This contactless tachometer project is based on an ATMEGA48 AVR micro controller, and is able to measure very high RPMs, as well as very low ones. It is based on an IR (Infra Red) opto-couple to detect shaft rotation.
As you can see in the short video above, the sensor is located at the back, next to a red narrow-beam LED that glows to help you point the invisible IR sensor beam to the target shaft.
The project site has code and schematics, or you can buy a kit for 29 euros.
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