John Ferrell writes:
> I can think of a few ways that may be possible to construct a mechanical
> matrix of pins by combining current technologies with very old
> mechanical technology.
> What would you consider a minimum dot mechanical array?

	There are a couple of schools of thought reflected in
the designs of refreshable Braille displays that are
commercially available. The more common ones have one line of
maybe 40 or so character positions called cells. Each cell
contains up to 6 dots, 2 columns of 3 in each cell.

	When you reach the end of the line, you hit a button and
a new line of Braille pops up so one's fingers keep going back
over the same cells but new text appears.

	Even those minimal displays are a couple of thousand
Dollars and I believe most of them use piezoelectric reeds. They
work well but are expensive to repair and do not pass the rough
handling test very well.

	The other school of thought is to create a sort of
tactile screen that might have several thousand pins on it to
render not only Braille but raised line drawings that one can
examine with several fingers at one time such as a map or some
sort of diagram.

	Again, since every dot is some sort of electromechanical
transducer, things get very expensive and precise.

	I seem to recall hearing someone say that such a display
might sell for ten-thousand US Dollars if such things were even
mass-produced.

	I remember reading about some company who tried memory
metal pins and heat to raise and lower their display pins but it
must not have been anything revolutionary because I never heard
anything else about it.

	Since one's fingers can only be in one place at a time,
there have been attempts to make displays in which your hand
fits in to a receptacle that moves like a mouse. the electronics
follow one's hand movements and a matrix of several pins under
one's fingers activates so you get the experience of running
your hand over a tactile surface.

	There are a number of people trying really clever things
but nobody has made it cheaply yet.

	I use no electronic Braille at all but do use the
old-fashioned mechanical methods of what is called a slate and
stylus and a device called a Braille writer which is a bit like
a typewriter but with only 6 keys. I tend to write pin-outs for
IC's on Braille pages and keep them in notebooks and use speech
to read the screen on the computer. A Braille display is in that
nice to have, but not that much more necessary category. I am
sure everybody can think of things like that in your own life
that you could afford if you had to, but they are not essential
to function.

	I would have an electronic Braille display if they ever
got down to somewhere near the cost of a video monitor but they
have a long way to go at this point.

Martin
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