meters Equipment Remington 870 Acoustic Triangulation Device External GPS Background The ATD should be able to produce the GPS coordinates of a target sound at ranges of over 400 meters When the event occurs a sound wave travels in all directions and arrives at different places in
71. ntroller has a high enough transfer rate e Trangulate targets while moving under 20mph We will accomplish this as described by the equations shown in detail in Chapter 3 Triangulation Theory e Work in any orientation We will accomplish this as described by the equations shown in detail in Chapter 3 Triangulation Theory Figure 1 1 b Acoustic Triangulation Block Diagram Sound Wave Pressure and time data Coordinates Source Vector sound Wave and time data GPS Coordinates And Pressure Source Vector Source Factor Image Source GPS Coordinates And Image sound Wave and time elative Source data GPS MEANE ele Initial Amplitude OM Lacation Frequency and Coordinates Vector diga iiam Pressure and cae Image Chapter 3 Triangulation Multilateration Section 1 2D Multilateration There are several different ways to find the location of the source of a sonic event In our initial attempt to accomplish this task we used mulitilateration This method needs only one array with at least three microphones for the two dimensional case and at least four microphones for the three dimensional case Another benefit that the hyperbolic multilateration method has over triangulation is that the array can be any shape When using the time difference of arrival of a sound wave between two microphones the possible location of the sound source is a hyperbola as shown in figure 3 1 a Knowi
72. ode Plotter XBP1 0 ftagnitude Phase Save Set Vertical Honzontal 0 011 dB pe gt l 2 066 kHz f n v f Out v Below is a phase plot of our designed band pass filter Figure 4 3 8 Bode Plotter XBP1 Magnitude Phase Save Set f In fe f Out fe The reason for using the LM 358 in our band pass filter for the ATD is that it 1s a single supply operating voltage amplifier Single supply operating voltage is important in our design because with this we do not need to worry about the negative voltage required to operate the operational amplifier Since we will be powering all the band pass filters from our Arduino Mega microcontroller it will make our prototype easier to build The single supply voltage range for the LM 358 is 3V to 32 V which is excellent for our prototype since the Arduino microcontroller has an output power supply of 3V and 5V The figure below is of the connection diagram of the LM 358 chip The LM 358 contains two operational amplifiers For our design we will require up to four LM 358 chips Using this connection diagram we can then proceed to design our wiring schematic for the microphones and band pass filters 29 Figure 4 3 9 OUTPUT A OUTPUT B INVERTING INPUT A 3 NON INVERTING INPUT A INVERTING INPUT B NON INVERTING GND INPUT B Top View LM 358 The figure below is the schematic of how we will be wiring each of the components for the signa
73. of approximately 500 Hertz to around 1 KHz 51 Figure 4b 27 DG dk 1f4Hz 347Hz 681Hz 1KHz 3KHz BKHz 11KHz Cursor 1152 Hz D6 3 dB Peak 1148 Hz UG Spectrum 512 Hanning window Loa frequency Figure 4b 28 Time domain representation of the 44 Magnum a o m E e er Eie dt Yew Project rege Fier gayoo tip E 4i A d i ELE E D SEGAL MES S E iwi se Mw 21 9 Pe 00 Sa he T SS 19 5 50 52 AK 47 7 62mm The figure below is the waveform of the AK 47 round 7 62 mm This figure is a visual representation of our recorded sound wave using the Matlab dis function in DSP tools library Notice as you can see in the wave at around 0 01 seconds there is a small sharp fall followed by small slight sharp rise This is the representation of the bullet noise ground reflection of our recorded gunshot This bullet noise ground reflection is much attenuated This sound wave is much different that that of all the other rounds In this plot we can barely notice the bullet noise ground reflection As you can see right after this extremely slight bullet noise ground reflection the signals slope increases significantly high and begins to attenuate at a high rate This is the visual representation of the gunshots muzzle blast This muzzle blast is what our ATD prototype will be detecting from the AK 47 s round Figure 4b 29 File Edit V
74. of the frequency spectrum of our recorded sound wave using the Matlab spec function in DSP tools library provided by Dr Kasparis This program calculates the Fast Fourier Transform over the entire signal As you can see from this figure the frequency axis has been normalized Notice from this figure at around 0 normalized frequencies the magnitude is max at around 9 At around 0 01 normalized Figure 4b 2 File Edit Wiew Insert Tools Desktop Window Help N Dr o IIS L v RIETI T spectrum 45 way 10 Magnitude Cn R T n REA EFL 04 0 06 0 04 0 02 U a02 004 0 06 DDS Di 012 Normalized Frequency frequencies the magnitude is around 3 5 magnitude At a normalized frequency of around 0 03 as you can see from the plot the magnitude is approximately 3 7 These characteristics in our plots are extremely important because we will be comparing these characteristics of each gunshot recording to an event gunshot in order to best compare which type of gunshot has been fired 33 Bode Plot of 45 caliber Below is a figure of the Bode Plot of the 45 caliber round This figure is a visual representation of the 45 caliber sound wave s Bode Plot using the Audacity software As you can see in the Bode Plot figure the peak frequency is at 1249 Hertz and its magnitude at this specific frequency is 2 dB Also it is to be noted from this figure that the max amplitudes of the of the 45 caliber sound wave occur in the
75. of the guns and repeat part one with the AM FM radio playing within one meter of the ATD 87 Experiment 4 Durability Objectives To determine the ATD s resistance to shock pressure weather and external RF interference Equipment Remington 870 Acoustic Triangulation Device External GPS One Truck Light Rain Background The ATD must be durable enough to withstand the demands of its philosophy of use It must be all whether as its main arena is outdoors It must be impact resistant both in transport and use as it will be used in battlefield situations It must also be pressure resistant and shielded from external interference The ATD will be housed in an aluminum casing to protect it from each of these elements This case and the ATD functionality after severe trauma must be extensively tested Preparation A Calculate the expected force the ATD will experience in a one meter and three meter drop Do you expect the ATD to still be functional after experiencing this shock B Calculate the expected deformation of the aluminum case when put under a half ton and a ton of pressure Do you expect this case deformation to affect the functionality of the ATD C Under what weather conditions do you expect the ATD to be most accurate What weather conditions will damage the ATD How could the ATD be made waterproof while still triangulating the acoustic wave Experiment 1 Set up the Remington 870 and external GPS at a distanc
