Measure RPM – DIY portable digital tachometer

This Instructable will show you how to make a Portable Digital Optical Tachometer using an Arduino Uno. This project is inspired from This instructable and is an enhanced version of it with an LCD display and a modified code.

Instead of a slotted sensor , it has a reflection based sensor. So :

1. You don’t have to worry about the thickness of the rotor

2. The number of blades won’t change your readings

3. It can also read the RPM of drum style rotors which slotted sensor can’t

What is a tachometer ?

A tachometer is a device used to measure the RPM or Revolutions Per Minute of any rotating body. Tachometers can be contact based or non-contact ones. The non-contact or contact-less optical tachometers usually use laser or Infrared beam to monitor the rotation of any body. This is done by calculating time taken for one rotation.

Measure RPM – DIY portable digital tachometer

  • It can measure RPM over 20k
  • Sensor range extends upto 7~8 cm
  • Displays Maximum RPM when left Idle
  • Automatically toggles modes from “Idle” to “reading”
  • Can be adjusted to match the ambient lighting conditions
  • It is comparatively cheap and easy to build
  • Can work without an LCD
  • Programmable and supports customization
  • Connect an SD card to the Arduino to keep logs

Step 1: Part List :

  • Arduino
  • Resistors – 33k , 270 ohm , 10k potentiometer
  • LED – blue
  • IR LED and Photodiode
  • 16 x 2 LCD
  • 74HC595 shift Register
  • Ribbon cable ( 3 wire )
  • Perfboard and headers
Tools and Hardware
  • Soldering Iron
  • Solder
  • Pins
  • Screws
  • Motors and DC fan

Step 2: Build the sensor

For the sensor you’ll need an IR LED and a Photodiode.

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1. Start by sanding the LED and photodiode to make it flat ( do not sand it too much or you’ll destroy it ).

2. Then fold a strip of paper sheet as shown. Make two such Structures so that the LED and Photodiode fit tightly into it. Joint these together by glue and paint them black.

3. Insert your LED and Photodiode in them in such a way that the positive ( longer ) lead of the LED is right above the shorter lead of the photodiode.

4. Glue them into the cover using superglue and solder the positive ( longer ) lead of the LED to the shorter lead of the photodiode.

5. Solder the 3 wire ribbon cable to the remaining leads

In my case :

1. Orange wire –> LED’s positive pin and photodiode’s shorter lead

2. Yellow wire –> photodiode’s longer lead

3. Green Wire –> LED’s ground pin

You’re ready to make the board >>


For more detail: Measure RPM – DIY portable digital tachometer

This Post / Project can also be found using search terms:

  • Diy digital contactless tachometer
  • how to make DIY LED Tachometer
  • arduino uno based digital tachometer electronics project
  • contactless tachometer working using arduino pdf

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