Jinx wrote...

>> First, from the variable voltage output you cited above; what's
>> the required output current?
>
>2 or 3 mA is enough

OK...

>> And second, how much current is required by the solenoid
>> when it is on, how long is it on when it is on, and how often
>> do you intend to fire it?
>
>An instantaneous pulse from the cap will do. It's part of a clock
>mechanism that uses a pair of ratchet drivers. They operate
>on alternate minutes, so there are 2 minutes to charge the
>1000uF cap for each solenoid. The PIC presently does back-
>up timing, power management, push buttons, LEDs etc. If I
>could use it to generate the voltage for the solenoids then
>the 12V gel cell can be replaced by a 6V. Although nominally
>12V coils, the solenoids will operate from 8V (albeit weakly)
>to 25V (pulses only, not constant DC). I know from other
>clocks I've made that connecting the cap to the solenoid for
>1/4 second is enough to drive it reliably.

Hmmm.  I think you might be in luck.  I'd use the diagram Russell
posted, though perhaps with one less cap/diode stage.  And I wouldn't
drive it directly from a PIC pin, rather from a high-current buffer of
some kind, as in my first reply.

This can work.  It's worth a try.

Dave

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