Hi everyone!!

>It is better to drop the voltage down to about 3V, the PIC will use less
>current and battery life will be extended.  A battery consisting of 3 or
>4 AA or AAA cells in series could be connected to the PIC directly and
>run it for much longer than a 9V would.
>
>>>I am not bothered if the odd one gets fried in this application
>>also as current drain will be very low I can use a large current
>>limiting resistor of 330 Ohms or so in the supply line
>
>A simple regulator of a voltage divider with fairly large resistors
>setting the voltage to the base of an NPN transistor voltage follower
>could work.  Of course there are reasonably-priced micropower 3-terminal
>linear regulators which would be ideal for longest battery life if that
>is important.

    Anyway a 9V battery has a charge of about 100mAh. Any regulator you
intend to use must have a very tiny bias current (78L05/LM317) so it would
not "suck" the battery... I'd rather better use an IC or two NPN
(2N3904/BC549C) with high hFE in Darlington configuration with resistors
around 100k. That should do it.

>
>>As a last resort suppose I could put a led in the supply line
>
>Yes, this is practical.  Depending on the color of the LED about 1.5 to
>3V will be dropped.  And the power lost by the LED isn't completely
>wasted (as it would be with a linear regulator) since it could act as a
>pilot light.
>

    Other good idea is to use two CR2032 (3V-coin type) batteries! They have
about 180mAh, are much smaller and much lighter then 9V batts and it's not
too dificult to find holders for them! Check RS Components!

http://rs-components.com



    Rafael Pinto