PELTIER TEMPERATURE CONTROLLER - ECE
Contents
1. Because the peltier plate requires a switching of the voltage s direction to either absorb or distribute the heat the control signal has to be shifted to generate a negative voltage Moreover the voltage has to be amplified to achieve the full swing of the peltier plate 12V 12V To achieve this result a difference amplifier is added into the circuit The buffer before the negative input is to separate the voltage divider from the rest circuits so that the voltage of the negative input can be decided only by the voltage divider After the difference amplifier the output range is shifted and amplified to 12V 12V Since the peltier plate has a power consumption of 60W which means a 5A current under 12 volts drive a power amplifier is needed to drive the peltier plate The circuit is built as shown in figure 4 In ideal situation the output of the power amplifier should has a range of 12V 12V However because of the voltage drop caused by the CMOS transistor the actual output has a range of 6V 6 V Unfortunately the performance is downgraded by half compared to the original design However in section 4 the test result will prove that this output range is large enough Actually the final output is 4 5V 6V limited by the over heating problem of PMOS By tuning the PID parameters the output control signal satisfied the system requirement More detail result is showed in section 4 MEng Project Report Hanting Lu 2 3 Temp2. To install MATLAB Compiler Runtime 8 1 on your computer click Next MATLAB MATLAB and Simulink are registered trademarks of The MathWorks Inc Please see Aveda eit lal aay www mathworks com trademarks for a list of additional trademarks Other product or brand R2013a names may be trademarks or registered trademarks of their respective holders WARNING This program is protected by copyright law and international treaties Copyright 1984 2013 The MathWorks Inc Protected by U S and other patents See MathWorks com patents Cancel MathWorks Click Next and follow the instruction in the installer window to finish installing process After completion the install in addition to the test_pkg exe file following files will be shown in your document MCRInstaller exe the compiler installer readme txt and test exe Double click the test exe the GUI interface should be shown on your computer You may have to wait for a while when the program is responding Running the System Click Control Panel System Hardware Tab Device Manager Button Ports to find out which serial port is connected to the USB dongle For example the following figure indicating the use of a COM port 18 MEng Project Report Hanting Lu 25 35 45 5 gt 6 gt o r9 File Action View Help e ell Hrs e a n PH238 04 sl Computer ca Disk drives By Display adapters c83 DVD CD ROM drives Os Human Interface De
3. ATRPA1 This is a temperature and voltage gated cation channel that regulates drosophila behavior related to different temperature environment Previous work has shown that neurons expressing dTRPA1 begin firing action potentials when ambient temperatures rise above 25 C By delivering modest heat pulses sets of neurons can be remotely activated in freely behaving animals 4 To observe and analyze the neurons response to the heat stimulus students who conduct this experiment need a device which can give heat pulse to drosophila A simple way to achieve this goal is to give a random voltage to a peltier plate so that heat is generated to increase the bath temperature of the petri dish However this open loop method has an obvious problem that the heat pulse cannot be controlled In other words people can only give a positive or negative voltage to the peltier plate to either increase or decrease its surface temperature however the detailed amount of degrees the bath temperature will be changed is not controllable To conduct experiments more accurately and controllable a feedback temperature controller is needed 1 2 Problem Statement amp Constrains There are devices on the market which satisfied the lab requirement mentioned in the last section However these devices have two problems First the price of the existing device is expensive Most of them cost more than one thousand dollars Second the way to use the device is compl
