[calcmogul]

Rather than using a DigitalInput, I recommend using a Counter instead. It counts up all of the pulses coming from a DIO for you in the FPGA.

In C++, the RPM can be found with "60.0/GetPeriod()" where GetPeriod() is a function in the Counter class which returns the time between pulses in seconds. If there is more than one pulse per revolution, you would use "60.0/(pulsesPerRev * GetPeriod())".

That's the general idea, but the implementation varies depending on which language you are using.