Lab 2 Temperature Measurement System

Transcription

1 GOALS Lab 2 Temperature Measurement System 1) Build and test a thermistr circuit. 2) Write an Arduin prgram t acquire and send vltage data t a cmputer using the serial prt. 3) Write a MATLAB prgram t: a. Read data frm the serial prt. b. Prcess the raw data int temperature. c. Display a plt f temperature vs time. 4) Perfrm sme fun experiments with yur temperature measurement system! GENERAL GUIDELINES 1) Each student must build his/her wn circuit. 2) Due t the limited number f test statins, sme students need t pair up and share the test equipment. 3) Students are encuraged t help each ther. Of curse, Buma will be arund t prvide assistance as well. 4) Ask questins! The mre questins yu ask, the mre yu learn! REQUIRED MATERIALS Lab kit + pwer supply + scillscpe + test prbes Arduin Un + USB cable + cmputer with Arduin IDE and MATLAB AD620 instrumentatin amplifier (ne) 1.0 khm (brwn/black/red) resistrs (tw) 10 khm thermistr (cmes with a lng cable) 10 khm resistrs (brwn/black/range) (three) 100 khm resistr (brwn/black/yellw) (ne) LAB ACTIVITIES (4 PARTS) Fig. 1: Thermistr (Vishay BC Cmpnents). 1) Set up temperature measurement hardware. 2) Develp the Arduin data acquisitin prgram. 3) Develp the MATLAB data prcessing and display prgram. 4) Perfrm sme experiments with yur awesme temperature measurement system. 1

2 INTRODUCTION In this lab, yu will develp a temperature measurement system. A system blck diagram is shwn in Fig. 2. Here s hw it wrks: 1) The thermistr (in a quarter bridge) cnverts temperature t a vltage signal. 2) The instrumentatin amplifier increases the signal amplitude. 3) The amplifier utput is recrded by the Arduin and vltage data is sent t the cmputer. 4) The cmputer prcesses the data (using MATLAB) t prduce a plt f temperature versus time. Fig. 2: Overall temperature measurement system. PART 1: THERMISTOR CIRCUIT The thermistr circuit is shwn in Fig. 3. Task 1a: Build the quarter bridge circuit and instrumentatin amplifier (Fig. 3). Keep yur wiring neat! Yu can cnsult Buma s (r a neighbr s) breadbard fr guidance. Yu can re-use the AD620 chip and ther cmpnents frm Lab 1. Prperly clr cde yur wiring! RED = +5V BLACK = GND YELLOW = ther The thermistr cable has tw wires that plug int the bard it desn t matter which wire ges t pwer. 2

3 Fig. 3: Schematic fr thermistr circuit. Remember t clr cde yur wiring! Task 1b: Test the circuit. (End f Part 1) Use the scillscpe t measure the utput vltage at Pin 6 f the instrumentatin amplifier. Turn n the scpe, then press Frce Trigger t enable lcal (e.g. Frnt Panel) cntrl Press Default Setup t reset the scpe Make sure bth the scpe and prbe are set t 1X Adjust the scpe s vertical setting t 1V/div the trace shuld be near 2V. Zm in n the trace. First, center the trace in the middle f yur screen (use the small knb t scrll dwn). Next, zm in by changing the vertical setting t 500 mv/div. Finally, squeeze the thermistr between yur thumb and index finger the vltage shuld increase by rughly 200 mv r s. When yu let g the vltage shuld slwly return t its riginal value. If yu have cld fingers and cannt see a vltage change, yu can either: D abut 386 jumping jacks t warm up yur bdy. Ask a classmate with htter fingers t test yur circuit. 3

4 PART 2: ARDUINO Fr this lab, the Arduin will recrd Vmeas and send it t the PC. Unlike Lab 1, this lab will invlve mre cmmunicatin between the Arduin bard and the PC. This cmmunicatin is needed t minimize any lst data during transmissin. An utline f the Arduin cde is shwn belw: (a) Setup( ) rutine (b) Lp( ) rutine Initialize the serial prt Send message t PC Wait fr message frm PC If PC requests data, Recrd ADC utput Cmpute Vmeas Send Vmeas t cmputer Wait 500 ms STEP 2a: Dwnlad and unzip the Arduin template. G t the curse website and dwnlad Lab2_files.zip t yur desktp. Duble-click n the zipped flder. Select Extract all files (near tp f the windw) t unzip the cntents f the flder. Duble-click the Lab2_Arduin flder and pen the template. Yu can cnsult the Lab1 handut r Ggle fr help and/r examples using Arduin functins. STEP 2b: Write the setup( ) rutine. Initialize the serial prt using the Serial.begin cmmand Replace the??? with apprpriate cde. Use the Serial.begin cmmand and set the data rate t 9600 bits per secnd. Dn t frget the semicln at the end f each line! Send message t PC Use the Serial.println cmmand t send the single letter a. Duble qutes are imprtant! 4

