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Topic: Bullet sensor build help (Read 4 times) previous topic - next topic

AWOL

The straight-line speed is 16 million instructions a second, but like most things, bends (or branches) slow things down.
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dc42


I was originally planning on using the continuous illumination method and hoping to capture an IR reflection off the bullet as it passes up to a foot above the photo diode.  Do you think this would work?  Also, do you think that the 20us or so the bullet reflects above the photo diode would be sufficient to trigger a digital pin on an Arduino?


The continuous illumination method is simpler so it's worth trying first. The best way to trigger the Arduino is probably to use a rising or falling interrupt, that way it can response to very short pulses.
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velocity101


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The best way to trigger the Arduino is probably to use a rising or falling interrupt, that way it can response to very short pulses.



Ah, good idea. Thanks!
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dhenry

You probably need very bright light on a very reflective bullet over a very dark background to detect it.

Another approach is to use an aluminum foil and glue a sound sensor to it. The bullet would breach the foil and the sensor (pizeo) would pick up that breach. It needs a very quiet background.

kg4wsv

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very interesting that all your chrono needed was to watch for a drop in light.  I'm wondering how far above the sensors the bullet can be as still be detected.


The window is a triangle about a foot or 18" tall.

I just visited the manufacturer's web site (not much hard data there), looks like some of their newer models include IR illuminators, so it's watching for a reflection rather than a shadow.  The older passive models are still available.

-j

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