On 23/04/2011 03:13, YES NOPE9 wrote:
> What a great idea !  I will check with my Linux friends to see what it ta=
kes to
> #1 capture audio, convert the DTMF and produce digital data.
> #2 convert digital data to DTMF, ship it as bluetooth audio.

Creating DTMF is simple enough in software.

Decoding in SW isn't simple. there is a a couple of DSP shortcuts=20
instead of a full FFT. Note that the HW chip to decode DTMF compares the=20
outputs of the Switched Capacitor filters for each of the 8 possible=20
tones and also out of band energy.
If the signal from valid pairs of the 8 filters  vs invalid combinations=20
or out of band energy is poor, it's deemed to be noise and not a signal.
There are four high tones and four low tones. Each of the 16 codes is=20
only one high tone + one low tone.

I doubt you can do it on a phone easily without native programming =20
unless there is an API to access existing DSP HW or HW DTMF decoder, if=20
there is one.

Google Goertzel algorithm

I've used DTMF control over Mobile PSTN, VOIP and voice Radio links.=20
Usually with HT8870 chip. Though I have used (inferior) DTMF decoding in=20
SW on Windows.
http://www.mikroe.com/esupport/index.php?_m=3Ddownloads&_a=3Dviewdownload&d=
ownloaditemid=3D94&nav=3D0,10

A good datasheet of HT8870, or original Mitel MT8870 will show how the=20
detection rules are applied for reliable operation. You need more spec=20
than the list of tones and timing.



--=20
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