[sdiy] Mysterious ground noise

[Antti Huovilainen]

On Sun, 25 Nov 2001, Ingo Debus wrote:

> Perhaps this isn't noise at all. Try a very short sweep time on your
> scope and play a little with trigger level or trigger mode settings.
> Perhaps you'll find the frequency of the quartz of your microprocessor,
> or of a RF station. 4mV is quite low and can easily be picked up with a
> shorted scope probe. With low sweep time settings it looks like noise.

It's not totally random, but digital interference seldom is. It doesn't
have any clear frequency, but it clearly is from PIC/UART. However, the
weird thing is that it appears the moment I touch the circuit gnd. The
frequency is low enough (4MHz xtal) that transmission-line effects
shouldn't apply here.

Antti

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 How can you have any pudding if you don't eat yer meat!?"
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