Let me see if I can help answer Richard's question. I've been out fo the
country for a few weeks and am now catching up on my email.
>"So, does anyone know if our timing systems confirm a double trip at the
>start and finish or do they just accept what they get while rejecting any
>additional trips for a half second or so afterwards? Are the lights even
>capable of resetting and retripping in two tenths of a second?"
It has been interesting reading the discussions in this thread. The answer
is that the timer was designed to be precise to 0.001 second over the
course of a one day autocross. Making the timer absolutely accurate to
0.001 sec over a period much longer than that makes the timer very
expensive for the very reasons cited by some of you. First, I must credit
Jim Willittes from Intel for the design of the system. He designed it to
my specifications back in 1993.
The system runs an Intel 8051 microprocessor at 12 MHz (this is a decent
chip that accommodates emdedded control - it is becoming an endangered
species now <g>). It is fed by a 30 ppb crystal oscillator with only
moderate temperature compensation. Time is broken into discrete 0.001
second chunks and the system monitors all control activity (photohead and
pushbutton trips) that occurs whithin those chunks and then makes the
appropriate calculation to determine the timer's response. The 0.001
second chunks are like a football field with respect to the amount of time
it takes to make the calculations. The timer is always waiting on the
control inputs.
To be more specific about the possibility of multiple trips, each photohead
goes 'blind' for 1 second after the initial trip to deal with all the other
issues about multiple trips.
The issues about photohead height with respect to the vehicle can come into
play if different clubs put the photoheads at different heights. If, by
extreme coincidence, the air dam barely trips the timer normally, but the
vehicle under acceleration now trips the timer at a spot further rearward
can cause a time greater that anticipated depending on the speed of the
vehicle and the distance behind the original trip point.
With the ChronoMode firmware, the timer can employ all 4 photoheads and you
can write some PC software to monitor the photohead output.
JACircuits is hoping to soon release a software package that has mand
different timing modes based on the output of 4 photoheads. One of them is
the Safe Mode where there are 2 start and 2 finish photoheads. The heads
have to be tripped in the proper order and within a 'reasonable' time delay
for a start and a finish to be registered. The system also maintains a log
of all photohead activity in case that is necessary.
Hope this helps, I apologize in advance for jet lag induced typos.
John Carriere
JACircuits Autocross Timing Systems
http://www.jacircuits.com
- Timing the SCCA Solo II Nationals since 1985
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