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Dark / Light sensor

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conntaxman

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I have tried about all of the cir. on the net/ lol. and I cant get one to work with the "Cadmium sulfide Photocells from Radio shack. I just tested one and the readings were 80.00 and down to 7.5 ohms. I used the cir with the 547 tran and the one with the 555 timer. What could be going wrong?i mean their is only about 6 parts. H E L P.
John.
 
Hi John

show us one of the circuits that you have tried. its a bit difficult for anyone to make any specific reccomendations without seeing at least one of the circuits you have tried
It can then be commented on as to if it will work or not. If the circuit will work, then we need to look at your construction methods and see if you are making an error there :)

Dave
 
I just tested one and the readings were 80.00 and down to 7.5 ohms.
Presumably those are the 'totally dark' and 'as light as possible' readings? If so, they are much lower than many CdS cells give. It's possible that the circuits you tried were intended for higher-resistance cells. As Dave says, show us the circuits. I'm sure we can come up with a solution.
 
As I suspected, that circuit is intended for a higher resistance cell than the one you have. Try replacing the 100k resistor with, say, a 330 Ohm resistor. The downside is that by reducing the resistor value the current drawn from the battery will be higher.
 
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