At 08:00 AM 06/01/2012, you wrote:

>When using an NPN transistor I use a small signal diode from ground to
>base to protect the base-emitter junction from reverse biasing. The PIC
>will never see the -0.7V because the base-collector junction will be
>reverse biased, but the transistor's base-emitter junction may be
>damaged as they are usually rated for -5V.

I guess if you like to live dangerously you could do this and
save a part:


                           Vdd o
                               |
                              .-.
                              | |
                          30K | |
                              '-'
                               |          Out
                               +-----------o
                               |
                      ___    |>
               In  o-|___|- -|
                             |\  NPN
                    4.7K       |
                               |
                              =3D=3D=3D
                              GND


Best regards,

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



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