jeeep Posted May 5, 2007 Report Share Posted May 5, 2007 I have an AVR who's pin outputs 3Vdc. I would like to be able to turn on, or allow to connect, 12Vdc with this 3Vdc output. There will be two power supplies. What sort of electronic part am I looking for? Thank you Quote Link to comment Share on other sites More sharing options...
esp1 Posted May 5, 2007 Report Share Posted May 5, 2007 hi,The simple solution would be a transistor controlled by the 3Vout, switching a 12Vdc relay, the relay contacts would then be used to connect the +12v elsewhere as required.Is this clear enough? Quote Link to comment Share on other sites More sharing options...
jeeep Posted May 5, 2007 Author Report Share Posted May 5, 2007 Thank you esp1, that makes perfect sense. Is there a particular relay you can recommend that will handle 12Vdc @ 1amp? Quote Link to comment Share on other sites More sharing options...
esp1 Posted May 5, 2007 Report Share Posted May 5, 2007 hi,Most general purpose relays will handle 12Vdc 1amp, just check the relays spec sheet, dont forgetto specific the relay coil operating voltage to suit 12Vdc.What components do you have on the shelf?Dont know where you are posting from, so cant suggest a local source! Quote Link to comment Share on other sites More sharing options...
jeeep Posted May 6, 2007 Author Report Share Posted May 6, 2007 Found a relay in my junk pile that should work, only thing is I cant figure out how to hook it up! I've tried searching google but no luck. Here is a diagram of the relay (from the bottom) This is what I'm guessing:2 attaches to the +12Vdc5 attaches to the -12Vdc1 COM attaches to +3Vdc4 NC, 3 NO attaches to -3VdcPlease correct me if I'm wrong Quote Link to comment Share on other sites More sharing options...
audioguru Posted May 6, 2007 Report Share Posted May 6, 2007 A relay has a coil with a low resistance that needs a fairly high current at a certain voltage. Your AVR can't drive a relay coil directly, but the AVR can drive a transistor that can drive the relay's coil.The relay's coil is an inductor that makes a high voltage spike when its current is turned off. The high voltage will destroy anything that drives it so a reversed diode should be connected across the coil to arrest the high voltage spike.You don't know the voltage rating of your relay's coil. It is probably more than only 3V. It won't operate if the voltage is too low and it will get hot and maybe burn out if the voltage is too high. Maybe you should buy a relay that has a 12V coil and drive it with a transistor.1A is a little high for a single transistor to drive with the small input from the AVR. Two transistors or a darlington transistor could drive your 12v/1A load without a relay.You got most of the relay's pins wrong. Here is a picture of it: Quote Link to comment Share on other sites More sharing options...
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