jim wrote:
>
> Well then, physics must work differently in my part of  Texas than
> anywhere else, because this very circuit works well.  I can't explain it
> beyond what I've already stated.
>
>  And I agree about the PNP transistor.   I also stated this a few emails
> back.


Sorry Jim, I can't see how your circuit works
either. :o) You say it turns on whenever the
base voltage is 0.7v greater than the emitter,
but the emitter is supplying the PIC power! How
can the PIC drive the base at Vcc+0.7v???

Using the PNP is viable on the ON state as the
PIC can sink to the base and turn it on. However
it will be OUT OF SPEC in the OFF state as the
base is at high potential of input voltage-0.7v.

As far as I know the only single device way to
do it (without 2 transistors, or a high voltage
PIC pin) is with an SCR. I put up a circuit and
description here:
http://centauri.ezy.net.au/~fastvid/self_swi.htm

Just one note, some PICs do indeed have a high
voltage output pin (open drain). The 16F628
RA4 output is 8.5v I think.
But the SCR solution is the best. ;o)
-Roman

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