Im building a laser target. It consists of a box, with a black plexiglass circle in the center of one of its sides, and a larger white circle around it.
The black for the inside shots, and the white for the shots close to being inside.
There will be a camera(and a fresnel lens) to detect shots inside the inner circle, but for the outer circle im relying on light sensors.
The problem is that for a light sensor to work… well, there has to be light, and while a laser has light its way too focused to be measurable when not aiming directly at the light sensor.
To be more precise, aiming directly at the sensor means 50k+ lux(sensor limit), but aiming outside results in less than 4 lux of variation (the smallest unit that the sensor is able to measure when at its fastest timming), which is not enough to measure with confidence.
I tried to use a thin layer of spongy polyethylene, and it does glow and diffuses a good part of the light evenly, but still has a low overall variation. There's still one focused point, and a slight gradient coming from it.
The box is not thick, it should have at most 30cm from the target to the opposite side.
Any material which glows even more than polyethylene when illuminated?
Mirrors and a polyethylene cylinder around the sensor would also work, but it would be a pain to build, and it can send a laser back to someone's eye. And that's not to mention that it would be possible to reflect the shot to the area which the camera evaluates as a valid shot, unless isolated, which would mean at least three light sensors to cover the area around the valid shot area, and … enough pain!
Ideas to diffuse that light? 😉
Best Answer
White paper works well as a diffusor. If you can make the box a couple centimeters thick, then you can place sensors at least 10cm apart and they will easily detect the laser's light. For signal processing purposes you always want to modulate the laser with a couple kHz and use narrowband AC amplifiers to detect the signal of your photodiodes. This will basically eliminate most background signals and give you orders of magnitude more dynamic range on your sensors. If you are detecting with a microcontroller, I would also use a logarithmic amplifier to limit the range of the signal to something that is useful for the controller (i.e. 40dB signal range, at most). The overall electronics circuit won't require more than maybe a quad opamp (one AC preamp x10, a bandpass filter and one opamp for the logarithmic amplifier, which leaves you with one more amp for a second bandpass or more gain, if necessary).