Light activated circuit

[Souper man]

As for one of my new robot features (Farfalle, the walking robot), I wanted Farfalle to turn on when it is light out, using a photoresistor. The only problem is that I cant find a schematic that I am looking for. I was going to use a LM339 (quad Comp) or a LM324 (quad OPAMP). The output of the transistor would control the base of a PNP transistor, which would switch on the power supply to the 7805. For more details on Farfalle, go to the Farfalle:coming soon! thread under robotics chat. Also, it must be able to be ajustable using a potientiometer. Thanks!

 

[HarveyH42]

Search for 'dark activated switch', plenty on the web. I built on a while back for a solar garden light, LDR and 2 transistors. No idea where to look for the schematic right now, maybe after work.

 

[Souper man]

Couldnt I just use a Comparator or an OPAMP, with a pot. and a LDR on the positive input side, and a 500k ohm resistor on the negative input side that then goes to ground, and the output controls a transistor that would control the negative bus. I think that would work, wouldnt it?

 

[HarveyH42]

There likely a dozen different ways to do it. Here are a couple I found still on the computer, not the one I was looking for though.

Well, went a little crazy and dug up some more, most untested....
1 transistor
3 transistors
555
741

Quite a variety. I know you are interested in PIC, so didn't include my AVR work (still kind of buggy), but uses a red LED as the detector and the AVR's analog comparator.