On Sun, 2007-04-01 at 17:06 +0000, Peter P. wrote:
> Dario Greggio <adpm.to <at> inwind.it> writes:
> 
> > wouter van ooijen wrote:
> > 
> > > relays driven directly by a PIC????
> > 
> > In theory, 5V (or 6v) low-current relays like those used in series with 
> > telephone lines could work. Diode in antiparallel needed anyway!
> 
> Not just in theory. 10-15 mA relays (even bistable ones, even single coil ones
> using capacitor coupling) can be driven ok by a PIC IO pin (or two in parallel
> if need be). However, now the parallel suppressor diode must be Schottky and
> that makes it more expensive.

And still you've violate specs. Diodes don't turn on in zero time, they
need time to switch from forward conduction to reverse conduction.
During that time the voltage on your PIC pin will be out of spec, by
quite a bit depending on the turnaround time of the diode.

Shottky's are MUCH faster then PN junction diodes, but they still have a
finite time to switch.

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).

TTYL

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