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1. 3 4 Making an Electromagnet Objective To demonstrate the equivalence of a bar magnet and a current carrying solenoid coil Procedure e Connect the 3000T coil from OD1 to GND e Suspend the cylindrical magnet in front of the coil e Enable Check button OD1 to make it 5 volts e Repeat by reversing the coil connections 31 Observation When OD1 is set to 5 volts the magnet will be either repelled or attracted depending on the direction of the current and the pole of the magnet near the coil The direction of force can be reversed by changing any one of them 32 Chapter 4 Electronics The non linear elements like diodes and transistors are studied by drawing their characteristic curves and making simple circuits to demonstrate their function ing Photo transistor is used for transparency measurements optical signal transmission and for timing mechanical movements Amplitude and Frequency modulation are explored A bread board is required to carry out some of the experiments described in this section 4 1 Half wave rectifier PN junction Objective Learn the working of a PN junction diode Making DC from a sinusoidal AC Filtering to reduce the AC component e Assign Al to CH1 and A2 to CH2 Procedure e Add different values of filter capacitors from A2 to ground Observation The negative half is removed by the diode as shown in figure 4 1 a Also notice that the voltage in the positive half is reduced by aroun
2. Figure 2 2 a A 0 to 5V square wave with DC component blocked b Mea suring electrical resistance of human body e Set SQR1 to 500 Hz Procedure e Assign SQR1 to CH1 and A2 to CH2 e Adjust the horizontal scale to see several cycles Observation The observed waveforms with and without the series capacitor are shown in figure 2 2 The voltage is swinging between O and 5 volts After passing through the capacitor the voltage swings from 2 5 volts to 2 5 volts What will you get if you subtract a 2 5 from the y coordinate of every point of the first graph That is what the capacitor did It did not allow the DC part to pass through This original square wave can be considered as a 2 5V AC superimposed on a 2 5V DC You may need to connect a resistor from A2 to GND to see a waveform swinging between 2 5 to 2 5 volts Remove the resistor and observe the result 2 10 Resistance of human body Objective Get some idea about the resistance of the skin and how it varies e Assign Al to CH1 and A2 to CH2 Procedure e Join PVS and A2 through your body and measure voltage at CH2 e Calculate your body s resistance as given in section 2 6 e Repeat using SINE instead of PVS Enable FIT to measure voltage Observation The observed waveform is shown in figure 2 2 b Voltage at A2 is 3V The ripple in the output is due to the 50Hz AC pickup can be eliminated by performing the experiment far away from power lines using a lapt
3. Try different frequencies e Capture with larger NS lt 1800 for doing Fourier transform Observation The resonant frequency of the Piezo crystal is around 3600 Hz Driven by a square wave the piezo gets a kick on every rising and falling edge and it undergoes several cycles of oscillations at its natural resonant frequency The Fourier transform shows a peak at the resonant frequency and side band 200 Hz separated from the peak It may be interesting to repeat this study using a variable frequency sine wave instead of the square wave 5 6 Capturing a burst of sound Objective Digitize sound from a transient source A bell or two metal plates can be used as source of sound The capturing of sound is synchronized with the burst of sound by waiting for microphone output to go above a threshold A better way is to make IN1 go HIGH with the sound and the capture routine waiting for that 46 MIC A1 IN e From EXPERIMENTS select Capture Burst of Sound Procedure e Check Wait on HIGH if the diode and resistor are wired e Click on Start Scanning and make the sound Observation A burst of sound captured is shown below AT 48 Chapter 6 Mechanics Optics amp Heat Resonance phenomena is studied using a driven pendulum Value of acceleration due to gravity is measured using a pendulum Cooling of a liquid is studied using a PT100 sensor 6 1 Resonance of a driven pendulum Objective Demonstrate the resonance o
4. Selected CH1 for fitting EXPERIMENTS QUIT Figure 1 3 The croplus screen showing 1000 5 Hz sine wave connected to Al 1 5 3 Measure frequency amp Duty cycle e Set SQR 1 to 1000 e Right Click on SQR1 to display frequency and duty cycle e To set 488 Hz 30 PWM enter set_sqr1_pwm 30 inside the Command window e Measure again by Right Clicking on SQR1 1 5 4 Accuracy and resolution Figure 1 3 shows a 3V 3000 5 Hz sine wave from an Agilent 33220A Function generator connected to Al The voltage at IN1 is measured as 3 000 by a Keithley 2100 multimeter off by 2mV The frequency of audio frequency sine wave is measured with less than 0 1 error The voltage measurement has 12 bit resolution but the absolute accuracy may change slightly with ambient temperature 1 6 Experiments The expEYES hardware can generate measure different kinds of voltage signals For measuring any other parameter it should be converted into a voltage using appropriate sensor elements For example a temperature sensor will give a voltage indicating the temperature A GUI program is provided for every experiment given in this manual How ever it is possible to do the same by writing few lines of code in Python lan guage All the communication to expEYES is done using a Python library called eyesj py Data analysis and graphical display is also done in Python If you are interested in developing new experiments based on expEYES it would be a good id
5. 2 14 Measuring Capacitance 0 o 2 15 Measuring Dielectric Constant 2 16 AC Phase shift in RC circuits 2 17 AC phase shift in RL circuits 2 18 Study of AC circuits e 2 19 Transient Response of RC circuits 2 20 Transient Response of RL circuits 2 21 Transient response of LCR circuits 2 22 RC Integration amp Differentiation 2 23 Fourier Analysis e o NINA KRW 10 10 11 11 11 3 Electricity amp Magnetism 3 1 Electromagnetic induction 0000004 3 2 Mutual induction transformer 3 3 A simple AC generator 20 ee eee 3 4 Making an Electromagnet 204 4 Electronics 4 1 Half wave rectifier PN junction 4 2 180 0ut of phase sine Waves ASS Fullsvave Tectile pas na ea 4 4 Diode I V characteristic 0000020008 4 5 Transistor CE characteristic 0 0 00 000 4 6 Transmission of Light Photo transistor 4 7 Opto electric signal transmission 2 AK LC Oe ISCINALOL rara oe ga SG oe a 4 9 1IC555 Monostable multivibrator 0 0 Ar NO LOIC LATES eog sa ake s4 ac i Ses Se he Ae Gan ba ep Be ae Bes ed AN Clock Divide a ii Ste Sak OB BOG OH EEG SO e
6. Pulse Width Modulated PWM waveforms at some fixed frequencies gt gt gt print p set_sqri_pwm 30 30 duty cycle 488 Hz gt gt gt t v p capture_hr 6 300 50 get the wave form gt gt gt plot t v The result is shown in figure 7 3 b expE YES can measure time interval between voltage transitions at the dig ital inputs The results returned are in microseconds Connect SQR1 to IN1 and try gt gt gt print p set_sqri 1000 1kHz square wave gt gt gt print p r2ftime 3 3 rising to falling 500 gt gt gt print p multi_r2rtime 3 two rising edge 58 1000 gt gt gt print p measure_frequency 3 1000 Try to set square waves of different frequencies and measure them From a captured waveform we can measure the amplitude and frequency by curve fitting The results are accurate with a sine wave input but frequency measurement works with other shapes also Connect SINE to Al and try gt gt gt import expeyes eyemath as em gt gt gt t v p capture_hr 1 400 50 gt gt gt vfit par em fit_sine t v gt gt gt print parlO par l1 1000 Amplitude Frequency The peak voltage and the frequency will be printed For more information read the Programmer s manual You can get a brief description of all the functions by giving the command gt gt gt help expeyes eyesj Once you learn Python language it will be easier to read through the source code eyesj py to understand the working of the progr
7. Vs Time a Graph of DC and AC b AC mains pickup 2 8 DC AC and power line pickup Objective Introduce the concept of time dependent voltages using a V t graph Compare the graph of DC and AC Learn about the AC mains supply Explore the phenomenon of propagation of AC through free space Procedure a e Assign Al to CH1 and A2 to CH2 e Set PVS to 1 volt e Assign CH1 to FIT to measure AC parameters e Disconnect SINE and connect a long wire to Al Mains pa Power O O Socket Observation Figure 2 1 a shows that the graph of DC is horizontal line and for AC it changes direction and magnitude with time The voltage is changing with time It goes to both negative and positive around 150 cycles per second This voltage waveform is generated by using electronic circuits Enabling FIT option calculates the amplitude and frequency by fitting the data with the equation V Vosin 27 ft 0 where Vo is the amplitude and f is the frequency What is the significance of 0 in this equation The power line pickup is shown in figure 2 1 b The frequency is obtained by fitting the data Without making any connection how are we getting the AC voltage from the mains supply Why the voltage increaes when you touch the end of the wire connected to A1 by hand Wire near power line but NO connection 2 9 DC amp AC components of a voltage Objective Separating AC and DC components of a voltage waveform using a capacitor 17
8. along with the modulating signal is shown in figure 4 12 b Power spectrum is calculated using Fourier transform To get better results a larger sample 1800 samples with 50 usec gap is taken for this purpose The two sidebands are clearly obtained on both sides of the carrier peak separated by the modulating frequency The AM output looks similar to the sound beats we obtained in section 5 4 but taking a power spectrum of beats gives two peaks corresponding to the individual frequencies How do they differ despite of the similar looks Doing frequency modulation just changing the connection from AM to FM is left as an exercise to the user 42 Chapter 5 Sound Pressure variations about an equilibrium pressure transmitted through a medium is called sound They are longitudinal waves Moving a sheet of paper back and forth in air can generate these kind of pressure waves like the paper cone of a loudspeaker When the frequency is within 20 to 20000Hz range we can hear the sound In this chapter we will generate sound from electrical signals detect them using the built in microphone a pressure sensor and study the properties like amplitude and frequency Velocity of sound is measured by observing the phase shift of digitized sound with distance 5 1 Frequency of sound Objective Digitize sound and measure its frequency Use the Piezo buzzer or any other source of sound like a tuning fork MICH At e Set SQR1 around 35
9. and other programs already using expE YES Only one program can use expEYES at a time We will start by measuring the stray capacitance of the socket IN1 55 Channel 4 Analog Comparator output SQR1 readback SQR2 readback SQR1 output a ODA output 7 10 11 CCS output control 12 PVS Readback Table 7 1 Channel numbers of Input Output terminals gt gt gt p measure_cap measure C on IN1 A value of 30 to 35 pF will be printed Connect a capacitor smaller than 0 01 uF from IN1 to GND and repeat the command Subtract the stray capacitance from the values obtained Digital Input Output features are available To test them connect OD1 to IN1 using a piece of wire and try the following gt gt gt print p get_state 3 status of IN1 gt gt gt p set_state 10 1 make OD1 logic high gt gt gt print p get_state 3 new status of IN1 For the second call get state 3 should print 1 Now let us start generating measuring voltage signals Connect PVS to IN1 and try gt gt gt print p set_voltage 2 5 returns the value set gt gt gt print p get_voltage 3 channel 3 is IN1 It should print 2 5 volts within 2 3 millivolts Now connect SINE to Al and try gt gt gt print p get_voltage 1 You will get different results every time you issue the command use cursor and backspace keys to edit previous commands Since the voltage is changing periodically it makes better sense to measure this voltag
10. given 2 1 Measuring Voltage Objective Learn to measure voltage using expEYES and get some idea about the concept of Electrical Ground A dry cell and two wires are required GND _cell_ H At e Click on Al to display the voltage Procedure e Repeat by reversing the cell connections Observation Voltages measured value is 1 5 volts and it becomes 1 5 after reversing the connections We are measuring the potential difference between two points One of them can be treated as at zero volts or Ground potential The voltage measuring points of expEYES measure the voltage with respect to the terminals marked GND We have connected the negative terminal of the cell to Ground The positive terminal is at 1 5 volts with respect to the negative terminal Wall it show correct voltage if GND is not connected If the input voltage is within O to 5V range use IN1 which is directly connected to the ADC input Resolution of bipolar inputs Al and A2 are half 13 of that of IN1 The offset and gain errors of the level shifting amplifiers also affect the accuracy of Al amp A2 2 2 Voltage current amp resistance Objective Learn about Current Resistance and Ohm s law using a couple of resistors The voltage across a conductor is directly proportional to current flowing through it The constant of proportionality is called Resistance This is known as Ohm s Law expressed mathematically as Procedure e Set PVS to some vo
11. of resistors R R1 R2 using a constant current source A 5600 and alk resistors are used Procedure e Connect R1 R2 alone and then both e Measure IN1 for each case R Q V volts 360 008 Ob i E ee 1000 0 998 Since the current is same the total voltage drop gives the effective resistance It can be seen that it is the sum of the individual values within the measurement error For more accurate results use the value of current measured as explained in section 2 3 instead of ImA 2 5 Resistances in parallel Objective Find the effective resistance of parallel combination of resistors given by SB mtpto eos oxo Procedure R2 e Connect 1kQ resistor from CCS to Ground e Repeat the same with two resistors connected in parallel canpeeioa R Vinensurca V Observation 1000 1 008 1000 1000 0 503 Since we know the current we can calculate the resistance from the measured voltage As per the measured voltage the resistance of the parallel combination a 0 503V __ is 250Y 030 2 6 Measure resistance by comparison Objective Learn to apply Ohm s law to find the value of an unknown resis tance by comparing it with a known one Voltage across a resistor is given by V IR If same amount of current is flowing through two different resistors the ratio of voltages will be the same as the ratio of resistances J E ya Procedure e Connect the unknown resistor R from PVS to IN1 e Con
12. of series LCR elements in an AC circuit The total applied AC voltage is measured on Al and the voltage across the resistor on A2 Subtracting the instantaneous values of A2 from Al gives the voltage across the inductor and capacitor We need to use an inductor with negligible resistance for good results The phase difference between current and voltage is given by A arctan EL SINE GND e Use 1k resistor Resistance of the inductor should be less than 10 Ohms Procedure e select Study of AC Circuits from EXPERIMENTS Observation The total voltage voltage across R and the voltage across LC are shown in figure 2 5 The phasor diagram shows the phase angle between the current and the voltage The inductance used in this experiment is around 300mH having a resistance of 52 You may use an external sine wave generator with variable frequency to study the variation of Xe Xy with frequency At the resonant frequency this will become zero and the current and voltage will be in phase 2 19 Transient Response of RC circuits Objective Plot the voltage across a capacitor when it is charged by applying a voltage step through a resistor Calculate the value of the capacitance from the graph http www play hookey com ac_theory ac_inductors html 23 SERIA DAE vott div MLI Save Traces to cro txt XmGrace QUIT Traces saved to cro txt Figure 2 5 AC response of series RLC circuit 5 0 5 0 mS mS mS div _
13. open Transistor CE e Enter the Bias supply voltage to the base and START Repeat for different Vb Observation The characteristic curves for different base currents are shown in figure 4 4 The collector current is obtained from the voltage difference across the 1k resistor The base current is set by setting the voltage at one end of the 200 kQ resistor the other end is connected to the transistor base The value of base current is calculated by I Vii Oe x 101 A Tf the FIT is not successful transfer data to 2mGrace and use the option Data gt Transformations gt Nonlinear curve fitting with equation y a0 exp al x 36 Figure 4 5 LED and photo transistor Electrical connections and mechanical mounting 4 6 Transmission of Light Photo transistor Objective Measure the transmission of light through semi transparent ma terial using a photo transistor The material is kept between an LED and the photo transistor The collector current depends on the amount of light falling on the transistor Procedure e Set SQR1 to 0 Hz to turn on the LED e Assign SEN to CH1 e Measure voltage at SEN by clicking on it e Repeat by changing the material between LED and photo transistor Observation The voltage at the collector of the photo transistor reduces with the intensity of light falling on the transistor The voltage measured after placing a piece of paper between LED and photo transistor is shown in figure4 6 a 4 7 O
14. to move with the difference in frequency Procedure e From EXPERIMENTS select Stroboscope e Connect the White LED from SQR1 to GND e Power the motor by a battery and illuminate it with the LED e Adjust SQR1 to make the motor appear stationary Observation As you adjust SQR2 the movement of the disc on the axis of the motor appears to slow down and then at some point reverses the direction of motion Note down the frequency at the direction reversal When viewed in a pulsed light source of frequency 11 Hz a motor rotating clockwise at 10 rotations per second will look like rotating anti clockwise once a second During stopping and starting the ceiling fans sometimes looks like rotating backwards in the light of fluorescent tubes How is the RPM of a car engine adjusted 92 6 6 Speed of rotation of a motor Objective Learn about making sensors to detect mechanical movements Use a photo transistor to find the rotational speed of a motor Procedure A single leaf is attached to the motor and it is placed between the photo transistor and the LED intercepting the light once during every rotation e Set SQR2 to 100Hz to rotate the motor e Assign SEN to CH1 e Right Click on SEN to measure the frequency FIT option may not work for these pulses Observation The photo transistor output goes HIGH when the light is ob structed The observed values can be cross checked by using a magnet and coil as explained in sectio
15. very fast at this point The plate B also gathers the same charge as plate A that is how a capacitor works The current to plate B is flowing from ground through the resistor and we are measuring the IR drop across the resistor it will be already positive when plate A is at zero This results in the phase advance 2 17 AC phase shift in RL circuits Objective Measure the AC voltage phase shift in an RL circuit Impedance of an Inductor X 27 fL where f is the frequency in Hertz and L is the inductance in Henry In an LC circuit the phase lag across the inductor is given by the equation Ad arctan ES i where R is the resistance in Ohms rat sine ror axa 22 Procedure e Assign Al to CH1 and A2 to CH2 e Adjust the horizontal scale to view more than 4 cycles e Right Click on Al to view voltage frequency and phase difference Observation The measured phase shifts are shown below Waveforms for the 125 mH inductor is shown in figure 2 4 b The resistance of the inductor also should be included while calculating the phase shift L mH R Reoil an Res 9 AD inesewred 565 560 Insert an iron or ferrite core to the coil and observe the effect of ferromagnetic 2 materials Self Inductance of a solenoid is given by L EA A where N is the number of turns A is the cross sectional area p is the permeability of the surrounding media and is the length 2 18 Study of AC circuits Objective Study the effect