4. I and derivative p values P depends on current error I on the accumulation of past errors and D keep track on the trends of future errors The weighted sum of these three values provides the control signal to the peltier plate Figure 2 illustrate the flow chart of a typical PID controller The value of P I D was calibrated by the required specification of the device listed in section 1 5 The rising time should be less than 12 second per 1 Celsius degrees rising from 20 to 30 C The temperature should be settled within 10 seconds after reaching the desired temperature Under this requirement the way to get the P I and D is to start from calibrating the proportional gain and left other two zero After a proper P is set so that the rising time is satisfied for the requirement D is than modified to smooth the overshooting By setting a proper P and D the controller is smooth enough but with a steady state error around 3 Celsius degree Then Integral gain is modified to eliminate the steady state error Current Desired Temperature Temperature Figure 2 PID Controller Flow Chart 2 2 2 Peltier Plate This section briefly introduces the principle of a typical modern peltier plate A peltier plate is based on the thermoelectric effect A typical thermoelectric device works one of two ways as follow It creates voltage when there is a different temperature on each side of the device or conversely it creates a temperature differ
5. user only need to follow the user manual to connect two units together and plug in the power supply In order to make the device more user friendly a GUI is implemented using MATLAB The interface is very easy to understand and use User only needs to type the desired temperature into the GUI interface The value will then be passed to the microcontroller by serial communication The interface also contains a dynamic plot to allow the user to monitor the trend of the temperature Table of Contents L Jutrodochon AGANG AKEN AL 1 1 1 Backeround and Motivation ada NBA 1 1 2 Problem Statement amp Constrains sseseseverersvnnnennnenenerenenennnnnnnnnnenesesesesenenevevevennennnnnnnenenenenennnnnnnnenenener 1 EA R nge Of Solong ua AGA AG aaa anak 1 14 Project Design Overview s memensnnnsnnsnsesnsnnenenenevennnnnnnnnnnnnnenenenennnnnnnsnnenesenenenenenevevevnnnennnnnnnenenenenennnnnnnnenenener 2 1 5 Design Specification mumumsmesesesenesenenvevenenesnsnnnnvannnnnenenesenenenvevevenesesnnnnvnvnnnnenevenesennnenvevenevesennnenvnnnnnnenenenennen 2 E E ERT E 3 2 1 High level Design mamana 2n GAAN aan 3 2 2 Control Unit Design ee 3 2 2 PPID Controller sees an aa NABA a ran ter ett eli bade eet leer 3 2 2 2 Peltier Plateau ere gua see a ce ee 4 2 23 Control Circuits sche aaa ee ee ie 5 2 3 Temperature Detection Unit mnmmesersesernnsvseneenenennnnvnenennenennnneneneenenennnneneneenenennnnesenennenennnnesenensenennnnenener 7 2 4 Graphical
6. User LE TE 8 2 5 Microcontroller Pin Assignment sesenenenenenennnnnnnnnnvnvnvnvnnnenenenenenevennennnnnnnenenenenenennnnnnnnnnenenenenenennnevevevener 9 2 6 Combine Together s u unlsungerisdsmdnkussnk enmjeihjess summen 10 3 Implementation and Packaging sesersvsvnenvnnvnvnennnnnnvnenennennnennnnnnenenennenenennnnnnsenenennenesennnnnsesenennennr 11 31 Project BOK a LANA haa NN ada 11 3 2 Pelti r thermistor Plato rm Xp NAKA 12 3 3 Stand alone Program eege EENS 12 4 Tests and Results sicissicsccsseiscsccsunaccnssarsaeasennnasacennsssuecnncnsndnescnueedtededdussnsineneedetnilancetnanivesinvauedusnes 13 4 1 Maximum Output Voltage Test nrnrnenenvnenenonennnnnnnnvnvnvneneneneneneneveveennnnnennnenenenenenennnnnnnnnnenenenesesenenevevenn 13 42 Tuning PID Aramefd S GAAN EE an 13 ba A Ee EE 14 Gi Acknowledgement ANAN MAA AA AA AA AA 14 SR E ER 15 Appendix A User Et E E 16 Appendix B COS mma NATAN NANANA 20 Appendix C Microcontroller Source Code s nsnsesenennennnnnnnnnnnnenennnnnnennnnnnnnenennennnennnnnnenenennenenennnnnnenene 21 Appendix D MATLAB Script anna INANGKIN TINA 25 MEng Project Report Hanting Lu 1 Introduction 1 1 Background and Motivation Fruit flies Drosophila can be engineered to have thermo sensitive channels which are useful for turning off and on function in biological experiments One of these channels to be considered as a promising new tool is called Drosophila Transient Receptor Potential channel
7. for a long period of time The time period is set to 10 minutes The results shows that there are no problem for NMOS and the pletier plate but the PMOS is overheated and has potential risk to burn out As a result several smaller voltage are tested and it turns out 4 5V is the maximum voltage PMOS can stand Modification is then made on microcontroller to set threshold on lowest output voltage so that the maximum negative output control voltage is 4 5V 4 2 Tuning PID Parameters Using the method described in section 2 PID controller is tuned under constrains discussed in section 4 1 The final value of PID used for the project is listed as follow P 10 1 50 D 500 Under this set of parameters the final product performance is listed below e Cost 94 018 e Rising time 5s C settled within 10 s Falling time 10s C e Temperature range 15 35 C A comparison between the data above and the original design specification shows that the performance requirements are satisfied The development cost can be found in Appendix B 13 MEng Project Report Hanting Lu 5 Conclusion The first version of the Peltier Temperature Controller has been built and packaged completely The device has been tested with different computers and worked well All the device specification satisfied the design goal and with a User Manual in Appendix A students can easily learn how to use it to conduct related experiments For possible
