CE351 2020 Fall
Lab 5: PID Control - Photocell
Sophie Turner 
sjturner@fortlewis.edu

PID Control - Photocell

1. Introduction
The purpose of this lab was to use a proportional-integral-derivative controller (PID controller) to stabilize the light detecting resistor (LDR) system. An Arduino Uno and photocell were used to sense light intensity. The PID feedback system was used to calculate the error for the data to oscillate around a set point.

2. Materials and Methods
A photocell also known as a light detecting resistor (LDR) was used to sense light intensity. The light intensity was graphed on the Arduino serial plotter as well as plotting in Python. Two LEDs, a push button, and a photocell was used for this lab. For more detailed methods section go to http://www.yilectronics.com/Tutorials/Arduino_Basics/Tutorial_5_PID_Photocell/PIDPhotocell.html

3. Results
The ambient light was tested to see the lowest value the photocell can detect. 

Figure 1. Checking the ambient light.

A maximum light intensity was checked using a LED.

Figure 2. Testing the maximum light intensity value that the LDR can detect.

The setpoint was set below the ambient light detection, resulting in the graph not being able to oscillate around the set point.

Figure 3. Set point was set at 400.

When the set point is set within range, the data can then oscillate around a set point.

Figure 4. The sensed light oscillates around the setpoint fixed at 760.

A push button was added to the board along with a second LED. A second LED will turn on when the button is pushed. In the video below, the light intensity of the first LED will adjust in order to oscillate around the set point.

Figure 5. Light intensity adjusts to keep oscillating around a set point with two LED and a push button.

The Arduino serial data was read into python and graphed.

Figure 6. Light intensity adjusts to keep oscillating around a set point with two LED and a push button.


Figure 7. Python graph for Task 2.

In the video below, the setpoint would increment by 10 every time the button was pushed. The light intensity data oscillates the set point path as the set point increases.

Figure 8. The data oscillating around a changing set point.



Figure 9. Code to have the data oscillate around a changing set point.

The Arduino serial data was read into Python and graphed.

Figure 8. Python code for Task 3.


Figure 9. Python graph for Task 3.

4. Discussion
I was able to gain experience by working with the photoresistor and the PID control feedback system. The photocell is very sensitive, and the lighting had to be perfect. The most challenging part was coding in Python and getting the axis to be readable.