How To Make A Laser Camera Trigger For Under $2

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Shooting a bullet in mid air requires a special type of detector to ‘catch’ the bullet in mid air. Usually, a special sensor called a ‘gate sensor’ is used. The trick is a gate sensor is that it can calculate the speed of the bullet and ‘nail’ the shot at the right time. Those are not trivial to build.

This is why I was pleasantly surprised when I got this tutorial from Matt Kane who managed to build a bullet catching circuit for under $2.

Matt used a phototransistor along with a red laser to build cheapass bullet detector with the entire cost of the build being under $2:

done

First up is the laser itself. The main decision here is visible or infrared. Using a visible laser has the major drawback of showing up in your photos, but it has several benefits that outweigh that. First, they’re cheap and easy to buy. Second, if you’ve ever tried to align an infrared laser then you’ll appreciate being able to see the beam. Finally, visible lasers are a lot safer. You could accidentally shine an infrared laser into your eye without triggering your blink reflex, which is a recipe for toasted retinas…

The final bill of materials. Prices via Octopart.

  • TRS1: 3.5mm jack socket. Switchcraft 35RAPC4BHN2. $0.88 from Arrow.
  • Q1: Phototransistor. Vishay TEPT4400. $0.25 from Avnet
  • U1: Optocoupler. Vishay 4N35. $0.30 from Allied
  • R1: Resistor 68Ω
  • R2: Resistor 4.7KΩ

Total price $1.44 (plus a few pennies for the resistors)

This works quite well and Matt did mange to catch a few bullets mid flight.

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Head over to vela.io to read the entire tutorial.