At 10:07 AM 5/10/00 +1000, you wrote:
>Hi All,
>I have a little problem that my Pic that is switching on a motor
>via a relay is locking up :(
>The relay has a diode across it, and if I run it with no motor
>there is no problem. Only when the motor runs (12v windscreen
>washer motor) for over 2 - 3 seconds things lock up.
>
>Putting a diode across the motor seems to solve it,

It's a DC motor with a commutator, so it produces a lot of
electrical noise that gets coupled back through the relay.
The diode will kill some of the noise, especially if you
put it right at the motor.

> but have I only just solved the problem?

Determining the margin you have is not easy. It's possible
it could act up with slightly higher voltage or with a worn
commutator.

Maybe you could improve the grounding and relay circuit so
it works *without* the diode, then add the diode.

Operating the relay with an optoisolator is one way to
(potentially) improve things.

Best regards,
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Spehro Pefhany --"it's the network..."            "The Journey is the reward"
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