My project is a home made reliable tachometer that is easy to make. I needed to build a tachometer to measure the speed of a DC motor, I could not find a reliable way of building a tachometer. I tried many ways to build a reliable tachometer until I succeeded.

Speed and Spin: The Digital Tachometer

How fast is that motor spinning? The Easy Peasy Tachometer is a contactless measurement tool that calculates Revolutions Per Minute (RPM). It's an indispensable tool for robotics builders, RC car racers, and drone enthusiasts.

The Principle of Interruption

1. The Marker: You place a single piece of white, reflective tape on the edge of the black wheel or fan blade you want to measure.
2. The Sensor: An IR Obstacle Sensor is pointed at the spinning object. It "sees" the white tape only once per full rotation, creating a digital HIGH pulse.
3. The Hardware Interrupt: Measuring high-speed pulses using digitalRead() is too slow. Instead, the Arduino uses a Hardware Interrupt (attachInterrupt()) which forces the processor to stop everything and count the pulse the exact microsecond it happens.

The RPM Math

The code counts how many pulses occur in exactly one second. It then multiplies that number by 60 to find the RPM. If it saw 50 pulses in one second, the motor is spinning at 3,000 RPM!

Hardware Config

• Arduino Uno/Nano: The high-speed counter.
• IR Reflective Sensor Module (TCRT5000): Very precise short-range sensor.
• 16x2 LCD Display: To display the exact RPM.
• A Motor/Fan: To act as the test subject.

This project is a masterclass in Arduino Interrupts, a crucial concept for any project that depends on precise, high-speed timing.