At 11:59 AM 12/18/2006, you wrote:
> > But if you're powering the PIC from the handshake lines, anyway, how does
> > connecting the transistor buffer to them versus the PIC VCC any different?
> > There's no quiescent drain when you use a PNP transistor.
> >
> > Personally I've never been much of a fan of scavenged power, since I have
> > owned several laptops each with at least quirk per port.
>
>
>I am powering the RS232 circuit from a serial line from the other device,
>not the MPU. So the other device is getting it's own signal back, the MPU is
>just switching it, not being powered from it.

You have the gate going to the outside world? Bad news. Very bad news.

If you use a BJT, you should (must!) also add a diode to ground to prevent
reverse breakdown of the B-E junction, even though the current is 
limited it can
cause problems long-term. RS-232 receivers are normally loaded with
5K or so. A 10K to ground and a 10K to the base (any decent transistor
like an MMBT4401 will do).

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




-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist