Open Source Non-contact Tachometer Calibrator

Initially, I thought of using the usual micros() to set the output for the LED. Soon, I found out that micros() is not very accurate. 4us resolution and too much overhead for producing stable frequency. Even though I replaced the micros() with another library , it seems that software-based waveform generation is not too reliable.

Then I discovered PJRC's FrequencyTimer2 library. A little less flexible, since it only allow you to output waveform on pin 11. I was prototyping this on a perfboard and with Arduino's standard digital pin spacing I need to drill a set of new holes, so I'm moving to Arduino Nano and custom PCB.

By the time of writing, the project is undergoing its first beta phase. I noticed several room for improvement here:

• Change the LED to a red one. White LED often contain phosphor on top of the silicon substrate to make it emit light with spectrum what our eyes see as white. This phosphor layer will glow for a short time after current removed from the silicon ("afterglow"), potentially affecting accuracy of the rotation simulation. This effect does not appear on the plain red LED.