Remote telephone detection circuit

[djc]

Hi,

I have one hardware in which a mic and mp3 module is attached using ATMEGA8 and TDA2822 amplifier IC. Prerecorded messages plays continuously but for the announcement through the mic a push button attached with controller has to be pressed so that recorded messages will stop and announcement through the mic will be done. Now I have to interface this circuit with remote telephone.Telephone will have a highest priority. So message through the telephone will be played first. So how to incorporate this telephone detection circuit.

 

[BradtheRad]

Old-fashioned telephones were detectable from the phone company's end, because they had a standard resistance of 600 ohms (I think).

Not sure about modern telephones. Is it dedicated to your system, or is it hooked up to the phone company? The phone company sends -60V (negative polarity) through its line.

The ring signal is about 90 VAC. So you might be able to detect a phone by sending low voltage AC (so that you don't make it ring), and measuring how much current goes through.