5 STEP 2c: Declare variables fr the lp( ) rutine. The lp rutine uses five variables. Declare these befre the lp( ) rutine. As shwn in Fig. 4, Buma wrte the first ne fr yu (he is s kind.). Replace any ther??? with apprpriate cde. Data Type Name Value Purpse char PCstatus Stres ne byte f text data frm the PC int A0_PIN 0 Name f Analg Pin 0 int ADCutput Stres the ADC utput flat Vmeas Measured vltage int T 500 Time between readings (ms) Dn t frget semiclns at the end f each line! Fig. 4: Declare sme variables befre the lp( ) rutine. STEP 2d: Write the lp( ) rutine. Replace all the??? s that yur cde lks like Fig. 5. Cmments abut the cde. The Serial.available cmmand checks if the serial prt has received any data. The while lp repeats this prcess and stps when data has been received. The Serial.read cmmand reads ne byte f received data frm the serial prt. The Serial.read cmmand reads ne byte f received data and stres the value in PCstatus. If PCstatus is the character y, then we prceed t make a vltage measurement: Use the analgread cmmand t read the data frm A0_PIN. Cnvert ADCutput t Vmeas (see Lab1 handut if yu frgt hw t d this). Serial.println(Vmeas, 3) sends the Vmeas value (3 decimal places) Use the delay cmmand t wait T secnds befre the next sample acquisitin. 5

6 Fig. 5: The lp( ) rutine checks fr a message frm the PC and then makes a vltage measurement. STEP 2e: Uplad yur cde and bserve the Arduin utput using the Serial Mnitr n the cmputer. Yu shuld ntice the letter a n the first line (Fig. 6a). Nthing else shuld be happening, since the Arduin has nt received a y frm the cmputer. Type in the letter y in the cmmand line and press the Send buttn (see Fig. 6b). Yu shuld see a vltage value appear belw the letter a. Yur cde wrks if a new vltage value appears every time yu send y t the Arduin. Nice! Fig. 6: (a) The Serial Mnitr shuld nly shw the letter "a" when the Arduin cde starts. (b) Typing in "y" and pressing "Send" shuld cause the Arduin t recrd and send a vltage signal. Repeating this prcess results in new vltage values. STEP 2f: Cnnect yur thermistr circuit t the Arduin bard. 6

7 We want the thermistr circuit t be directly pwered by the Arduin bard. First, TURN OFF and DISCONNECT the benchtp pwer supply frm yur breadbard. Yu can put away the banana cables since they wn t be needed anymre. Secnd, DISCONNECT the USB cable frm yur Arduin bard. Third, use a RED wire t pwer yur breadbard frm the Arduin s +5V utput (see Fig. 7). It is OK t use a lng wire (e.g. few inches lng). Then use a BLACK wire t cnnect the breadbard grund t the GND pin f the Arduin. Finally, use a YELLOW wire t cnnect the amplifier utput (Pin 6) t the A0 pin f the Arduin. Re-cnnect the USB cable t the Arduin and re-run yur Arduin cde. View the Serial Mnitr t cnfirm that yu get a fairly steady vltage (e.g. smething like the right side f Fig. 7). Clse the Serial Mnitr when yu have cnfirmed that everything wrks OK. Fig. 7: Discnnect the benchtp supply, then pwer yur breadbard frm the Arduin s +5V utput and GND. Pin 6 f the AD620 chip is cnnected t A0 f the Arduin. It is perfectly OK t use lng wires (e.g. few inches) fr all three cnnectins. When yu re run yur Arduin cde, the Serial Mnitr shuld shw a fairly cnstant vltage. (End f Part 2) 7

