KcW wrote:

> Ok, that's one I never thought of. That's the kind of thing I need
> though, good non-linear thinking.

  We thought of this one for the (IronMan series) Triathlon tracking,
but even on a bike, it is very difficult to mount a barcode to be
reliably visible from a given angles, let alone a runner (or swimmer?).
Having volunteers read the 3" high numbers (on the rear struts of the
bike) has been a real headache, impossible to use with sufficient
reliability for real-time tracking.

  Presently, transponders are used by a specialist firm to track the
intermediate and final finish lines, but they want (much!) more money
to provide intermediate checkpoints.  (The transponders are worn on a
Velcro band on the leg.)  Understandably, as the interrogation point
electronics are presumably fairly sophisticated, and a set of 1000
transponders is non-trivial if we were to look at only two or three
events a year.  Some "disposals" ones are offering though; Philips
PCF7930CP/25 but I have had no success finding data on these even to
determine range and method of interrogation.  Any ideas?

  Except for the noted potential dirt problem, the barcode idea has
merit for cars though.  Laser scanners would not work in daylight, but
CCD scanners would.  If you can chicane the cars of course, and mount
the code longitudinally, they would self-scan like packing crates on the
conveyor belt.  We have already noted this limitation however with the
Triathlons, competitors won't be chicaned!

  Most (CCD) scanners I have seen use the 68HC11 or 80C51 and the code
is non-trivial, but perhaps an overhead boom could hold a photocell
every 200mm or so with a PIC (pre-)processor, using 300mm wide barcode
decals...

  Cheers,
        Paul B.