Tachometer (RPM) on 8digit 7segment led display with MAX7219 using Arduino

Bibliography:

- https://www.gammon.com.au/forum/?id=11504

- http://www.mikrocontroller.net/attachment/189505/Drehzahlmesser.ino

- Modul de afisare cu 8 cifre LED din 7 segmente fiecare controlate de MAX7219

- my sketch: https://github.com/tehniq3/tachometer-RPM-/blob/master/RPM_intr_nick_gammon_1.ino