16. 00Hz keep buzzer in front of the microphone Procedure e Enable FIT to measure the frequency e Repeat with other sources of sound Observation The amplified output of the microphone is shown in figure 5 1 a The amplitude is maximum near 3500 Hz due to resonance Driving with 1200Hz gives more amplitude than 2000Hz due to the third harmonic of the Square wave matching the resonant frequency Sound waves create pressure variations in the medium through which it travel The microphone generates a voltage proportional to the pressure Since this signal is very small we amplify it 51 times before digitizing it The volt age variations are in tune with the pressure variations You can consider the microphone as a pressure sensor but working only for time varying pressures 43 x 1 800 5 9 Y 0 800 x 3641 667 2 0 0 4 0 8 1 2 1 6 2 0 0 010 1 825 ms 00 0 3000 0 3500 0 4000 0 4500 0 5000 req SQRI1 set to 3654 6 Figure 5 1 a Digitized sound wave b Frequency response curve of the Piezo disc 5 2 Frequency response of Piezo Objective Plot the frequency response curve of the Piezo disk by scanning through the frequency and measuring the amplitude of the microphone output e From EXPERIMENTS select Frequency Response e Press START button Observation The Frequency Vs Amplitude plot is shown in figure 5 1 b The amplitude is maximum around 3700 Hz 5 3 Velocity of sound Objective Calculate the velocity of
17. 5 volts Change the gain field entry accordingly ol 90 80 40 o 60 lt E Temperature J 50 3 0 400 0 800 0 1200 0 1600 0 2000 Time Read Every 1000 mS fortotal 2000 Seconds Range 0 to 1po c START STOP CLEAR 0 500 1000 1500 2000 2500 Gain 11 Current 0 96 ma Xmgrace SAVE to pt100 dat Time Seconds Freezing Point Boiling Point Calibrate QUIT ls Figure 6 3 Cooling of water a Screen shot of the program b Graphs for clear water and coloured water Observation Cooling curve of water is shown in figure 6 3 The temperature is changing in big steps this can be improved by using an amplifier between CCS and IN1 as explained in section 4 12 Instead of measuring the current and calculating the actual amplifier gain one can follow a calibration procedure to obtain good results This procedure assumes a linear variation of resistance with temperature To do calibration place the sensor in ice and click on Freezing Point Immerse the sensor in boiling water and click on Bowling Point After that click on Calibrate Once the calibration is done the temperature is calculated using the calibration constants 6 5 Stroboscope Objective An object executing periodic motion will appear stationary when it is illuminated with a light pulse of the same frequency since the object is illuminated every time only when it reaches the same point If the frequencies are slightly different it will appear
18. EP 5 to OV STEP CLEAR Saveto ridat Xmgrace Rext 1000 Calculate R L QUIT L R 0 087 mSec Rind 599 Ohm L 138 4 mH Figure 2 7 Transient response of RL circuit In an RL circuit V IR LS and solving this will give ine The coefficient of the exponential term R L can be extracted from the graph of voltage across the inductor The resistance of the inductor coil should be included in the calculations R Rex RL Procedure e Inductor is the 3000 Turn coil e From EXPERIMENTS select RL Circuit e Click on 0 gt 5V STEP and 5 gt 0V step Buttons to plot the graphs e Adjust the horizontal scale if required and repeat e Calculate the value of inductance e Insert an iron core into the inductor and repeat Observation The transient response of the inductor is shown in figure 2 6 The exponential curve is fitted to extract the L R value The resistance of the coil is measured by comparing it with the known external resistance under DC conditions IN1 is connected to OD1 for a more accurate measurement of the coil resistance The applied voltages are above zero but the graph went to negative voltages Why What was the current before doing the 5 gt 0 step What is back EMF Repeat with two coils in series by a placing them far away b placing one over the other and c after changing the orientation The effect of mutual inductance can be seen 2 21 Transient response of LCR circuits Object
19. EXP EY E 5 Junior User s Manual Experiments for Young Engineers and Scientists http expeyes in from PHOENIX Project Inter University Accelerator Centre A Research Centre of UGC New Delhi 110 067 WWW luac res in Preface The PHOENIX Physics with Home made Equipment amp Innovative Experi ments project was started in 2004 by Inter University Accelerator Centre with the objective of improving the science education at Indian Universities De velopment of low cost laboratory equipment and training teachers are the two major activities under this project expEYES Junior is a modified version of expEYES released earlier It is meant to be a tool for learning by exploration suitable for high school classes and above We have tried optimizing the design to be simple flexible rugged and low cost The low price makes it affordable to individuals and we hope to see students performing experiments outside the four walls of the laboratory that closes when the bell rings Hardware design is open and royalty free The software is released under GNU General Public License The project has progressed due to the active par ticipation and contributions from the user community and many other persons outside IUAC We are thankful to S Venkataramanan and Prof R Nagarajan for correcting this document by carrying out the experiments described inde pendently expEYES Junior user s manual is distributed under GNU Free Documenta ti
20. Oto5VSTEP 5to0VSTEP CCCharge CalculateRC QUIT msjdiv Oto5VSTEP StoOVSTEP CCCharge CalculateRC QUIT ViewAll Xmgrace CLEAR Save to rc dat ViewAll Xmgrace CLEAR Save to rc dat Done Done Figure 2 6 a Transient response of RC circuit b Charging of capacitor with constant current e From EXPERIMENTS select RC Circuit Procedure e Click on 0 gt 5V STEP and 5 gt 0V step Buttons to plot the graphs Adjust the horizontal scale if required and repeat Calculate RC time constant Use CCS instead of OD1 to charge capacitor with constant current Observation Applying a 0 to 5V step makes the voltage across the capacitor to rise exponentially as shown in the figure2 6 a By fitting the discharge curve with V t Vye RT we can extract the RC time constant and find the values of capacitance from it The voltage across a capacitor is exponential only when it is charged trough a linear element a resistor for example When charged from a constant current source the voltage shows linear increase as shown in figure 2 6 b because Q It CV and voltage increases linearly with time as V 4 les 2 20 Transient Response of RL circuits Objective Explore the nature of current and voltage when a voltage step is applied to resistor and inductor in series By measuring the voltage across the inductor as a function of time we can calculate its inductance 24 mS mS div _ _ 0 to 5V ST
21. am If you find mistakes send a mail to ajith iuac res in 59
22. apture the voltage before and after the capacitor by gt gt gt t1 v1 t2 v2 p capture2 1 2 300 100 gt gt gt plot t1 v1 t2 v2 gt gt gt plot v1 v2 The out put is shown in figure 7 2 a The last line plots a Lissajous figure as shown in figure7 2 b There are more than one ellipse one over the other since we captured more than one cycle In some experiments the captured voltage may be generated by some other actions like changing a voltage level This is done by implementing capture modifiers This can be easily demonstrated by capturing the voltage across a capacitor just after applying a voltage step to it through a resistor Connect 1k resistor from OD1 to Al a luF capacitor from Al to GND and run ov Figure 7 2 a Phase shift of sine wave across a capacitor b Lissajous plot of the voltages Figure 7 3 a Capacitor discharge b PWM waveform gt gt gt p set_state 1 0D1 5 volts gt gt gt p enable_set_low 10 Effect only during capture gt gt gt t v p capture_hr 1 300 20 OD1 gt 0 before capture gt gt gt p disable_actions No more actions on 0D1 gt gt gt plot t v The result is shown in figure 7 3 a The outputs SQR1 and SQR2 can generate square waves ranging from 7Hz to 200kHz function returns the actual frequency set They can also be pro grammed to generate
23. ated to get spikes at the transitions im Procedure e Set SQR2 to 1000Hz e Assign SQR2 to CH1 and Al to CH2 http en wikiversity org wiki RLC _ circuit 26 3 0 0 8 1 6 2 4 3 2 4 0 5 0 5 0 3 0 3 0 1 0 1 0 v v 1 0 1 0 3 0 3 0 5 0 3 0 8 0 16 0 24 0 32 0 40 ms Figure 2 9 a 1kHz Squarewave after RC Integrator b 100Hz after RC Differ entiator e Adjust the horizontal scale to view more than 4 cycles e Set SQR2 to 1kHz T 1mS and other values and view the waveforms e Repeat the same for RC differentiator at 100Hz SQR2 s GND Observation Integration observed at 1kHz and differentiation at 100Hz are shown in figure 2 9 using an RC value of 1 milliseconds When the time period becomes comparable with the RC value the output waveform is triangular The differentiation can only be shown at lower frequency since capturing the narrow spike requires a fast oscilloscope 2 23 Fourier Analysis Objective Learn about Fourier Transform of a signal Time and Frequency domain representations e Set SQR1 to 150Hz Procedure e Assign Al to CH1 and SQR1 to CH2 e Assign CH1 amp CH2 to FTR to view the Fourier transform Observation In the Fourier transform plot frequency is on the x axis and the y axis shows the relative strength of each frequency components of the signal This is called the frequency domain representation For the sine wave there is only one dominant peak the smaller ones are a measu
24. d 0 7 volts the voltage drop across a silicon diode A load resistor is required for Figure 4 1 a Half wave rectifier input and output b With capacitor filter 33 5 0 5 0 3 0 3 0 1 0 1 0 v v 1 0 1 0 3 0 3 0 5 0 5 0 2 0 4 0 8 0 8 6 11 5 14 3 ms i i j ms Figure 4 2 a Inverting Amplifier making 180 out of phase sine wave b Fullwave rectifier two inputs and the output the proper operation of the circuit it could be more than 1kQ but do NOT use very low values since our AC source can drive only up to 5 mA current The effect of a capacitor is shown in figure 4 1 b We can see that the capacitor charges up and then during the missing cycle it maintains the voltage The remaining AC component is called the ripple in the DC Can we use very large capacitance to reduce the ripple During what part of the cycle does current flow through the diode Amount of peak current is decided by what 4 2 180 out of phase sine waves Objective To demonstrate the working of a full wave rectifier using two diodes we need two AC waveforms differing by 180 degree in phase We do this by inverting the output of SINE using an inverting amplifier The gain is made near unity by feeding the amplifier input through a 51k series resistor Procedure e Assign Al to CH1 and A2 to CH2 e Right click on CH1 to measure phase difference Observation The result is shown in the figure 4 2 The amplitudes are not exactly e
