I need to build a device to measure the speed of a pine wood derby car. One idea was to use two photo censors connected to a programmable logic controller with the output going to a simple display. Is there an easier way to accomplish this?
Hi Tom, The Photo sensors are the way to go. I use an old laptop, printer port or com port for input and a simple basic program for timing. The display is already there. Dave
Tom wrote in news:cZ_Pg.10183$2P3.8233 @trnddc02:
Have you Googled "pinewood derby timer" ? 505 hits. 24600 hits if you leave off the quotes.
Just asking.
Ken
"Tom"
** Errr - a laser / radar gun ??Lots of other uses for one of them too.
See them for under US$300 on line.
....... Phil
Depends on what you want to measure. What you described would measure average velocity. You might be interested in maximum velocity or velocity versus time or versus position, which would be different problems.
Maybe you could dispense with the PLC if there's a good way to divide one analog signal by another, like using voltage-controlled resistors in an inverting amplifier (I'm not one of those electronics cognoscenti). Preset one voltage (or turn a pot) to represent the distance, and use an integrator to get a voltage representing time between the two photocells.
Yup. And the very first link shows project 14, "The Worlds Least Expensive Pinewood Derby Timer". That will work just fine, but I'd use a regulated +5V wall wart instead of the unregulated 6V supply shown in the link. I'm not comfortable about an unregulated +6V (which may peak as high as 9VDC) attached to a printer port input pin with a 10K resistor between.
Use an old laptop, and amaze the kids.
Good luck Chris
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