8. timer 0 ISR void main void begin UCSROB 0600011000 hex 0x18 UBRROL 103 using a 16 MHz crystal 9600 baud init the UART uart_init is in uart c uart_init stdout stdin stderr amp uart_str fprintf stdout Starting n r crank up the ISRs set up timer 0 OCROA 249 1 mSec TIMSKO 1 lt lt OCIEOA Atum on timer 0 cmp match ISR set prescalar to divide by 64 22 MEng Project Report Hanting Lu TCCROB 3 turn on clear on match TCCROA 1 lt lt WGM01 blink port DDRD 0x04 A and d 2 which runs another LED DDRA Oxff test led ports PORTA 0x00 switch port DDRB 0x00 PORTB OxcO turn on pullups on d 6 and d 7 for pushbuttons set state machine swState nopress sw0 0 sw1 0 sei while 1 begin temp UCSROA amp 0x80 if temp begin inchar UDRO fprintf stdout d_ nr inchar if inchar s begin fprintf d d r n SWO sw1 fprintf stdout d d r SWO sw1 fprintf stdout od An sw sw0 0 sw1 0 end else if inchar gt 48 amp amp inchar lt 100 second higher bits is check bit begin fprintf stdout c r Ki des_temp inchar 48 PORTA des_temp end else if inchar gt 100 amp amp inchar lt 1 10 begin fprintf stdout c r Ki des_temp inchar 128 des_temp 7 PORTA des_temp end end end hile 1 end main 23 MEng Project Report Hanting Lu 24 MEng Project Repor
9. 25 Connect one end of the red white head cable to the red white banana sockets on the Peltier thermistor platform Connect the other end of the cable to the red white banana sockets on the project box Note that red plug should match the red socket and the white plug should match the white socket 35 Connect the USB port on the project box to a computer by the USB cable 45 Plugin the power If the red light on the project is on the system is ready to work IMPORTANT DO NOT OPEN THE PROJECT BOX ANYTIME WHEN POWER IS ON 3 Install Software Double click the test pkg exe file It will automatically extract the MCC compiler and the libraries inside this file as the following picture shows s meng gt ECHO OFF a p Computer E Local Disk d WinZip Self Extractor MCRInstaller exe Gia Network Ml PH238 01 jE PH238 04 Ml PH238 06 Ml PH238 08 188 PH238 09 188 PH238 11 Ml PH238 12 Ml PH238 14 Ml PH238 15 18 PH238 16 J PH238 18 jl PH238 19 ol PH238 20 Ml PH238 21 oll PH3R 27 22 Extracting MATLAB Compiler Runtime A2013a for ED installation Installation wil start once all fies are extracted Uvelppirg Jssejar Cancel About MCC compiler has to be installed before using the MATLAB GUI interface After the extraction the program will start to install MCC compiler An installer window will show as the follow 17 MEng Project Report Hanting Lu 4 1 gt PEN
10. GUI interface The temperature detection unit keeps detecting the current bath temperature of the petri dish and sending it back to microcontroller The control unit starts from running the PID control algorithm inside the microcontroller based on the current temperature detected by thermistor and the desired temperature input by the user through the GUI interface The output from the microcontroller went through the digital to analog converter a difference amplifier and then a power amplifier The signal after the power amplifier will have enough power to drive the peltier plate to distribute or absorb heat on its surface F Detection Unit i Temperature Control Unit ee om pm am em ov User Interface I I U I I I m m m m m m m vm wm o wm wm m m em m mm mm gt r U Figure 1 Overview of the Project 2 2 Control Unit Design 2 2 1 PID Controller The control unit starts when the microcontroller receives the desired temperature from user There is a PID control algorithm implemented inside the microcontroller which output the MEng Project Report Hanting Lu control signal based on the current temperature detected from thermistor and the desired temperature Considered as one of the best and common use controller in industrial control systems PID controller can provide control action design for specific process requirement by tuning the three parameters The three parameters are the proportional P the integral
11. PELTIER TEMPERATURE CONTROLLER A Design Project Report Presented to the School of Electrical and Computer Engineering of Cornell University In Partial Fulfillment of the Requirements for the Degree of Master of Engineering Electrical and Computer Engineering Submitted By Hanting Lu MEng Field Advisor Bruce Land MEng Outside Field Advisor Bruce Johnson Abstract Master of Engineering Program School of Electrical and Computer Engineering Cornell University Design Project Report Project Title Peltier Temperature Controller Author Hanting Lu Abstract This project is designed to build a controller to control the bath temperature of a petri dish The device will be used by student lab of neurobiology to conducting experiments on fruit flies thermo channels An ideal device should have the following feature easy to use small development budget less than 100 and satisfying the performance requirement for conducting experiments The project is based on an atmega 1284 microcontroller as the main control unit with a PID control algorithm running inside The petri dish s bath temperature is heated or cooled by a Peltier Plate A Thermistor is used as the temperature detection device and sent feedback to the microcontroller regarding to current bath temperature of the petri dish All components are connected with analog circuits to form a close loop feedback controller in order to dynamically control the petri dish s bath tempe
