SILLY DISPLAYS

I've had various ideas for displays over the years. Some are 
vaguely practical, so I'll reserve them in case I do build one and 
want to describe it on my non-anonymous website. So these are my 
silly displays - of little practical value and requiring much 
effort to create, but with a novelty that might find value amongst 
the public (either as a one-off, or some sort of product) if 
someone was in a position to build and publicise them.

 SHADOW DOT DISPLAY

I won't deny it, this idea is the product of me standing in a dark 
room playing with a bright torch. The observation at the heart of 
the idea is that with a opaque ball suspended in front of a light 
surface that then points at a screen, the angle from which the 
light shines on the ball determines the position of the round 
shadow on the screen.

To create a display you need the shadow of the ball (the "dot") to 
appear to the eye in multiple places on the screen at once, to form 
an image.

The screen would need to have some sort of phosphorescent coating 
that would permit (over multiple "exposures" of the projected 
image) the areas less exposed to light due to their coverage by the 
shadow of the ball, to be visible as areas emitting less light when 
the projector light is turned off. The idea is that the average 
light absorbed in shadowed areas over the time required for the 
scanning of the projector beam to complete, is less than those 
areas never behind the shadow. The light source may need to be 
switched on/off with a particular duty cycle during projection to 
ensure that shadowed areas do not reach saturation of their light 
absorbtion capability before scanning completes. Projection with 
light wavelengths invisible to the eye, IR, UV, or even X-Ray, 
could allow the display on the screen to be observed while the 
projector continuously operates, rather than having to observe the 
screen only after scanning is complete and the projection light it 
turned off. Alternatively, the image could be seen through a 
shutter that permits viewing only during the off part of the 
projector light's duty cycle.

For an X-Y vector display, the angle of the projector light could 
be moved directly to trace out lines as with a laser projector. 
Depending of the size of the projector's light beam, additional 
scanning without a shadow of areas not meant to be exposed, but not 
illuminated by light surrounding any projected dot, may be required.

For a raster display, the angle of the projector light mechanism 
could be scanned in a repeating pattern, but with the light only 
turned on where the corresponding location of the dot forms a point 
(black pixel) in the image. Again, additional exposure without a 
dot may be required if not all areas of the screen are exposed due 
to the limited number or position of the dots, and the limited 
width of the projector light beam.

Additional effects could be possible by replacing the opaque ball 
with glass structure exhibiting a lens effect.

Issues:

The exposure of areas surrounding a dot would have to be carefully 
controlled where other nearby dots are at risk of being saturated. 
The width of the light beam, as well as the exposure timing and, 
the qualities of the phosphorescent coating, would be the key means 
of controlling this. A limit to the total area that can be 
displayed under visible shadow would naturally be reached due to 
exposure of previously shadowed areas on each exposure required per 
frame.

The update rate would obviously be very slow, though ideally the 
transition between frames would fade in/out in a naturalistic 
mannor.

 WHITEBOARD DISPLAY

This is simple: An X-Y plotter is designed to write on a whiteboard 
(nothing that unusual, 3D printable designs for such devices are 
described on thingiverse.com), and also to erase parts previously 
drawn. It fills an area, a camera takes a pictures, it erases and 
redraws parts of the whiteboard, another picture is taken. You end 
up with a time-lapse animation of things being drawn on the 
whiteboard.

Of course that's already been done by humans (or at least those 
vastly more accurate at drawing things than I am) drawing on 
whiteboards, I'm pretty sure. What I really want is to create some 
sort of whiteboard Matrix effect where maybe the camera moves up 
the board so that the symbols look like they're moving down the 
screen, while the X-Y machine redraws them randomly between frames. 
I guess you could probably do that by hand too, but the machine 
would be less frustrating for someone as artless as me.

 DOMINO TV

Have a large frame with a board behind. The frame forms rows on 
which dominos are positioned, each in front of hole in the board. 
The holes are so positioned that when one domino falls, the hole is 
uncovered and a light source shining from behind can be seen. But 
when a domino on a row behind the front falls, it block s the path 
of the light again.

The falling of the dominos, as well as their resetting in an 
upright posistion, is mechanically controlled (maybe using 
electromagnets?). A computer controls the mechanism, and the 
sequence of falling dominos esposes light in a pattern that 
projects a raster image onto a screen.

Multiple rows permit lights to be turned on and off again in rapid 
succession, preferably so arranged that the time for the first 
domino to be stood up again automatically, comes within one frame's 
duration of the domino in the last row falling after a light is 
alternately turned on/off on every frame (the worst case).

The sound could be quite interesting too, maybe also able to be 
used as a sort of musical instrument.

 SIMPLIFIED VOLUMETRIC HOLOGRAPHIC DISPLAY

A vertical shaft is spun, along which are vertically strung strands 
of wire on sprung, or otherwise stretchy, mounts at both ends (top 
and bottom). At the middle of each length of wire is mounted an RGB 
LED and possibly some additional weight. As the shaft spins faster, 
the LEDs are pulled outwards from the shaft, permited by the 
flexible moutings of their connecting wires.

The speed of the shaft alternates rapidly fast/slow, completing a 
cycle of fastest-slowest within the duration of each frame. 
Individual LEDs are lit at different distances away from the 
central shaft, as well as at different points in their circular 
trajectory, so as to form a volumetric image. Only one LED is 
required for each pixel of vertical resolution, while horizontal 
resolution is determined only be the accuracy and speed of the 
circuitry controlling whether the LEDs are turned on or off. 
Electrically then, this is simpler than other LED-based volumetric 
display designs that rely on multiple layers of LEDs mounted in 
fixed positions on spinning surfaces.

The variation in speed (slow to fast) during each frame could be 
controlled by a cam system, and driven from a stepper motor for 
accurate control and synchronisation of the overall speed / frame 
rate.

Alternative to the LEDs: Fibre-optics fed out of the shaft, pulled 
outwards as it spins like a straight bit of wire being spun. 
Wouldn't maintain a fixed vertical location though.

 Issues:

The speed required for the shaft to reach in order for the LEDs to 
cover a reasonable horizontal resolution at numerous depth levels 
would be very high. A rough calculation for 24fps and ten depth 
levels suggested a speed of around 14,000RPM. Perhaps there are 
solutions that could reduce this required speed, or make it easier 
to control?

 Derivative Idea:

For the really sci-fi: Ultrasonically levitated tiny LEDs 
controlled and powered by induction and/or radio.

- The Free Thinker, 2020.