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MT8880 DTMF Transceiver — Parallax Forums

MT8880 DTMF Transceiver

Mike CookMike Cook Posts: 829
edited 2008-01-16 17:44 in General Discussion
I was doing some work with the MT8880 DTMF chip, that Parallax sells, today and did some updates to the sample programs. I though I would post them here for future reference.·

I'm building a car alarm/door unlocker for my truck using the BS2p24, EMIC module, MT8880 DTMF chip, and a GSM Cell Modem. Probably way over kill, but didn't want to have to add the car alarm transmitter to my key ring, and decided to use my cell phone as the input device for the truck alarm/controller.

Any way here's some links:

MT8880 chip on the Parallax web site:· http://www.parallax.com/detail.asp?product_id=604-00003
BSP
BSP
8880_DTMF_DIAL.BSP
3K
BS2
BS2
8880_DTMF_RCV.BS2
4K
mt8880_3.gif
808 x 505 - 12K
MT8880_Debug.gif
601 x 374 - 10K

Comments

  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2004-08-21 19:50
    Mike,

    ·· I just received two of these chips in my most recent order from Parallax...I bought them for HAM Radio Tone Decoding using a Scanner.· I downloaded your code to peruse later, but I wanted to ask, the screen shot of DEBUG, when it detects 10 & 12, are these like the * and # keys?


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    Chris Savage

    Knight Designs
    324 West Main Street
    P.O. Box 97
    Montour Falls, NY 14865
    (607) 535-6777

    Business Page:·· http://www.knightdesigns.com
    Personal Page:··· http://www.lightlink.com/dream/chris
    ·
  • Mike CookMike Cook Posts: 829
    edited 2004-08-21 20:09
    Chris,

    The output from the MT8880 is:

    DTMF KEY:······· MT8880 to Stamp Value:

    · 1······················· 1
    · 2······················· 2
    · 3······················· 3
    · 4······················· 4
    · 5······················· 5
    · 6························6
    · 7······················· 7
    · 8······················· 8
    · 9······················· 9
    · 0······················· 10
    · *························11
    · #······················· 12

    I haven't connected to my·2m yet but I would assume that:

    · A······················· 13
    · B······················· 14
    ··C······················· 15
    · D························· 0 ???

    I'm having a little trouble ALWAYS decoding * (11) over the GSM Cell phone, so I've probably got some work to do on an audio filter.

    Just checked the Nuts'n'Volts article, the chart above is correct. Here's a link to the article:

    http://www.parallax.com/dl/docs/cols/nv/vol1/col/nv7.pdf

    Mike

    Post Edited (Mike Cook) : 8/21/2004 8:24:29 PM GMT
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2004-08-21 20:43
    Thanks for the N&V column...I will check it out before I use the chip myself...I do have one more question on your project (Again without looking at your code)...I know you're using a Cel-Phone to call the car, but what's answering?· Another Cel-Phone?· If so, how are you accomplishing this task?


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    Chris Savage

    Knight Designs
    324 West Main Street
    P.O. Box 97
    Montour Falls, NY 14865
    (607) 535-6777

    Business Page:·· http://www.knightdesigns.com
    Personal Page:··· http://www.lightlink.com/dream/chris
    ·
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2004-08-21 20:51
    Disregard, I went back up and saw the GSM Cel Modem...I am not familiar, however, with this device...



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    Chris Savage

    Knight Designs
    324 West Main Street
    P.O. Box 97
    Montour Falls, NY 14865
    (607) 535-6777

    Business Page:·· http://www.knightdesigns.com
    Personal Page:··· http://www.lightlink.com/dream/chris
    ·
  • Mike CookMike Cook Posts: 829
    edited 2004-08-21 21:00

    Chris,

    I work for a company that manufactures GSM/GPRS Modems, I'm using one of our SA-G's (www.enfora.com) cell modems, besides being able to do data and SMS it will work like a standard cell phone. I'll probably use a pre-paid SIM in the truck modem (SA-G) and then use my standard cell phone to call it and do stuff, like lock/unlock doors, honk horn, flash head lights, ect., using DTMF from my cell phone to the truck's cell modem. The stamp connected to the cell modem (truck) will decode the DTMF and provide audio prompts using the EMIC module.

