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Decoding DTMF with the propeller — Parallax Forums

Decoding DTMF with the propeller

electromanjelectromanj Posts: 270
edited 2012-02-09 17:15 in Propeller 1
Hello all, I have a question concerning DTMF and the propeller. I would like to recieve the touch tones from a phone and then execute an action based on the numbers that were dialed. I have seen circuits for the bs2 that use a DTMF decoder chip. Do I need a chip for the propeller? Any suggestions would be greatly appriciated! Thanks!

Comments

  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2010-03-12 18:27
    See here:

    http://forums.parallax.com/showthread.php?p=876749

    It's not a complete solution, but it should get you started.

    -Phil
  • electromanjelectromanj Posts: 270
    edited 2010-03-12 18:50
    Thanks Phil, for the quick reply and the good info!
  • WossnameWossname Posts: 174
    edited 2012-02-09 04:49
    Nice work Phil,

    This looks just the ticket for my latest project. You may have saved me a good deal of time and headscratching :)
  • Mark_TMark_T Posts: 1,981
    edited 2012-02-09 14:28
    I've just had a thought - recently there was news of a new faster alternative to the fast fourier transform optimized for spectrally sparse signals - perhaps that could be applied to this problem? Have only skimmed the paper so far though.
    http://arxiv.org/pdf/1201.2501.pdf
    http://groups.csail.mit.edu/netmit/sFFT/
  • LeonLeon Posts: 7,620
    edited 2012-02-09 14:44
    The Goertzel algorithm is often employed, as the frequencies are known.
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2012-02-09 16:04
    Leon wrote:
    The Goertzel algorithm is often employed, as the frequencies are known.
    Exactly. That's what my program uses. An FFT -- or any full spectrum analysis -- would be overkill.

    -Phil
  • pedwardpedward Posts: 1,642
    edited 2012-02-09 17:15
    Just thinking outloud here, but couldn't you just use the counter bits as an FFT? Say, to output 140Mhz you set the 80Mhz and the 40Mhz and the 20Mhz bits in FRQx, wouldn't it work the other way too? The PHS register would represent all of the frequencies received in a 1 second sample period?
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