76. olute even location which will be plugged into the online map software and displayed in a way that 1s easy to understand for the user Along with this display will be a recording of the sound wave and the ATD s best guess as to what the event is Beyond these coordinates the ATD will also be calculating the event type for example the explosion or gunshot round type based on the wavelets calculated from the saved acoustic wave form This process is described in further detail in Chapter 4 Sound Detection Once the event type and location are determined the event will be relayed and stored for further analysis if need be The user will be able to see the shots location on a 72 map of the area as shown in figure 6 1 An online map database will be accessed to bring up the location Figure 6 1 a Map of gunshot location a Ese 7 ae a TERS EIN Kg R d 4 D Ke WA pon e A1 ne ip gem sa Centaurus Or VV NI T H i T j i inn el I Wh a Bn t g t el e ec I DEA e G p n Gr RS n L D L i T af i EE EE TIE Ee T Enron 7 di ya U ed ten T PAPAS wis eee Report a problem e ER An activity diagram for the ATD is shown in figure 6 1 b This diagram shows that the ATD will start by initializing all necessary values and then calculate other initial values Then the system will wait for either input from the user or the sensors and then take appropriate action
77. om the figure it shows the decomposition of the low and high pass filter This wavelet will be used in our project to divide our time signals into different scaled components After each component is scaled we will be studying each component This data compression technique will then allow us to compare our event gunshots with our database of stored characteristics Figure 4 2 3 2 Wavelet Display File View Insert Tools Window Help Scaling function phi 1 2 3 4 5 6 7 1 2 Decomposition low pass filter E 0 5 1 3 4 5 6 7 0 1 2 Reconstruction low pass filter Wavelet function psi Information on Daubechies Family DB All Wavelet Families 4 5 6 7 Decomposition high pass filter 4 5 6 Li Reconstruction high pass filter Figure 4 2 4 Filo View Insert Tools Window Holp Scaling function phi n 4 6 a ul Decomposttion low pass ter Sg le Tl Ki 2 4 6 s 10 Reconstruction low pass fitter E eo A Wavelet Display Wavelet function psi 6 L an Decomposhion high pass fitter Reeg Reconstruction high pass filter Bet pem 27 The above figure shows a Daubechies wavelet in Matlab with a decomposition level of six As you compare the difference of decomposition levels you can notice the wavelet functions difference The higher the decomposition level the more compressed the signal becomes The Daubechies family can either be orthogonal or biorthogonal
78. ormalized Frequency Bode Plot of 9 mm Kel Tec Below is a figure of the Bode Plot of the 9 mm Kel Tec This figure is a visual representation of the 9 mm Kel Tec s sound wave s Bode Plot using the Audacity software As you can see in the Bode Plot figure the peak frequency is at 1285 Hertz and its magnitude at this specific frequency is 5 dB Also it is to be noted from this figure that the max amplitudes of the of the 9mm Kel Tec s sound wave occur in the frequency range of approximately 500 Hertz to around KHz 39 Figure 4b 11 8 Frequency Analysis 1f4Hz 34fHz Cursor 1286 Hz E6 5 dB Peak 1285 Hz Ep Spectrum 512 Hanning window Log frequency wie we sem Semper Sr 1894 n Gees On 9 mm Beretta The figure below is the waveform of the 9 mm Berretta round This figure is a visual representation of our recorded sound wave using the Matlab dis function in DSP tools library Notice as you can see in the wave at around 0 004 seconds there is a sharp V shape that looks similar to a razor tooth This is the representation of the 9 mm Beretta s 40 Figure 4b 13 WI File Edit view Insert Tools Desktop Window Help Derek S bian all DES 9 GO Binary Data Smilbar waw IW Magnitude 0 005 1 0 005 0 01 0 015 0 02 0 025 D DEG 035 Time si bullet noise ground reflection of our recorded gunshot As you can see right after the bullet noise ground reflec
79. ove additions are beyond the scope of this paper 93 Chapter 9b User Manual Step 1 Plug Arduino Mega into laptop using USB connection Step 2 Plug microphone array data cables into filter data cable inputs making sure array 1 goes into filter 1 Step 3 Place microphone arrays one meter apart from each other making sure they face the same direction Microphone 1 and Microphone 4 facing exactly same direction Step 4 Place Arduino Mega with PCB attached to it with digital compass s North facing horizontally with microphone arrays Step 5 Turn on laptop Step 6 Open ATD application Note At this point the ATD is ready to detect any acoustic event To train events to the database continue with the following steps Step 7 Select Train New Event Type from Action Menu Step 8 Enter a Name in the dialog box Step 9 Click OK Note The next event will be saved in the database under the proper name chosen 94 Chapter 10 Conclusion The ATD uses many concepts that we have learned in our Electrical and Computer Engineering classes at the University of Central Florida We believe that our ATD prototype has many useful applications that it can be implemented with In the beginning we were focused on working on a project that we would all be interested in The ATD was exactly what we were looking for in a design project The ATD has been a fun and exciting experience as our first design project Not only was the research and design
80. r testing phase to be able to easily adjust the bandwidth by re computing the values for the resistors and capacitors to meet our specifications ZI Figure 4 3 5 2 0 Wo C H pp 4 3 dB Passband 2 Q Wo C Q Wo C 20 H Bandaidth 2 fl R 6 H p lt 20 Fl Fre quency The figures below are simulations of our designed filter using the Multisim 2001 program Figure A was simulated with an input voltage of 1V at 200 Hz As you can see from this figure the output voltage is extremely low exactly how we need it to be since it is not in our pass band range Figure B is a simulation with an input voltage of 1V at 1 KHz As you can see from this figure the voltage is high since it is in our pass band region Below is the magnitude and phase response plot for our designed band pass filter Figure 4 3 6 Oscilloscope 5C1 E Oscilloscope 5C1 Fa au TI 2 7ms Tz 10 0ms T2 TI 7 3ms EEN EE C Ti 1 Dms Tz 10 Dms Tz TI 8 dms Reverse C wap 1397mwv wez 1295mw MAN 262 2 mv PU war aam w l 13mv wear 4v Deeg vB VEE 8281 E Grou vaT VEZET ava Groun Channel B Scale E m y Di Y position foo Level o v Channel B Scale a mi Diw Edge Y position foo Level o VW Timebase Seale 1 ms Diw X position foo Channel X 28 Below is a magnitude plot of designed band pass filter Figure 4 3 7 Bode Plotter XBP1 0 Plotter B
