Stamp2 based simple acoustic modem?

[everest]

Hi Everyone,

I have a requirement to transmit a very small amount of data (less than 25 bytes) over what has the potential to be a fairly long range, up to 10 miles or more. I've done some testing, and I can easily rig up a system where I can transmit some simple tones to convey the data I need. . .but I'm hoping to avoid buying a ton of expensive hardware to interface this with a PC on the receiving end. . .

So my question is this: Is there a way to quickly decode a series of tones into numerical values on the receiving side of this system? Right now I have the Stamp2 sending out a series of beeps that represent data. . .and I have to manually decide the data on the receiving end (yuk). Any ideas on a cleaner and more sophisticated solution?

FYI, currently the best solution I'm investigating is a DTMF solution as described here: http://www.parallax.com/dl/docs/cols/nv/vol1/col/nv7.pdf but I can't seem to find any source for the CM8880 IC. . .any suggestions on alternatives would be great. . .I'd love to just use the N&V article as a guide here but it doesn't seem that I can!

-Jeff

Post Edited (everest) : 2/8/2010 9:02:09 PM GMT

[Phil Pilgrim (PhiPi)]

Do a Google search for pc dtmf decoder software. You will find several free programs that work with the PC's sound card to decode DTMF data.

-Phil

[everest]

Thanks Phil! Any ideas on where I might go to find a CM8880? Google is failing me utterly here :(

[Phil Pilgrim (PhiPi)]

If all the Stamp is doing is sending DTMF, you don't need the CM8880. Just use the DTMFOUT instruction with some filtering on the output.

-Phil

[everest]

HA! Thanks Phil, I was just looking at some sample code that used the DTMFOUT command, which I was totally ignorant of prior to 10 minutes ago. There I go again making things 100x harder than they need to be. Thank you for steering me in the right direction!

-Jeff

[upand_at_them]

Any reason why it has to be DTMF? Decoding a single frequency would be much easier. I think packet radio uses a single frequency and the bits are determined by the length of the pulse...It would certainly be easy to come up with some workable scheme.

Is this being transmitted over wire, or radio? If radio, be careful. In the US you can get into some serious hot water for violating FCC regs. Even with a ham license certain bands are limited to certain types of transmissions.

Mike

[everest]

I suppose it doesn't have to be DTMF, but I'm a rather unsophisticated Stamp2 hobbyist. . .my projects tend to leverage things that are proven and easy to work with, that's why I love the Stamp series vs. all the other microcontrollers out there (just about all of which I've played with). I looked at packet radio, but it's pretty expensive and complex. . .DTMF is just super super simple, reliable and noise resistant. Since I have such low byte counts to send it seems the best solution.

But if you are aware of any simple/cheap solutions that use other technology, definitely let me know!! I'm always open to new/better options.

-Jeff

[upand_at_them]

Stamps can generate DTMF, but can they decode DTMF? They'll decode other protocols, even one you make up.

[everest]

Actually I can decode on a laptop if I use some of the software that was recommended by Phil. This isn't a Stamp2Stamp application, it's a Stamp2PC application. I have a few hammers I'm working with on this, and the system will only be transmitting for a minute or two on authorized frequencies. . .

-Jeff

[everest]

For anyone else interested. . .here's another interesting solution:

http://kengracey.com/Home/RadioCommunication/tabid/73/Default.aspx

Very "off the shelf" approach. I love it!

-Jeff

[upand_at_them]

Yes, provided the operator has the proper license and is using the proper band.

Mike