Re: gEDA-user: buzzing board

[DJ Delorie <dj@xxxxxxxxxxx>]

> Get an electret mic running off a battery on one scope lead

Circuit?  I tried the mic+scope trick, but nothing came out of it, so
I figured it needed some biasing.

> Probe around with other scope lead to see what is in sync with it
> just to make sure you are looking at the right part of the circuit.

I can "see" the oled's image in the +12v noise, kinda like looking at
a video signal through a low-pass filter, but you're right - I might
not be hearing *that* signal.

> You could spend ages looking at that switcher for the OLED and find
> out that the buzz was a slightly different frequency coming from
> somewehere else.

The OLED uses an LDO linear regulator.  The switcher is for the +3.3v
rail.  If I pull the jumper off for the +12v to the OLED (independent
circuit), or just cover the photocell so it goes to "dark mode"
(almost no pixels on), the buzzing stops.


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