At 07:08 PM 3/28/00 -0500, you wrote:
>Hi,
>
>Anyone have a cheap ( also real-estate is at a premium ) method for
>detecting wheter or not ANY tone is present?

It's kind of a requirement like that of a watchdog timer, you can
take the tone, amplify and clip it, and use it to reset a 555 or
use software in the PIC to measure the time between transitions..
if your timer times out (minimum frequency) then there is *no*
tone, otherwise there is a tone.


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Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:
http://www.speff.com
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