ehsjr said:
I think there are some up front design considerations that
need to be incorporated in looking for the solution.
You need 4 batteries (2 if you use reflective beams) for a
no cable solution, plus an RF link from one of the beam
detectors to the clock (for either start or stop).
If you can run a cable between the start and stop lines,
it greatly simplifies things - no RF link needed, 1
battery (or 2 if you go non-reflective on the beams).
My initial concept was for one battery with cables to the start and stop
"gates". Each gate would be reflective so no cables across the horses path.
The gates are at the entry and exit points to a roped off area so the cables
(extra low voltage) will be run along the "fence line" out of harms way. The
long cable (stop gate) would normally be maximum of around 60 metres in
length
Assuming you can do it with a single battery, the car
battery is fine, but nevertheless wrong. The current
requirements for the electronics should be small, well
under an amp total, with properly designed electronics.
A car starting battery wouldn't have a problem powering
the setup for a couple of days. But gel cells are more
practical for this application.
I appreciate the battery I already have is not ideal but it will be in use
anyway for the pa system and for its remaining life it will serve. When it
finally dies it will be replaced with a more suitable type.
You also need to consider the mechanical setup of the
beams. "There is no way a horse will ever run into
the start line post to which the the beam is affixed."
Hello, Mr. Murphy! The point is that if something happens
during the event to cause either beam to be misaligned,
you need to be able to adjust it quickly without delaying
the event extensively.
My concept would be to have a simple sighting tube on the tx/rx head to
point it more or less at the reflector and the beam arriving back at the
head unit would be monitored by an led on the head to confirm its presence.
The professional (hired) setups I've seen but not studied at shows are
normally mounted on tripods which rarely get knocked over or disturbed but I
take your point they need to be easily and rapidly put back into alignment.
Some input from those who have done this sort of thing
might be real helpful. To me, the electronics isn't the
problem - it's the overall design that is worrysome.
Having seen the sort of thing at shows it seems that commercial (but
expensive) sets work on the same general principles as I have in mind. I
have recently found that the security industry make break beam sets which
run on 12 volt dc supplies and can be found on ebay for a few pounds. This
will take care of the start/stop gates, now I have to sort out the timer.
I'm minded to go down the CMOS 4017 road to do this for the counting, using
a crystal oscillator and divider so I have a 10Hz clock pulse. I havent got
a mains supply in reach or the power could come from that and I could divide
down the 50Hz for clock pulse. A 0.1 second counter overflowing into a 1
second counter, then a tens of second counter with a reset pulse derived
from the 6 outlet for 60 seconds producing a 1 minute pulse to count and so
on. Reaching 9 minutes 59.9 seconds would inhibit the count and show
overflow but typical rounds are over within 3 or 4 minutes. All counts
resettable to zero by a manual reset for next competitor. I can make an
etched pcb using copperclad board with ferric chloride and an led display
using 7 segment blocks should not be difficult too
Does this sound ok to you or can you throw in any other suggestions?
(Ideally I need to be producing a working unit for next season which starts
in March)
John
