I am designing a detector to count the passing of spokes on small wheels.
My plan is to use a light source like an LED and a receiver like a photo-diode to create a sort of break beam setup.
The signal will be sent through an amplifier with filtering, to the mic input of a PC to be used for measuring the passes per hour of the spoke of the wheel.
I am having a hard time finding the right product combination and circuit to make this happen.
The wheels are suspended so the spoke casts a shadow on the collector to trigger the signal as the wheel rotates / oscillates. The wheels range in sizes from 8mm to 20mm and have spokes from 1mm to 2.5mm wide.
This should be a very simple device to build and I have made some but it is hard to get both a signal that has enough gain and low noise with the sensitivity to accurately trigger. The make pulse would be around 30k per hour so the wheel is not moving very fast.