piclist 2005\08\24\072842a >
Thread: Excessive 12F629 current usage
www.piclist.com/techref/power.htm?key=current
face picon face BY : email (remove spam text)(Olin Lathrop)



Matthew Miller wrote:
> My measurement
> for the current consumption was a surprise. The different values I got
> all were around 280uA.

Are you really sure it's running from the external RC oscillator, not the
internal one?  Also show the whole schematic, don't just wave your hands
around describing it.  Think about every possible current path.  Remember
that all I/O pins are potential current paths, both for source and sink.
Are the internal pullups enabled?  Are any digital inputs being held at a
mid range voltage?

How fast does the LED need to blink or the circuit respond to an external
event?  My knee jerk reaction is that an external RC oscillator to run the
instruction clock is not the best answer.  I would try to keep the PIC in
sleep for as much of the time as possible.  One way is to use the watchdog
to wake up the PIC periodically.  On older PICs, the watchdog was a bit of a
pig itself.  This has gotten better on some newer PICs but I don't remember
if the 12F629 is one of them.  I had a problem like this on a 16F630 which
has the old watchdog timer, and ended up using an external micropower wakeup
timer but running the PIC off its own internal oscillator when woken up.
The external wakeup timer draws something like 300nA average worst case.
Some new PICs have a similar circuit built in, but I know the 12F629 is not
one of them.


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