Reading number entered after call answer


How to read single number entered from some phone ?
I will write some example so you can understand what i mean.

User calls.
Module send answer_Ok and waits until user has entered number 1.
Then i hangup.

Its much like when you call some answering mashine and after call she ask’s you to enter some number. I dont need this “please enter your number” part, just a way to detect the last entered number.

So my problem would be, that i dont know how to read this number, entered after the accepted call.

You mean, you want to do DTMF detection?

Hi awneil.

I was thinking to make the DTMF detection becuse (correct me if am wrong ) this is the only way to make this work. ?

The call / keypress is comming from mobile and standard networks and i dont need the whole keypad. Just first 4 numbers will do.

I guess i have to find a way to read the high and low grups and then try to make decoding. Look’s simple but … :slight_smile:.

How would you do that ?

I suspect that it might not work at all? :frowning:

You can’t send DTMF over GSM - as I understand it, the CODECs are specifically designed for the human voice, and mess-up DTMF. :frowning:

When you send DTMF from a mobile phone, it doesn’t go in-band as audio - it goes as signalling messages, and the DTMF is generated at the point where the call leaves the GSM network (the MSC?).


I don’t know if there’s any similar facility for recognising DTMF in “incoming” calls, and signalling this to the mobile… :question:

You’d probably have to use an external DTMF detection curcuit and adapt your program to use the external circuit. It’s not going to be “easy” even then.

Would that actually work?

As I understand it, the GSM voice path just won’t pass DTMF intact:

We have been using an external DTMF detection circuit in our hardware for many years. If there is a way to detect it in the module itself it would be great.

I can’t give you exact instructions on how to do it, but I can say for certain that it works.