Re: EDM wire tensioning

The electronics is not a problem, I can use a triangle wave compared
with a reference generated from the op-amp to produce the PWM if I
decide against just driving the motor from a transister linearly.

I certainly like the idea of the shutter (tapered or otherwise) to
produce a signal. I could possibly modifiy a slotted opto sensor if I
can find the type with an unprocessed output.

I also found some reflective photo transisters that will produce a
fairly linear signal over a small range as an object gets closer or
further from them. They consist of an IR led and phototransister
positioned next to each other, the non focused type would seem to be
suitable. They are very cheap so a comparison might be worth a shot.

thanks again

Graham