Reply to post: Re: Projection displays

A steam punk VDU ?

John Smith 19 Gold badge

Re: Projection displays

"There's a whole area of projection displays where you have a little wheel containing the symbols and project them into a back-projection screen."

You've half described the core of a photo typesetter, the sort of machine that NROFF & TROFF were written to drive.

Basically the film wheels (there were other architectures) were what we'd today call the font ROM, with an inner and outer ring for lower and upper case characters.

The difference was a single optical path and the stepping across the output (the film for the plate) being optical.

With some work this would illustrate the different trade offs in design when you shift from electronic to opto/mechanical.

Instead of a disk per pixel you could have a smaller number with separate drives and 2 postion mirrors. Effectively if the disks would write every copy of a letter (EG all the T's) across the screen, then all occurrences of the next character on the line until you ran out of disk, by which time the 1st disk had moved to the next Nth unique character on the line. 2 position mirrors should move much faster (and be easier on tolerances) than multi-position systems.

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