12. ack quit 1 close define the stop button stop button uicontrol style pushbutton string stop fontsize 12 position 300 400 50 20 callback stop 1 make some axes axeshandle axes position 2 2 7 7 xlim 0 100 ylim 20 60 initiate button signals quit 0 wait for a quit button push set_C 0 start 0 plus 1 neg 0 detect 0 stop 0 wait for a stop command setbkgnd 0 saveit 0 num S z 0 flag 1 null out x and y x y bkgndcolor 1 1 1 time 0 frame begin 0 frame end 100 Hanting Lu 26 MEng Project Report Hanting Lu frame limit 99 while quit 0 pause 1 l drawnow Yneed this in the loop for controls to work if set C 1 amp amp flag 1 flag 0 0pen a serial connection set its rate to 9600 baud SR830 terminator character is ACSII 13 use fprintf s m mode to write and fscanf s to read the SR830 port get communication_ports_set string s serial port baudrate 9600 terminator 13 fopen s end if flag 0 if start start 0 Switch 0 des temp 48 str2num get desired temperature string fprintf s des_temp end if detect fprintf s s Switch fscanf s d d num_s Switch 1 Switch 2 10 plot time num s rs LineWidth 2 MarkerEdgeColor g MarkerFaceCo
13. ence on each side of the device when a voltage is MEng Project Report Hanting Lu applied to it Peltier plate is known for the second way described above Specifically in figure 3 when the voltage difference is positive between wire a and b surface A will generate heat while surface B will absorb heat However when a negative voltage appears between wire a and b then the opposite effect occurs With its quick response and an inexpensive price on market peltier plate serves as a good component for this temperature controller design NAY na Figure 3 Peltier Plate Working Demo 2 2 3 Control Circuits Because of the output current limitation of the microcontroller the control signal coming out from microcontroller has to be amplified and shifted to drive the peltier plate The ideal result is that the driving voltage of the peltier plate has a range 12V 12V In order to reach this goal a circuit schematic shows in figure 4 is designed This circuit is composed with three main parts A digital to analog converter DAC A difference amplifier and a power amplifier MEng Project Report Hanting Lu Power Amplifier p Figure 4 Control Circuit The DAC is a 4114R 2 RC which can convert an eight bit digital input to an analog output A 5 volts from output pin is a logic 1 and a 0 volts corresponds to a logic 0 The combination of the eight output pins from microcontroller forms a range from 0 to 3 2 V at DAC s output
14. erature Detection Unit The Temperature Detection Circuit is illustrated in figure 5 It is a voltage divider with a thermistor inserted as a variable resistor As the thermistor I used is a NTC thermistor its resistance would decrease as the increasing of the temperature The disadvantage of using a thermistor is that its resistance changing is non linear which makes it hard to convert back to its corresponding temperature after ADC sampled by microcontroller Because the range of the temperature is not large I first tried to use a look up table inside the microcontroller This scheme worked but the problem is that the look up table is based on the datasheet of the thermistor which is unfortunately not very accurate Furthermore the error is not regular which means it is hard to compensate it in software To get a better look up table I have to measure every 0 1 degree changing for the thermistor which is not doable The final solution I took is to sample enough data for the temperate and its corresponding thermistor s resistance and using MATLAB to find a best fit function The function I chose is demonstrated in figure 6 By doing so the error is within 0 5 C which is acceptable for this project ADC sample Ba Thermistor WAI Dish Figure 5 Temperature Detection Unit MEng Project Report Hanting Lu Cin re File Edit View Insert Tools Desktop Window Help a D de bk AA 9A BA OE imi Ng Ee ENEE EA AE Figure 6 Usin
