photoresistors

[completeandutterNEWB]

i want to add a photoresistor to my 4 12" cc's so it'll turn on in the dark and turn off when theres light

so i took a photoresistor from on of those nightlights that do that

i wanted to kno if i could use the same photoresistor from the AC nightlight and if it would be able to supply enough power for all the cc's
and can i use this with the voice activation feature

[mattg2k4]

That will work, but I'm not familiar with how nightlights work, and doubtless some of them work differently. I don't think you would power the cc's straight from the photoresistor, you set up a circuit to turn on a relay, a mosfet, or something based on the phototransistor's resistance. If you know what you're doing I bet you could use it and save yourself the trouble of what I'm describing the next paragraph.

The easiest way in my mind to make your own circuit would be to set the photoresistor in series with a regular resistor to make a voltage divider, use that on an input to a comparator, and put a potentiometer across the supply with the wiper pin going to the other input, to calibrate it. Then connect the output of the comparator to a mosfet or relay.

To give you specifics I'd need to know what resistance you want it to turn on at and whether resistance is directly or inversely related to light level.

[completeandutterNEWB]

um i have no experience with electric stuff so i didnt understand a thing you said
maybe a picture would help lol

inside the nightlight i found a small circuit board
it had a resistor, a black thing with 3 pin things which i assume is the comparator(i dunno wut that is), and the photoresistor

i dont really need to calibrate it i'll use the same settings as the night light

i was just wondering if the photoresistor would blow up or something if the wrong amount of electricty went through it or something

P.S. i cant just use the circuit board to wire it up cus i kinda cracked while taking it out lol

[enhanced08]

Originally posted by completeandutterNEWB inside the nightlight i found a small circuit board it had a resistor, a black thing with 3 pin things which i assume is the comparator(i dunno wut that is), and the photoresistor

that small black thing is a transister. the same thing thast in a CPU only bigger.
i think the best way to get that to work would be to use the circuit board from the light and just hook it into the computer.
since you said its broke, just make a new one. make sure you get the same components as what is in the light, or just take them from the light. i don't know what all is there but make sure you heatsink the transisters (black thing) or you can fry it.

good luck!

[mattg2k4]

You might want to check what wattage bulb the nightlight is rated for, and see if your 4 cc's exceed that rating.

And as for calibrating it, its a heck of a lot easier to stick a pot on, calibrate it, and leave it set that way than to find out what the precise resistance the photoresistor is at when you want it to turn on, and then calculate the proper resistor divider. Or you could build a prototype with a pot, measure the resistance its at when calibrated, then switch it out for some regular resistors.

And yes the photo resistor would be destroyed if you ran too much current through it. However, most photoresistors have fairly high resistances IIRC, so it would not allow a destructive amount of current at 12v, but it also would not be sufficient to turn on the cc's.

Do you want to make the circuit I described? If so, I could draw up a diagram.

[completeandutterNEWB]

ok forget about the cc's
can i wire it up to a colorchanging LED in front of my computer which gets quite annoyiing?

p.s. on the bulb it said 120V/17W
and a diagram would be great thanks

[mattg2k4]

Yes, you could easily wire it up to a LED. After I get back from lunch I'll draw you up a diagram.

Do you happen to have a multimeter that can measure the resistance of the photoresistor in light, and darkness?

edit:

Okay, here is the schematic. I'm not positive the photoresistor goes precisely there. If resistance on it decrease when light decreases, then its correct. If resistance increases as light decreases then you need to switch R2 and R3.

http://coppercavern.com/images/photo...or%20schem.JPG

The lm339 is a quad comparator, you only need to use one of the comparators. You can buy it at radioshack. All you need to do is connect power, IN1+, IN1-, and Out1, you should tie all other inputs to ground. You can use a 2n3906 PNP transistor, or any similar general purpose PNP transistor. Resistor values are only general guides, you don't need to follow precisely.