Arduino-Based Optical Tachometer

Step 5: Putting it All Together

The IR LED should be pointed at the IR detector over a gap of a few inches. While you can tape the detector to the table and hold the IR LED in your hand (as I did during testing), this is pretty awkward. What you want to do is to build a makeshift frame that keeps the emitter and detector aligned, but leaves enough space that the motor coil can rotate between them and break the light path with the strip of tape.

I built a KNex frame where the upper arm can slide up and down and used rubber bands to secure the wires that go to the LED and phototransistor, but you can whatever you can find - LEGO, Popsicle sticks, stiff wire, whatever.

You can test to see if the circuit and program is working by downloading the sketch to the Arudino and using your finger to break the light beam between the LED and photodetector. Every time you break the beam, the status LED should toggle on and off. You can turn on the serial monitor in the Arduino software and you should see a "0" being out every second. If you break the beam a few times, the "0" should change to a small number.

If that is working, you are ready to integrate the motor.

Get the motor spinning with the tape on the coil, make sure the detector circuit is working and the serial monitor is on, then slide the motor in between the LED and detector. If everything is working, the RPM of the motor should show up on the serial monitor on the PC.

The best performance I've got so far was around 1200 RPM. Leave comments if you do better and what you did differently!

Comments

[Lenny24]

Hello. Great Instrucrable; I need the kind of Script for an RC-Car Engine-RPM-Meter (OMG, Creepy Word ;))
And i Found out, That you can also Use a Reed Sensor for Measuring. Or an Hall-Sensor. I Tried out Both and  the Hall sensor worked best for me.