A small reference of my tachometer project for my Volvo 340. This project uses the raw ignition signal and displays the rpm on the screen. The arduino code has 5 screens (splash, RPM, short time graph, long time graph, highest rpm).
The high (275v) voltage of the ignition signal is clamped (<5v) so it's readable for the ATmega328P. I've used JLCPCB to develop my PCB. All gerber files and BOM is available.