25. d It is widely accepted that per sonal experience in the form of experiments and observations either carried out by students or performed as demonstrations by teachers are essential to the pedagogy of science However almost everywhere science is mostly taught from the text books without giving importance to experiments partly due to lack of equipment As a result most of the students fail to correlate their classroom experience to problems encountered in daily life To some extent this can be corrected by learning science based on exploration and experimenting The advent of personal computers and their easy availability has opened up a new path for making laboratory equipment Addition of some hardware to an ordinary computer can convert it in to a science laboratory Performing quick measurements with good accuracy enables one to study a wide range of phenomena Science experiments generally involve measuring controlling phys ical parameters like temperature pressure velocity acceleration force voltage current etc If the measured physical property is changing rapidly the mea surements need to be automated and a computer becomes a useful tool For example understanding the variation of AC mains voltage with time requires measuring it after every millisecond The ability to perform experiments with reasonable accuracy also opens up the possibility of research oriented science education Students can compare the experim
26. dth Modulated waveforms SQR1 is wired to channel 6 for read back and SQR2 is wired to channel 7 Setting frequency to 0Hz will make the output HIGH and setting it to 1 will make it LOW in both cases the wave generation is disabled When the wave generation is disabled SQR1 and SQR2 can act as digital outputs on channel 8 and 9 respectively SQR1 output has a 1000 series resistor so that it can drive LEDs directly Infrared Transmission An Infrared Diode connected to SQR1 can transmit data using IR transmission protocol The 4 byte transmission can be used for emulating common TV remotes It also supports a single byte transmission that can be received by a program running on a micro controller SINE wave Fixed frequency sine wave generator frequency is around 150 Hz Bipolar signal output with an amplitude of around 4 volts Constant Current Source CCS The constant current source can be switched ON and OFF under software control The nominal value is 1mA but may vary from unit to unit due to component tolerances To measure the exact value connect an ammeter from CCS to GND Another method is to connect a known resistance 3 3k and measure the voltage drop across it The load resistor should be less than 4k for this current source Microphone MIC There is a built in condenser microphone on the side near CCS Its output amplified 51 times is available on MIC output Connect it to Al or A2 for viewing Inverting Amp
27. e 4 12 Non inverting Amplifier 4 13 Amplitude amp Frequency Modulation 5 Sound 5 1 Frequency of sound 4 4 9 26 4 4 BD 2S oe EE ERA BGS 5 2 Frequency response of Piezo 0 5 3 Velocity of sound 2d asa iia aa 5 4 Interference of sound 0 00000 ee eee 5 5 Forced Oscillations of Piezo electric crystal 5 6 Capturing a burst of sound 208 4 6 Mechanics Optics amp Heat 6 1 Resonance of a driven pendulum 6 2 Value of g Rod pendulum 6 3 Oscillations of a pendulum a a a a a a a a 6 4 Temperature measurement PT100 6 9 SODOSCOPE ds a a ae ok 9 a ds de Soe ta Be e e Be a 6 6 Speed of rotation of a motor oa e a e a a 7 Coding expEYES in Python 7 1 Installing the Python Libraries 7 2 Hardware Communication a e 1 lFor an updated list of experiments visit http expeyes in experiments with expeyes junior 2 Chapter 1 Getting Started 1 1 Introduction Science is the study of the physical world by systematic observations and exper iments Proper science education is essential for cultivating a society where rea soning and logical thinking prevails and not superstition and irrational beliefs Science education is also essential for training enough technicians engineers and scientists for the economy of the modern worl
28. e for some duration and plot it We will import the matplotlib library for plotting capture the sine wave and plot it gt gt gt from pylab import gt gt gt ion set pylab interactive mode gt gt gt t v p capture 1 300 100 gt gt gt plot t v 56 Figure 7 1 Inputs captured and plotted using pylab a Sine wave b Sine and square We have sampled the voltage on A1 300 times with a delay of 100 micro seconds between two consecutive readings i e the voltage is captured for total 30 milliseconds Each data word is 1 byte in size and the maximum number of samples possible is 1800 limited by the RAM on expEYES The graph will popup in a new window as shown in figure 7 1 a For measuring with higher resolution 12 bits you may use capture_hr but the total number of samples will be limited to 900 in that case gt gt gt t v p capture_hr 1 300 100 gt gt gt plot t v Now let us add a square wave to the plot by gt gt gt print p set_sqri 100 set 100Hz on SQR gt gt gt t v p capture 6 300 100 channel 6 is SQR1 readback gt gt gt plot t v The output is shown in figure 7 1 b Some experiments will require capturing more than one waveform with tim ing correlation use capture2 capture3 or capture4 for this For example to view the phase shift of a sine wave connect SINE to Al a luF capacitor from Al to A2 and a 1k resistor from A2 to GND C
29. ea to learn Python programming language Almost every experiment can be extended in several ways and some hints are given in this direction The following chapters describe experiments from different topics like elec tricity magnetism electronics sound heat etc Since the expEYES kit is meant 2 For information about all the commands refer to the Programmer s manual 11 for self learning we have included some very trivial experiments in the begin ning Photographs of experimental setup are not included in this document to reduce size They are available on the website 3http expeyes in experiments with expeyes junior 12 Chapter 2 Electricity We start with the simple task of measuring the voltage of a dry cell Current and resistance are introduced next followed by resistances changing with tempera ture and light The concept of Alternating Current is introduced by plotting the voltage as a function of time The behavior of circuits elements like capacitors and inductors in AC and DC circuits are explored by measuring parameters like amplitude frequency and phase The transient response of a resistor and capacitor in series is used for measuring the capacitance Inductance also is measured in the same manner The Fourier analysis of waveforms are done to study the harmonics Integration and differentiation of a square wave using RC circuits also is explored For each experiment make connections as per the diagram
30. eak is bigger than the first peak Why Where will be the magnet at the zero crossing of the induced voltage Drop the magnet from different heights and plot the voltage vs square root of the height 3 2 Mutual induction transformer Objective Demonstrate mutual induction using two coils One coil is powered by the SINE output The axes of the coils are aligned and a ferrite core is inserted 29 CLEAR VIEW QUIT Peak voltages 2 29 and 2 666 separated by 10 500 msec Figure 3 1 a Voltage induced on a coil by a moving magnet b Mutual Induc tion between two coils the applied and induced voltages are shown Procedure e Assign Al to CH1 and A2 to CH2 Observation The applied waveform and the induced waveform are shown in figure 3 1 2 A changing magnetic filed is causing the induced voltage In the previous two experiments the changing magnetic field was created by the movement of permanent magnets In the present case the changing magnetic field is created by a time varying current The output should have been in phase with the input as per the theory However this is not happening if the coupling is not enough With more ferrite material the phase shift is as expected from the theory Try doing this experiment using a squarewave of 100 Hz 1000 Hz etc Connect a 1kQ resistor across secondary coil to reduce ringing 3 3 A simple AC generator Objective Measure the frequency and amplitude of the volta
31. ecting anything to INI and subtract that value from the C measured with capacitor This method can be used for values upto 10000 pF Touching the capacitor during the measurement will corrupt the result l Beyond that you need to use the Python function that can specify the charging current duration of charging etc 20 Procedure a e Measure C without anything connected to get the stray capacitance e connect the capacitor from IN1 to ground e Click on the ButtonMeasure C on IN1 e Repeat with different capacitors Observation The empty socket measures 34 pF Several capacitors were mea sured Measured value pF 34pF 2 15 Measuring Dielectric Constant Objective Measure the dielectric constant of materials like glass paper polyester etc by making a capacitor Capacitance C egk4 where 9 is the permit tivity of free space k the dielectric constant A the overlapping area of plates and d the separation between them We have used a 13 cm x 10 6 cm piece of window glass having 4 mm thickness to make a capacitor by pasting metal foil on both sides Procedure e connect the capacitor from IN1 to ground e Click on the Button Measure C on IN1 e Repeat without connecting anything to IN1 Observation The measured capacitance is 255 pF The stray capacitance is measured after removing the wire from IN1 and it is 30pF means C 225pF ce BRA 7 38 Touching the capacitor during the mea surem
