> I understood that to be true (to make
> matters worse, I'm driving two giant
> 1/4 scale servos (343 oz/in of torque)
> which draw 800ma each, so I'm sure that
> probably has something to do with it..

Yeah, I'd say that would be a safe bet.  My problems *mostly* went away when
using a 2.5A linear power supply, but the PIC would still have problems
occasionally until I just fed the servos separately.

> However, when I drive the servos seperate
> from the circuit is when I am seeing the
> problem of them rotating on their own.
>
> I have noticed if I use two seperate power
> supplies, and tie the grounds together
> everything does appear to work fine.

Yes, you've got to have a common ground.  Since the servo references the
incoming pulse signal to ground, if the servo ground is not the same as the
PIC ground you're bound to have trouble.

> Also, how & what do I couple anything anywhere?
> I'm only using a single 30k cap between GND
> and +5V on the power regulator.  I've also heard
> of people doing wierd things with their clocks
> as well, I'm running a 20 Mhz XTAL with 2 33k
> caps (1 on each lead) to GND.
>
> Any suggestions for making this circuit more
> well rounded?

I'd suggest a decoupling cap on the order of .1uF to 1uF located close to
the PIC (like connected directly to the PIC power and ground pins), and a
larger one (maybe 10uF or larger) across the servo ground and +V.  I don't
think you could get too large a cap across the servo.  The idea is for the
cap to smooth out spikes in the power supply caused by the servo's current
spikes.

As for the xtal, a couple of smallish caps between the xtal pins and ground
are recommended for reliable starting of the oscillator; check the PIC
datasheet for all the gory details.  I seldom use them and have never had a
problem with an oscillator starting, but I may just lead a charmed life.
The only weird thing I've heard of people doing is using faster xtals than
the PIC is rated for.  I've tried it just for the heck of it, my -04 part
ran fine at 10MHz, but I figure why bother then the -10 part is so cheap.

Dale

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