81. re filter schematic The thermometer is also connected to the voltage source as well as the RX1 serial input on the Arduino Mega The current temperature will be stored in the board s memory and updated every ten seconds This way if a cloud moves overhead or the temperature drops suddenly the unit will still maintain accuracy Temperature affects the speed of sound very profoundly and is not to be overlooked The current temperature will be used to calculate the speed of sound more accurately and this information will also be sent to the triangulation subroutine The digital compass also powered on the 3V3 Arduino output has a clock which is connected to the clock regulating signal SCL on the Arduino board This signal allows the output input from the compass to sync with the input on the Arduino The high low signal SDA is then transmitted to digital pin 22 for storage and the value is decoded then 91 used in reference frame setup in the triangulation subroutine Without the digital compass it would be impossible for the ATD to give the coordinates of an event and as such it is imperative that the compass transmits an accurate bearing at setup time The GPS is again powered on the 3V3 line As a side note the sum of all amperages specifications of the components does not exceed the Arduinos 3V3 output specifications The GPS transmit line is connected to the RXO serial input on the Arduino Mega and transmits a NMEA 0183 standard string Thi
82. re pre drilled holes The Vcc Gnd and AOUT from each microphone have pre etched traces running to their proper positions on the mega 3V3 Gnd AIN 0 15 The microphones were ordered with the break out boards attached which will make soldering them to the PCB simpler All six of the microphones will be raised off the board to an elevated position using PVC Inside the PVC pipes are wires running through the middle from the traces on the board to the pins on the microphone break out board 83 The digital compass has three pin holes for Vcc Gnd SDA and SCL with corresponding traces to 3V3 Gnd DI22 and SCL at the microcontroller end Note on the board the compass orientation is indicated with the arrow The same arrow is drawn on the compass unit and these should be aligned accordingly before soldering the compass in place The direction chosen relative to the microphones and GPS 1s arbitrary but must be known in order for the triangulation algorithm to provide useful results The thermometer has three pins and there are three holes for it on the PCB They are Vcc Gnd and DQ with Vcc and Gnd going to their usual places and DQ traced to the microcontroller digital pin 48 All of the components will be soldered and not surface mounted to keep the ATD inexpensive Size is not an issue as the microphones have a minimum volume they must fill which negates the size of the PCB board making surface mounting unnecessary Below is picture of the ce
83. ring the event that we have received from our band pass filters with our database and then deciding which type of database signal best matches the event In order to do this we must have a large knowledge in the understanding of how the Fourier transform and wavelets transform works The Fourier Transform The Fourier transform is often called the frequency domain representation of the original function The frequency domain representation is used to show which frequencies are present in the original function The Fourier transform can separate low and high frequency information of a signal and is mainly used for processing signals that are composed of sine and cosine signals From our vast 19 knowledge and experience using the Fourier transform it would be extremely nice if this could be implemented in the design of the ATD The equation for the Fourier transform is as follows afi 6 The figure below is an example of a Fourier transform 11 done on cosine signal 1 with thirty samples sampled at ten samples per period Figure 4 1 c Im EES File Edit view Insert Tools Desktop Window Help File Edit view Insert Tools Desktop Window Help Dee bk Sange UE Dee bk Ramo e 0H C N 60 1 D 1 0 2 0 3 0 4 0 5 0 6 0 7 D 8 0 9 1 Unfortunately after further research the problem with the Fourier transform being used in our project 1s that 1t can tell what frequencies are in the original signal but 1t does no
84. rophones how microphones work html National Semiconductor Online HYPERLINK www national com www national com Our Approaches to the Project Online HYPERLINK http www owlnet rice edu elec431 projects97 Dynamic approaches html http www owlnet rice edu elec43 projects97 Dynamic approaches html The Discrete Wavlet Transform Online HYPERLINK http www dtic upf edu xserra cursos TDP referencies Park DWT pdf http www dtic upf edu xserra cursos TDP referencies Park DW T pdf Sparkfun Electronics Online HYPERLINK Wwww sparkfun com www sparkfun com Kel Tec CNC Industries INC Online HYPERLINK http www kel tec cnc com http www kel tec cnc com Awaiting permission Jim Lesurf The Sampling Theorem Signal Reconstruction Online HYPERLINK http www st andrews ac uk www pa Scots Guide 1andm part7 page3 htmI http www st andrews ac uk www pa Scots Guide iandm part7 page3 html Cuthbert Nyack 2005 Wide Band Pass Butterworth Filter Online HYPERLINK http cnyack homestead com files afilt afilt Butterworthwbp htm http cnyack homestead com files afilt afilt Butterworthwbp htm 96
85. s function in DSP tools library This visualization is the equivalent to what a digital oscilloscope would show As you can see from the wave in this plot at around 0 004 seconds there is a sharp fall followed by a jump in the wave This is the representation of the bullet noise ground reflection of our recorded gunshot As you can see right after the bullet noise ground reflection the signal then jumps extremely high This is the visual representation of the 38 calibers gunshots muzzle blast This muzzle blast is what our ATD prototype will be detecting from the 38 caliber round From this figure and comparing with the sound waves the slope of the fall in the representation of the bullet noise ground reflection 1s not as steep as the other figures As you can tell from the figure the gaps between the Figure 4b 21 Figure 1 Oe gt File Edit view Insert Tools Desktop Window Help N EE IE N E ER R S au Binary Data 20 wavy Magnitude E em l 0 004 0 006 0 008 0 01 0 012 0 014 0 016 0 018 0 02 Time 51 signal of the muzzle blast can be noted as wider apart that that of the other gunshot characteristics of the other types of guns 47 Spectrum of the 38 The figure below is of the frequency spectrum of the 38 caliber round This figure is a visual representation of the frequency spectrum of our recorded sound wave using the Matlab spec function in DSP tools library As you can see from this figure the