32. ent gives wrong results Using two parallel plates the dielectric constant of liquids also can be mea sured 2 16 AC Phase shift in RC circuits Objective Explore the effect of a series capacitor in AC circuits under steady state conditions Impedance of a Capacitor Xe TFC where f is the fre quency in Hertz and C is the capacitance in Farads 21 AWWA 16 0 ms CH1 3 695 V 147 31 Hz CH2 2 44 V 147 319 Hz Phase difference 47 7 degree CH1 3 695 V 147 31 Hz CH2 2 30 V 147 308 Hz Phase differ 4 5 degree Figure 2 4 Phase shift of AC in an a RC circuit b RL circuit e Assign Al to CH1 and A2 to CH2 Procedure e Adjust the horizontal scale to view more than 4 cycles e Right click on CH1 to calculate the phase shift For a detailed study select Study of AC Circuits from EXPERIMENTS Observation The voltage waveform before and after the capacitor are shown in lea 2 4 a and the calculations are shown in the table feun ne ea ey 8 arctan Soin cite ie where Xe a is the impedance of the capacitor Frequency is 147 3 Hz X r is the resistance Current through a capacitor leads the voltage across it by 90 Why Why does the phase of the voltage advance Assume we have connected the AC to plate A and at an instant t t the input voltage is at zero volts We can see that the slope of the curve is maximum there i e the rate of change of voltage is maximum The capacitor gets charged
33. ental data with mathematical models and examine the fundamental laws governing various phenomena Research scientists do the same with highly sophisticated equipment The expEYES expEriments for Young Engineers amp Scientists kit is designed to support a wide range of experiments from school to post graduate level It also acts as a test equipment for electronics engineers and hobbyists The simple and open architecture of expEYES allows the users to develop new experiments without getting into the details of electronics or computer programming This User s manual describes expE YES Junior along 3 with several experiments there is also a Programmer s manual available 1 2 The equipment ExpEYES Junior is interfaced and powered by the USB port of the computer For connecting external signals it has several Input Output terminals arranged on both sides as shown in figure 1 1 It can monitor and control the voltages at these terminals In order to measure other parameters like temperature pres sure etc we need to convert them in to electrical signals by using appropriate sensor elements Even though our primary objective is to do experiments you are advised to read through the brief description of the equipment given below The device can be also used as a test equipment for electrical and electronics engineering experiments IMPORTANT The external voltages connected to erpE YES must be within the allowed limits Input
34. erence Re activate the check buttons after changing frequency or phase difference e SQR1 can be set using a slider also e To Set PVS type the voltage 0 to 5 and press Enter key The PVS output has a readback and the read back value is displayed in the message field e Checkbuttons are provided to control OD1 and CCS e Capacitance connected between IN1 and GND can be measured e Python functions to communicate to the hardware can be entered in a Command Window 1 5 Basic measurements using expEYES Before proceeding with the experiments let us do some simple exercises to become familiar with expEYES Junior Boot your computer from the LiveCD connect the device a USB port and start the ExpEYES Junior program from the menu Applications gt Science 1 5 1 Generate amp measure voltages e Connect PVS to IN1 and Assign IN1 to CH1 e Set PVS to some voltage and observe the trace e Click on INI to display the voltage 1 5 2 Observe voltage waveforms e Connect SINE to Al and Assign Al to CH1 e Adjust the horizontal scale ms Div to view 4 or 5 cycles of the square wave e Set frequency to to 100 and Check SQR1 e Assign SQR1 to CH2 e Change frequency Uncheck and Check SQRI1 e Explore the FIT and FTR options 10 Set PVS 0 v Set State OD1 CCS Measure C on IN1 SQ2 SLO 1 0 OD1 HTP Type command lt Enter gt v Al 3 00 V 1000 5 Hz Save Traces to cro txt LOOP SCAN XMG BE
35. f a driven pendulum Procedure Make a pendulum using two button magnets and a piece of paper Suspend it and place the 3000T coil near that as shown in figure 6 1 a e Connect the coil between SQR1 and ground e From EXPERIMENTS select Driven Pendulum e Scan the frequency upwards starting from 1Hz very slowly Observation When SQRI reaches the resonant frequency of the pendulum the amplitude goes up due to resonance A 4 cm from the center of the magnet to the axis of oscillation long pendulum resonated at around 2 5 Hz almost tallying with its calculated natural frequency The resonant frequency of the pendulum is given by f s h where is the distance from the center of the magnet to the point of suspension and g is the acceleration due to gravity Repeat the experiment by changing the length of the pendulum 6 2 Value of g Rod pendulum Objective Measure the period of oscillations of a rod pendulum using a light barrier and calculate the value of acceleration due to gravity Period of oscil 26 3g length and g is the acceleration due to gravity The pendulum T shaped a knife edge attached to a 6mm dia rod is made to swing between an LED and lation of a uniform rod about one end is given by T 27 where is the SQR1 cannot go below 0 7 Hz AQ Figure 6 1 a Driven pendulum setup b LED amp photo transistor mounted on a bracket photo transistor connected to expEYES The LED and photo tra
36. ft 6 C Vo and f will be displayed Dragging the channel to NML will disable the FIT option Right clicking on IN1 IN2 SEN SQR1 or SQR2 will measure the fre quency and duty cycle of the voltage waveform present at the terminal If two adjacent channels are assigned Right clicking on the first will cal culate frequency and phase difference between the two inputs Dragging a channel to FTR will show the Fourier Spectrum of the wave form in a separate window To remove a displayed input drag it to DEL Horizontal scale ms division adjustment Set this to the minimum value and increase to view more number of cycles on the screen Drag the rider or click on the left right sides of it Vertical scale volts division Maximum values is 5 volts per division Vertical offset sliders are provided for each channel to shift the trace up or down The Check button LOOP selects Single Continuous mode of scanning The traces can be transferred to an Grace plot window using XMG SAVE button to save the data to the specified file in two column text format In addition to the CRO features you can also control SQR1 SQR2 PVS etc from the GUI You can execute Python functions to access the hardware from a command window e For the Square waves the frequency and phase difference in percentage are entered in two text fields SQR1 amp SQR2 can be set to different frequencies or to a single frequency with desired phase diff
37. ge induced across a solenoid coil by a rotating magnet Gain some understanding about the AC generators by looking at the output and the drawbacks of the setup Use the 10 mm x 10 mm magnet and the 3000T coils that comes with the kit Procedure e Mount the magnet horizontally and power the DC motor from a 1 5 volts cell e Hold the coil perpendicular to the axis of rotation of the motor close to the magnet Be careful not to touch it e Assign Al to CH1 A2 to CH2 e Assign CH1 and CH2 to FIT http sound westhost com xfmr htm 30 Figure 3 2 Wiring schematic and voltage output of the AC generator with coils placed on opposite sides of the rotating magnet Figure 3 3 Photograph of the simple AC generator Observation The voltage output is shown in figure 3 2 The phase difference between the two voltages depends on the angle between the axes of the two coils Bring a shorted coil near the magnet to observe the change in frequency The shorted coil is drawing energy from the generator and the speed get reduced The magnetic field in this generator is very weak The resistance of the coil is very high and trying to draw any current from it will drop most of the voltage across the coil itself It is possible to power the DC motor from SQR2 set to PWM mode as shown in figure 3 3 The function set_sqr2 pwm 40 is equivalent to applying 2 volts DC Do NOT give duty cycle more than 50 percent to avoid damage to the unit
38. gital mode any voltage less than 1 volt is treated as logic O LOW and anything higher than 2 5 volts is treated as logic 1 HIGH If the voltage input is changing periodically between HIGH and LOW these 4 EXPE YES Junior www expeyes in Your Lab Home GND 31 aH GND IN1 P gt 3 1q A1 IN2 gt 4 tM 2 gaz SEN gt 5 0 12 PVS SQR1 lt q 8 6 Gain OUT SQR2 lt q 9 7 0 IN OD1 lt q 10 B MIC CCS lt q 11 B SINE GND 1 IF GND 7 PHOENIX Project IUAC New Delhi www iuac res in Figure 1 1 The ExpEYES Junior top panel showing the external connections on both sides The channel numbers shown against some terminals are meant for those who write software to access them The arrows indicates the direction of the signals for example arrow from Al gt 1 means the signal from terminal Al goes to channel number 1 terminals can measure the frequency and duty cycle of the connected signal Time interval between voltage transitions on these pins can be measured with microsecond resolution Digital Output OD1 The voltage at OD1 can be set to 0 or 5 volts using software Square Waves SQR1 SQR2 Output swings from 0 to 5 volts and frequency can be varied 0 7Hz to 100kHz All intermediate values of frequency are not possible SQR1 and SQR2 can be set to different frequencies It is also possible to set them to same frequency with a specific phase shift between the two These outputs also can be programmed to generate Pulse Wi
