An interval timer with a trap

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texasclodhopper
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An interval timer with a trap

Post by texasclodhopper » Sat Feb 13, 2010 4:36 pm

I've been subscribed to N&V for a very long time, but I have recycled my old mags to some younger folks at the school.

I seem to remember an article on a trap timer with a couple of LED start and stop traps or gates. You could shoot a bullet through them and either time it or trigger a strobe to take a picture.

It seems like it was on the cover, but I don't know if it was as far back as the large format magazine.

I can't find it by searching for "timer" or "interval" or "intervalometer" or similar searches.

I would appreciate any help in locating this article. Thanks!


texasclodhopper
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Re: An interval timer with a trap

Post by texasclodhopper » Sat Feb 13, 2010 6:50 pm

I found that one, too, but it isn't the one I was looking for. Thanks.

I remember that it had 2 LED/PHOTOTRANSISTOR gates that detected what went through.

Please don't stop looking!

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CeaSaR
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Re: An interval timer with a trap

Post by CeaSaR » Sat Feb 13, 2010 8:26 pm

N&V, June 2009, starting on page 36. Search term "Chronograph".

CeaSaR
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texasclodhopper
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Re: An interval timer with a trap

Post by texasclodhopper » Sun Feb 14, 2010 3:57 am

That's the one exactly that I had stuck in my brain! It wasn't that long ago, either. I just didn't / couldn't think what it was called. (Man, don't ever look up the word "timer" on N&V! :) )

Thanks, guys! Job well done to both of you and to all else that took that extra bit of time to look it up, too.

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CeaSaR
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Re: An interval timer with a trap

Post by CeaSaR » Sun Feb 14, 2010 7:30 am

texasclodhopper,

Thank you.

You are quite welcome. I had remembered that article, but I couldn't recall just what the device was called.
I thought it was "chronograph", but I thought that a search with that would trigger lots of hits on watches
or other time keeping devices. I tried just "bullet" in the N&V search, but got absolutely nothing. Discouraged, I
went to my default search engine (Yahoo! search) and typed in: "what is the name of the device that measures
the speed of a bullet?" I finally found a good enough link on the 3rd page of the search and voila!, there it was,
chronograph. (Memory vindicated :mrgreen: ) Back to the N&V home page for a search with chronograph and the link
I posted was the first hit.

It pays to double check yourself when you are unsure. My search went from no hits to bullseye.

Again, you are quite welcome. If I can help, I will. If I can't, there are many more here that can and do (in this
particular case, SETEC_Astronomy).

CeaSaR
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jimmy101
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Re: An interval timer with a trap

Post by jimmy101 » Sun Feb 14, 2010 9:46 am

Besides the N&V article there are a couple other pretty simple ways to do a shooting chronometer (a device to measure the time of flight between to detectors). All you really need is a pair of phototransistors (RadioShack has suitable ones for a buck or so) and a laptop with a sound card. There a somewhat rambling description at http://www.inpharmix.com/jps/Jims_chrono.html.

With a bit more work on the electronics, LEDs can also be used as photo detectors.

The sound card setup is a bit marginal for a real rifle with a small bullet moving at say Mach 2 (~2200 FPS, ~1400 MPH) but for slower things it works well.

For a rifle (or canon or ...) and if you just want velocity you can sometime just use a MIC + laptop and bounce the round off a hard target (taking due care to consider where that ricochet is going). The MIC will record the muzzle blast and the sound of the round hitting the target. Easy enough to use something like Audacity to extract the times from the recordings. Along this line there is a small app created by Paintballers to measure muzzle velocities using this method. Google for "SoftChrono" to find a download site.

If you want to trigger a flash unit and/or camera then a Google search for "slave flash trigger" should find some pretty simple circuits that can be modified for what you want. You should be able to find circuits that trigger on both a photo gate and on a sound (such as a projectile hitting a target). For example;
http://xray.bmc.uu.se/markh/cam_trig/ca ... unior.html
http://www.hiviz.com/tools/triggers/makeown.htm

You can also buy a shooting chronometer for about $80. Search For "Chrony F1" for example. Occasionally they can be found for cheap on eBay.

What exactly are you trying to do?

texasclodhopper
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Re: An interval timer with a trap

Post by texasclodhopper » Sun Feb 14, 2010 10:10 am

Jimmy, I wanted to look at that app for the photo detector & amp. I'm going to use at least one for a generic trigger for lots of applications. I'm going to miniaturize that circuitry.

Thanks for the additional information. It's fun chasing this down to a conclusion.

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