DIY DTMF Encoder/Generator

Tymkrs

Hi all,

Our latest project involved an old school rotary phone! We've been working lately on a series of telephone projects and the first one just happens to be a DTMF Encoder/Generator.



The mcu of choice of course is a Propeller and we, at some point last year, made a custom tiny board for another project. Decided to use it for this one instead. You may of course use any board with a Propeller, and as long as you have the right components connected, you're good to go!

Schematic and code can be found:

http://tymkrs.com/code/dtmf.zip

Or if you'd rather not download a zip file/would like to browse the code first, here're pastebin versions of the Object and the main code:

Object: http://pastebin.com/tGjmzWvP

Main Code: http://pastebin.com/4U93hGs2

And for the sounds that we make: https://soundcloud.com/tymkrs/dtmf-mf-acts-st-kp-kp2-redbox-bluebox

avsa242

That's so funny, I was just thinking of checking to see if anyone had made a propeller-based DTMF generator a few days ago.
I come here this morning and *poof* there it is
Works great on the demoboard (with pin change, of course). I definitely advise against headphones that don't have a volume control that you can turn waaay down if it's 6am and you aren't quite awake yet, though, otherwise you might have a spaz moment in your chair as the DTMF goes straight to your brain, hahaha
Thanks guys!!

Cheers,
Jesse

LoopyByteloose

The DTMF code certainly can work. But the conversion of digital audio output to useful analog with good clear audio can be a bit tricky. The output needs to be filtered via analog circuitry to get rid of unwanted harmonics.

At some point, you may need to put an oscilloscope on your output and see what the speaker is seeing. It may be too noisy to work without getting into experimenting with analog filter designs.

Tymkrs

Lol Jesse, glad you were able to get some use out of this

Loopy - we had it working well enough to have it call a house phone . And the soundcloud link plays exactly what we hear - sounds pretty clear to me?

xanadu

Phreaking awesome!

LoopyByteloose

Great!!! Years ago, we had a lot of people doing this with SX-28 chips and not getting audio quality that would work. That's why I mentioned what I did.