My son and I are working on a science fair project. Unfortunately, I'm a mechanical engineer with virtually no electronics savvy. We want to use a solar cell to turn on the power from a 6 volt DC power cell to a motor. Essentially I need a NO switch that closes when someone puts light on the solar cell. Is this something we could bread-board easily with components from Radio Shack?

Many Thanks!
Paul & Jon

 

this is usually done with a cadmium sulfate cell i think, try looking up circuits for that.

 

You can do this with a small relay(to connect your batt to your motor) which is normally off. To turn the relay on, use a small transistor on the coil of the relay with the base tied to a voltage divider running off of your 6V. The voltage divider consists of a resistor and your solar cell. You'll need to calculate and possibly tweak your resistor value to adjust the sensitivity if your design. If you strike out with the web searches, I can post a schematic of what I'm talking about. These parts can all be purchased at Radio shack

 

Thanks for your info. Yes, I guess I need a schematic. I haven't been able to find anything simple enough for my mechanical brain on the web.

Thanks!
Paul

 

We need to know how much current your motor draws. Also, you would be better off using a photoresistor. The cheap ($4.99!) solar cell on Radio Shack's web site puts out plenty of current, but only 0.55v. This is not enough to turn on a transistor. We can give you a schematic if you can provide the motor current specification.

 

I've made some assumptions like your motor is a small DC (< couple 100 mA's) and that the CDS cells you'll get from radio shack have something like Megohm resistance in full darkness and couple of 100 ohms with alot of ambient light shining on them.

You'll likely have to tweak the resistor divider to find just the right amount of light you want to switch your motor on.

I'm also assuming that the 5V relay won't have a problem running with almost 6V across the coil. A darlington switch transistor would have been better here dropping that extra volt for you but I couldnt find radio shack offering a darlington.

If you have trouble actually getting these components, get something as close as you can, there will likely be an easy way to make it work.

Radio shack numbers:

#271-1335 10K 1/4W 5% resistor
#271-1321 1K 1/4W 5% resistor
#276-1657 CDS cells
#276-2058 2N4401 NPN transistor
#276-1102 1N4001 rectifier diode
#275-240 5V, SPDT relay, 1A contacts

 

I don't know if it works but anyway you can try this circuit
http://www.aaroncake.net/circuits/lightdrk.htm

 

Thank you!! We'll give it a try.
Very much appreciate all your work on this.

Paul & Jon

 

This one uses solar cels (it thurns on wean there is light)

whith the potencimeter you select the sensetivety (lover resistance higher senetivety)

If the solar cels are big enugh to power the motor wire it directly


If you want the motor to thurn on in dark conect it on the green dot(on the shematic)

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