microcontroller driving relay

Posted on Feb 6, 2014

I usually use an NPN Bipolar transistor to do the relay switching, mainly because my relays are 12v coil rated, but it also keeps everything nice and seperated. and yes i add a diode. with no problem. ( do I or did I need to drive it with a transistor ) but it seam like radio shack is getting out of the parts business. I`ve got to place a order wit

microcontroller driving relay
Click here to download the full size of the above Circuit.

h digikey and though I mite find something better and cheaper. If you know the coil resistance it`s easy to calculate if you need a transistor. If it`s too low (say 125 ©) then you can use two pins to provide 40mA. Make sure you connect between the pins and 5V as the pins can sink more than source. The 100R series resistor is only required if the supply voltage is too high for the coil. The schematic also lacks the all-important back EMF protection diode.

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