Hello everybody!
I have built kind of PLC controller which is setting / resetting some signals depending on absolute encoder's position. But I need one more function for my device : speed measuring.
I want to display speed in "Turns per Minute" and I am looking for ideas, how to measure the speed. It is only information, I don't need very good accuracy.
I have one input which can be using for speed measuring. I can put on this input START signal from machine which is repeating only once per rotation of machine's wheel. Minimum speed is about 10 rotations per minute, maximum about 300.
Could anyone help me a little and give the main idea how to do it? I am not looking for ready solution (but why not...?), I want to know your opinion and use your experience.

Regards,
Jacek