Mark Willis wrote:

> Should be easy enough to add a nice grey coded optical rotary encoder,
> wouldn't that be easier?

  Only if you have a (mechanical) engineering workshop!

  I think the question equates to interfacing a LVDT, which I am sure is
in the archives.

  I'd think of generating three sine phases using maybe PWM or (less
phase shift) R-2R networks, amplifying using a couple of stereo amps (or
even one stereo amp using a transform) to drive all the 3-phase windings
of the synchros, then resolving each synchro output with a comparator
and matching zero-crossings with the generated phases.
--
  Cheers,
        Paul B.