Hi, we are trying to use a LED (from a car alarm) to trigger a relay. My guess is that the LED will operate around ~10mA and will be under powered to use as a trigger. I was told that I would need to use a bipolar junction transistor between the LED and the relay. Does this sound feasible? If so, what would be a good transistor (part number) to use, and how would we wire it to both the LED and the relay? Thanks.

 

A relay usually means a bit of power to operate. a led is a a source of light that you must transform into a electron flow. so now you need a photo diode to sense it or other means of detecting photons or light. there is plenty of info on that on the internet.

 

I'm just interested in the coil side of the relay. True, a photo diode would work, but wouldn't be feasible for our application. We are interested in only electrical means of modifying the LED to work with a relay. Thanks.

 

A led can act somehow like a photodiode but it may not have enough sensitivity.

 

Yep, it will require oodles of gain. A LED is reversable as a *very* weak photocell, but there are better ways. Why an LED?