86. s a small lightweight low power consumption accurate solution to the problem The HMC 6352 breakout board shown to the right makes attachment to the Arduino Mega seamless and manufacturer support for the compass is excellent The following specifications make the 6352 perfect for the ATD s intended philosophy of use e 2 7 to 5 2V supply range D e Simple DC interface H MC 6 392 e to20Hz selectable update rate 4 i e 0 5 degree heading resolution gt E e degree repeatability W c e Supply current ImA 3V 39 OR Shown below is a portion of the block diagram for the ATD that displays the interconnections between the EM 408 and the Arduino Mega Figure 5 4 1 SCL HMC 6352 Arduino Mega 3V3 69 The HMC 6532 uses the Inter Integrated Circuit I2C serial bus developed by Phillips In I2C the SCL line can be used to hold the HMC 6532 clock line low while the Arduino Mega receives the message The Arduino will receive a digital heading to the nearest 0 1 degrees which will be stored in a specified memory location The HMC 6532 will be oriented along a predetermined reference line with respect to the microphones Note that the breakout board top right shows the orientation of the chip When the arrow points to magnetic north the chip should output zero degrees Section 5 Digital Temperature Sensor The digital temperature sensor will be used to get the exact temperature of the environment that our ATD prototyp
87. s string is then decoded by the GPS decode subroutine and the GPS coordinates of the ATD are extracted These GPS coordinates are then sent to the Triangulation subroutine and used to set the reference frame from which to calculate the target event s GPS location as follows The variable for temperature is initialized and the speed of sound is calculated by using this formula C 331 5 606 x T The variable for the event arrival time from each of the eight analog inputs is passed into each of these equations 1 cx G7 x8 O yg G zg yx y z tg ty Tap 1 ee C are PP OA eH ze hay a a ie tie 1 cx G7 xp O yo Z Z yx y z tp t4 Tap and the coordinates relative to our predefined x and y axis are calculated The x and y axis are defined by the north south east and west provided by the digital compass and the origin is defined to be the ATD coordinates provided by the GPS Note that each microphone will have its own coordinates as well calculated by the ATD s dimensions in conjunction with the physical GPS location onboard the unit Once the reference frame 1s set the calculation variables are initialized from microphones temperature sensor compass and GPS and the source location 1s multilaterated then passed to the user Once the exact even location has been calculated the signal analysis subroutine takes over and analyzes the wavelet breakdown of the event A predefined set of
88. se equations there are two locations that the source could come from one on each side of the line which connects the first and second microphones The third microphone tells us that the source came from the opposite side that it 1s located There are two equations which can tell us the value of Ay The first is based on the speed of sound and the times of the second and third detections of the sonic event The second equation is based on the triangle made up of Ay and the base of the array and the angle determined by the previous equations Ay 2 C X tc tg Ay S x cos 180 60 6 If these two equations are not equal then there is some error involved in the calculations This error could be caused by the source being at a location other than ground level Alternatively the error could be caused by inaccuracies in the time readings All of the above equations that were used to find the values of the first array and therefore the angle o can also be used to find the values of the second array and therefore the angle a2 Using the angles a and o found by the previous equations we can determine the angles Di B2 and P3 of the larger triangle formed by the lines connecting the two arrays and the sound source as shown below in figure 3 1 The relationship between the D angles and the a angles will have to be determined by knowing the orientation of each array with respect to the line that connects the two arrays This infor
89. sent to the multilateration section for analysis The actual output string of the GPS has more information than we need As it outputs the stream of characters it starts each section of the message with a label and then outputs the information associated with that label The label GPGGA precedes the Global Positioning System Fix Data information This is information about the current 3D location including latitude longitude and altitude It also tells how accurately the GPS is fixed to its current position The label GPGSV precedes information about GPS TI satellites in view It will tell information on how many satellites are in view as well as other information about the satellites These satellites are not necessarily the ones used to find the position though The label GPGSA precedes information on the GPS DOP and active satellites This information tells about the dilution of precision as well as the type of fix no fix 2D fix or 3D fix that the GPS has made with a particular satellite The label GPRMC precedes the Recommended minimum specific GPS and Transit data This contains the position data as well as the velocity and time data In order to read in this data we need to set up a loop that scans the input pin that the GPS signal is on for the start bit Once the start bit is found then a valid string will stream from the GPS The first few bits will contain the label that needs to be checked to get the right type of input In th
