Here is a motor speed sensor module, the major goal is to check the rate of an electric motor. The module can be used in association with a microcontroller for motor speed detection, pulse count, ...
With time on my hands, I decided to try a technique that I noticed first in a L200 voltage regulator data sheet. It is fig 25 in STM’s ‘A Designer’s guide to the L200 voltage regulator’ (ST webpage ...