Hey all, I’m working on a project to measure the spin of a BB fired from an airsoft gun, where one side of the BB is painted black and the other is left white.
Previously, I used the https://cdn.sparkfun.com/assets/6/5/2/2/2/QRD1114-D.PDF reflective object sensor for this. I made a track of many of them, and hooked the output of each to a microcontroller with very fast ADCs. The BBs pass overhead at around 100 meters per second, and I’m able to see significant dips in the data when they pass overhead.
However, the experiment was difficult to work with because the attached IR LEDs didn’t produce a ton of light, so the BB had to pass very close over the track to be picked up. This is hard across a long track because it risks me destroying the track if I aim too low, and the whole reason the BB spins is to generate lift to counteract gravity, so after a short distance, it would be higher than it started.
So I switched to visible light. I replaced the sensors with the https://www.sparkfun.com/products/9088 mini photocell, and put a hole in the track between each sensor group for a very bright light source. The idea is that with visible light, it’s easy to buy very powerful sources.
However, while I can detect something above the track that’s stationary, it no longer shows a dip in the voltage output from a BB. I suspect that it’s because of a different response time vs. the phototransistor, but the https://cdn.sparkfun.com/datasheets/Sen … -09088.pdf doesn’t specify the response time, only that it has a “quick response”.
Does anybody know what the response time is expected to be for that SEN-09088 photoresistor? And if it’s too slow, does anyone know of a product (ideally from SparkFun) that would work in its place? I expect the BB passes over the sensor for around 1/20 of a millisecond.