90. so has an x coordinate and a y coordinate that we will call x and y respectively This gives us three equations x x4 O MATE CX ty V x xg y yp C X tp y x xc LW yc C N L Unfortunately since we do not know the exact time the sonic event initially occurs we cannot know the time it takes the sound wave to travel to each individual microphone Instead since we know the time the sound wave reaches each microphone we can use the difference between the time of the wave s arrival at the first microphone and the time of arrival at each other microphone This difference is equal to the difference between the amount of time it takes the wave to reach each microphone Solving the equations for t and then subtracting gives us these equations 1 cv G7 og O ys LX xa O Y4 tg t Tag 1 cv G 7 xe O Mell AG x O ya te ta Tac Also if we choose an origin for the system at microphone A then we can simplify further This means that the locations for microphone B and C are relative locations with respect to microphone A There are then two equations and two unknowns which are the x coordinate and y coordinate for the sound source 1 S 1 Section 2 3D Multilateration Figure 3 2 Half hyperboloid of possible locations The three dimensional case is similar to the two dimensional case The possible location of the sound source based on the time difference of arrival bet
91. sound wave using the Matlab dis function in DSP tools library Notice as you can see in the wave at around 0 005 seconds there is a small sharp fall followed by small slight sharp rise This is the representation of the Kel Tec s bullet noise ground reflection of our recorded gunshot As you can see right after the bullet noise ground reflection the signal jumps extremely high This is the visual representation of the gunshots muzzle blast This muzzle blast is what our ATD prototype will be detecting from the Kel Tec 9 mm caliber round Figure 4b 9 Figure 1 Te E File Edit View Insert Tools Desktop Window Help N Dee kR SIP uui Binary Data Smil way L 1 0 08 0 06 UA Magnitude The figure below is of the frequency spectrum of the 9 mm caliber round This figure is a visual representation of the frequency spectrum of our recorded sound wave using the Matlab spec function in DSP tools library As you can see from this figure the frequency axis has been normalized Notice from this figure at around 0 normalized 38 frequencies the magnitude is max at around 7 At around 0 01 normalized frequencies the magnitude is around 1 6 magnitude At around 0 03 normalized frequency as you can see from the plot the magnitude was approximately 0 733 Figure 4b 10 File Edit Wiew Insert Tools Desktop Window Help N Dee RiISIS Zn dl Uc spectrum Smil wav Magnitude 0 1 0 1 0 2 0 3 1 4 Uz N
92. space at different times This 1s used to the advantage of the ATD By listening to the event with spatially varying microphones and measuring the time difference of arrival TDA of the event at each microphone one can determine the origin of the event That is the sound wave should arrive at the closest microphone first and each subsequent microphone that hears it will be able to produce information about the events bearing Preparation A For high low and level event altitudes what 1s the expected variance in event coordinates that the ATD will produce through multilateration through triangulation B What is the expected effect of ambient sounds ie Birds car engines on accuracy C What is the expected effect of temperature variation on accuracy Experiment 1 Ground Level Set up the Remington 870 and external GPS at a distance of 400 meters due north of the ATD Make sure the ATD and shotgun are at the same elevation Orient the ATD so the digital compass arrow faces due north Fire three shots from the shotgun and record the external GPS results Record the ATD triangulation results Calculate the variance 1n coordinate locations of each shot and record the results 2 Elevated Event Repeat part one with the ATD turned upside down and located one meter above the event Maintaining the ATD orientation move the unit to five and ten meters higher in elevation than the event Note for safety reason the shotgun will not be eleva
93. sult in an x y and z coordinate for a possible location Iterating through all possible combinations produces 58 estimations of the location of the sound source The easiest way to estimate the location 1s to average all of the x coordinates then all of the y coordinates then all of the z coordinates using the following equations X1 X2T X5g y1tya2t tysg _ 2442244258 Xavg sg Jag sg Zeng 58 It turns out that this estimation method is not accurate enough to be within the specifications that we desired Another method using non linear least squares regression is a better method for estimating the source location This method is very difficult to accomplish After much trial and error we realized that not only was this method not very feasible it also required the use of faster and more expensive equipment which would have also put us outside our specifications 11 Figure 3 3 b shows some sample points generated by several array subsets and the average of those points This point Xayg Yave Zavg 1s the estimated relative location of the sound source with respect to the array Figure 3 5 a Cube shaped array b Estimated source location 1 2 Section 4 2D Triangulation After having much difficulty with multilateration we decided to derive our own equations using triangulation instead For two dimensional triangulation we need two arrays of three microphones each oriented in an equilateral triangle to determine the ex
94. t sample 6000 times per second for the frequency ranges in getAmplitude int question the array is 6000 units wide Each voltage in the getFrequency int voltage array arrived at a certain time These times are store getTimeofArrival int in the time integer array also 6000 units wide The frequency can be calculated by determining the number of local peaks and dividing by the time The getFrequency function will perform this task and return a sing number describing the wave s frequency The getAmplitude function will return the highest peak value found in the wave frequency int amplitude int type int timeofArrival int To recap the wave class will completely describe an acoustic wave This wave will correspond to an event and the information contained in the wave class will be used by external functions to calculate the position and type of that event The event contains on information about the position of the waves origin and the type of event the ATD heard All coordinates in the device including the devices own coordinates will be stored in the position class variables just to keep things organized 79 Chapter 7 Budget and Milestones Section Expected and Actual Budget Our expected budget was actually a lot more than our actual budget Before our research we thought that this project would be relatively expensive and we had an initial estimate of around one thousand dollars The basic total in the tab
