I just tested my laser and sensor combination, with success this time!
To explain why, I will quickly describe both my setups:
- In my original setup, I was really just pointing the laser at the film, saw that it was neither blocked nor reflected and gave up. (Not very thorough, I realise … I had other things to do but really wanted to test the laser idea
) - So no, my new setup is a bit more thorough. I put the film gate from an old Bolex projector on a third hand tool. Then, I aligned my laser and the sensor using the same third hand tool, making sure the sensor does detect the laser through the claw-slots in the film gate. Next, I put the film through the gate, and *drum roll* the sensor easily detects the sprocket holes.
For all experiments the sensor was connected to digital pin 3 on an Arduino Uno, with both the sensor and the laser being connected to the 5V supply of the Arduino. The film used for testing was Kodachrome 40 (positive with black celluloid). Sensor and laser are the ones linked above and can be found just about anywhere that sells accessories for Arduino. I paid 4€ for the laser and 8€ for six sensors, but I have seen them offered from China for mere cents.
I will have to check how robust this is later down the line, but it seems to generally work quite well.