I'm designing a handheld PIC-based device (a handheld GPS / nav.
unit). It'll be using a PIC18LF2620 and will be battery powered. I'd
like to give it a software power-on/off feature so I can use one of
the control buttons for power on/off rather than having a big ugly
power switch. I was wondering what kind of circuit people would
suggest for the power on/off feature?

Just to complicate the issue some parts of the circuit operate at 5V
and others need 3.3V. The 18LF2620 can operate at down to 2.0V but
when the circuit's in full-power mode it needs to be running at 5V to
talk to some of its peripherals. My plan was to use a 6V Ni-MH battery
pack with MAX883 and MAX884 regulators. These have a low dropout
voltage and provide a shutdown mode. I was thinking I could power the
PIC through a schottky diode off the 5V normally and then have an
"off" mode where it's powered on ~3.6V (three Ni-MH cells) through a
different schottky diode. The "off" mode would power only the PIC
rather than the whole circuit. The PIC would be in sleep mode while
the device is "off". A button press on one of the interrupt-on-change
lines would wake the CPU and it would raise an output line to tell the
regulators to power up again.

Does this sound line a feasible plan? Is there an easier way of doing this?

Thanks,
Zik
(Apologies if this appears multiple times - I've been having some
problems with the mailing list)

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