On Sun, 24 Jun 2012 14:20:21 -0300
enkitec@gmail.com wrote:

>      I want to build a FM radio squelch using a microprocessor with an AD=
C.
>      The ADC will be sampling the FM radio audio output and turn on a
> LED when there is only noise present. The LED will be off when someone
> is using the channel (no noise, just voice).

Typical (analog) squelches work by having a filter at a frequency above
the usual range. Voice squelches on communications equipment detect
that the noise level at that frequency drops when a carrier comes on.

If the use of the FM channel is voice only (no music) you can probably
sample the channel regularly, sum the absolute values, and set a
threshold. Voice is low-duty cycle, which makes it relatively easy to
distinguish from noise. Music is much more difficult.

John
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