8 PART 3: MATLAB WARM-UP EXERCISES Nw that we ve acquired Vmeas using the Arduin, we need t prcess Vmeas and display a plt f temperature n the cmputer. We ll d this using MATLAB! Buma will assume that yu knw sme MATLAB, but have n experience using MATLAB t cmmunicate with an external device. In the Lab2_files flder yu recently dwnladed frm the curse website, duble-click n the Lab2_MATLAB.m file. EXERCISE 3.1 Our first MATLAB exercise is t receive a single vltage measurement frm the Arduin. Hw t d this? Fig. 8 is the flw chart fr the Exercise 3.1 MATLAB prgram. Create serial prt cnnectin Wait fr Arduin message Request Vmeas frm Arduin Clse the serial cnnectin Fig. 8: Flw chart f the MATLAB prgram fr Exercise 3.1. STEP 3.1a: Replace any??? in the template s that yur cde lks like Fig. 9. Cmments abut the cde are shwn belw: Creating the serial prt cnnectin: The serial cmmand creates a serial prt bject that we will name serobj. Make sure the COM number is the same as in yur Arduin cde! We are using the set cmmand t cnfigure the data rate fr 9600 bits per secnd. The serial cnnectin is started by pening serobj using the fpen cmmand. The disp cmmand displays a message in the MATLAB Cmmand Windw. Waiting fr the Arduin message: The variable ArduinReady stres the message frm the Arduin. We will initially assume ArduinReady is the letter n. We are using a while lp t repeatedly check fr a message frm the Arduin. The lp keeps ging as lng as ArduinReady is NOT equal t a. The fscanf cmmand reads the received data cntained in serobj. The %s ptin means that the message is a text string. 8

9 Fig. 9: Yur MATLABcde shuld lk like this. D NOT frget the semiclns! Requesting Vmeas frm the Arduin: The fprintf cmmand sends the letter y t the Arduin via serobj. The %c ptin means that the message is a text character. The fscanf cmmand reads the received data cntained in serobj. The %f ptin means the data is a flating pint number. Finishing up the prcess: The fclse cmmand clses serobj, which terminates the serial prt cnnectin. STEP 3.1b: Save yur prgram, then run it by clicking n the Run buttn (with green triangle) at the tp f the MATLAB windw. The cmmand windw (bttm f MATLAB windw) shuld lk smething like Fig. 10. If yu get a COM nt available errr, it mst likely means yu did nt use the crrect COM prt number when using the serial cmmand. 9

10 If yu get errrs: First, manually clse the serial bject via the cmmand line by ding the fllwing: >> fclse(serobj) Why d this? When yur prgram exits prematurely due t an errr, it leaves the serobj pen. MATLAB des nt like this and will prevent further cmmunicatin thrugh the serial prt. Highly annying! In yur prgram, make sure: Yu prperly use semiclns. Yu prperly use SINGLE qutes instead f duble qutes. Fr example, %s is crrect while %s is wrng. Once yur prgram wrks, lk at the Arduin while yu click the MATLAB Run buttn: The Arduin s L LED shuld quickly blink a few times, fllwed by a quick flash f the Tx and Rx LEDs. Fig. 10: The cmmand windw (bttm f MATLAB windw) shuld lk like this. EXERCISE 3.2 Our next MATLAB exercise is t make a plt f Vmeas streamed frm the Arduin. Fig. 11 shws the flw chart. Update data with new Vmeas Create serial prt cnnectin Wait fr Arduin message Create windw fr pltting data Request Vmeas frm Arduin Repeat Clse the serial cnnectin Update the plt with new data Fig. 11: Flw chart fr the MATLAB prgram t plt Vmeas that is streamed frm the Arduin. 10

11 STEP 3.2a: The first tw sectins f the MATLAB prgram are identical t yur Exercise 3.1 cde. Insert a new sectin f cde, as shwn in Fig. 12, just after the disp( Arduin is ready ); line f cde. This new cde will create the windw fr pltting data. Cmments abut the cde are shwn belw: We first need t create a 1-D array f time values fr pltting. The time vectr t has a length f N = 50 samples. The time increment is dt = 0.5 secnds. The time vectr is therefre [0, dt, 2dt, 3dt,..., 49dt] = [0, 1, 2, 3,..., N-1]dt We next create an array f vltage values. The vltage vectr Vdata will initially be defined as a 1-D array f nes. The figure cmmand creates a windw, where we assign h as the figure name. The plt cmmand plts t n the x-axis and Vdata n the y-axis. drawnw displays the plt immediately (this is necessary while the prgram is running). We want the prgram t STOP when the user clicks n the figure windw. We can d this using the ButtnDwnFcn in MATLAB. The ButtnDwnFcn is a functin that des smething when the user clicks n the figure. We use the set cmmand t cnfigure the ButtnDwnFcn t d whatever we want. We define a variable q that is initially equal t 0. When the use clicks n figure h, we want ButtnDwnFcn t make q = 1. Later in the cde we ll see hw q = 1 causes a while lp t exit. Fig. 12: This part f the cde creates 1 D arrays fr time and vltage, displays a plt, and cnfigures the ButtnDwnFcn feature. 11

