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DTMF input to the MT8870 IC

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Siddhat:
Hey, I am currently working on a project based on Dual Tone Multi Frequency (DTMF) and have used a MT8870DE IC to decode the DTMF tones. Referring to the datasheet I connected the circuit diagram as prescribed but I am having problems regarding DTMF input to the IC. The input was given using a head phone jack by connecting the 3.5 mm jack to the mobile phone and the other end to the DTMF input of the IC. But how do I know which wire to connect to the input of the IC as there are 4 or sometimes 3 wires of the jack. Anyone?
Here is the datasheet attached that I preferred.

Richard Crowley:
Use a 3-terminal connector ("TRS").
Do not use a 4-terminal connector ("TRRS")
That way you will not have to decode which is the ground/return node.
It will always be the "sleeve" ("S") terminal.



Then use the "tip" ("T") for your audio signal.
That will always be the "left" channel of the stereo audio.
In the case of a voice call, the left/tip and ring/right will be the same (i.e. "monaural")
But it is probably not a good idea to connect the tip/left directly to the ring/right terminal.

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