95. t tell at what time instances the frequencies occurred Since our recordings of our gunshots are non stationary meaning they do not repeat the Fourier transform is not a good method in order to compare our event gunshots with recorded gunshots Because of this the wavelet transform must be the method used for our non stationary recordings Section 2 Wavelet Analysis Wavelets are localized waves whose energy is concentrated in time and space and are perfect for the analysis of transient signals A wavelet transform is the representation of functions using wavelets Wavelets are scaled into copies of daughter wavelets over a finite length non periodic waveform referred to as the mother wavelet Wavelets are better used than Fourier analysis for our project because they are used for non periodic waveforms and they are also ideal at representing sharp peaked functions such as the characteristic of a gunshot 20 Figure 4 2 Demonstration of a A wave and a B wavelet A B The type of wavelet transformation that we are interested in using for the ATD is the Discrete Wavelet Transform The DWT is easy to implement and has a fast computation time with minimum resources required In order to get the DWT the use of high pass and low pass filtering 1s used on the signal The figure below is of the wavelet decomposition tree X n is the signal Ho are the High Pass filters Go are the Low Pass filters D n are the detail i
96. t and it 1s a requirement that the ATD works across most modern PCs The digital thermometer will provide the ambient temperature to calculate a more accurate speed of sound Since the speed of sound may vary significantly with temperature and the temperature may change by the minute the microcontroller must be able to take in a digital temperature signal every ten minutes and process the signal without interrupting the event listening function Most temperature sensors output the temperature in degrees Celsius in a 12 bit digital word in less than one second so the microcontroller must have at least one digital input and be able to retrieve information at this rate The digital compass provides a reference frame from which to measure the angle of attack of the events Without a proper compass reading no amount of calculation can provide the correct source location The digital compass will output a serial digital measurement and as such the microcontroller must have serial inputs Additionally the microcontroller must have a clock output to sync with the compass in order for the serial 63 data to transmit properly This input will only be used once at the beginning of setup so it will not need to be able to handle high traffic The microcontroller will also need power Ideally it would be able to be powered from USB to minimize the setup time and number of accessories involved Also the USB on the microcontroller will be used in outputting data
97. t the microphones closer together while maintaining accuracy Smaller units will therefore be more expensive Computing requirements The ATD must be able to give immediate feedback regarding the location of the source This means efficient software and a clean easy to use interface The sources GPS location must be apparent to the user within seconds in order for the source to be eliminated or contained The computing requirements for this are relatively low however we will need a higher clock frequency on the DSP to produce accurate results The faster the clock the higher the sample rate thereby creating a more accurate ATD As stated before this has a direct effect on the price Additionally the higher the clock rate the closer together we can place microphones and the smaller we can make the unit as a whole Portability The ATD must be portable enough for its philosophy of use If the ATD 1s being used as coverage for speeches by important public figures the unit may have to be taken with them to multiple locations This would require the unit be relatively light weight and small enough to pack perhaps to take on an airplane If however the unit is being used on the battlefield where it can be carried on armored personnel units it may not need to be as small or as light In fact for military applications it may be desirable to have a larger unit and increase accuracy In this application though the unit must be small enough to be mobile as
98. ted however turning the ATD upside down and elevating it with respect to the event simulates that the event is elevated Record the results from the ATD and external GPS 3 Elevated Triangulation Device Repeat part 2 with the ATD oriented face up Record all of the results and calculations including the variance in external and ATD coordinate results 85 Experiment 2 Range Objectives To determine the range to which the ATD may provide qualitatively accurate and useful results and to determine the ATD accuracy loss as a function of distance Equipment Remington 870 Acoustic Triangulation Device External GPS Background Most sniper fire is outside a range of 1000 meters Additional to be cost effective the ATD must be able to determine event locations at the large distance possible As the event moves away from the ATD accuracy fall off will increase dramatically Little variations over long distances may include buildings interfering with the ATD by producing sound reverberation signal attenuation from the distance itself or even varying temperature changing the speed of sound over the distance between the event and the ATD Additionally the built in inaccuracy of the multilateration algorithm only grows with event distance relative to the spacing between microphones Despite all of this the ATD should produce useful results at relatively large distances Preparation A Calculate the expected accuracy fall off ass a function of d
99. the calculation of the sound source location To reduce the effects of these inaccuracies estimation methods can be used These estimation methods use the data from additional microphones and essentially average the resulting solutions to produce a final answer For the three dimensional multilateration case only four microphones are needed We will instead be using eight microphones in a cube shaped array This will produce additional timing data and allow us to find several possible locations Since each array of four non coplanar microphones can produce a location for the sound source we will use each of these possible arrays in our configuration to find a location estimate The possible arrays include choosing three microphones from one face and one microphone from a different face Examples of valid arrays would include microphones 1 2 3 and 5 microphones 1 4 8 and 7 and microphones 5 8 7 and 3 as seen in Figure 3 3 a In total there are 58 valid arrays based on the cube configuration therefore there are 58 different possible locations for the sound source In the equations found in chapter 3 1 microphones A B C and D can be replaced with the first second third and fourth microphones respectively in the chosen subset array The microphones should be ordered from the first to hear the sonic event to the last to hear the sonic event so that the time difference of arrival values are positive The solving of these equations then re
