Activate a Photocell

Thread Starter


Joined Feb 10, 2010
I am a student working on a Science Olympiad project. I am to use a photocell that will provide the power to operate a motor. I am currently using a 3volt dc motor and two C batterries. I have done research and found the use of a relay in conjunction with the photocell may be the way to accomplish the task. Is this correct and if so I could use some help constructing the components.


Joined Dec 5, 2009
With out a transistor, you put the LDR in line with the motor. That will cause the motor to slow down as the light gets dimmer. You may want to add a POT or another resistor to make sure all current is limited.

You could also put the LDR in line with a relays coil. Not a good idea, but it would work. At dim levels, the relay could chatter. but at full bringht should be fine.