> >I tryed  to use  PIC16C621A, RA4 as output, open drain. I put a 10K
resistor
> >to Vcc and the base of a npn transistor in RA4 to drive a relay (relay
> >conected on colector with diode self induction protection, and emitter to
> >zero).
>
> Do you have a resistor between RA4 and the base? If not,
> put one in.

And why should that help?  If it is open drain, then he should be able to
connect the base of the NPN directly to the pin because the current into the
base can only come from the pullup resistor.  Adding an additional series
resistor has no advantage and will slow down the response.


*****************************************************************
Olin Lathrop, embedded systems consultant in Devens Massachusetts
(978) 772-3129, olin@embedinc.com, http://www.embedinc.com

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