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switching 12Vdc with 3Vdc


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Most general purpose relays will handle 12Vdc 1amp, just check the relays spec sheet, dont forget
to 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!

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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) relayoz7.jpg

This is what I'm guessing:
2 attaches to the +12Vdc
5 attaches to the -12Vdc
1 COM attaches to +3Vdc
4 NC, 3 NO attaches to -3Vdc

Please correct me if I'm wrong

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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:

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