How to connect telephone to the input of MT8870?

[chirag2239]

Hi,

I need someone who can help me to solve my problem.
I am confused that how to connect the telephone to the DTMF decoder? Please note that I have a circuit of DTMF decoder, but the problem is that I do not know which wire is connected to the input of the DTMF signal from the telephone line jack in which the RJ11 jack from the telephone line is inserted.

Thanks.
Chirag

 

[betwixt]

You cannot connect it directly, you should use an isolating transformer. Also note that for a telephone line to receive DTMF it normally has to be active ("off hook") so you also need the circuitry to seize the line or you have to use a conventional telephone to answer the line and connect the MT8870 to it.

Please bear in mind that voltages as high as 125V can appear across the phone wires so they can be dangerous. Also consider that many telephone companies prohibit the connection of unapproved devices to their lines.

Brian.