--On Tuesday, June 11, 2002 10:23 PM -0400 Matthew Carson <mcars@vt.edu>
wrote:
> Perhaps a standard light based trigger
> could be used in conjunction with an onboard GPS receiver. When the car
> breaks the beam, the receiver records the time from GPS and transmits it
> to the receiver. Since both start and finish triggers would be based on
> the same GPS time signals, accuracy could perhaps be accomplished. I
> have no idea how expensive that system would be though.
Perfectly doable with exactly that design, and you're right, GPS is more
than accurate enough (200 nanosecond), provided the receivers can see four
satellites every once in a while (it's probably okay if they drop down to
one here and there and their internal clocks are reasonably steady, but
they need four to get a proper initial sync).
It would be cheaper and easier to do exactly the same design based on the
NIST time signal (see http://www.time.gov/), but it's only accurate to about
10 milliseconds (0.01), which isn't enough.
Mark
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