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CM8880 DTMF decoding problems — Parallax Forums

CM8880 DTMF decoding problems

FlyingFishFingerFlyingFishFinger Posts: 461
edited 2006-02-01 15:06 in General Discussion
Hello!
I have the CM8880 and am having trouble with decoding tones. The generating works fine, but the decoding only recognizes about half the tones I send (more specifically only 4,5,6,7,9,12,13,14). I am using the circuit and the modified program from this Nuts and Volts article: http://www.parallax.com/dl/docs/cols/nv/vol1/col/nv7.pdf
I am using software to generate the DTMF and taking it from the earphone jack.
Thank you
Rafael

Post Edited (flyingfishfinger) : 12/22/2005 5:35:39 AM GMT

Comments

  • FlyingFishFingerFlyingFishFinger Posts: 461
    edited 2005-12-23 17:53
    Still haven't figured it. Could it have something to do with the filter cap on the sound input?
    Rafael
  • FlyingFishFingerFlyingFishFinger Posts: 461
    edited 2005-12-24 02:01
    Ah, it works. I hd some funny stuff in my code (initialization)
    I feel like i've been talking to mysef! LOL...
    Never Mind
    Happy Christmas
    Rafael
  • FlyingFishFingerFlyingFishFinger Posts: 461
    edited 2005-12-24 02:11
    Oh, but I do have a question. The Chip seems to remember the last tone I sent to it, and when I ask for it in a loop, I get that. I have the data lines pulled low and I would like to get a zero when there is no tone present, instead of the last one.
    Is this possible?
    Rafael
  • Siong BoonSiong Boon Posts: 1
    edited 2006-02-01 15:06
    Hi,

    I have not use CM8880 before, but I guess it should be similar to MT8870 IC

    In a MT8870 IC,
    you can use the TOE pin to mask all the 4 output pins or
    you can use TOE pin as the indication if any tone is present.

    Check out this website for brief introduction on the behavior of MT8870.
    http://www.siongboon.com/projects/2005-07-18_dtmf_circuits/

    Hopes this info helps.

    from:
    Lim Siong Boon

    siongboon@yahoo.com.sg
    www.siongboon.com
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