39. he equation v f x 35 3500x m55 34054 cm sec It is important to keep the mic and the Piezo disc on the same axis for accurate results 5 4 Interference of sound Objective Study the interference of sound from two individual sources Two Piezo buzzers are powered by two different sources and the sound is directed towards the microphone Procedure e From EXPERIMENTS start Interference of Sound e Set SQR1 to 3500 Hz and SQR2 to 3600 Hz e Adjust positions of Piezo buzzers from the mic to get clear beat pattern e Repeat with other values of frequencies e Capture with NC 1800 and take Fourier Transform 45 0 01 irl oL 1 1 1 1 fi 2000 2500 3000 3500 4000 4500 5000 a f sound dal reg Freq 3297 Hz A f empire A i Figure 5 4 Sound output from Piezo driven by 100Hz square wave and the Fourier transform of the output Observation From figure 5 3 a it can be seen how the low frequency envelope is created Distance between two minimum pressure points of the envelope corresponds to the beat wavelength The Fourier transform of the output is shown in figure 5 3 5 5 Forced Oscillations of Piezo electric crystal Objective Study the behavior of a Piezo electric disc at low excitation fre quencies using a square wave MIC At e From EXPERIMENTS open Interference of Sound Procedure Tick only SQR1 set it to 100 Press START to capture mic output
40. ive Explore the oscillatory nature of L and C in series Resonant frequency of series LC circuit is given by wo Nea The damping factor is 3http nptel iitm ac in courses Webcourse contents IIT KANPUR esc102 node14 html 25 ms mS ms div J Discharge Saveto ric dat FIT CLEAR Xmgrace Quit msidiv _1 PT Discharge Saveto ric dat FIT CLEAR Xmgrace QUIT Resonant Frequency 3 89 kHz Damping 0 128 Discharge Done Figure 2 8 Transient response of LCR circuit a Under damped b Over damped B E and it is equal to 1 for critical damping Depending upon the value of C L and R the response could be under damped critically damped or over damped Procedure From EXPERIMENTS select RLC Discharge e Click on 5 gt 0V STEP Adjust x axis and repeat if required FIT the graph to find the resonant frequency amp Damping Repeat the experiment with different values of L C and R Repeat with a resistor in series Observation We have used the 3000 turn coil and a 0 luF capacitor added a 2 2k series resistor in the second case The voltage across the capacitor after a 5 to OV step is shown in figure 2 8 The measured resonant frequency tallies with f 7 within the component tolerance values 2 22 RC Integration amp Differentiation Objective RC circuits can integrate or differentiate a voltage waveform with respect to time A square wave is integrated to get a triangular wave and differenti
41. lifier IN gt OUT The inverting amplifier is implemented using TLO84 op amp Rf 51000 and Ri 1000 giving a maximum gain of a 51 The gain can be reduced by feeding the input via a resistor For example using a 50k series resistor will make it a unity gain inverter Ground The four terminals marked as GND are the reference ground All the generated measured voltages are with respect to these terminals http expeyes in micro controllers for hobby projects and education 6 1 2 2 Accessory Set Some accessories are provided with expEYES Junior a photograph is given on back cover of the manual e Crocodile Clips with leads 4 If the connection to any terminal is changed many times during an experiment it is easier to make the con nection using the crocodile clip provided e 3000 Turns Coil 2 44SWG copper wire Inductance 125 mH Re sistance 550 Q These coils can be used for studying inductance electromagnetic induction etc e Piezo Electric Discs 2 Resonant frequency is around 3500 Hz Can be energized by SQR1 or SQR2 Discs are enclosed in a plastic shell that forms a cavity that enhances the amplitude of sound produced e DC Motor Should be powered by a DC voltage less than 3 volts e Permanent Magnets a 10mm dia length b 5 mm dia amp 10 mm length c Button size magnets 2 e 5mm LEDS RED BLUE GREEN WHITE e Capacitors 47uF luF 0 1uF 0 01 uF amp 100pF e Resis
42. ltage read the actual value set from the message field e Click on IN1 to measure its voltage e Repeat for different values of PVS e Repeat for other resistance values Observation The total voltage and the voltage across R1 are measured The voltage across R2 is Vpys Vri The current through R1 J Vr R1 The same amount of current flows through R2 and the voltage across R2 can be calculated using Vr Rl Via I x 2 2k Expand this experiment by connecting three resistors in series and connect ing the junctions to IN1 and IN2 Another exercise is to connect a 5 1k resistor from SEN to GND and measure the voltage at SEN Remember that SEN is internally connected to 5 volts through a 5 1k resistor 2 3 Calibrating Current Source Objective The actual output of constant current source may be different from the specified 1 mA due to the tolerance of the resistors used It can be measured by connecting an ammeter from CCS to GND or by connecting a known resistance to CCS and measuring the voltage across it The resistor should be in 2k to 4k range Procedure e Enable CCS 14 Observation The measured values of the resistance is 3 876k and the voltage is 3 725 volts The actual value of the constant current source is 3 725 3 876 961 mA For better accuracy the measured value should be used in experiments using COS 2 4 Resistances in series Objective Finding the effective resistance of a series combination
43. n 3 3 53 54 Chapter 7 Coding expEYES in Python The GUI programs described in the previous sections are meant for a fixed set of experiments To develop new experiments one should know how to access the features of expEYES Junior from software Important function calls used for communicating with the device is given below For more details refer to the Programmer s manual 7 1 Installing the Python Libraries The expEYES Junior package consists of three files eyesj py eyeplot py and eyemath py inside a subdirectory named expeyes This subdirectory should be inside your PYTHON LIBRARY PATH or inside your working directory On Debian based GNU Linux systems this will be done by installing the expeyes 3 x x deb file On other systems unzip the file expeyes 3 x x zip and follow the instructions in the README file 7 2 Hardware Communication Channel Numbers A channel number is assigned to identify every Ana log Digital signal as given in table 7 1 Start the Python Interpreter from the directory where you have the expeyes subdirectory by the command python Python 2 7 3 default Apr 20 2012 22 44 07 gt gt gt The triple angle bracket implies that you using Python in the interactive mode Type the following two lines to load the library and establish connection to the device gt gt gt import expeyes eyesj gt gt gt p expeyes eyesj open If you get an error message check the connections
44. ncy is given by f 1 In2xC x R 2R2 The HIGH time is given by ln 2 xC x R Ra and LOW time by In2 x C x Ro Procedure e Set OD1 to HIGH to power IC555 38 Figure 4 8 1C555 monostable multi vibrator a schematic b Output wave form e Assign IN1 to CH1 and enable FIT on CH1 e Right click on IN1 to measure frequency and duty cycle e Repeat by changing the value of R1 Observation The output waveform is shown in figure 4 7 b The HIGH and LOW times can be measured by using r2ftime 3 3 and f2rtime 3 3 functions 4 9 1C555 Monostable multivibrator Objective Make a monostable multi vibrator using C555 and measure the time delay at different RC values Procedure e Set SQR2 to 0 Hz to set it to 5V DC e Enter set _pulsewidth 1 in the command window e Assign LTP Low True Pulse to OD1 trigger input for 555 e Assign IN1 to CH1 watch it by varying R1 Observation The output of the circuit is shown in figure 4 8 b Enabling LTP on OD1 sets it HIGH and generates a 1 microsecond pulse just before capturing the output For more accurate results use ltpulse2ftime 10 3 that will measure the delay from a pulse given on OD1 to the falling edge on IN1 4 10 Logic gates Objective Study of logic gates using two square waves with a phase difference using TTL logic ICs 7408 and 7432 39 Figure 4 9 Testing of Logic gates Figure 4 10 Operation of logic gates with square wave inputs a AND gate b OR ga
45. nect 1kQ R1 from IN1 to Ground e Set PVS to 4 volts e Measure voltage at IN1 Observation Voltage at IN1 1 254 implies voltage across the unknown resistor is 4 1 254 2 746 Current I 1254 1 254mA Unknown resistor value SS 2 19k0 What is the limitation of this method How do we choose the reference resistor suppose the unknown value is in Mega Ohms what will be the voltage drop across a 1kQ reference resistor Our voltage measurement is having a resolution of TO We will use this method later to measure the resistance of solutions using AC 2 7 Voltage of a lemon cell Objective Make a voltage source by inserting Zinc and Copper plates into a lemon Explore the current driving capability and internal resistance Procedure e Click on A1 to measure voltage e Measure the voltage with and without the 1k resistor Observation Voltage across the Copper and Zinc terminals is nearly 9 volts Connecting the resistor reduces it to 0 33 volts When connected current will start flowing through the resistor But why is the voltage going down What is the internal resistance of the cell Current is the flow of charges and it has to complete the path That means current has to flow through the cell also Depending on the internal resistance of the cell part of the voltage gets dropped inside the cell itself Does the same happen with a new dry cell 16 Figure 2 1 Plotting Voltage
46. nsistor are mounted on a U shaped bracket as shown in figure 6 1 b Procedure 5 SQR1 YY GND SEN e From EXPERIMENTS Start Rod Pendulum e Oscillate the pendulum and click on START e Repeat with different pendulum lengths Observation The time period is measured 50 times using a 14 6cm rod pen dulum and the average value is 0 627 seconds The calculated value of g is 977 4 cm sec slightly different from the actual value due to the following rea sons The length is measured from the knife edge to the bottom and used in the formula But there is a small mass projecting above the knife edge that is not included in the calculation Another reason is that the pendulum may not be exactly vertical in the resting position 6 3 Oscillations of a pendulum Objective To study the nature of oscillations of a pendulum An angle en coder is required for measuring the angular displacement as a function of time But using a DC motor as a sensor we can measure the angular velocity as a function of time Procedure e Attach some sort of rigid pendulum to the axis of the motor Connect the motor between IN and GND e Connect OUT to Al e From EXPERIMENTS start Pendulum Waveform 50 econds FIT CLEAR Xmgrace SAVE to pendulum dat QUIT Completed the Measurements Figure 6 2 Pendulum oscillations digitized e Oscillate the pendulum and START digitizing Observation The observed waveform is shown in figure 6 2 b Fit