15. erfusion and temperature control J Neurosci Methods 25 19 27 3 Kingsley RE Barnes CD Pompeiano O 1976 A proportional controlled thermoregulator circuit of simple design Electroencephalogr Clin Neurophysiol 40 306 308 4 Jimena Bemi Alistair M Muldal Stefan R Pulver Using Neurogenetics and the Warmth Gated Ion Channel TRPA1 to Study the Neural Basis of Behavior in Drosophila J Undergrad Neurosci Educ 2010 Spring 9 1 A5 A14 5 Rose G 1983 A temperature controller for in vitro recording chambers Brain Res Bull 10 713 714 6 Tools for Physiology Labs An Inexpensive Means of Temperature Control Jacob L Krans and Ronald R Hoy the Journal of Undergraduate Neuroscience Education fall 2005 4 1 A22 A26 Datasheet 7 Atmel mega1248 Microcontroller SJIRF 9522 P Channel Enhancement Mode Vertical DMOS Power FETs 9 IRF 520 Power MOSFET 10 LM 358 Low Power Dual Operational Amplifiers 11 R 2R Series Thick Film Networks 12 44105 Thermistor with FEP Sheath 15 MEng Project Report Hanting Lu Appendix A User Manual 1 Components Project Box Ng Cable Peltier thermistor Platform USB cable 16 MEng Project Report 2 Connection Hanting Lu 15 Connect one end of the yellow head cable to the green banana sockets on the Peltier thermistor platform Connect the other end of the cable to the green banana sockets on the project box The orders of which plug match which socket doesn t matter
16. ermistor can be bend over so that the position the thermistor probes to the petri dish can be adjusted by hand Another two banana plugs are attached to the thermistor to connect to the project box The picture of this peltier thermistor platform can be found in Appendix A 3 3 Stand alone Program Since the computer in student lab of neurobiology doesn t have MATLAB installed a conversion is needed to make MATLAB script a stand alone program Otherwise purchasing MATLAB will increase the total development budget MATLAB s deploy tool and its MCC compiler is a good way to convert script to either exe for windows or app for MAC It converts the script as well as packages it with its GUI library so that a GUI interface can be running on a computer without installing MATLAB I tested the windows OS The whole package appears as a exe file and when it is running it automatically installs the compiler and related libraries before calls the GUI This solution has been tested well on computers which have no MATLAB installed The detail method can be found on MATLAB s official webpage under deploy tool 12 MEng Project Report Hanting Lu 4 Tests and Results 4 1 Maximum Output Voltage Test In section 2 it states that the actual output voltage after power amplifier is 6V 6V Since both CMOS and peltier plate may generate heat during the device running this maximum voltage has to be tested to guarantee the device can stand the maximum voltage
17. es 1 3 of circuits size horizontally and thus decreases the size requirement for the project box Same scheme is also used to put one power supply above another There are four different types of the connecters on the project box A USB port is used to connect to PC for serial communication between microcontroller and GUI Two banana sockets are used connect to the peltier plate so that the control signal can be passed from control unit to the peltier plate Another two banana sockets are used to connect thermistor of the temperature detection unit described in section 2 3 Finally a power plug is used to connect to the power supply The inside structure of the project is shown in figure 9 Note that there is space saved for further improvement such as adding a fan to distribute the heat The size of project box is 14 17x7 87x5 91 inches Pictures of the project box can be found in Appendix A Power Supply x 2 Heat Sink Figure 9 Project Box Structure 11 MEng Project Report Hanting Lu 3 2 Peltier thermistor Platform Since Peltier generates temperature difference on its two surfaces while one surface is used to control the temperature of the petri dish the other has to be attached to a large heat sink to distribute the heat Two banana plugs are attached to the input wire of the peltier plate so that it can be connected to project box The thermistor is put on the one side above the peltier plate The material I used to support the th
18. future improvement a better PMOS may be considered to use to increase the maximum positive voltage A fan can be added to distribute the heat inside the project box more effectively The Cable connected between project box and the peltier plate can be upgraded both in length and robustness An LCD screen can be added on the project box so user can use the device without a computer 6 Acknowledgement I would like to thank Professor Bruce Land who served as my MEng field advisor His insight full guidance and suggestions always helped me to move forward every time I got stuck by technical difficulty His course ECE4760 and ECE5760 also enlighten my understanding on digital system design which has positive effect on this project I appreciate his dedication and commitment to this project I would also like to thank Professor Bruce Johnson who served as my MEng outside advisor Our meetings were critical for me to calibrate the performance and the future design goal of the project He also introduces biology knowledge that is outside my major to me which I found very interesting 14 MEng Project Report Hanting Lu 7 Reference Paper 1 Correges P Bugnard E Millerin C Masiero A Andrivet JP Bloc A Dunant Y 1998 A simple low cost and fast Peltier thermoregulation set up for electrophysiology J Neurosci Methods 83 177 184 2 Forsythe ID Coates RT 1988 A chamber for electrophysiological recording from cultured neurones allowing p
