HELP! alphanumeric display using DTMF

Thread Starter

edski

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

t06afre

Joined May 11, 2009
5,934
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.
 

Thread Starter

edski

Joined Sep 22, 2010
65
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
 

Thread Starter

edski

Joined Sep 22, 2010
65
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
 

Thread Starter

edski

Joined Sep 22, 2010
65
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.
 

retched

Joined Dec 5, 2009
5,207
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.
 

retched

Joined Dec 5, 2009
5,207
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.
 
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Thread Starter

edski

Joined Sep 22, 2010
65
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!
 

retched

Joined Dec 5, 2009
5,207
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!
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.
 

Thread Starter

edski

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

Thread Starter

edski

Joined Sep 22, 2010
65
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? :)
 

t06afre

Joined May 11, 2009
5,934
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.
 

Thread Starter

edski

Joined Sep 22, 2010
65
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
 
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