Voice coil movement

[ollie1400]

The DAC can be replaced the by fancy 16-bit DAC used on the piezo board.
For the focus coil, the voltage summer inputs should be two channels of the dac, but the "weight" of each of the channels should not be equal.

e.g. channel A and B are summed to drive the focus coil. But the resistors for channel A and B are chosen such that A has unity gain, but B has less than unity gain. So the output of the summer is something like (-A - 0.01*B). This way we can have all digital coarse and fine control over the voice coil.

(same for the tracking coil)

[ollie1400]

Probably not necessary ikf we are using the 16bit DAC: the 16bit DAC gives us such fine control over the track/focus position as is.