47. odes it varies from 1 to 2 We have used a 1N 4148 silicon diode Procedure PVS IN1 GND 1K e From EXPERIMENTS select Diode IV e Click on START to draw the characteristic curve e Click on FIT to calculate the Diode Ideality factor e Plot the IV of LEDs 30 Figure 4 4 Transistor common emitter characteristics Observation The curves obtained are shown in figure 4 3 a The value of n for 1N4148 is around 2 We have calculated the value of n by fitting the experimental data with the equation Figure 4 3 b shows the IV curves of few LEDs of different wavelengths The voltage at which LED starts emitting light depends on its wavelength and Planck s constant Energy of a photon is given by E hv hc X This energy is equal to the energy of an electron that overcomes the junction barrier and is given by E eVo So Planck s constant h eVoA c where A is the wavelength of light from the LED e the charge of electron and c the velocity of light Repeat the experiment by heating the diode to different temperatures 4 5 Transistor CE characteristic Objective Plot the CE characteristic curve of a transistor Collector is con nected to PVS through a 1K resistor The base voltage is obtained by filtering a variable duty cycle pulse from SQR1 Base current is decided by this voltage and the 200 series resistor For better results use an external DC supply 1 5V cell will do for base voltage Procedure e From EXPERIMENTS
48. on License Ajith Kumar B P ajith iuac res in http expeyes in V V V Satyanarayana Jimson Sacharias Contents 1 Getting Started 1 1 Introduction 2 0 0 20022002 2 eee 1 2 The equipment 0 00 000 ee eee ee 1 2 1 External connections 20 1 2 2 Accessory Set 2 o 1 3 Software Installation 2200048 1 4 The main GUI program 1 5 Basic measurements using expEYES 1 5 1 Generate amp measure voltages 1 5 2 Observe voltage waveforms 2 1 5 3 Measure frequency amp Duty cycle 1 5 4 Accuracy and resolution 004 1 6 Experiments Electricity 2 1 Measuring Voltage 0 00 22 20 eee eee 2 2 Voltage current amp resistance 0 02048 2 3 Calibrating Current Source 0204 2 4 Resistances in series e 2 5 Resistances in parallel 0 0 2 2 2 6 Measure resistance by comparison 0 2 7 Voltage of a lemon cel 2 0202000 2 8 DC AC and power line pickup o ooo a 2 9 DC amp AC components of a voltage ooo a 2 10 Resistance of human body aoao aa 2 11 Temperature dependent resistors 2 12 Light dependent resistors 0 eo 2 13 Conductivity of water using DC ZAC
49. op 18 2 11 Temperature dependent resistors Objective Show the dependence of resistance on temperature using a thermistor 1k0025 C with negative temperature coefficient Introduce temperature sensor Procedure e Click on IN1 to measure the voltage e Repeat at different temperatures Observation 1200 0 933 2 12 Light dependent resistors Objective Learn about LDR Measure intensity of light and its variation with distance from the source Use the comparison method to find out the resistance Procedure 10K GND D GND e Set PVS to 4V and note down the value set e Click on IN1 to measure it Assign IN1 to CH1 e Calculate the LDR s resistance as explained in2 6 e Repeat by changing intensity of light falling on LDR e Connect an LED from SQR1 to GND Set SQR 1 to 10 Hz e Show the LED above LDR and watch waveform at IN1 Observation The resistance vary from 1kQ to around 100 kQ depending on the intensity of light falling on it The voltage is proportional to the resistance The resistance decreases with intensity of light If you use a point source of light the resistance should increase as the square of the distance Illuminate the LDR using a fluorescent tube and watch the waveform at CH1 The frequency of the ripple is related to the mains frequency 2 13 Conductivity of water using DC amp AC Objective Measure the resistance of ionic solutions using both DC and AC voltages We have used normal tap wate
50. pto electric signal transmission Objective Demonstrate the transmission of signals using light An LED is powered by a 1kHz signal and the light is made to fall on a photo transistor The SEN input is internally connected to 5 volts through a 5 1k resistor Procedure e Keep the LED facing the photo transistor and set SQR1 to 1000Hz e Assign SQR1 to CH1 and SEN to CH2 e Repeat the experiment by changing the frequency 37 ms i i l i mS Figure 4 6 a Voltage at the photo transistor with light passing through a piece of paper b Pulse transmission voltage driving the LED and the voltage across the photo transistor Figure 4 7 IC555 astable multi vibrator a schematic b Output waveform Observation The output of the photo transistor at 1kHz is shown in figure4 6 The square trace is the voltage across the LED When the LED is ON photo transistor conducts and the voltage across the collector drops to 2 volts When the LED is OFF the photo transistor goes into cut off mode and the collector shows almost the supply voltage The rise and fall times of the photo transistor seem to be different Repeat this experiment with a Fiber Optic cable to guide the light from LED to the photo transistor 4 8 1C555 Oscillator Objective Make an astable multivibrator using 10555 and measure its fre quency and duty cycle Circuit is shown in figure 4 7 a The 5 volt supply for 10555 is taken from OD1 by setting it HIGH The freque
51. qual The gain is given by G ESO 4 3 Fullwave rectifier Objective Make a full wave rectifier using two diodes Two AC waveforms differing by 180 degree in phase as required are made as described in the pre vious section The rectified output is connected to the third channel Eto diode iv dat FIT Grace CLEAR QUIT START SAVE to diode iv dat FIT Grace CLEAR QUIT Fitted with Diode Equation lo 9 13e 06 mA Ideality factor 2 01 Starting to plot I V Figure 4 3 I V characteristic of a Silicon diode b several LEDs Procedure e Assign Al to CH1 A2 to CH2 and IN1 to CH3 e Add Capacitor from IN1 to ground for filtering Observation The result is shown in the figure 4 2 Adding capacitors to reduce the ripple is left as an exercise to the user This experiment is only to demonstrate the working of a full wave rectifier it cannot provide more than few milli amperes of current Why full wave rectifier is superior to half wave rectifier 4 4 Diode I V characteristic Objective Draw the I V Characteristic of diode and compare the result with the theory The IV characteristic of an ideal PN junction diode is given by equation Io cir 1 where Jo is the reverse saturation current q the charge of electron k the Boltzmann constant T the temperature in Kelvin For a practical non ideal diode the equation is Z Ip erir 1 where n is the ideality factor that is 1 for an ideal diode For practical di
52. r 19 R1 Figure 2 3 Conductivity of water b Total voltage applied and the voltage across the 10k resistor Procedure e R1 should be comparable to R start with 10k e Assign A1 to CH1 and A2 to CH2 enable FIT on both e Calculate the resistance as explained in section 2 6 e Repeat using a DC voltage PVS instead of SINE Observation Observed values are shown in the table The DC and AC resis tances seems to be very different With DC the resistance of the liquid changes with time due to electrolysis and bubble formation The resistance does not depend much on the distance between the electrodes the area of the electrode is having some effect The resistance depends on the ion concentration and presence of impurities in the water used _v Vi Viau Vioro TI Ho Try changing the distance between electrodes Try adding some common salt and repeat the measurements Why is the behavior different for AC and DC What are the charge carriers responsible for the flow of electricity through solutions Is there any chemical reaction taking place 2 14 Measuring Capacitance Objective expEYES Junior has an internal programmable current source that can be enabled on INI Connect a capacitance C and switch on current 5 5 uA for a fixed time interval The accumulated charge Q It CV By measuring V the value of C is calculated For better results the stray capacitance need to be subtracted Measure C without conn
53. re of distortion of the sine wave A square wave function can be represented as f 0 sin sin sent In the Fourier transform of a square wave of frequency f there http en wikipedia org wiki Fourier_ transform 27 Figure 2 10 Frequency spectrum of a Sine wave b Squarewave will be a 3f component having an amplitude of one third of f 5f component amplitude one fifth etc as shown in the figure 2 10 b Note the peak at 0 Hz due to the DC component 28 Chapter 3 Electricity amp Magnetism Electromagnetic induction is demonstrated by dropping a magnet in to a coil Working of transformer is demonstrated using two coils A simple AC generator capable of generating multi phase output is made using a rotating magnet 3 1 Electromagnetic induction Objective Explore the voltage induced across a coil by a changing magnetic field by dropping a small cylindrical magnet into a coil Use a tube to guide the magnet through the coil Procedure Guo cols idad e From EXPERIMENTS open EM Induction e Click on Start Scanning A horizontal trace should appear e Drop the magnet through the coil until a trace is caught e Repeat the process by changing the parameters like magnet strength speed etc Observation The result is shown in figure 3 1 a The amplitude increases with the speed of the magnet From the graph we can find the time taken by the magnet to travel through the coil The second p
54. rom over voltage This circuit will be useful while measuring temperature using PT 100 and expEYES Procedure e To find out the offset Ground the amplifier input and measure the output e Set PVS to to 1 volts and Click on IN1 for the output voltage e Repeat it for several input voltages Ri Rf 1 Fe Vin Vout T Observation 4 13 Amplitude amp Frequency Modulation Objective Study amplitude and frequency modulation of a signal Analyse the AM output mathematically to see the sidebands This experiment requires some source of modulated waveform we have used the PHOENIX Analog Box Phoenix Analog Box has a sine wave generator around 100 Hz whose am plitude can be controlled using a DC control voltage It also has a 4kHz sine wave generator with AM and FM control inputs Use PVS to change the depth of modulation by changing the amplitude of the 100Hz sine wave Al 5 0 5 4 8 1 ms Vao Pal Capture Power Spectrum QUIT Number of Samples 900 Delay between samples 15 uS PVS 2 700 V Messages Procedure e Connect Analog Box and expEYES grounds e Assign Al to CH1 and A2 to CH2 Capture 900 samples with 20 microsecond interval De select A2 and capture with 1800 samples e Click on Power Spectrum to do a Fourier transform Observation A carrier signal having a frequency of around 4kHz is modulated by a sinewave of around 100Hz A small portion of the output 400 points with 20 usec gap
