In order to power the grid of electromagnets via the low current 5V PWM outputs on the Arduino Duemilanove, I had to design a basic drive circuit with the advice of the Electronics department.  It’s really simple: a Darlington stage increases the current output produced by the PWM pinout, this signal in turn is powerful enough to drive the IRF1405 MOSFET which is supplied by a 35V supply.

I modeled the circuit in LTSpice to better understand the operating points: