Airgun silencer part 2

This continues from part 1.

I’ve ordered faster phototransistors. I’m now using the following:

The OPL550 has a totem pole TTL output, and the output is high when the phototransistor has light falling on it, thus logic 0, or low pulses as the pellet breaks the light beam…


below we measure the time between the two falling edges as accurately as we can on the scope… 228us

at a distance of 50mm between sensors, that equates to 719fps…


Below one can see how clean a single pulse…

now let’s assume we can measure with a fine enough resolution, we could possibly use the pulse itself as a speed measurement, and maybe both pulses to determine whether the pellet is accelerating or decelerating… 😉


at a pellet length of 6.68mm and a pulse time of 27us, that equates to 811fps.. naturally I don’t think the scope has a great time-base resolution… 😉

Conclusion: MUCH better opto performance… these will be the ones I use..!  The next step will be to feed both opto outputs into an AND gate… and we should have the signal we’re looking for….

…continued on part 3