The most conventional unit of measuring the speed of a motor is RPM (revolutions per minute). The device used to measure RPM is called a tachometer. The tachometer is an RPM counter which counts the no. of rotation per minute. There are two types of tachometers one mechanical and another one digital. We have designed an Arduino-based digital tachometer using an IR sensor module to detect objects to count the rotation of any rotating body. IR transmitter transmits IR rays which reflect back to the IR receiver and then IR Module generates an output or pulse which is detected by the Arduino controller when we press the start button.
This project uses the fact that the IR sensor also reads the low number of IR radiations given off by the red laser. However when a blue/green laser is used these IR radiations get very less and the analog read voltage drops down to approx. 0. When a blade of the fan attached to the motor comes in the path of the laser beam it blocks up the pathway and the reading drops to 0. The fan blade keeps on spinning and its position keeps on changing with a constant supply of power and a constant change of path occurs. When the path becomes clear again, the laser pointer beam strikes the sensor again.
The output voltage of a proximity sensor is taken as analog input by the Arduino. It then calibrates the voltage in terms of RPM to measure the speed. The output voltage of the sensor is displayed in the 7-segment display as well as on a computer screen. The computer screen also displays the measured RPM. A multimeter is also used to measure the output voltage for verification. The actual RPM of the motor is also measured with a tachometer to validate the speed measured by the system.