How to read rpm with MCU through 48v input pulses

Thread Starter


Joined Jun 12, 2019
Hi, I need to read the motor speed with my raspberry pi. The motor provides an output of 48V and 5mA max, 1 pulse per revolution.

I can do it with a voltage divider but I guess that the waste of energy is high. How could I down that voltage to 3.3v in a simple/efficient way?

Thanks in advance!


Joined Jun 4, 2014
I would choose a 47k resistor and a 3V zener. This would draw 1mA from the sensor output and the power 'wasted' in the resistor would be 43mW.