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.

 

much information on the topic here:

http://home.cogeco.ca/~rpaisley4/PhotoDetectors.html

 

do you know anyway to do it without a transistor

 

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.

 

You can get a complete parts list and diagram on ebay: http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=180480025409&ssPageName=STRK:MESELX:IT