Comparator light sensor

Posted on Feb 6, 2014

Sense the amount of ambient light and switch the lights on when it was dark out. I was successful in building one on a bread board that used an lm324 (its the only comparator radioshack had) some resistors a trimmer resistor and a photocell. So I went and designed a board using the same basic circuit but I replaced the lm324 with a lm311 and made a board. However it dose not work smoothly when I have

Comparator light sensor
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light shining on the photocell I hear a high pitched hum and i`m getting around 5. 6volts on the output when I block the light the humming goes away and the output goes up to 12v like it should. Ii am not sure how to fix it. i do not own an oscilloscope so i cant check but i`m guessing its oscillating when there is light and that`s why i hear the humming Any input on how I could fix this would be appreciated. Thank you. use multiple photocell that sense every different direction and use logic AND to turn the light ON, the probability of hum and false OFF will be lower. the only condition thats surefire to trigger all condition TRUE is during the daylight. 2) put the 2N222 NPN on high 12V side, or change to PNP if you want to stick to that low side config (but you`ll also need to switch comparator +ve and -ve input), NPN works better on high side and PNP on low side (you got them backward in your schematics). thats what my experience tells from my unproven experimenting.

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