CE-351 Microcontrollers, 2022 Spring
PID control using a photocell
Name: Mychael Garcia
Email: mhgarcia@fortlewis.edu

Materials:
PID and photocell overview
In this project we developed a simple PID controller, this uses feedback from the system to get to a resulting value and correct itself to get to the desired value. This over all error is calculated from the P, proportional, I, Integral, D, derivative, hence the name. The simple system we want to integrate this controller into was a simple light sensing circuit. We have photocell which is a variable resistor that changes relative to light level. Knowing that light level is our variable that we can change, in the following task we will use this idea and apply it to our PID controller to vary the overall brightness of this LED.

Task 1:
For the first task we needed to find the relative ambient light level for the environment we are testing in. From this we increased the value a significant amount to see that the LED attached to our system would turn on and produce a change in current value readings. With this change the brightness was slowly adjusted to where the current value would equal the setpoint. My ambient light level was around 280-300 so to see a change in the LED brightness I increased the set point to 340, as seen by the blue linear line.
T1

Task 2:
After getting our PID controller working, and the LED brightness calibrated we added a second LED on a button. Whenever this new LED was powered the brightness on the original would have to be adjusted, decreased, to bring the overall light value back to the sent point. The opposite can be said when the new LED was powered off.
T2

Task 3:
For the final task we wanted to adapt a changing set point value and have the PID controller recalibrate automatically to the new value. We used the same button as before but instead of having an LED connected each press would increase the set point value by 20.
T3

Conclusion:
Overall this was a very useful and interesting project. In my robotics II class, we used a PID controller for our final project (balancing car) this was the same idea, but it was hard to visualize what happens. With this, it was easy to see how changing, increasing or decreasing, one of the PID constants varies the rate at which the brightness of the LED to the desired set value.
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