PR Experiment 1: Distance vs Resistance Output - reynold5/ECE387_Midterm GitHub Wiki

Purpose: The purpose of this experiment is to correlate the distance of a light source from the photoresistor in relation to the resistance output of the photoresistor within a simple circuit utilizing the Arduino Uno microprocessor. In this experiment, a 200 lumen flashlight was held as a constant and the only source of light throughout the experiment, from which all measurements were taken.

Materials Used:

  • Arduino Board/Arduino Software
  • Breadboard
  • Photoresistor
  • 10k Ohm Resistor
  • 3 Wires
  • 200 Lumen Flashlight
  • Tape Measure
  • Very Dark Room
  • PR Simple Circuit Source Code

Procedure:

  1. Arrange the photoresistor and the 10k ohm resistor as illustrated in the "PR Simple Circuit Source Code" document located in the "Code" tab above.
  2. Copy the source code provided into the Arduino software, compile the program, and upload it to the microprocessor.
  3. Ensure your Arduino microprocessor and attached circuitry are relocated to a very dark room. Ensure the measurement panel on the Arduino software is displayed.
  4. Shine the flashlight directly onto the photocell of the photoresistor at 2 inch increments from 2-98 inches away, verify your distance by utilizing the tape measure.
  5. At each 2 inch increment, record the resistance value displayed on the measurement panel of the Arduino software.

Results: The following figure plots the distance at which the flashlight was held in relation to the photoresistor versus the corresponding resistance value of the photoresistor at each distance.

Discussion & Limitations: As you can see from Figure 1, there is a direct correlation between the distance that a light source is in relation to a photoresistor, and the output resistance of that photoresistor. As we increase the distance between the photoresistor and the light source, as expected, the resistance increases. As the light source moves away from the photoresistor, the light intensity factor decreases which means less photons hit the photoresistor directly, thus causing less of a reaction in the photoresistors semiconducting material and an increase in resistance.

One limitation of this experiment was the ability to take measurements at a distance greater than 98 inches away due to the size of my dark room. Generally, as you continue to increase in distance exponentially higher resistance values (>1M Ohm) will be generated.