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From: crean@ny1mm.DEC
Newsgroups: net.analog,net.graphics,net.micro
Subject: Photosensitive device -- suggestions ???
Message-ID: <2478@decwrl.UUCP>
Date: Tue, 4-Jun-85 15:49:32 EDT
Article-I.D.: decwrl.2478
Posted: Tue Jun  4 15:49:32 1985
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I'd like to build a simple device for turning photographs into
raster-scan text files.  (You know -- various characters in each
line/column to approximate various shades of gray.)  The problem
is that I know nothing about light-sensitive devices.  The basic
idea is to replace the printhead on an old DECwriter with such a
device, then feed a photograph into it -- the computer will then
send a series of spaces to advance the head across the surface of
the photo, pausing to sense the grayscale value of each position.

The A/D conversion, computer interfacing, and software aspects
don't seem to present any particular problem.  It's the analog
circuitry that I need help with.

So:   o  How do I choose a device ?
      o  How do I treat it:  Physically -- mounting ???
                             Electrically -- support circuitry ???
      o  Is "aiming" critical -- if so, how do I do it ?
      o  Should I use just a detector, or an emitter/detector
            pair ?  If the latter, how do I power the emitter ?
                      (i.e.:  continuous vs. pulsed)

BTW, the DECwriter I intend to use has minimum pitch settings
of 16.5/inch H x 12/inch V -- so the idea is to sense a sort
of "average" intensity from an area about 1/16" x 1/12".

Also, I recall seeing an article in some computer hardware hacker
magazine which described a project like this one.  Does anyone
else remember seeing it ???  Does anybody remember the name of
the magazine, or the title of the article, or the date of the
issue, or anything like that ???

Thank You,

 Kevin Crean   ( ...!decvax!decwrl!dec-rhea!dec-ny1mm!crean )

 Assoc. Software Specialist
 DIGITAL Equipment Corp.
 200 White Plains Rd.
 Tarrytown, NY  10591

 (914) 684-5721