HELP! alphanumeric display using DTMF

Discussion in 'Homework Help' started by edski, Oct 13, 2010.

  1. edski

    Thread Starter Member

    Sep 22, 2010
    65
    0
    can anyone show me how to display alphanumeric characters using DTMF? pls i really need ur help. thnx a lot
     
  2. retched

    AAC Fanatic!

    Dec 5, 2009
    5,201
    312
    How to display them on what?
     
  3. t06afre

    AAC Fanatic!

    May 11, 2009
    5,939
    1,222
    Let us start with the basics first. Do you have DTMF circuit you use for your assignment?
     
  4. edski

    Thread Starter Member

    Sep 22, 2010
    65
    0
    lcd sir,, ............
     
  5. t06afre

    AAC Fanatic!

    May 11, 2009
    5,939
    1,222
    With this speed this may take very long time. I suggest to tell us what you have done so far, and why and how you struggle. This can be done by posting your schematic and your code.
     
  6. edski

    Thread Starter Member

    Sep 22, 2010
    65
    0
    im sorry for the late reply. actually i dont have yet the circuit and the code. i just wana know who has an idea of this , and cud help me
     
  7. edski

    Thread Starter Member

    Sep 22, 2010
    65
    0
    i know its hard to tell, but the idea is to transmit alphanumeric characters using the dtmf tones, and this tones will be decoded in the receiver that will be displayed in the lcd
     
  8. bertus

    Administrator

    Apr 5, 2008
    15,645
    2,344
  9. edski

    Thread Starter Member

    Sep 22, 2010
    65
    0
    from what is on my mind, the alphanumeric characters from the keypad will be converted into binary. ( 8 bits) then this 8 bits will be represented by the dtmf tones, in the receiver, the tones will be converted to back to binary and finally be displayed in LCD.
     
  10. bertus

    Administrator

    Apr 5, 2008
    15,645
    2,344
  11. retched

    AAC Fanatic!

    Dec 5, 2009
    5,201
    312
    This is not difficult.

    Actually you can use a standard number display circuit and change the lookup table to display characters instead.

    Thing is, you only have 0-9.

    If you want to be able to do the multi button press style of typing like used on cellphone text messages, that too would be done in software.

    If a button is pressed wait 2 seconds then display the character associated with that tone.

    If button is pressed again BEFORE the 2 seconds is up, check to see if it was the SAME button or a different button.

    If SAME, move to the second letter associated with that tone
    If DIFFERENT, display the character for the previous and start over counting to 2.

    So you will use a timer and interrupt to decide if they are still selecting the letter on that number button, or moving on to the next letter.
     
  12. edski

    Thread Starter Member

    Sep 22, 2010
    65
    0
    so every tone will be assigned a character?
     
  13. retched

    AAC Fanatic!

    Dec 5, 2009
    5,201
    312
    If you wanted to do something neat, you could convert the characters to binary like you suggested, then convert that into tones.

    For instance START transmission would be the tone for the number '1'

    then binary 0 would be tone '2'
    binary 1 would be tone '3'

    Done Transmission would be tone '4'

    That would be rather straight forward..ish..

    ;)

    That allows you to send:

    1(start TX) 2333232323222232333233323232323232322233332000 4(end TX)
    The 2s and 3s would equate to:
    01110101 01000010 11101110 10101010 10101000 11110111

    That would be grabbed by the receiving in 8 bit chunks and converted to the letter you want and displayed onscreen.

    This also gives you tones for 5,6,7,8,9,and 0 to do other communications stuff.

    For instance if you wanted to have the other end talk back,

    Then transceiver 'A' would use tones 1,2,3,4 as noted above, but transceiver 'B' would use 5,6,7,8 for (start TX, 0, 1, and end TX)

    You would also be able to have 'b' respond to 'a' to let it know it is online.

    For instance 'a' send the tone '1' for start then waits for 'b' to send : 5,8 which would be start-stop and 'a' would then know it could send the bit-stream.
     
    Last edited: Oct 13, 2010
  14. edski

    Thread Starter Member

    Sep 22, 2010
    65
    0
    i ddn't understand this part

    "If SAME, move to the second letter associated with that tone
    If DIFFERENT, display the character for the previous and start over counting to 2. "

    im sorry!
     
  15. retched

    AAC Fanatic!

    Dec 5, 2009
    5,201
    312
    If the number was the same.

    When you TXT message, if you want letter 'b' you have to press number '2' twice. first for 'a' then again quickly for 'b'.

    So the software waits a few seconds to see if you are going to press the '2' again to move to the next letter on that key.

    I would use the other idea.
    Using the bit-banging method.
    It would be pretty neat.
     
  16. edski

    Thread Starter Member

    Sep 22, 2010
    65
    0
    yes sir, that's what im trying to say :)
    the problem here is, im not good in programming, :(
    but thanks retched. great help
     
  17. edski

    Thread Starter Member

    Sep 22, 2010
    65
    0
    so meaning, the equivalent tone (w/c is the 8 bit ) will be decoded by dtmf decoder into 8bit equivalent, w/c will be displayed in lcd as characters, right? :)
     
  18. t06afre

    AAC Fanatic!

    May 11, 2009
    5,939
    1,222
    Is this a school project? And are you supposed to a certian DTMF circuit? The more details you can give us the better we can help.
     
  19. edski

    Thread Starter Member

    Sep 22, 2010
    65
    0
    yes its a school project, and im a bit late already, hehe. but thats ok...
     
  20. edski

    Thread Starter Member

    Sep 22, 2010
    65
    0
    i know the idea but im struggling coz i dont know how to program this. im planning to use pic16f877a. its the one that i have
     
Loading...