How to wire a photocell circuit

Updated July 19, 2017

A photocell is a device that changes its resistance based on the amount of light that illuminates it. This property is useful for circuits dealing with light detection and alarms. There are many types, but the most popular ones are CDs cells, which are made from cadmium sulphide.

Create a photocell circuit by wiring one in series with a voltage source and another electronic component. The component can be a motor, mini-fan, mini-lamp, milliammeter, piezo buzzer or light-emitting diode (LED). If the component is an LED, a current limiting resistor or potentiometer must be used.

Place the battery inside the battery holder. Attach the positive side, which is the red lead, to the breadboard.

Connect the photocell to the breadboard, with one side connected to the positive side of the battery. Attach the photocell’s free end to the left side of the potentiometer.

Wire the middle part of the potentiometer, which is the wiper, in series with the LED. Do this by connecting the wiper to the positive lead of the LED. Place the LED's remaining terminal to ground.

Complete the circuit by placing the black lead, which is the negative side of the battery, to ground. Make sure all connections are secure.

Test the circuit by shining a light source on the photocell, such as a flashlight. Adjust the potentiometer by turning the knob. The LED will change its brightness based on the amount of light on the photocell, and the value of the pot.

Experiment by varying the illumination on the photocell. Shield it entirely or partially, or place it in shaded areas, for example.


Be sure the threads on the chuck match the spindle threads. Typically spindle threads are 3/4 inch x 16 threads per inch or 1 inch x 8 threads per inch. If you are unsure of the spindle thread on the lathe or chuck, check the documentation that came with the chuck and the lathe. Do not force the chuck onto the spindle. The chuck should go on with little effort. If it is difficult to thread onto the spindle, remove it and inspect the threads for damage and refer to documentation to be sure the threads on both parts are the same. Do not over-tighten the chuck onto the spindle. See the documentation that comes with the chuck for specific information on tightening the chuck on the spindle.


The potentiometer must be placed high enough in value to limit the amount current in the LED, in order to prevent its destruction.

Things You'll Need

  • 9-Volt Battery
  • Battery Holder
  • Photocell
  • Potentiometer
  • LED
  • Breadboard
  • Jumper Wires
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About the Author

Kim Lewis is a professional programmer and web developer. She has been a technical writer for more than 10 years and has written articles for businesses and the federal government. Lewis holds a Bachelor of Science, and occasionally teaches classes on how to program for the Internet.