William Chops Westfield wrote:
> So I have an actual project that actually got built; a battery powered
> 12f675.  But it's flakey; sometimes it has to be power cycled several
> times before it seems to enter the correct operating state :-(
> It's a simple circuit with some LEDs (current limited by resistors),
> and a couple bypass caps.  (It implements a "Sims" cursor as a costume,
> fading back and forth between red (sad Sim) and green (happy Sim))
> It's powered from 3x alkaline or 4xNiMH cells (4.5 to 5V nominal; both
> version have been flakey.)  The MCLR pin is configured as an input and
> tied high with a 33k resistor (possible future remote control.)
> 
> I'm assuming that most of my problems are due to the bouncy nature
> of power-on in this circuit (cheap switch or cheaper battery clip.)
> The 12f675 has several robustness features (brown out detect, power
> on timer, watchdog), all of which I have turned off at the moment,
> under the assumption that the basic internal reset would be sufficient.
> Apparently not.  What sort of configuration settings and/or external
> circuitry do people find useful or necessary to ensure clean startup
> in battery-powered circuits subject to messy poweron?
> 
> Thanks
> Bill W

Is there a power switch? Or does it power up wrong as you insert the 
battery?  If there is no switch, you could try adding one.  This will be 
aided by some capacitance on the Vcc line, in case you don't have enough 
already.

One thing to try is to get it in the non-working mode and then using a 
clip lead, apply a reset pulse.  If that gets it running, then you could 
try a cap to ground from the reset pin.

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