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>(2) the wrist unit must detect collisions (the best place for the detection >hardware, actually), and must communicate problems to the transmitter. >More properly, the wrist unit must positively acknowledge successful >transmissions. Why such complexity? I very much doubt the Air-X or any of the similar beasts have two way comms, or anything more than a washing-machine controller running in the transmitter. I don't know, but I would guess it simply sends a "this is how much air there is" message along with a transmitter ID to detect crosstalk (as you suggest). Message collision doesn't matter, so long as the length of the transmission is small and the frequency of update is fairly high (eg once a second). It should pause between each transmission by a random number of milliseconds seeded from the ID, so that if you do get packet collision it cannot be synchronised between units. No need for a receiver in the transmitter or a complex processor (and no need for a transmitter in the wrist unit) therefore more reliable, less power consumption and cheaper. mike. ___________________________________________________________________________ Mike Salmon, Climatic Research Unit, | University of East Anglia, Norwich, UK | SCUBA diving in the United Kingdom m.salmon@ue*.ac*.uk* +44-1603-592875 | http://www.cru.uea.ac.uk/ukdiving/
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