At 05:37 PM 6/11/2008, you wrote:
>Bob Blick wrote:
> > On old 16C parts you do it with RA4 because the old process could
> > tolerate the voltage. But you'll need to use an extra transistor to
> > level shift. Attached is an example.
>
>You can simplify this by moving R1 to the emitter of Q1 and losing R3
>altogether.

Sure, at the expense of greatly increasing the Pd of Q1 and exposing the
PIC to damage from transients on the +12V power rail.

Also, although I wouldn't too much worry about it for a hobby design, and
probably Rds(on) of the p-channel in the PIC will suffice, but this seminar
explains how a simple emitter-follower can turn into a Colpitts oscillator
if the gods of poles and zeros don't smile upon you (and, as they point out,
there's never a guaranteed *maximum* ft)

http://ee.eng.usf.edu/gradcourses/wireless-seminar/sp05/abrahams-1-26-05-pres.pdf


>Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com



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