19. g MATLAB to Find A Best fit Function for the Thermistor 2 4 Graphical User Interface The user interface designed for this project is MATLAB based The interface is illustrated in figure 7 Since one of the important requirement for UI is easy to use I try to simplify the functional buttons arrangement on it and make it as simple as possible The only thing maybe confused is the text window at the bottom right corner The use of that is to set the communication port for a serial communication between MATLAB and microcontroller The communication rate is 9600 baud The MATLAB function fprint and fscanf does a good job on communicating with microcontroller By pressing the detect button the ADC sample from the temperature detection unit is passed from microcontroller to MATLAB which then converted to current bath temperature and is shown in the middle text window After input the desired temperature in the bottom left text box and pressing the start button the desired bath temperature is passed back to microcontroller The control unit starts to control the bath temperature The temperature changing will continually show in current temperature text window as well as in the dynamic plot By pressing the stop button the device stop to function and ready for new command The detail MATLAB code can be found in Appendix D MEng Project Report Hanting Lu Dynamic Plot Set Communication Desired Temperature Port Curre
20. icated because the device may have other functions that are fancy but redundant As a result a ideal device should be inexpensive and easy to use With the help of a simple user manual students conducting the experiment don t have to bother too much on learning how to use the device Despite constrains on cost and complexity the low noise environment is required in the lab so that PWM is unacceptable Furthermore in order to eliminate the electronic noise the control circuits power supply DAC power amplifier etc have to be completely separated and keep distance from the petri dish Based on these constrains the section 1 5 lists the design specification for this project required by students lab of neurobiology 1 3 Range of Solutions Previous work has been done to attempt to build a temperature controller An in expensive way is proposed by Correges P Bugnard E Millerin C Masiero A Andrivet JP Bloc A Dunant Y 1 mentioned the usage of peltier plate but since no control cirtuit was used the precision was low But the idea of using peltier plate as an inexpensive way of generating heat is adopt in this project design Other works tried with electronic device or circuits but either had a relatively higher cost or may lack an easy way to use the device GUI LCD monitor etc 2 3 5 6 MEng Project Report Hanting Lu The range of solutions can be divided into two categories pure analog circuit design and microcontroller based des
21. ign It is possible to build a pure analog circuit function as a temperature control unit The advantage of this design is a quick speed execution However since a GUI interface is required this solution is not the best for this project design problem On the other hand microcontroller based design provides a serial communication that can be used to build a GUI interface on any computer With a proper algorithm implemented the response speed of the microcontroller is fast enough to satisfy the specification The next section gives an overview of the scheme to design this project Design detail of each Unit is discussed in section 2 1 4 Project Design Overview The system can be divided into three parts which are temperature detection unit temperature control unit and GUI user interface In order to detect the current bath temperature a thermistor along with a voltage divider circuit is used When sensing the different temperature thermistor will have different resistance which is reflected as a different voltage drop in the voltage divider circuit By continuously taking ADC samples from this voltage the microcontroller can get the information about the current bath temperature of the petri dish For the temperature control unit the main components include an atmega 1284 microcontroller with a PID control implemented difference amplifier circuit digital to analog DAC circuit and a power amplifier circuit The microcontroller outputs contro
