timing an RC car

I want to make a timing gate for an RC car. I don't want to spend more
than $50. My thoughts would be to have a light beam sensor so it would
start and stop a timer when the car went through each of 2 timing
gates. What would be nice is if I could find a cheap stop watch that
has an external trigger attachment or one that I could open and hack
into the button with out much difficulty. Any one have any suggestions
on this or a better way to time an RC car? The goal is to find out how
fast they are going by measuring the distance between the 2 gates and
then doing the calculation. But I am also thinking of hooking up one of
the timing gates up to my camera to take a photo right as the car passes
by, since my camera (Nikon N90S) already has an connector for an
electronic remote control I don't think that will be hard once I get the
timing gates figured out.

--
Chris W

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Hi,
You have some sound ideas but as you progress you may go over your $50.00
limit. If you use a basic start/stop timer with external switches you may do
it.
Check these guys out for some ideas : http://www.raceamerica.com/
Good Luck,
Tom

 

---
Use a couple of modulated infrared LEDs as light sources and two
infrared receivers to catch the beams. Use an RS flip-flop as an
enable for a counter and use the output of the first IR receiver to
SET the flip-flop and the output of the second to RESET it. Manually
RESET the flip-flop and CLEAR the counter at the beginning of a speed
run, then when the car goes through the first gate it'll turn on the
counter which will accumulate clocks until the car goes through the
second gate, when it will stop accumulating clocks. Display the
contents of the counter on seven-segment LED or LCD digits, and you'll
have all the information you need to determine how fast the car was
going. If you wanted to, you could choose a particular clock
frequency for the counter and space the gates to have the display read
out directly in units of speed.

What kind of speed and accuracy do you need, and do you want a
schematic?

 

Greetings John,
Though I didn't post the original message I'd sure be interested in a
circuit for timing gates. More than once I've wondered how fast things
were going. I can picture portable gates that could be set up to
measure anything from skateboarders to bullets.
Thanks,
Eric R Snow

 

I would love a schematic, thanks. The speeds will mostly be in the 15
to 40 mph range but some go over 60 so so up to about 70 mph would be
good. I don't want to put the gates more than about 50 ft apart. I
would like the reading to be accurate within +/- 1/2 of a mph. I can
easily put the gates closer if that doesn't effect the accuracy too
much. I could move them a little further apart but that would make the
whole thing much less useful. If the accuracy falls off to say +/- 2
mph at the high end of 70 mph I can live with that, I mostly want it
more accurate in the middle range.

--
Chris W

Gift Giving Made Easy
Get the gifts you want &
give the gifts they want
http://thewishzone.com

 

Long time ago when my son was in high school I made some of these
timers for his science competition. I used laser pointers for a light
source and photo diodes for the receivers. With the laser source I
could trigger cmos circuits with just a 20k pull up resistor. The clock
was a crystal IC and all of the counters were cmos 4518 dual BCD
counters and displays were BCD led displays. Start/Stop/reset latches
were cmos NAND gates. The LED displays came from my junk box and the
rest of the circuits were under $20. Power was a 1000ma 5VDC was a wall
wort. 12V battery and 7805 regulator was used for outside operation.
The counter would display up to 99.999 seconds or five stages of
counters.
Dave

 

Thanks very much for the schematic John.
Eric R Snow