Motor sub-assembly taken from a broken Canon printer. I've seen several of these opto -tachometers (or position sensors), but I liked this one, especially as it was so easy to test. There are only 4 wires for the sensor which turned out to be +5volts, GND and 2 sensor output wires. If you look carefully you can just see the plastic disc driven by the motor which has a lot of fine black lines on it which interrupt the beam of light in the sensor. The beam is visible rather than infra-red which is handy because you can see it so that means something is working! With the motor running and one sensor connected to a multimeter set to measure frequency, I got a steady 6.3kHz and when a bit of resistance was applied (i.e. a finger and thumb) the speed reduced and the frequency with it. Handily the meter also reads duty cycle (ON/OFF ratio of the pulses) and I got 49.5%; almost 50/50 cycles. Interestingly on the other sensor wire I got... 51.5% as would be expected so I'm guessing t...
