Signal Presence Detectors?

[Hairy Harry]

Separate supplies will help... but you still need to have a ground
reference from one to the other, or you can't sense the signal
(could use a transformer...nah)

The problem is not current draw... but changes in current draw. They
will make voltage drops across the ground conductors... and everything
that uses that ground as a reference will pick up and maybe amplify those 
changes.  It would not matter if there was a large current
(though its not recommended), only that the current changed. Regulators will 
be there "too late" to stop it. Careful layout and lots of decoupling caps 
are the answer.

H^) harry


>From: Buck Buchanan <voltagecontrolled at home.com>
>To: synth-diy at node12b53.a2000.nl
>Subject: Re: Signal Presence Detectors?
>Date: Mon, 04 Dec 2000 13:50:28 -0800
>
>Don Tillman wrote:
> > Martin and Juergen both suggested using a current steering technique
> > to drive the LEDs instead of simply switching the LEDs on.  This is a
> > *great* idea.  Otherwise, if I had a couple dozen LEDs triggering off
> > a common musical signal it would involve current glitches of 100mA or
> > more, sure to mess up a high fidelity audio signal somewhere.
> >
> >          (snip description of solution)
>
>Hi all,
>
>Ok, right off the bat I'll admit that I'm probably missing the bigger
>point.  My comments are strictly in regards to large current draws
>dirtying up the power supply.   I immediatly wondered if a just plopping
>down another regulator (78xx, 78Lxx, etc) and filter cap to drive the
>display section might be easier.  There's a couple of volts dropout to
>contend with but that doesn't seem like a big problem for a display.  Or
>is it that these regulators w/cap still won't provide enough isolation
>for your needs?
>
>Just a thought,
>
>Buck

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