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I'm trying to create an ammo counter for an airsoft gun. I'm going to control it with an attiny series MCU and i want to detect the projectiles exiting the barrel using a light based sensor. Now that's the question:

Which method of detection is the best for such application? A photodiode, a phototransistor or other, perhaps laser based sensors?

The projectile is 6mm in diameter and at 115 m/s after exiting the barrel which means that the sensor will have around 70μs to detect it.

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    \$\begingroup\$ Can you say something about how it would be mechanically mounted? At the exit of the barrel? I think it is important to mention if ambient light will be reaching the sensor or if it could be in the dark, protected from ambient light. \$\endgroup\$
    – payala
    Apr 10, 2016 at 21:11
  • \$\begingroup\$ I have 3D printed a mount for a photodiode + led couple which i tried using before but the resutls weren't so great (the circuit couldn't detect such fast moving object) so i want to rebuild the circuit. It had no trouble with ambient light back then. \$\endgroup\$
    – DELTA12
    Apr 10, 2016 at 21:13
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    \$\begingroup\$ Yes but direct projectile detection is the most reliable way since it can as well find out whether the weapon did actually fired or just shot blank. \$\endgroup\$
    – DELTA12
    Apr 10, 2016 at 21:19
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    \$\begingroup\$ Hey we're talking about an airsoft gun not an actual firearm. There's not muzzeflash explosions or vapors. The bulled is fired by compressed air nothing more. \$\endgroup\$
    – DELTA12
    Apr 10, 2016 at 21:26
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    \$\begingroup\$ Can you post a schematic of the circuit you used last time?, maybe you already had an interesting approach, and just need some running for the speed. \$\endgroup\$
    – payala
    Apr 10, 2016 at 21:50

1 Answer 1

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You can try a Photo Interrupter. Such self contained emitter / detector devices are common and can be found in a variety of configurations. This one has a 10mm opening (ball is 6mm wide) and a max low to high response of 9us + a max high to low of 15us. Assuming this represents the shortest (worst case) possible detectable obstruction of 24us. Which, if correct, is << 70us.

https://www.sparkfun.com/datasheets/Components/GP1A57HRJ00F.pdf

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