100. ther guns The reason for this is because the 22 is a very small round and while we were firing it it was definitely not nearly as loud as all the other guns Figure 4b 18 Figure i CI ze File Edit Yiew Insert Tools Desktop Window Help N R EE S D 5 ee e Eilen Spectrum ZZ way 5 Magnitude LI 0 01 D mg D DES DO UA CJ 0 06 DD Mormalzed Frequency Bode Plot of the 22 Below is a figure of the Bode Plot of the 22 caliber This figure is a visual representation of the 22 caliber sound wave s Bode Plot using the Audacity software As you can see in the Bode Plot figure the peak frequency is at 1197 Hertz and its magnitude at this specific frequency is 4 dB Also it is to be noted from this figure that the max amplitudes of the of the 22 calibers sound wave occur in the frequency range of 45 approximately 600 Hertz to around KHz This frequency range must be noted and it must be compared to all other types of gunshot characteristics Figure 4b 19 Cursor 1184 Hz DG 4 dB Peak 1197 Hz D6 Spectrum e 512 ba Hanning window Eh 22 Fie Edit ew Peopect Generate Erec Aname Hele EE ze a Da x de 20 Pg 21 0 einn EET l 13 E 1 00 SR Pepe re 4109 Laar UU 362368 eene psnag To Of 46 38 Blackhawk The figure below is the waveform of the 38 caliber round This figure is a visual representation of our recorded sound wave using the Matlab di
101. tion the signal increases and attenuates extremely high This is the visual representation of the 9 mm Beretta s gunshot muzzle blast This muzzle blast is what our ATD prototype will be detecting from the 9 mm Berretta round Spectrum of the 9 mm Beretta The figure below is of the frequency spectrum of the 9mm Beretta caliber round This figure 19 a visual representation of the frequency spectrum of our recorded sound wave using the Matlab spec function in DSP tools library Notice from this figure at around U normalized frequencies the magnitude is at around 0 9 At around 0 01 normalized frequencies the magnitude is around magnitude Also from the plot at around 0 03 normalized frequency as you can see from the figure the magnitude is max at approximately 3 5 4 Figure 4b 14 File Edit View Insert Tools Desktop Window Help N Dee tb ees ce D spectrum Smilbar wawv 2 9 Magnitude Uz rn enk p oae Pete Es EE DESCH ES o 0 05 U 00s Ui 015 2 25 OF O35 O4 Normalized Frequency 9 mm Beretta Bode Plot Below is a figure of the Bode Plot of the 9 mm Beretta round This figure is a visual representation of the 45 caliber sound wave s Bode Plot using the Audacity software As you can see in the Bode Plot figure the peak frequency is at 1249 Hertz and its magnitude at this specific frequency is 2 dB Also it is to be noted from this figure that the max amplitudes of the of the 9 mm Beretta s sound wav
102. tioning System GPS unit will be present in each array This will provide the triangulation software with the absolute position of each unit and allow for central reference points in our calculations These reference points will then be coupled with the relative vectors produced by the microphone array to provide an absolute position of the source The source location can then be transmitted to the authorities emergency services or other remote user enabling them to take appropriate action in a timely manner The real time triangulation software will act as a central hub for all sensor array and GPS information The event times for each speaker array will be processed through the triangulation algorithms described in Chapter 6 Software and a unit vector in the direction of the source will be calculated The three dimensional intersection of the unit vectors from each array will be calculated to provide the source location relative to the sensor location The software will then use this relative location as well as the absolute location of each array to calculate the absolute coordinates of the source The source coordinates will be displayed in the user interface along with an alert letting the user know an event has occurred and a map of the event s location User options will include relaying step by step directions to the source saving the source sound waves in a database for later playback and transmitting the source coordinates to a remote user
103. to a computer or other device for further analysis The USB will be used additionally to change settings on the ATD or upload additional wavelet libraries These USB transfers must not interrupt the ATD from listening for an acoustic event Another large deciding factor is clock speed As discussed in Chapter 3 Triangulation the faster we can sample inputs the more accurate we can be If we minimize the difference between actual arrival time and perceived arrival time we can greatly increase accuracy We do this by sampling often which means we need a processor with enough power to complete all necessary calculations while still having clock cycles left over for sampling Based on the criteria the search can be narrowed to just a few such microcontrollers Each of them has unique advantages and disadvantages which we will go over in detail in the following pages Price is outlined in Chapter 7 and will not be discussed in detail here Arduino Mega Listed Features e Microcontroller A Tmegal280 e Operating Voltage SV e Input Voltage recommended 7 12V e Input Voltage limits 6 20V e Digital I O Pins 54 of which 14 provide PWM output e Analog Input Pins 16 e DC Current per I O Pin 40 mA e DC Current for 3 3V Pin 50mA e Flash Memory 128 KB of which 4 KB used by bootloader e SRAM 8 KB e EEPROM 4 KB e Clock Speed 16 MHz Based on the features of each microcontroller and the specifications of the ATD the Arduino Mega is an extremely capabl
