Temperature Control

This lab will introduce you to the temperature control. Embedded systems programming is probably different from the programming you are used to, since it presents an interface to the user, and user interaction generates events.

See the program tempControl.ino. This should be used as a starting point. You will have to alter it.

The website buildr.com has a tutorial on the sensor probe, including getting and using the OneWire library (that you will need for this lab).

Notes on safety: Be careful working with the equipment in this lab, especially since it involves water. Water DOES allow electricity to flow (supposedly pure water will not, but the water you will use does contain salts and other chemicals that do allow electric flow).

• Plug the Switch-Tail II into a ground fault circuit interrupter (GFCI). This will shut off the electric flow if there is a problem. You probably have (a) GFCI outlet(s) in your home or dorm. If not, these can be purchased for a reasonable price and are a smart thing to have.
• Make sure to use the grounding strips any time that you work on electronics.
• Use a drip-loop in any cable that needs it. A drip-loop is where the cable has slack, forming a point well below the outlet, such that any water on the cable will accumulate at that point and drip off instead of flowing into the outlet.

Put a pot of water on the burner. Put the temperature probe into the pot, and secure it so that it does not move around. Plug the burner into the Switch-Tail II, and connect the Switch-Tail II leads to the Arduino. In the video that I showed the class, the Power switch tail II has 1 + connected via the white wire to the Arduino pin 3, and 2 - connected via the black wire to the Arduino ground. Use red wire for the 1 +, and black wire for the 2 - connections if you can. It's OK if you have different colors for wires, or use something different than pin 3, but be sure to wire it correctly.

Also connect the temperature probe to the resistor and Arduino, being VERY CAREFUL to get the wiring correct. Failure to do so may burn out the probe. Use a 4.7k Ohm resistor (color bands are Yellow, Purple, Red).

Once the code has been uploaded, turn on the Serial Monitor (see the icon on the upper-right corner of the Arduino window).

Your goal is to heat the water up to 50.0 degrees C, and keep it there. Turn the burner on, being careful. Plug the Switch-Tail II into a Ground Fault Control Interruptor, if possible. Record the temperatures, at least once per second. Copy the output from the serial monitor, and save it to a file (called myfile.txt in the example below).

Edit the file, to remove any misformed lines. For example, you may have something like "0:0:0 60.8 C, Target: 65Low temp - turning on the burner." in one of the first few lines, as the Serial Monitor starts up. The "65Low" are a temperature and message strung together, and this can cause problems when we try to plot the data. Also, remove any text-only lines, such as "Low temp - turning on the burner." Make sure that each line contains a data point. An easy way to do this is to use the grep utiliity, as in this line:

        grep : myfile.txt > myfile2.txt

Use a utility, like awk to isolate the data. For example,

        awk '{ print $2", "$5", "$10 }' < myfile2.txt > mydata.csv

will put the three numbers into a comma-separated-value (CSV) file. Then use a program to plot the numbers, such as MATLAB:

        y = csvread('mydata.csv');
        plot(y.');
        title('Plot of temperature data by Your Name');


Put a copy of your plot in your lab report.

Questions

1. How much water did you use? How do you think this impacted your results?
2. What kind of container did you use? Did this have any impact on your results?
3. What was the temperature (of the water) when you started? How long did it take to initially raise the temperature to the target temperature?
4. You probably saw some variation in temperature. After getting to the target temperature, what was the highest temperature, and what was the lowest temperature?
5. For the measured temperatures after reaching the target temperature, produce an error signal, defined as the measured temperature minus the target temperature. (MATLAB is a good choice to answer this question, but you instead could use a spreadsheet or write a program.) Divide the error signal into groups according to zero-crossings. That is, put the positive values into the first group until you run into a negative value. Then put the negative values into the second group until you run into a positive value. Then put the positive values into the third group until you get to a negative value, etc. For each group, what were the accumulated over-shoots in degrees per second? What were the accumulated under-shoots? (That is, add all the values of the first group together and record that number. Then repeat this will every group until you have a sum for each group.) Adding all the accumulated over-shoots together, how does this compare to the sum of all the accumulated under-shoots?

What to Turn In

Follow the directions on Lab Report format, given on the class web-page. Write-up what you did IN YOUR OWN WORDS. Do not simply re-word the directions, but explain what is going on. Avoid listing steps. Use outside sources as appropriate, and be certain to cite your sources. If you copy and paste ANY text, put it in double-quotes and include a citation immediately after it.

• Include your answers to the questions.
• Include a printout of your code. You only need to include the files that you changed. For example, creating a new application project may in turn create a files. If you do not change those files, you do not need to include printouts of them.
• Clearly indicate the author (and source) of any code, such as out of a book or from a web-page. If you modified it, clearly state this.
• Include a screen-capture of the simulator's screen (or Arduino's serial interface screen), when there is something to see. For this assignment, one screen capture is enough.
• Do keep electronic copies of any files, in case the TA or professor asks for it. Do NOT turn in excessive printouts. Instead, for a long print-out (like the temperature log), you can show it with an ellipsis: print the first few lines, print an ellipsis (three periods in a row ("...") on a line by themselves), then print the next few lines of interest, print another ellipsis, repeat as needed, then show the last few lines. You can also put this in anytime you need; it conveys the idea that you are skipping something similar and non-note-worthy. You can also do this for code that someone else wrote, e.g. to show lines that you changed.
• Turn in one report per person.
• Make sure it is stapled.
• Include on the lab when your appointment with the TA to demonstrate your lab is (or was). It is your responsibility to demonstrate your labs to the TA. The time you and the TA agree on is up to you. You are required to set this up BEFORE turning in the lab.

Please see the link to the lab format.