I need a robust and reliable way of taking a RPM signal from the W terminal of a standard automotive alternator. Most of the time the signal will come from a 12V alternator but there is a requirement for it to be compatible with 24V (28v when charging).
So my questions are:
Is the noise in the last picture a problem, if so how do I get rid of it?
Is this signal (with or without the noise) suitable and reliable to feed into a MCU to read RPM?
How can I improve the circuit to make it reliable and robust for production grade products?
Starting from scratch what would be the most reliable circuit?