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Help with Dark activated relay circuit please

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Hi everyone

I want to build this circuit:
Dark/Light Activated Relay

My question is will it work on 12V? Or must I put in a resistor to limit the current to the transistor? I did print documents on how transistors work but didn't get time to read throught it. Transistors still make's me confused. If there is a great tutorial on transistors that I can understand, something like "Transistors for dummies" LOL. can you please post a link.
I would appreciate any help please. I want to build this circuit this weekend to see if it works on the light a want to use it on. During the week it's work work work and no time to play.
 

ericgibbs

Well-Known Member
Most Helpful Member
Hi everyone

I want to build this circuit:
Dark/Light Activated Relay

My question is will it work on 12V? Or must I put in a resistor to limit the current to the transistor? I did print documents on how transistors work but didn't get time to read throught it. Transistors still make's me confused. If there is a great tutorial on transistors that I can understand, something like "Transistors for dummies" LOL. can you please post a link.
I would appreciate any help please. I want to build this circuit this weekend to see if it works on the light a want to use it on. During the week it's work work work and no time to play.
hi,
You would need a 12V relay and would increase R3 to 2.2K.

Bob Bowman's Free Educational Technologies: Votech Links
 

ericgibbs

Well-Known Member
Most Helpful Member
Thanks for the reply.
hi,
If you are stuck with a 6V relay, if you know the relay coil resistance you could connect a fixed resistor of equal value in series and use it on 12V.:)
 
Did thought of that but luckilly I have a 12v relay. But to think of it I do have 6v relay's and they are a bit smaller. What is the formula to work out the resistor value when I have the coil's resistance? The 6v relays might work better because they are smaller in size.
 
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