Light Sensing Problem

[mcclurm]

I know this is probably simple and stupid for most of you, but I can't find what I'm really looking for. I need as simple a circuit as possible to come on at dark and off at daylight. I've found a lot of circuits I can build, but I think there has to be a simpler solution for what I'm doing.

All I need is something that will run at 6V or 12v. It needs to stop the current flow in the daytime and start it at dark. If 6V goes in then 6V needs to come out. The same with the 12V. I can handle the rest of the circuit from there out, but I've never done anything with light sensing. Please help.

 

[ericgibbs]

hi,

A circuit like this would do the job, it uses a LDR [light dependant resistor]

 

[mcclurm]

Thanks for the response. That would work, but we're actually looking for something significantly simpler than even that. We're going for build speed at this point, so the fewer parts the better. We don't even need the same circuit for the 6V and 12V version, but we need extremely simple. 6V to 6V and 12V to 12V dark sensors.

Thanks again for the quick response.

 

[Andy1845c]

I posted this one here yesterday.

Evil Mad Scientist Laboratories - A dark detecting circuit for your jack-o'-lantern

Its about as simple as its going to get.

 

[mcclurm]

That is definitely more like what I'm looking for. After reading it the only catch would be that its really only meant to handle up to 5V. I would have to see how it could be modified to run at higher voltages. Any suggestions before I blow something up playing with it?

 

[Andy1845c]

Its a pretty dirt simple circuit. They even have a detailed explanation of how it works on the site. You should be able to just sub parts to make it work at whatever voltage you need. You will at very least have to change the value of the resistors. I think the 2N3904's will be okay. I can't find a datasheet for the photo transistor.

What is this for? What will it be switching?

 

[mcclurm]

You're right, its as simple as it gets. I just thought you might have taken this one further before. The 50Ω resistors are just the drop for the LEDs, so those are irrelevant for me at this point. I would just have to swap out the 5K resistor with something like a 10K pot to adjust sensitivity. The 2N3904's were my concern. I just wasn't sure what I would swap those out with. I can play with it though. That is why they make breadboards.

This will be running a small motor, a few high intensity LEDs, and a couple of other small parts. I've got that piece running fine already. I just needed something to help out with switching.

Thank you very much for helping me out with this. Its really appreciated.