On Sun, 2007-04-01 at 20:26 +0000, Peter P. wrote: 
> > I just wouldn't be personally comfortable connecting a relay directly to
> > a PIC (or any other MCU) pin, it's just asking for trouble IMHO (heck, I
> > even go as far as putting the relays on a seperate power supply if
> > possible).
> 
> Try that when running from a single cell supply boosted by a low power booster
> to 3V, or straight off a Lithium cell, or from a 'derived' power supply that can
> take no load and no noise (like USB and so on).

Well obviously you can't always get away with multiple supplies, I never
said you could, I just stated that I would try my best to isolate ANY
inductive load from the digital "stuff", if you only have one supply
then heavy filtering on the power supply to the MCU is required.

I once had a case where I was supplying an ultrasonic range finder and
MCU from one supply. I put the range finder on the raw supply, the PIC
being fed through a linear regulator and some caps. 

Result? Random reboots of the PIC when the range finder was being used.
I tried larger caps, more direct power supply to the PIC, even caps
directly on the PIC pins. The problem improved, but didn't go away. In
the end I needed to put the PIC on an RC filter for it's power supply,
very extreme, but it got rid of the problem.

TTYL

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