The WPSE347 is a LM393 speed sensor module, widely used in motor speed detection, pulse count, position control, etc. The sensor is very easy to operate: To measure the speed of a motor, make sure the motor has a disk with holes. Each hole should be equally spaced on the disk. Every time the sensor sees a hole, it creates a digital pulse on the D0 pin. This pulse goes from 0V to 5V and is a digital TTL signal. If you capture this pulse on a development board and calculate the time between the two pulses, you can determine the revolutions speed: (time between pulses X 60)/number of holes. For example, if you have one hole in the disk and the time between two pulses is 3 seconds, you have a revolutions speed of 3*60 = 180 rpm. If you have 2 holes in the disk, you have a revolutions speed