Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!uflorida!ukma!tindle
From: tindle@ms.uky.edu (Ken Tindle)
Newsgroups: sci.electronics
Subject: Digital noise in audio fixed
Summary: Watch small multiple output switching supplies for noise
Message-ID: <13927@s.ms.uky.edu>
Date: 1 Feb 90 06:29:17 GMT
Reply-To: tindle@ms.uky.edu (Ken Tindle)
Distribution: na
Organization: U of Kentucky, Mathematical Sciences
Lines: 25


I posted here a short while back with a problem in a microprocessor-
controlled audio project.  I received some help from several people, and
have the problem fixed.

For reference, I was using two power supplies in the project to keep digital
switching noise out of the audio, but had noise anyway.  The digital side
was being driven by a TI 99/4A supply, and this was the problem.  Not that
it was sub-par per se, it just wasn't designed for the use I needed.  All
+12 volts is not created equal!

The five volt output was clean, but the +12 didn't like to give me the LED
multiplex current pulses I needed, and made a noisy ground plane.  Switching
to optoisolators driven by the TI +5 with a constant-current o-c circuit,
and a small separate six volt supply with an isolated ground cleared this
mess up.

Thought I'd post this to tell folks to watch these small switching power
chassis with multiple outputs; sometimes they bite!

--------------------------\ /-----------------------------------------------
INTERNET:tindle@ms.uky.edu | "Could you please continue the petty bickering?
BITNET: tindle@ukma.bitnet |  I find it most intriguing."   ---    Data, 
Ken Tindle - Lexington, KY |  Star Trek, The Next Generation, "Haven"
--------------------------/ \-----------------------------------------------