well I want to switch a relay on wit my stereo remote control acros the room(5m) but i cant think of a way to do it. i have tried to use different ways to amplify the current from the diode but still nothing. I have one LM324N amplifier also but i dot know how to use this ops:

 

It sounds like you just wanna switch on the relay w/ your remote, r u planning on having a series of flashes that will be recognized by the sensor or do you just want the sensor to pick up light? Cuz ur gonna have trouble doing the latter because the sensor is going to be picking up ambient light and therefore be always on. As for amplifying the signal, I'd just make a real simple emitter follower light sensor circuit. If you dont know what that is, just give the word n i or someone else wil tel u bout it.

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I'm no electronics god, i just talk too much.

 

You can buy modulated IR xmit & recieve modules. You can get a single channel version and the receivers usually come with some kind of digital output. use that to switch your relay (via many methods). Unless you want the learning experience, just buy the modules.