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Topic: Bullet sensor build help (Read 4326 times) previous topic - next topic

velocity101


Yes, that photodetector looks a good one to me. You can connect several of them in parallel.


Great, thanks!  I order a dozen of each and will report back with my results.  Thanks for the tip on Element 14; saved me over 50% off what I would have paid over at Mouser with better parts no less!
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dc42

btw there are 2 ways you could attempt to detect the bullet:

1. By illuminating the area with steady IR and looking for a fairly sharp change in the received IR.

2. By modulating the IR and using a synchronous detector to look for received IR at the modulation frequency. Since the bullet will only be over the sensor for about 20us, you would need to use quite a high modulation frequency, say 500KHz (which is about the maximum possible, given the 800nS rise/fall time of the emitter). This approach should be less sensitive to muzzle flash.
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velocity101

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?
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AWOL

Quote
Also, do you think that the 20us

Think of it as 320 instruction cycles.
"Pete, it's a fool looks for logic in the chambers of the human heart." Ulysses Everett McGill.
Do not send technical questions via personal messaging - they will be ignored.

velocity101


Quote
Also, do you think that the 20us

Think of it as 320 instruction cycles.


So at 16Mhz, the Arduino is capable of handling 16 Million cycles per second, right? Then I'd say it'll do, lol.  Thanks, AWOL.
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AWOL

The straight-line speed is 16 million instructions a second, but like most things, bends (or branches) slow things down.
"Pete, it's a fool looks for logic in the chambers of the human heart." Ulysses Everett McGill.
Do not send technical questions via personal messaging - they will be ignored.

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.
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

velocity101


Quote

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

velocity101


Quote
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



Great! So this is essentially what I'm trying to achieve! Good to know the approach I plan to take is feasible.
JOPIN STUDIOS | Trusted Web Design since 1998 | www.jopin.com

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