Great link.  Having read the book excerpt, I find:

1. The damping coil is used as a sensor. It is not driven.  The damping coi=
l
outputs what amounts to velocity information.  This can be used as feedback
to ramp the drive up and down to produce "smooth operation".  If you don't
care about smooth operation, you can probably ignore this part of the
device.

2. The driving coil is effectively an analog motor.  Current is applied in
either direction to open or close the iris, until the circuit is in
balance.  Motor position is balanced against light reported by the luminanc=
e
signal (which is posing here as the light sensor).    The inductance and
mass of the motor would probably filter PWM pulses appropriately, but it ma=
y
make more sense just to take the PWM drive and convert back to an analog
signal.

PWM by itself won't work because the digital signal can't reverse polarity.
But you could build an H-bridge and use a PIC that has the motor control
peripheral.

Barry
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