Are there any arduino devices that can handle pulse frequency input? For example can it interpret pulses of varying frequency from say a motor speed sensor?
Most (if not all) arduinos can count pulses from an external device and thus calculate the frequency, limited by the clock speed of the arduino and maybe other factors.
Important is that the signal you input into the aduinino is compatible with the particular MPU/board you have (say 5 volt TTL for a Uno). If you use an optcoupler, then you have a good chance of generating a compatible signal.
Maybe give more detail for a more detailed answer.