22. l signals based on the desired temperature it get from user and the current temperature detected by the thermistor The DAC and difference amplifier is used to convert the eight bits output from microcontroller to an analog signal ranging from 12V to 12V The control signal is then output through a power amplifier to drive the peltier device to either increase or decrease the bath temperature of the petri dish For the GUI interface MATLAB is chosen as a foundation The interface is designed to be easy to understand and use To use the device user only need to type the desired temperature into the GUI interface The value will then be passed to the microcontroller by serial communication using USB The interface also contains a dynamic plot to allow the user to monitor the trend of the current bath temperature in petri dish 1 5 Design Specification The following is the design specification note that it s not the final result of the product but a minimum requirement to ensure the product can be used for related experiments e Cost less than 100 e Rising time 12s C settled within 10 s e Temperature range 20 30 C Design requirement low noise low cost easy to use MEng Project Report Hanting Lu 2 System Design 2 1 High level Design Figure 1 illustrates the overview of the project design As the diagram shows the device can be divided into three parts temperature control unit temperature detection unit and
23. lor g MarkerSize 2 grid on hold on if time gt frame limit frame begin frame begin 100 frame end frame end 100 frame limit frame limit 100 end axis frame begin frame end 20 60 time time 1 27 MEng Project Report set current temperature string num2str num eil end if stop stop 0 detect 0 set desired temperature string 0 set current temperature string 0 fprintf s t end end end if flag 0 fclose s end Hanting Lu 28
24. nt Temperature Figure 7 User Interface 2 5 Microcontroller Pin Assignment The atmel mega 1284 used in this project is developed and used on the development board used for Cornell ECE4760 course The detail of this hardware can be found in the course webpage http people ece cornell edu land courses ece4760 To illustrate the pin assignment on the development board figure 8 is demoed as a simplified version of the development board It includes all the pins on the board but the location maybe different PCO 7 is used for output the control signal Thus they are connected to the DAC PAO is the default port for ADC sampling it is connected to the thermistor VCC and Gnd are also connected to the temperature detection unit to finish the voltage divider An LED is connected to PDO to indicate the system is on MEng Project Report Hanting Lu Figure 8 Microcontroller Development Board 2 6 Combine Together The following process shows the common steps after the system s power is on Note it also reflects the basic coding process on microcontroller since the whole process is controlled by it A detailed source code of microcontroller can be found in Appendix C Step 1 Power on LED turned on indicating the system is running An initial static control signal is output from microcontroller result in a OV control voltage on peltier plate Step 2 Current temperature is detected by the temperature detection unit and passed to microcont
25. ource Code define F CPU 16000000UL include lt inttypes h gt include lt avr io h gt include lt avr interrupt h gt include lt stdio h gt include lt avr eeprom h gt serial communication library include uart h FILE uart_str FDEV SETUP STREAM uart putchar uart_getchar FDEV SETUP RW define begin define end define nopress 1 define maybe 2 define pressed 3 define maybeno 4 unsigned char inchar volatile unsigned char SWO sw1 char des_temp volatile unsigned char blinktime volatile unsigned char sw SWO sw1 volatile unsigned char swState volatile unsigned char swtime char temp char temp2 ISR TIMERO COMPA vect begin switch detection state machine swtime if swtime 30 begin swtime 0 switch swState begin case nopress if PINB Oxff begin swState maybe sw PINB end break 21 MEng Project Report Hanting Lu case maybe if PINB sw begin swState pressed sw PINB sw0 SWO char sw amp 0x80 gt 0 sw1 SW1 char sw amp 0x40 gt 0 end else swState nopress break case pressed if PINB sw swState pressed else swState maybeno sw PINC break case maybeno if PINB sw swState pressed else swState nopress sw PING break end case end button state machine blink the LED to show it is running blinktime if blinktime 200 begin PORTD 0x04 blinktime 0 end blink routine end
