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Need help with finding schematics for millisecond timer


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Hello,

I have not been succesful finding an appropriate schematics for a small science project I want to built.

It's actually very simple: I want to measure the drop time of different objects through a metallic tube (copper).

The objects will vary from a stone, an ordinary magnet to the strongest possible neodymium magnet.

At the top and end of the tube I want to mount IR-detectors that will respectively start and stop the counter, which result should be shown on a (old-fashioned) LED-display.

I want to use as much as is possible old stuff I have lying around, or cheap CMOS IC's.

An ordinary stopwatch as I found on this site isn't fast enough, but anything which comes close to one of these two schematics would be wonderful.

Any help is appreciated!

Ronald Werner
Norway

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Hi,

See what you mean. The signal could be used to drive a simple 4-digit counter (74c926) I found some place.

But it's still a bit complicated. I need to find a good solution for the sensors that start and stop the counter.

Accuracy is not a first concern, the osciallator could also be a 555 I adjust in such a way that the result is aceptable.

It's the hopefully big difference between normal objects and the neodymium magnet that do the trick.

Anyway, thanks for you help.

Ronald

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