Level Detector

Archiver

Looking for ideas/circuits to accept a "line level" audio (analog)
input and generate a digital (zero or five volt) output. The idea is
for my Stamp to see a "1" if a (selectable?) level of audio signal is
present, or a "0" if the line is momentarily silent. Something like
the notion of an audio "squelch" control signal.

Any suggestions?

Thanks,

Steve

Archiver

Steve:
I assume that line level means ~100-200 mv rms audio. How about using an
opamp precision rectifier fed into a comparator? The parts for this are
cheap.

Ray McArthur

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Original Message

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From: S Parkis <parkiss@e...>
To: <basicstamps@egroups.com>
Sent: Thursday, April 06, 2000 1:31 PM
Subject: [noparse][[/noparse]basicstamps] Level Detector


> Looking for ideas/circuits to accept a "line level" audio (analog)
> input and generate a digital (zero or five volt) output. The idea is
> for my Stamp to see a "1" if a (selectable?) level of audio signal is
> present, or a "0" if the line is momentarily silent. Something like
> the notion of an audio "squelch" control signal.
>
> Any suggestions?
>
> Thanks,
>
> Steve
>
>
>

Archiver

One reasonable way to do this is with an open-collector dual comparator
like the LM393. The first comparator has its '+' input tied to a reference
voltage perhaps 50~100mV above ground. The other input sees audio. Its
output sucks down the voltage on a capacitor every time the input goes
above threshold, while a pullup resistor charges the cap if there's no
audio. The second comparator gives you a decisive 'digital' output. It
should be set up with a little positive feedback (hysteresis) to prevent
chattering around the decision point.

>Looking for ideas/circuits to accept a "line level" audio (analog)
>input and generate a digital (zero or five volt) output. The idea is
>for my Stamp to see a "1" if a (selectable?) level of audio signal is
>present, or a "0" if the line is momentarily silent. Something like
>the notion of an audio "squelch" control signal.

Mike Hardwick, for Decade Engineering -- <http://www.decadenet.com>
Manufacturer of the famous BOB-II Serial Video Text Display Module!