Drew Vassallo wrote...

>...I have had applications where noise from servos or motors caused
>very bad reset conditions when the battery supply dropped to ~5.1 VDC.
>Worked fine with the source at >5.1 VDC, but once the battery dropped, I=
 had
>major problems.  To make matters worse, different PICs would behave
>differently, even among those from the same series (i.e. 16C71 worked =
100%
>better in the same application than the 16C711 did).  I never did get =
that
>problem figured out, though I haven't done much testing on cleaning up =
the
>noise on the servo lines.  If you find a good solution, please post it; =
I'd
>be interested.

One entire area of design that's often overlooked, especially when
breadboarding, is grounding topology.  I've run into trouble in the past
when, despite what I thought was careful Vcc/Gnd bypassing of every
chip, I didn't pay enough attention to where currents--especially large,
switched currents--were flowing.  The large dI/dT caused by a
sharp-edged signal returning through the ground system to its source can
generate transient voltages that cause major problems if the ground
system isn't planned carefully.

I absolutely HATE grounding-related problems; they're by far the most
difficult to debug of all the kinds of problems I've seen, and I've
found that it's well worth the trouble of being absolutely anal about
ground system design, just to be rid of these problems entirely.

Dave

--
http://www.piclist.com hint: To leave the PICList
mailto:piclist-unsubscribe-request@mitvma.mit.edu