26. rature Graphic user interface is built with MATLAB to provide easy user access and monitoring Executive Summary This Master of Electrical and Computer Engineering project is designed to control the bath temperature of a petri dish through a microcontroller based system It provides a way for students in neurobiology lab to conduct experiments on a temperature sensitive channel of fruit flies This system should have an easy to use graphical user interface GUI so that students can use it easily with a simple user manual It is also required to have a development budget under S100 The design and implementation of the project has completed and the first version of the device is ready to use The device has an average rising time of 5s C and settles within 10s Tests shows it works stable and accurate among the range of 15 35 C which satisfies the requirement The total cost is less than 100 and with a simple user manual students can easily use it to conduct related lab experiments The final product contains two parts a control unit and an execution unit The control unit packages all the circuits as well as the microcontroller into a project box The execution unit is a peltier thermistor based platform where the petri dish should be put The complexity and detail of both units are hidden from the user Separating the two units also largely reduce the negative influence the control circuits may have on electronic noise To use the device
27. roller Step 3 A desired temperature is input and passed to the microcontroller Step 4 PID algorithm is running based on the error between current temperature and desired temperature A dynamic control signal is output to drive the peltier plate This step is continually repeated until a stop signal is sent from user Step 5 Get the stop signal stop the current process and go back to step 1 10 MEng Project Report Hanting Lu 3 Implementation and Packaging 3 1 Project Box In order to separate the control circuits away from the petri dish all the control circuits are put separately in a project box including the microcontroller Since the CMOS generate large amount of heat when the system is running heat sink is required for both NMOS and PMOS The initial implementation used the small heat sink which can be attached to the CMOS so that they don t need to be taken off from the circuit board However tests show that these small heat sinks cannot efficiently distribute the heat away As a result big heat sink has to be used and CMOS has to be moved off the circuit which increase the size of the device One optimization to decrease the device size is to build the circuit board in three dimensions Instead of building all circuits on one board circuits are divided into three portions and put on three boards These circuit boards are then connected together vertically This three folded sandwich scheme effectively sav
28. t Appendix D MATLAB Script UI interface for temperature controller clf clear all try fclose instrfind close any bogus serial connections end Yoset gcf CloseRequestFcn delete define the plot button start button uicontrol style pushbutton string Start fontsize 12 position 100 400 60 20 callback start 1 define the detection button detect button uicontrol style pushbutton string detect ontsize 12 position 200 400 50 20 callback detect 1 define non editable text field for showing current temperature current temperature uicontrol style text string fontsize 12 position 220 1 100 40 3 define edibale text file for inputing desired temperature desired temperature uicontrol style edit string 0 fontsize 12 position 100 1 100 40 define edibal text field for setting communication port communication ports set uicontrol style edit string COMT fontsize 12 position 400 1 100 40 define the set button Hanting Lu 25 MEng Project Report setbutton uicontrol style pushbutton string Set ontsize 12 position 500 1 50 20 callback set C 1 define the quit button quitbutton uicontrol style pushbutton string Quit ontsize 12 position 500 400 50 20 callb
29. vices Gq IDE ATA ATAPI controllers SE Jungo Keyboards D Mice and other pointing devices Bu Monitors S Network adapters a TP Ports COM amp LPT i YP USB Serial Port COM7 bin om rm rm pm pm mm e it vm mm m mm mm mm mi Processors DP Security Devices a Sound video and game controllers Q Storage controllers sk System devices Universal Serial Bus controllers Input the port ID found in step 1 gt into the bottom right corner in GUI Press set button Press detect button the current bath temperature of petri dish will be shown in the middle bottom text box Input the desired temperature in the left bottom corner text box Press start button The device will start running and you should see the current temperature change both in the middle bottom text box and the dynamic plot Press stop button to stop the current process And then another desired temperature can be input and repeat step 4 gt Press quit button when you finish the experiments 19 MEng Project Report Appendix B Cost Hanting Lu Iterm Unit Cost Quantity Subtotal Cost Atmaga 1248 5 00 1 5 00 Project Box 29 95 1 29 95 Peltier Heat Sink Module 10 00 1 10 00 12 V Power Supply 21 98 2 43 96 IRF 9522 1 20 1 1 20 IRF 520 0 30 1 0 30 LM 358 0 40 3 1 20 4116 R2R 0 40 1 0 40 Total 92 01 20 MEng Project Report Hanting Lu Appendix C Microcontroller S
Download Pdf Manuals
Related Search