Fan RPM Measurement

Electromania world has come out with a technique to measure rotational speed in RPM for one modified computer 3 pin fan using internal Hall Effect sensor. Hall Effect sensor (HES) works on the principle of interaction of magnetic field with electrons flowing in the conductor and this is the concept used in this project.

This project aims to introduce some of the topics including usage of Interrupts of Arduino boards, interfacing Hall Effect sensor of fan, interfacing and displaying real time information on LCD display and implementing basic logic in programming. Further, there are many ways of measuring speed, IR sensors, photo diode etc.

The computer fans are equipped with internal Hall Effect sensor which can be used to pick up the ticks per revolution of rotor. Moreover, the measurement algorithm may also vary depending upon the required accuracy and response time. Here the fan speed is measured at approx. in 1 sec interval using basic microcontroller interrupt driven algorithm, giving accuracy of few 10s or RPM.

Fan speed setup

Figure 1: Fan RPM Measurement

Generally yellow colored wire is output of HES, in three pin fans with internal Hall Effect sensor. Further, external pull-up resistor of few values is required most of the time, depending on supply voltage but internal pull-up resistor of the Arduino board pins can be used instead of external resistor.

Depending on type of fan and number of magnets attached to rotor, with every rotation of rotor, 1, 2 or 4 ticks are available as output signal from HES. These ticks are picked up to interrupt the Arduino program using “hardware interrupts“. Interruption helps to let the Arduino do its regular job until some signal is received at interrupt pins and enables us to use Arduino to perform other tasks while waiting for signal at interrupt pins.

Here, a RGB LED is used to provide quick idea about speed range, the LCD displays actual speed in RPM and values updated in every second. Materials used in this project are Arduino due board, resistors, PC fan or any other motor with inbuilt Hall Effect sensor, LCD display with 12C interface, power supply depending on the fan or motor capacity and 3 LEDs or single RGB LED, to use as optical indicator of fan RPM range.

Code or sketch is available in the video and also on the github. For reference, visit the following website