Reading number entered after call answer


#1

Hi,

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.


#2

You mean, you want to do DTMF detection?


#3

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 ?


#4

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?).

See AT+VTD, AT+VTS, AT+WDTMF

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


#5

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.


#6

Would that actually work?

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


#7

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.