On Monday 01 September 2003 10:50, Olin Lathrop scribbled:
> > Nope.  I can't.  The RB outputs here control the columns of 7-seg LED
> > displays, which is why they go to the MOSFET gates.  If I just shorte=
d a
> > switch between an RB output and ground, then the output will be force=
d
> > low all the time when the switch is pressed.
>
> I didn't realize the B ports were the outputs and the A port the input.
> In that case the mechanical switch is fine.
>
> However, the NPN should be a PNP with emitter to the RB line, collector=
 to
> the RA line, and base to the level being sensed via a 10Kohm or so
> resistor.  The transistor can pull the RA line high only when its RB li=
ne
> is high.  This does invert the logic for sensing the line from the way =
you
> had it, but that's a minor software change.

Correct.  I've got it to work now with the NPN, but intend to change it t=
o=20
PNP, now that I know why it should be so.  The software change is indeed=20
minimal.

Cheers,
-Neil.


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