Thinking a bit sideways.....touch tone (DTMF) is audio, and therefore easy to record on an audio recorder. You'd probably only be able to realise a rate equivalent to about 200 baud , but it is a very robust data format, and no framing issues to worry about.....

Why aren't there framing issues? Framing is nothing more than determining when one symbol stops and another symbol starts. So with DTMF you have to end one tone pair and begin another tone pair is such a way that this transition can be reliably detected -- that's a framing issue.

Also, why wouldn't you be able to realize a rate much in excess of 200 baud? Even using the same tones as traditional phone DTMF you can probably get over 600 baud and since each tone pair conveys four bits of information, you can get over 2400 bps of data transfer. And there are many games you can play, particularly using high frequency tone sets, using larger tone sets, and broadcasting more than two tones simultaneously in order to increase both the baud rate and the data rate.

 

You mean the Cowon D2, since the Zoom H1 didn't even record anything. The Cowon most likely has something, plus it's recording in mp3 not raw wav.



Actually I need this method to work with a Roland VSR-880 multi-track recorder. I want to use one of the 8 tracks to record specific sync and other digital data. The VSR880 has a coaxial in/out, although I'm not sure how that might work, gonna have to do some researching on the spdif format.

I loved the VSR-880 for about 3 months.

Too many damn menu, jumping around moves, for me.

It did have excellent built in guitar effects, though.

 

Why aren't there framing issues? Framing is nothing more than determining when one symbol stops and another symbol starts. So with DTMF you have to end one tone pair and begin another tone pair is such a way that this transition can be reliably detected -- that's a framing issue.

Also, why wouldn't you be able to realize a rate much in excess of 200 baud? Even using the same tones as traditional phone DTMF you can probably get over 600 baud and since each tone pair conveys four bits of information, you can get over 2400 bps of data transfer. And there are many games you can play, particularly using high frequency tone sets, using larger tone sets, and broadcasting more than two tones simultaneously in order to increase both the baud rate and the data rate.

My apologies for my incorrect terminology. I should have said 'timing issues' not 'framing issues'. I also think your suggestion of 2400bps is a little optimistic.
I have used variations of touch tone frequencies for low speed bi-directional data transfer for many years, and have found it particularly useful where there was no microprocessor control available, and /or where galvanic isolation and short circuit protection was necessary....
Not quite sure why you found it necessary to reply quite so aggressively?... it was only a suggestion!

 

Thinking a bit sideways.....touch tone (DTMF) is audio, and therefore easy to record on an audio recorder. You'd probably only be able to realise a rate equivalent to about 200 baud , but it is a very robust data format, and no framing issues to worry about.....

Thanks for mentioning this. I have a lm567 IC, although never played with it. I've looked at the data sheet, but it's a bit complicated for me. I wonder if the lm567 can detect a frequency in a harmonics signal, i.e. if the signal contains a few frequencies, e.g. 5000, 5500, 6000, 6500Hz and the lm567 is set to detect 5500Hz, will it be able to detect it, and how fast?

If it can do that fast enough (a few mS) for a signal with 8 distinct frequencies, then a byte of info could be transmitted in parallel and 8 lm567 IC's would decode it and output it in parallel to a port on an MCU, (e.g. Atmega8a) which would read the port and send the value over the UART.

 

If you do consider using touch tone, then it's probably best to decode it using the industry 'standard' DTMF decoder IC the MT 8870 or one of its clones (like the Holtek 9170). Cheap and easily available from nearly anywhere - and all the hard work is done in the IC!

It simply needs to receive a valid DTMF audio input signal for a few milliseconds (probably about 10-15mS minimum, for reliable decoding) , and it will decode and update the 4 bit output latch pins on the IC to match the received tone pair. It contains internal circuitry to reduce false decoding, and has a very large audio input range ,with up to almost 30dB variations in amplitude.

I don't personally think you can achieve anything like the data speed that WBahn suggested above, but you can experiment with the 'data valid' time constants to check that out.

There are loads of ways of generating the touch tones themselves, from software routines written into microcontrollers to cheap dedicated hardware ICs like the Holtek 9200

You could also investigate using alternative crystal frequencies to extend the number of available 4 bit codes, if required

As I said above, it's just a suggestion for a simple way to use audio as data.. albeit fairly slow data!

 

If you do consider using touch tone, then it's probably best to decode it using the industry 'standard' DTMF decoder IC the MT 8870

I'll probably get one of those and a MT8880CE transceiver on eBay.

Thanks for the suggestion.