Yes, the concept is good -- however there is at least one basic
problem with your circuit.

You'll never get more than about 4.4V at the emitter of the transistor,
since the PIC can only supply ~5V of base drive to the transistor. Use
a PNP transistor (or P channel FET) with NPN driver stage (or N channel
FET) to supply the regulator circuit.

Matt Pobursky
Maximum Performance Systems

On Sat, 10 Aug 2002 13:04:31 +0100, Les Otter wrote:
>Hello I am trying to move from a toggle power switch to a NO momentary
>membrane switch.
>
>My circuit thoughts are :-
>http://www.saurel.demon.co.uk/files/Membrane.bmp
>
>(Caps not shown)
>where the membrane switch S1 supplies power to the circuit at startup,
>which boots the pic.
>The first thing the PIC does is sets Pin B0 high, so S1 can be
>released.
>When the PIC detects button press of another membrane switch ("OFF"
>- not shown) pin B0 can be set low, thus powering off the circuit.
>
>Is this a sound design concept, and anyone suggest how to do it
>better?

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