PIC relays control

[bill12780]

Ok here is the deal,


You MUST use a diode across the coil of ANY relay (unless its got one built in) Its for the back EMF (colapsing magnetic field) of the coil when you un-energize it.

If your looking for a latching type of switch depending on what your doing you have lots of options. relays with NO and NC contacts (probly your best bet), scr's, Triacs etc..

If your worried about not being able to drive the coil from the PIC. You can just use a FET. The input impedence of the gate of a FET is really high and takes almost no current to turn on. Just make sure to use a series resistor in the gate circuit in case the FET ever fails (If the fet ever shorted gate to whatever it could hurt the PIC)

Oh, one other thing to consider is what your switching. If your switching AC with lots of current you will need a snubber circuit to reduce the arching on the relay contacts. I just went through this on my predesesor's motor control circuit at my work. His "new" design would fuse the contacts together about the thrid or forth time the motor started.

Well that is my two cents (probly all its worth) hope it helped. If you want to post a schematic of what your doing I would be more then happy to look it over.

Best!
Bill12780