55. roplus screen showing four traces Installing on Debian or Ubuntu GNU Linux distributions Download expeyes 3 0 0 deb or higher version from the software section of http expeyes in and install it It depends on python serial python tk python scipy and grace a 2D plotting program For other GNU Linux distributions Download expeyes 3 x x zip from http expeyes in or https github com expeyes and follow the instructions in the README file It is important to give read write permissions for all users on the USB port where expEYES is connected This can be done by running the postint shell script included in the zip file On MSWindows Even though expEYES is Free Software and is developed using Free and Open software it runs on non free platforms also To install it on MS windows you need 1 MCP2200 drivers 2 Python 2 x version python serial python tk python numpy and python scipy 3 expeyes 3 x x zip Unzip the file expeyes 3 x x zip and double click on croplus py inside the newly created directory named expeyes 3 x x eyes junior If you have expEYES liveCD browse inside the directory names WINEYES All the files mentioned above are inside that directory Double click on them in the order mentioned above to install them See the software section on the expeyes website for more details 1 4 The main GUI program Start Applications gt Science gt EYES Junior from the menu A four channel os cilloscope screen with
56. s Al and A2 must be within 5 volts range and Inputs IN1 and IN2 must be in 0 to 5V range Exceeding these limits slightly will flash an error message If the program stops responding exit and re connect the USB to reset the device Larger voltages will result in permanent damage To measure higher voltages scale them down using resistive potential divider networks 1 2 1 External connections The functions of the external Input Outputs terminals are briefly explained below Programmable Voltage Source PVS Can be set from software to any value in the 0 to 5V range The resolution is 12 bits implies a minimum voltage step of around 1 25 millivolts There is a read back to verify PVS 5V Analog Inputs A1 amp A2 Can measure voltage within the 5 volts range The resolution of ADC used is 12 bits Voltage at these terminals can be displayed as a function of time giving the functionality of a low frequency oscilloscope The maximum sampling rate is 250 000 per second Both have an input impedance of 101 0 5V Analog Inputs IN1 amp IN2 These terminals can measure voltages in the 0 to 5V range Resistive Sensor Input SEN This is mainly meant for sensors like Light Dependent Resistor Thermistor Photo transistor etc SEN is connected to 5 volts through a 5 1kQ resistor It also has a built in analog comparator Digital Inputs IN1 IN2 The inputs IN1 IN2 can act as both analog and digital inputs In the di
57. several extra features will open as shown in figure 1 2 The EXPERIMENTS button pops up a menu of programs for several exper iments The main window will become inactive when an experiment is selected and running The Plot Window The plot window works like a low frequency four channel oscilloscope The maximum sampling rate is 250 kHz only sufficient for exploring audio frequency range A brief description of this GUI program is given below On the left side the Inputs A1 A2 IN1 IN2 SEN and read backs of SQR1 amp SQR2 are shown Clicking on any of them will display the voltage logic level present To plot any of them drag it to the desired channel CH1 to CH4 The names of inputs selected for display are shown on the right side of the plot window using a unique color for each channel For online help place cursor on any item press and hold the left mouse button Dragging ATR to any of the inputs will make it the CRO trigger source This program allows different types of triggering For example dragging WRE to INI will enable rising edge triggering on it It also supports setting levels or generating pulses on Digital outputs just before capturing the waveform Dragging SHI to OD1 will keep OD1 HIGH during the capture process For more details refer to the programmers manual Dragging any of the channels CH1 to CH4 to FIT will enable calcu lating amplitude and frequency by fitting the data using the equation V Vosin 27
58. sound by measuring the pressure variation with distance Sound travels as a series of compressions and rarefactions Figure 5 2 a shows the High and Low pressure regions along the direction of travel along with output of a pressure sensor at corresponding positions We can display the pressure variation at any point with respect to the vari ation at the starting point The phase of the microphone output changes as you change its distance from the Piezo Moving by one wavelength changes the phase by 360 degrees If the phase changes by X degrees for AD cm change in distance the wavelength is given by A 360XAD The velocity of sound can be calculated by multiplying the frequency with this e From EXPERIMENTS start Velocity of Sound e Set frequency to resonant maximum by measuring the frequency response 5 2 e Keep the Piezo facing the microphone on the same axis e Measure Phase difference at different distances 44 Microphone output gt 3 0 1 0 v 1 0 Air Pressure gt Wavelenth gt Figure 5 2 a Propagation of sound waves variation of microphone output with pressure b Output of microphone 3300 3400 3500 3600 3700 3800 v Freq 3503 Hz Figure 5 3 a Sum of sound having two nearby frequencies b Fourier trans form showing the frequency components Observation At 3500 Hz for a 2 cm change in distance the phase changed from 176 to 102 Using t
59. te a ee eae no sari t 8 Procedure e Assign SQR1 to CH1 SQR2 CH2 and IN1 to CH3 e Set 100Hz 25 and enable BOTH SQR1 amp SQR2 e Check OD1 to power the TTL AND gate 7408 e Repeat using the OR gate 7432 Observation The input and output waveforms are shown in figure4 10 The results will not be accurate for high frequencies because the sampling rate is limited to around 80 000 per second for 3 channel capture 4 11 Clock Divider Objective Study of a clock divider using a D flip flop TTL family 7474 Procedure e Set SQR1 to 500 Hz Assign SQR1 to CH1 and IN1 to CH2 e Check OD1 to power the flipflop 40 x 24 333 i 25 0 Y 11 500 128 0 Y 11 500 2 0 3 0 4 0 8 0 E 12 0 16 0 20 4 0 8 0 12 0 16 0 20 Figure 4 11 A clock divider circuit using a D flipflop Outputs for two different types of input are shown Observation The output toggles at every rising edge of the input resulting in a division of frequency by two The output is a symmetric squarewave irrespective of the duty cycle of the input pulse The HIGH output of the TTL IC is around 4 volts only 4 12 Non inverting Amplifier Objective Make a non inverting amplifier using op amp OP27 and measure the gain The gain and input should be chosen such that the output is in the 0 to 5 volts range otherwise the device will malfunction The op amp is powered by an external 9V supply A series resistor is added to prevent any damage to expEYES f
60. ting it with equation A Apsin wt 0 x exp dt C using Grace gave an angular frequency of 10 Hz The pendulum should be made with a heavy bob and a light weight rod connecting it to the axis of the motor In this case the DC motor acts like a generator and the voltage is proportional to the instantaneous angular velocity 6 4 Temperature measurement PT100 Objective Record the temperature of a liquid by using a Platinum Resistance Thermometer Resistance of a PT100 element is related to the temperature by the equation Rr Ro 11 AT BT where A 3 9083e 3 and B 5 775e 7 Procedure To measure the resistance of the PT100 element we connect it from the CCS to ground and measure the voltage across it The actual current of CCS should be measured as explained in section 2 3 The voltage across CCS is amplified using an external DC amplifier gain 11 1K e From EXPERIMENTS start PT100 Sensor e Enter the measured current value e Select the required parameters and press START 2 The resistance of PT100 is100Q at 0 C It changes nearly 0 40 C changing the voltage by 0 4 milli volts The 12 bit ADC output changes by 1 LSB for 1 22 mV change in input voltage hence any temperature change less than 3 degrees will not be detected Use an external non inverting amplifier to increase the resolution The gain of the amplifier should be such that the maximum temperature measured should give an output less than
61. tors 5609 10 2 2kQ 10kQ 51 0 and 200 kQ e LDR amp Thermistor e Two silicon diodes 1N4148 and a Transistor 2N 2222 e 5 pieces of wires 8cm and a Screwdriver 1 3 Software Installation ExpEYES can run on any computer having a Python Interpreter and a Python module to access the Serial port The USB interface is handled by the device driver program that presents the USB port as an RS232 port to the application programs The communication the expEYES is done using a library written in Python language also available in C language Programs with GUI have been written for many experiments There are many ways to get the software running The expEYES Live CD The easiest way to get started is to boot your PC with the expEYES Live CD From the PC BIOS make the CD drive as the first boot device insert the live CD and reboot the PC A desktop will appear and you can start expEYES Junior from the menu Applications gt Science gt ExpEYES Junior You can also start 1t from a Terminal using the command python usr share expeyes eyes junior croplus py Setting Squarewaves 100 Hz dphi 50 SQR1 SQR2 M BOTH Bal Set Pvs jv Set State OD1 CCS Type command lt Enter gt Al 15 0 A2 sql SQ2 Save Traces to cro txt 25 0 Trig level 3 0 16 0 32 0 A 48 0 64 0 80 LOOP SCAN XMG mimi SQR1 and SQR2 set to 100 0 Hertz Shift is 50 00 of Period EXPERIMENTS QUIT Figure 1 2 The c

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