This speed sensor has an optical sensor that allows you to measure revolution per minute (RPM). It requires an encoder disc to count the number of times the sensor goes low to high or vice versa we can calculate the revolution in a given period of time. It has an analog and digital output.It is commonly used in robotics speed sensing printers and motor drivers. Feature: Main Chip: LM393 Working Voltage: 3.3V to 5V Output Form: digital switch output (0 and 1) Output: Covered output high level; Without sunscreen the output low level PCB Size: 31mm x 14mm Mounting Hole Size: 3mm Slotted Width: 5mm Specification: The DO output interface can be directly connected to a microcontroller IO port if there is a block detection sensor such as the speed of the motor encoder can detect DO modules can be connected to the relay limit switch and other functions it can also with the active buzzer module compose alarm Interface: VCC: Connect the positive 3.3v5v power supply GND: Connect power negative DO: TTL switch signal output AO: This module does not work the module do not have