Fuelled by insatiable curiosity
The first encounter I had with a design that used a microcontroller was a contactless tachometer. At the time, I wanted to know the RPM of my RC aeroplane engines for various reasons. After searching, I came across a tachometer design by Philip Sun that seemed easy enought to build. For some reason or another, I couldn't quite get mine going. Odds are that I had incorrectly programmed the PIC16F84 or that I had incorrectly soldered up the circuit, or both!
This project was shelved for a while, but then I started it up again as I thought it would be interesting to log the RPM of the propeller during the flight of my aeroplanes. Again, I started off by looked at existing designs, but decided to make my own analog and filtering circuitry. Since I only wanted to record the RPM rather than display it, my design did not require a LCD or a seven segment display. I could have added onboard logging on the tachometer module, but since I already had another board logging data other sensors, it was not required.
The schematic of the resulting design: