COSC 3215 Embedded Systems Laboratory

Transcription

1 Introduction COSC 3215 Embedded Systems Laboratory Lab 5 Temperature Controller Your task will be to design a temperature controller using the Dragon12 board that will maintain the temperature of an object at 12+/-1 C. This will be accomplished by varying the current through a Peltier Cooler using the pulse width modulated outputs of the HCS12 chip. The temperature of the device is monitored using Analog Devices AD592AN Precision IC Temperature transducer. The AD592AN is connected to an operational amplifier located on the breadboard area of the DRAGON12. Specification Outline of program function: The temperature controller will have a default temperature setting of 12 C. The temperature will be monitored continuously using the Analog Converter, with the temperature displayed on the 7-Segment display in C, ex. 20 C will be displayed as Note the decimal point will appear as a superscript on the 7- Segment display. Control of the temperature is by means of a PWM signal, where the temperature will increase with decreasing duty cycle. The complete program will be developed in parts over two lab sessions. Note these are 1- week lab sessions. You will only be graded at the end of the second session for this lab. Pre Lab Even in simple programs such as this it is advisable to partition well and to test your modules independently. You should have test programs written to test your code for the important functions as well as the overall program. The software can be readily decomposed into functional components: temperature measurement and display, cooler set-point adjustment and the temperature controller. Testing the code in parts will make the project more manageable. You should plan on completing steps 1-4 during week one so that the entire lab can be completed by the second week. 1. VR2 on the DRAGON12 is connected to channel 7 of the Analog Converter. Write an interrupt-based program that will read the voltage level on channel 7, convert it to degrees Celsius and display the temperature value on the 7-segment display. You can average several readings using the ATD peripheral and get

2 smoother measurements. (Hint: one possibility is to have a timer that gives an interrupt every 1ms to time the display update. After 100 display updates, you could initiate an ATD conversion that will generate an interrupt upon completion. You could maintain a counter in the timer ISR, initialized to 100, to keep track of the number of display updates and thus know when to do the conversions. The mainline can concentrate on controlling the temperature without having to worry about the details). 2. Write a program that will accept a set-point value in terms of PWM duty cycle (initially from the DIP switch on the Dragon-12 board but eventually from the temperature controller) and generate the corresponding PWM output to the cooler. 3. Write appropriate programs for testing the components in 1 and The final demonstration program for these two functions should integrate the setpoint measurement and the temperature measurement functions. This program should continuously read the set-point from the dip-switches and drive the coolers at the specified duty-cycle. The current temperature at the sensor should be displayed continuously. Based on the characterization of the Peltier cooler performed in the lab (and described below) 5. Write a simple open-loop temperature controller that attempts to set the temperature at the sensor based upon an assumed ambient temperature and a desired temperature specified above. 6. Write a closed-loop controller that adjusts the set-point of the cooler based upon the error between the current temperature and the desired temperature specified above. Hints The HCS12 timer module can provide precision timing. The use of interrupts for the ATD converter and the timer module will greatly reduce the complexity of your program. Use the methods you developed in Labs 3 & 4 to show characters on the seven-segment display. The temperature sensor and the cooler have a long thermal time constant. Remember to allow some time for settling when doing your measurements. The output of U2-6 located on the breadboard is connected to the ATD of the DRAGON12. This output voltage is what your program will read as the temperature.

3 The output of U2-6 has a gain and offset adjustment. These two adjustments can be used to tailor the output voltage to the level your program requires, if necessary. Reference Reading Standard references from previous labs Enhanced Capture Timer user s guide S12ECT16B8V1.pdf ATD Converter user s guide S12ATD10B8CV2.pdf Data Sheets for Analog devices AD592AN Temperature Sensor AD592.pdf Dragon12 schematics Temperature Sensor Interface Schematic Note: Ensure that you are wearing your antistatic wrist strap prior to handling the DRAGON12 board. Failure to do so could result in severe damage to the DRAGON12. Make appropriate notes and answer all questions clearly in your lab book. PRELAB MUST BE COMPLETED BEFORE STARTING THE LAB! Week 1 Procedure 1. Connect the DRAGON12 to the PC and launch the MiniIde program. 2. Download and debug your assembled or compiled programs. Once you feel comfortable that your programs are working move on to the experiments below. 3. Using your temperature measurement program measure the ambient room temperature. Note this measurement. Does it meet your expectations? If not can you explain/correct the problem? 4. Using the program developed for pre-lab part 4 measure the relationship between cooler duty cycle and sensor temperature (both absolute and with respect to ambient).

4 5. At several duty cycles, measure the reported temperature and compare it with the voltage at the output of U1-6 located on the breadboard. Note the temperature in C is calculated as follows: T = (Vo 2.73) * 100 (the voltage at this point is negative). Does it meet expectations? If not can you explain or correct the discrepancy. 6. Measure the temperature/duty-cycle relationship of at least eight different dutycycles. Start with a low duty-cycle at first and repeat the measurements in reverse order. a. What type of relationship was there between duty cycle and temperature? b. Where the measurements repeatable? c. Was there any indication of hysteresis? 7. Demonstrate your working program to the lab demonstrator. Return all equipment and boards before leaving the lab. Evaluation There will be no grade for week 1. The entire lab exercise will be evaluated in week 2. Week 2 procedure 1. Before starting to debug your controller ensure that you have completed the week one work and demonstrated it to the TA. 2. Debug and test your open loop controller. How does the system respond to changes in room temperature? 3. Debug your closed loop system. If you have trouble with stability apply the control changes more slowly. What is the advantage of closed loop control versus open loop. Any disadvantage? 4. Demo the result to the TA. If the closed loop controller does not work or is unstable demo your open loop controller. Evaluation You must demonstrate a working version of your code to the lab demonstrator (note this means you must show convincing evidence that it works) and have acceptable written documentation about your programs performance. Please submit the final version of your code using the 'submit' command. This includes the temperature controller code and the experimental code from week 1.

5 The first goal of the lab is the characterization of the cooler. You should have documented the results of the experiment and answered the questions posed in the procedure in your lab book. This will be given significant weighting in the evaluation. You should also be able to answer questions about the program, the use of the test equipment and your test and debugging techniques. Successful demonstration of the temperature controllers is the second goal of the lab. At a minimum you should demonstrate the open loop controller. Perfect implementation of the closed loop controller is difficult and will be considered a significant bonus. However, you should have at least a full and reasonable implementation developed that you have partially debugged.