TELECOM Digest OnLine - Sorted: Re: Touch Tone Blocking

Re: Touch Tone Blocking

Gordon S. Hlavenka (
Sun, 10 Apr 2005 11:06:18 -0500

Takoma Park Volunteer Fire Department wrote:

> I need to devise a way to keep users from playing touch tones over the
> paging system. If you can suggest a way to prevent users from
> sounding touch tones over the paging amplifier circuit post it here or
> E-mail direct.

Use a DTMF receiver chip to detect the tones. Feed the PA audio input
into the chip and connect the DV output to the PA Mute input.
Probably a $5 investment in parts, or a minimal drain on your junkbox

You'll still get a brief burst of tone (20-50msec) at the beginning
but the rest of the tone will be muted.

Gordon S. Hlavenka
Tragically, as many as 9625 out of every 10,000
individuals may be neurotypical

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