104. ugh the board s analog to digital converter ADC This new digital signal 1s then processed through the digital signal conversion subroutines written in the main program The subroutines will take the amplitude and time of each sample and store these in a wave class which can be used to reconstruct the wave when necessary The Nyquist Shannon sampling theorem allows the ATD to limit the sampling 90 to only twice the frequency of the sound wave however it is advantageous to sample even more often to obtain a more accurate arrival time from each microphone In the ATD s case the sound waves will be in the range 300 to 3000 Hz requiring 600 6000 samples Where we will sample at the full potential of the board 19kHz we will only save the amplitudes of 6000 of these samples congruent with the sampling theorem and the rest will only be used to calculate and accurate time of arrival That is if microphone one detects an event at time zero and microphone two detects an event at time three the more often we sample the better chance there is that the arrival time was actually at time three and not just sampled at time three Small errors in arrival time quadratically affect the ATD s accuracy Once the arrival times for all microphones are obtained the ATD will only save the next 6000 samples Limiting the number of samples we actually save will help conserve our limited memory The main filter works as follows The number of local maxima in the digit
105. velet transforms and coefficients into a database in the Arduino Mega microcontroller After the storing process is complete we will then be able to take the gunshot events and do the process in order to normalize them in real time After we have the normalized signal the discrete wavelet transform will be done on the signal We will be first taking the input signal of the gunshot events out of the external microphone and then we will send them to MatLab to normalize them The next process will be to store these events into a database in the microcontroller After the storing process is complete we will then proceed and compare the event gunshots with our database of stored recordings in the computer After the gunshot comparison of the coefficients and signals we will then use our tolerance algorithm to output the best match of the type of gun that was used from the gunshot event Section 3 Amplifier Design For our prototype we decided to purchase Breakout Boards for our Electret microphones The reason why we decided to use these in our design is that they were fairly cheap and it amplifies our signals coming out of the microphones by one hundred The figures below are of our Electret microphones set up with the Breakout Board These are the actual units that will be transferring the sound wave into electric signals After these signals are created we can then take these signals and send to them to a filter and then finally they can b
106. wavelets will be saved into the Arduino s memory bank and the current waveform will be compared with all previously saved waveforms The wave that most closely matches the current wave will provide the signal analysis routine with the initial type of explosive caliber of bullet or type of gun of the event The user will have the option of classifying and storing a new wavelet for future acoustic even analysis An additional option for scalability would be the ability of the ATD to store and classify its own new wavelets based on what it learns from previous information If a close enough match is not found the ATD will store the wavelet with an arbitrary name and wait for an external input to give it a classification In the time between storage and 02 classification the ATD would still be able to match new event waves to this arbitrary waveform The map locations and types of events will be stored in an ongoing record until the ATD is reset This will become useful in investigations steak outs and case studies of crime in certain areas where event patterns may emerge that would be useful to certain authorities The Arduino will then transmit this information to an external monitor or to a computer where the information is further analyzed If the information is sent to the computer a map of the GPS location will be pulled up using Google maps a screen shot will be taken and a picture of the round explosion or gun type will be inlayed into the
107. ween two microphones is a hyperboloid as shown in figure 3 2 instead of a hyperbola To find the exact location of the sound source at least four hyperboloids and therefore four microphones are needed find a single point of intersection These microphones can be located at any position as long as they are not all 1n the same plane If all the microphones are in the same plane there will be two points at which all hyperboloids intersect As before any microphones located in the same plane beyond the first three will give no new information The equations used to find the sound source are the same as the two dimensional case except that the locations of each microphone are represented by an x coordinate a y coordinate and a z coordinate Also the use of a fourth microphone gives us a third equation to solve and therefore the ability to solve for the three unknowns which are the x coordinate the y coordinate and the z coordinate of the sound source 10 1 cN Gc me O yg re ll y z tg t4 Tap 1 or es C rate Oa Ve haze Sa eoa L A Tg 1 cx Oe xp O yo z Zp yx y z tp t4 Tap section 3 Error When using multilateration there are several possible sources of error The microphones can be too low resolution and cause inaccurate event times the clock used to find the time difference can be inaccurate or general noise in the system can give inaccurate readings and therefore cause inaccuracies in
108. y we obtained the Bode Plot of each individual sound wave using the built in Plot Spectrum tool provided in the Audacity software We then used Audacity to convert the raw sound wave into a Wav file in order for Matlab to be able to read the data Below is the data that we have obtained from our gunshot recordings Section 2 Sound Wave Analysis 45 caliber The figure below is the waveform of the 45 caliber round This figure is a visual representation of our recorded sound wave using the Matlab dis function in DSP tools library This visualization is the equivalent to what a digital oscilloscope would show Notice as you can see in the wave at around 0 012 seconds there is a small sharp fall followed by small slight sharp rise This is the representation of the bullet noise ground reflection of our recorded gunshot As you can see right after the bullet noise ground reflection the signal jumps extremely high This is the visual representation of the gunshots muzzle blast This muzzle blast is what our ATD prototype will be detecting from the 45 caliber round Figure 4b 1 Figure 1 Bis Ea File Edit View Insert Tools Desktop Window Help N DS E e x amp ak uiis m Binary Data 45 way m Magnitude Cc 41 2 U nnns 0 01 0 015 002 0 025 0 03 0 035 0 04 0 045 Time s Spectrum of the 45 caliber The figure below is of the frequency spectrum of the 45 caliber round This figure is a visual representation

Acoustic Triangulation Device - Department of Electrical

Contents

Download Pdf Manuals

Related Search

Related Contents