Ultrasonic data transfer

jq

I'm new to microcontrollers and electronics to some degree, so this may all be pretty basic stuff.

I'd like to build a pair (set) of devices that can communicate via ultrasonics (application is submerged - but in air would be ok for testbed work). Basically, there would be a datalogger (Device-1) that would ping out a coded ID signal WHILE logging temperature, for instance (or heart rates!). That device would also listen for an 'interrogation signal' from a second device (Device-2).

Device-2 would listen for, and recognize the coded ID signal from Device-1. When a clear signal is secured, Device-2 could send an 'interrogation signal' to initiate handshaking with Device-1. Once completed, Device-1 would transmit a timestamped data set (or maybe even the coefficients for a fourier transform?) for the logged data. This data could be written to a flash drive or something on Device-2.

Device-1 would need to be small. The extensions of this basic idea go on and on (triangulate positions of Device-1 from the pings, etc) and are elaborations on parts that are out there in various forms. (Like underwater modems...)

So...
I've been through all the basic stamp WAM and sensor examples, I've read a lot of the discussion here and generally get it, though some of it is over my head. I'm a decent programmer (my basic is rusty, but my c, fortran, matlab, and OOP is pretty good and I know just enough about acoustics to make mistakes in assumptions). What I need are some pointers on likely avenues to pursue. Which microcontrollers have the right capabilities (I don't think its the basic stamp)? What sort of transceivers are readily available and cheap (this is an out of pocket project)? How do I make the package small?

Anyway, thank you all very much
Looks like a great support site

Leon

I'd use standard 40 kHz transmitters and receivers for initial experimentation in air. They won't work in water, though. Virtually any MCU would do, like a PIC or AVR. You could use a Propeller, but you'd probably find it too complex. You basically need to modulate the 40 kHz signal with your data at the transmitter and demodulate it at the receiver. I'd start by getting a transmitter to just send 40 kHz using a software delay for timing or one of the counter/timers, and get the receiver working. You can then build the system up gradually. It would help if you have some test equipment, like a 'scope. You could use a PLL (I've used a 74HC4046 successfully) to extract the data, or do it in software if you have enough processing power. You'd probably need something like a dsPIC for that.

Leon

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Post Edited (Leon) : 5/18/2008 3:34:29 PM GMT