Tachometer is a device that counts the revolutions per minute (RPM) of a rotating shaft. This projects describes how to make one that requires no contact with the rotating shaft. The microcontroller used is AT89C51 from Atmel, and the RPM value is displayed on a character LCD.
An IR Tx/Rx pair is used as a proximity sensor. The counted pluses will come from the proximity sensor, when it will detect any reflective element passing infront of it, and thus, will give an output pulse for each and every rotation of the shaft, as show in the picture below.
For circuit diagram and programming, read rest of the project.