so im attempting to hook my train horn up to a cheap alarm, so that i can hit the panic button and my train horn goes off. the problem is that it takes 12v to turn the relay for the horn on...and the alarm only puts out 2v....i have read that transistor switch could be used but don't understand it, and cant find a relay that will take a 12v draw and trip with only 2v. any help is greatly appreciated.

 

Ohhh!

Transistors are my friends - I used them to turn on my LEDs under my doors!



I have to think about it more, but I think you can use a PNP transistor from radioshack to do this. You will need to hook one end to ground, one to the source that gets the 2 volt turn on signal, and one end to your horn which will be powered. I'm not totally positive on this, but you can test it they only cost a few dollars at radioshack.

I am NOT an electrical engineer. I figured this out with help from a member on here and trial and error. I spent probably 100 hours or so doing lights on my evo and 04 edge.

 

you could use a mosfet, if i remember from class correctly, most of them had a turn on of 1 volt, so if you have 2 volts you would be in the clear. like he said an n-channel one would work heres the wiki to let you understand them better...

MOSFET - Wikipedia, the free encyclopedia

 

or, you use a relay to supply the 12v to the horn. the 2v from the alarm activates the relay, which then sends 12vs to the horn.

 

Will only 2v jump the relay though?

2v might not jump the relay... or he needs a transistor that can handle the power the horn wants.