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Pinewood derby car mph calculation device

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New Member
I posted this question on the wrong board "General Chat"...what i really wanted to do was post it on here here....

I want to build a pinewood derby calculation device to measure how fast the car is going? I want to start the clock when the car takes off, and stop the clock when the car reaches the end, and do the d/t = speed. What electronic circuit can I use to do this? 555 timer? 8 bit micro? any help would be appreciated.


New Member
My assumption: You are wishing to conduct a pinewood derby race using pinewood derby cars (typically for Cub Scouts). That means you want something that is simple to build and setup away from your home. Also, a benefit would be if race results could be tracked and displayed for the spectators.

If so, I would suggest you use a notebook computer along with the serial port RS-232 handshake lines hooked to photo sensors. You could then create a Visual Basic program to do the calculation. With some additional effort you could also keep track of the contestants and their individual times. If you know someone that has a projector that can be connected to the computer, then the race times and standing can be displayed for all spectators to see.

Newer notebook computers will require an USB to RS-232 converter.

Also USB based I/O devices are also available off the shelf.


This is commonly done by someone watching the car from start to finish with a stop watch... Click on start, stop on it getting to the end. If you have a situation where you need finer timing than that you're taking pinewood derby cars WAY too seriously. Then you just measure the distance with a roll tape and BAM DV/DT.
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