12 STEP 3.2b: Nw we need t implement a live feed f data frm the Arduin! Replace all??? with apprpriate cde shwn in Fig. 13. Cmments abut the cde are shwn belw: The while lp keeps running as lng as q is equal t 0. Requesting Vmeas frm the Arduin: The fprintf cmmand sends the letter y t the Arduin via serobj. The %c ptin means that the message is a text character. The fscanf cmmand reads the received data cntained in serobj. The %f ptin means the data is a flating pint number. We want the mst recent Vmeas value t be the LAST element in the Vdata array. We shift the existing Vdata elements t the left. We then assign the last element in Vdata t be equal t Vmeas. Pltting the updated data: The plt cmmand plts the updated Vdata as a functin f t. The ylim cmmand sets the y-axis limits f the plt. The drawnw cmmand is necessary t display the updated plt immediately. We then assign the last element in Vdata t be equal t Vmeas. The last sectin f the prgram ( Finish up the prcess ) is the same as befre. Fig. 13: The data acquisitin lp des tw things: (1) request Vmeas frm the Arduin (2) display an updated plt. 12

13 STEP 3.2c: Save yur prgram, then run it by clicking n the Run buttn (with green triangle) at the tp f the MATLAB windw. If yu get any errrs, remember t manually clse the serial bject via the cmmand line: >> fclse(serobj) A plt shuld appear with a wavefrm that is scrlling t the left. An example is shwn in Fig. 14. When the prgram starts, the vltage will quickly jump t rughly 2.4V r s. Pinching the thermistr causes the vltage t increase. Releasing the thermistr causes the vltage t drp. Fig. 14: Example f streamed data frm the Arduin. The live data stream keeps ging until yu click the figure just utside the white plt area. (End f Part 3) PART 4: TEMPERATURE MEASUREMENT OK, nw it s time t implement the temperature measurement system! Our MATLAB cde shuld receive ne sample f Vmeas frm the Arduin, cnvert Vmeas t RT, then use the Steinhart-Hart equatin t cmpute temperature Temp in degrees Celsius, and update a scrlling plt f Temp vs t. Frm PreLab 2, Vmeas is cnverted t RT using the fllwing tw equatins: / ; /0.5 ; The extended Steinhart-Hart equatin is given belw (T is in Kelvin): 1/ lg lg In MATLAB, the natural lgarithm functin is lg (it is nt ln). Yu want temperature in degrees Celsius, s yu need t slightly mdify the abve equatin! 13

14 Task 4a: Using yur Exercise 3.2 cde as a starting pint, mdify yur cde t prduce a live plt f temperature. Cmments abut the cde are shwn belw: Yu shuld replace Vdata (vltage vectr) with Temp (temperature vectr). In Exercise 3.2, we initially defined Vdata as an array f 1s (e.g. [1, 1, 1,, 1]). When creating Temp, it shuld be initialized as an array f 25s (e.g. [25, 25, 25,, 25]). It is a gd idea t define any cnstants (e.g. Ad) befre the data acquisitin lp. It is fine t assume Ad = and Vref = 2.5. Be careful with units! Since the equatin fr RT invlves khms, yu shuld use R25 = 10. The Steinhart-Hart cefficients fr the thermistr are: A = e-3; B = e-4; C = e-6; D = e-8; The y-axis limits f the temperature plt shuld be between 10 and 35 degrees Celsius. Due t the lack f a calibrated temperature surce, we will nt calibrate ur system. Please d nt be t disappinted Task 4b: When yu run yur cde, a plt shuld appear with a wavefrm that is scrlling t the left. If yu get any errrs, remember t manually clse the serial bject via the cmmand line: >> fclse(serobj) A successful example plt is shwn in Fig. 15. Remember that the temperature is initially assumed t be 25 C. The actual temperature in Buma s ffice was arund 22 C, which explains the sudden drp in the wavefrm. The temperature increased when Buma pinched the thermistr. The temperature drpped when the thermistr was released. The acquisitin was stpped by clicking OUTSIDE the white plt area f the figure. Task 4c: Recrd and save a warm plt with yur thermmeter. Yu can pinch the thermistr with yur fingers r dip the thermistr tip int a cup f warm water. Task 4d: Recrd and save a cld plt (dip the thermistr tip int ice water) with yur thermmeter. Task 4e: Dem yur awesme system t Buma! Fig. 15: Example f streaming plt shwing temperature rise and fall versus time. (End f Lab 2) 14