[SOLVED] Play DTMF to already OFF-Hook phone line

[tiwari.aditya13]

Hi

In my setup I have a fixed phone on a telephone line.
I want to connect another 'DTMF generator' to phone line so that i can play DTMF tones..

It will only need to use 'DTMF generator' when my primary phone is off hook.

Is there a way I can avoid a relay in my 'DTMF generator' as it will only be used when line is already in off-hook state?

For above requirement, what if I add a 600 ohm audio transformer's secondaty side in series with the phone line and play
DTMF on it's primary. Will it add a lot of drop to the line.

Regards
Aditya

 

[FvM]

I don't exactly understand the problem. DTMF dialing is always performed in off-hook state.

Besides primary dialing, DTMF tones are often used to control automatic voice mail systems etc. during a call, just pressing dial keys.

 

[tiwari.aditya13]

Was lookin for this circuit diagram, Thanks found answer online
https://colinfahey.com/phone_interface/phone_interface.html

 

[baha eddin]

Dear all, I am new to use the DTMF decoder MT8870D, I have followed what ever there in the datasheet but can not have any output. I have replaced the mic jack with new one. tried calling the phone and answering the call then pressing the keypad from the sender mobile. I still can not find the output.

Please help me figure out the problem. I just need to test the DTMF decoder in order to build mobile controlled appliances.

 

[Audioguru]

The datasheet for the MT8870D shows you how to use it. A mic jack is not used.