Or soundcard method
http://www.seattleairsoft.com/modules/news/article.php?storyid=15&page=0

RP

On 23/07/06, Russell McMahon <apptech@paradise.net.nz> wrote:
> Very simple multi microphone based system with interface to PC
> parallel port.
>
>        http://www.elecdesign.com/Articles/ArticleID/2513/2513.html
>
> Stunningly trivial circuit diagram
>
>        http://www.elecdesign.com/Files/29/2513/Figure_01.gif
>
> Three microphones give you both muzzle velocity and ballistic
> coefficient.
> This is so cheap to do that you could make a bank of, say, 8 and see
> if the bullet baheaved as expected ballistically over a small
> distance.
> eg coning will alter what happens over time. A marginally stable
> bullet may well change it's apparent BC over a short distance.. .
>
>
> ____________
>
> Optical method
>
>        http://www.elecdesign.com/Articles/Index.cfm?AD=1&ArticleID=3597
> .. .
>
> Circuit
>
>        http://www.elecdesign.com/Files/29/3597/Figure_01.gif .. .
>
> They note:
>
>        Optical detection of a projectile whizzing past a given point
> is not always trivial-especially for BBs and other small-caliber air
> gun pellets that may fill only a small fraction (about 1%) of the
> detector's field of view. The logarithmic optical-detection method
> employed here is borrowed from an earlier IFD ("Available-Light
> Phototachometer Simplifies Outdoor Remote Sensing," Electronic Design,
> January 25, 1999) and has a wide dynamic range compatible with
> low-contrast signals in both outdoor and indoor lighting.
>
>
>
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