"Bill Powell" wrote in message
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Simple Tone Detector

I'm looking for a SIMPLE circuit to detect the presence of a tone -
any tone in the audible range.

My quest: Consider the poor radio dispatcher, sitting there wearing a
pair of headphones when the next town / county over tones out an
ambulance or fire department.

I'm looking to be able to detect any audible tone and use the results
to decrease the operator's headphone sound level during the tone.

I have already tried a DSP tone elimination and found that:
1) It's too effective: I need do decrease tone volume - not eliminate
it.
2) Way too complex and expensive for the seemingly simple task.

The circuit needs to be compact and inexpensive - connected between
the dispatch console headphone jack and the operator's headphones. It
must NOT interfere with normal speech!

I have spent several hours online seatching and came up empty. Any
thoughts or suggestions?

Bill Powell


You could build a circuit using a 567 tone decoder IC, but the problem is
that you will first need to know what freq the tone is. Still you could use
multiple tone decoders, feeding to a muteing circuit. If you can specify
the tones you want to mute, we may come up with a circuit to help. The 567
would output to a relay that would simply mute the audio only when the tone
is present. JTT KF4HUF .