Circuit that can convert current pulses to voltage
You don't want a "frequency to voltage" conversion.  That tends to be tricky, error prone, and generally a hack of a solution.

What you really want is to run the pulses directly into the MCU and measure the frequency directly.  

Here is an app note on exactly how to do that with the AtMega MCU's.  How you actually do it with the Arduino software is something I can't answer.

AVR205: Frequency Measurement Made Easy with Atmel tinyAVR and Atmel megaAVR