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It's been a while since I've touched electronics, so bear with me :)

Since I can not attach DTMF tones to an on-going phone call (https://stackoverflow.com/questions/16949867/unable-to-make-a-call-from-service), I had another idea.

If I modified a set of headphones (that have a microphone), would it be possible to directly output the speaker audio from an earpiece to the microphone and get decent results playing DTMF phones from the phone?

Android has a buit Tone Generator, so I can play DTMF tones to the sound output programmatically.

If I have to, I can fallback to SMS, but I'd have to have more logic in place for managing the 5% failure rates.

Any suggestions?

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  • \$\begingroup\$ did you solved that without getting feedback noise? any need in resistors/capacitor filters? \$\endgroup\$ – kagali-san Dec 26 '13 at 16:50
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Yes. Back in the day, we used acoustically coupled modems that you sat the telephone handset in and that was fine. For DTFM, in particular, when many phones were still rotary, there were things like hand held speed dial devices where you just held the small speaker up to the handset while it audibly produced DTFM tones. DTFM algorithms in both hardware and software are pretty robust.

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