VT52s, VT61s lots of DEC and DG keyboards- return trip through Maine, MA, NY, PA, OH, IN to IL

Paul Koning paulkoning at comcast.net
Tue Oct 13 12:32:46 CDT 2015

> On Oct 13, 2015, at 1:22 PM, tony duell <ard at p850ug1.demon.co.uk> wrote:
> The Versatec electrostatic plotters are not the same as the VT52 printer, they are
> yet another process. WIth those the paper passes between a set of electrodes that
> build up a charge image on the paper. I beleive the paper is specially treated to 
> make it more resistive so the charge doesn't leak away too quickly, and there is 
> a clever multiplexing scheme for the electrodes to reduce the number of HV drivers
> needed (IIRC there is around 600V between the electrodes on the 2 sides of the 
> paper.
> The paper then passes over a stream of liquid toner, which is attracted to the charge
> image. The liquid evaporates leaving the toner on the paper. That's it, no further
> processing.

Speaking of Versatec: at University of Illinois, there was a PLATO terminal that had a "Versatec screen printer".  I never understood how that worked.  It smelled like the same electrostatic liquid toner technology.  But how the image got from the terminal to the printer is unclear.  Remember that these were plasma panel displays, where the graphics state exists only inside the gas pixels in the panel.  I wonder if they read out the on/off state of the pixels somehow, but how to do that when there's a 100 volt or so square wave voltage across the panel is not obvious.  I have never seen any documentation of this machine.


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