    I still haven't done Jon Williams "Plan the work, work the plan" suggestion, so I'm building modules, testing and designing "on the fly". I've attached a picture of the MT8880 decoder board that I built, still have more work to do!

    Mike

    Post Edited (Mike Cook) : 8/21/2004 9:03:32 PM GMT
    MT8880_BRD.gif
    494 x 662 - 35K
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2004-08-21 21:06
    Nice...And a great idea...In a very large Car Computer Project from a long time ago, I implemented a remote access function, but that was merely a coded remote transmitter to unlock the doors and startup the car computer.· Once inside the vehicle you'd have to enter your password on a KeyPad...Your idea is more secure, and very configurable.· Good luck with it.· And I hope you'll post your progress on here.· I'm sure more people would be interested to see what you can do with the DTMF Chip, as well as GSM/Cel equipment.



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    Chris Savage

    Knight Designs
    324 West Main Street
    P.O. Box 97
    Montour Falls, NY 14865
    (607) 535-6777

    Business Page:·· http://www.knightdesigns.com
    Personal Page:··· http://www.lightlink.com/dream/chris
    ·
  • dk_akjdk_akj Posts: 37
    edited 2004-08-22 11:16
    Off Topic:

    Mike >>
    I use the Enfora modems *** well. Great product to a sensible price. beside that your company gives a great support.

    //akj
  • Mike CookMike Cook Posts: 829
    edited 2004-08-22 12:32
    Neat! Fell free to PM me if you need any info on the modem.

    Mike
  • Mike CookMike Cook Posts: 829
    edited 2004-08-22 14:06
    Chris,

    A procedure that worked for me: When you get around to building your MT8880, run the 8880_DTMF_RCV.BS2 first. You will need to amplify the output signal from pin 8 of the chip. I first connected pin 8 to an 8ohm speaker and could just barley make out the transmitted DTMF from the MT8880, then used a·pair of amplified computer speakers (I bet you have a lot of these! wink.gif ), to test the output. If you do this first you can verify that the MT8880 is working and then go onto decoding DTMF from whatever audio source you desire.

    Mike



  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2004-08-22 14:34
    Mike,

    ·· Thanks for the information.· I'm sure it will help when I get to using this chip (One I've never used before).




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    Chris Savage
    Parallax Tech Support


    Post Edited (Chris Savage (Parallax)) : 1/15/2008 3:12:17 PM GMT
  • FrankHFrankH Posts: 1
    edited 2008-01-15 07:03
    Mike CooK or Chris Savage:
    I used the schematic and code from Mike Cook to test the function of MT8880. I used a microchip PIC16F876A is used to control MT8880CE.
    I can send out DTMF by MT8880 but can not detect input DTMF signal.
    Could you both give some hint to resolve it?
    Thanks for your attention.
    Frank Huang
    604-590-8396
  • Mike CookMike Cook Posts: 829
    edited 2008-01-16 01:29
    FrankH,

    I've never use the MT8880, with any other processor besides the Parallax Basic Stamp (BS2 or BS2px24)·or the MicroMint Z8 (1983' version). So I might not be much help.

    When I tested the MT8880, as detailed in the previous posts, I was able to get·MT8880 to work with the above posted micro's.

    Please detail out what is 'not working' and I'll try to help.





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    Mike
  • Bruce BatesBruce Bates Posts: 3,045
    edited 2008-01-16 04:27
    Frank -

    Have you used the bypass capacitors on the power input (Vdd) as Mike's schematic shows? If not you need to add them, regardless of how stable you feel your power supply is. These capacitors are NOT OPTIONAL, they are REQUIRED.

    The very symptom of NOT having them is that you can send but not receive DTMF tones!

    Regards,

    Bruce Bates

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    Veni, Vidi, Velcro! - I came, I saw, I stuck around!
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2008-01-16 17:44
    My memories of this device are that it was very touchy about the oscillator used. I believe we used a resonator, though a TV Colorburst crystal is what it was designed for.

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    Chris Savage
    Parallax Tech Support
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