DTMF decoder using microcontrollers?!

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nvd said:
Why not listen to ring signal heard through the speaker?
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You are funning to us. We need to recognize this by a MCU
 



No ... Wait...


He may be trying to say something!!!

Is he suggesting to do something with audio coming through?

picstudent
 

Ok...

1) If you want to communicate with telephone lines(ringing signal etc.) you can use something like CH1840. You can also do it with analog circuit but it saves you a lot of trouble.

2)Detecting DTMF. Again you can do it by using MT88xx but using the Groetzel algorithm does the job very well.

3)Producing DTMF. MT..... or PWM or DAC (with look up sine tables).
 

Yoy might find this useful
 

You can not. U need to put external Transformer to interface with the telephone lines and then u need to use filters to decode the DTMF tones.
Using Line transformer and MT8870 DTMF decoder is the best and simple solution.
 

i have a project using mt8870, i use to control equipment with the telepone number can some one help me how to make it works, the transformer is should needed? sory i'm indonesian so my english bad, thanks before
 

When you dial a number, telephone exchange gives you a tone on the speaker.
There is some pause between between these tones. When the party on the other side picks the phone, these tones stop. But it does not indicate for sure that the phone line has been picked. You may wait for reply from the party (like DTMF tones sequence). If there is no reply then hang up. For the processing of the tones, use some analog circuitary. It may be useful to find the frequency of the tone by applying frequency analysis. May be it helped.
 

Call Progress decoding is not done by DTMF, so you are wasting your time trying to decode those tones. It is done instead by the cadence and frequencies of the call progress tones that are produced by the central office (CO) and sent to the caller. You can use a precision call progress decoder IC like the Teltone M-982, combined with a microcontroller to count the cadence of the tones to detect when ringing has stopped or if there is a busy signal present. We have used the M-982 and its cheaper, but less capable little brother, the M980 for several years with excellent results. You will also need a method for tapping the phone line audio and feeding it to your call progress decoder. At the least, this will be a good transformer and high Voltage capacitor. Or you might go for an FCC registered DAA like one of the Cermetek DAAs or CircuitWerkes MPC-2.
 

lookin11 said:
... that are produced by the central office (CO) and sent to the caller..
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So that is the clue and a "solution"

picstudent
 

Ok, Thanks Lookin11 for your advice. I will try, Hope that Life's Good!
 

Hey, I have found a solution of this problem when I roam in my lib. You could use just one Transistor to know when other side pick up the handset.
 

phucdull said:
Hey, I have found a solution of this problem when I roam in my lib. You could use just one Transistor to know when other side pick up the handset.
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How?

picstudent
 

Elson said:
Hi sayfollah,

This project is a dtmf Remote control. The dtmf detector is integrated in software.

h**p://www.geocities.com/constantinescuradu/content/dtmf.htm
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Thanks a lot

This was something I was looking for.


picstudent
 

mt8870 = cm8870
 

Hello there

search DTMF in "www.circuitcellar.com". It has explain very good method to decode DTMF and also it has code.
 

With picbasic for instance, you have DTMF functions to generate and to decode DTMF.
 

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