how to calculate current from square pulses

[milner]

my device giving output as square pulses.but would like to control current from the range 50uA to 500uA of square pulses.how to calculate it. can someone help me

[milner]

I need to connect my nrf51822 to an electrode. and an electrode is connecting to rat brain.but the square pulses should be controlled. a current of the square pulses should be in the range of 50uA to 500uA. how to calculate the current and voltage from the square pulses