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RE: HMDs

How about a prism based device. use 3 primary colours (no refraction). If
you project a beam onto prism and then rotate the prism, the beam sweeps
from one side to the other. Once you transition over the corner of the
prism, you should jump back to one side. That only leaves the vertical axis.
If you can change the angle of light entry into the prism, then the prism
should exaggerate the effect. So spin the prism, and then tilt is slightly,
spin it again.. etc.

Sounds passable in theory.

Chris Hardaker

-----Original Message-----
From: Thor Harald Johansen [mailto:]
Sent: Friday, August 06, 1999 12:15 PM
To: Wearable Hardware
Subject: HMDs

Hi!

I've been thinking about HMDs lately.

What's the cheapest possible way of making the smallest possible graphical
display?

I've got this idea, it could be bad, but let's go:

Build some kind of a fast, tiny rotating device, allowing for rotation in
both horizontal and vertical directions, directed by two currents (an X
current, and a Y current). Put a very small, but focused light source on the
front of the device (could be a led with a lens or something). Make
electronics that controls the rotating device to steadidly increase the X
voltage to the maximum, then increase the Y voltage one "step", and decrease
the X voltage down to the minimum again. Repeat this until the max Y voltage
has been reached, then reverse the process by decreasing the Y voltage
instead of increasing it. At the same time as doing this, get the driving
electronics to load values from a buffer, setting the focused light source
to that value (a led has approx 2 volts max, so 0-255 will turn into 0-2
volts). Aim this construction against a partially transparent surface (could
be very thin white paper). Voila! You have a television screen using lights
instead of a catode cannon, and a piece of paper instead of a phosphor
surface. Of course, this way of doing it would cause some vibration, but it
may be worth a try.

Only one problem: What would this rotating device be?

Another display device, that'll cause less vibration:

First, put a reasonably strong light source behind a surface that'll blur
and spread the light. Then get a motor, and make a disk with holes going
towards the center in a spiral. Make an extra hole on the disk, and put a
sensor detecting if something is in the way of an IR light "over" the disk,
so one pulse will be generated for each disk rotation. Put the light behind
the disk. Make some electronics that'll load pixels from a RAM buffer into
the light source as in the previous paragraph, and you've got yourself a
screen.

Another problem: You need to convert from linear coordinates to circular
coordinates.

BTW: If you recognize the disk display, it's actually a quite old invention.
The first TV was made that way. ;)
--
Thor`n

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