Looks great! I’m thrilled to see someone building test rigs and trying out new sensors. It really makes me happy. You have a great setup!
I have done a few experiments myself with the photo-interrupter and can share some of my findings. Please don’t read these as criticisms, rather just sharing what I experienced in my own trials.
it works great until you have clear film. The light source in the interrupter can be seen through clear celluloid very easily and renders the sensor unreliable. But if you’re sticking to black celluloid, it’s a great option!
Due to my findings with #1, I tried a reflective sensor instead and it worked well.
Although the reflective sensor worked better, I still had trouble if the film’s perfs were damaged. I’ve considered trying to use multiple sensors and averaging the values so that a missing perf does not throw off the machine completely but have no implemented it yet. Instead, I’m going to try using computer vision to detect frames, thereby bypassing the need for additional circuitry.
@VitalSparks has propsed an interesting system that could work with just one sensor (reflective/interrupter, etc). It relies on a a concept called Phase-Locked Loops. It would average the rate of perfs detected and use that as a “pulse” signal to the machine to capture frames. It’s a great idea and I look forward to trying it with the reflection sensor some day soon.