Introduction: Arduino Based Portable Digital Tachometer

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A tachometer is an instrument that comes in handy for all electrical engineers and DIYers who love to tinker around with motors and other rotating objects. It is a device that measures the speed of rotating objects such as a motor or a crankshaft in terms of the revolutions it makes in a minute, i.e. RPM. Today we’re going to make an easy-to-make and cost-effective digital tachometer for ourselves! We’re going to make this tachometer with the help of evive, an IR sensor, jumper wires, and some DIYing!

So, what are you waiting for? Let’s begin!

Step 1: Required Components


  • evive
  • IR Sensor
  • Chassis
  • Jumper Cable
  • Nuts and Bolts


  • Arduino IDE

All the above Hardware can be found into the evive Starter Kit.

Step 2: Making of the Tachometer

We are going to make a simple and handy yet accurate Tachometer.

Take an acrylic base plate with some holes in it, to fix the components.

I have fixed evive (Arduino Based Embedded Platform) onto the base plate using some bolts and nuts.

We are going to use the IR Sensor for making the tachometer.

Take the sensor and fix it onto the front hole of evive.

We have attached the components onto the base plate to keep the assembly steady. You can eliminate the base plate too.

Step 3: Connections

Once I have made the assembly, I'll start connecting the pins of IR Sensor to evive:

  • VCC: 5V of evive
  • GND: GND of evive
  • OUT: Digital pin 2 of evive

Once done with the connection, the only this left is uploading the code into our system. But before that, we will understand the logic behind the tachometer first.

Step 4: Logic

We know that when the shaft rotates, it takes some time to come back to the point from where it started. The IR sensor that we have connected to evive, measures how much time it takes to complete one revolution. How?

I have attached a thin white strip onto the wheel. Thus, when the shaft starts rotating, the strip passes in front of the IR Sensor once every rotation. The number of times the strip passes by the sensor will be the speed of the wheel. To get the speed in terms of revolutions per second, multiply the value by 60. And display the final value onto the TFT Screen.

Step 5: Code

Upload the following Arduino Code to evive.

The .ino file is also given below. You can download the code directly.

Step 6: Find the Gear Ratio

I have experimented the tachometer using the Gear Blix. Whereupon changing the gears, the rpm of the wheel changes.

Thus, when the assembly has two or more gear and the rpm of one of the gear cannot be found. We are going to use the below formula for the same.

S1 * T1 = S2 * T2

Once you know the rpm of any gear using tachometer, you can easily find the number of teeth in both the gears. Thus, the rpm of the other gear can be found.

Hence, Gear Ratio = T1/T2 = S2/S1.
In my case, S1 = 164 for gear with less number of teeth.
S2 = 540 for the gear with more number of teeth.

Hence, Gear Raito = 540/164 = 3.19 (Around 3).

Step 7: Conclusion

With this, your DIY digital tachometer is all set to measure your motors’ speed.