# Feasibility of a purely mechanical grayscale “computer monitor”

Based on a previous question asking about mechanical computing (Babbage engines, etc.) I wondered how a steampunk story could present the concept of a modern computer monitor in a steam-driven mechanical world.

Background: While pondering the problem of shrinking or otherwise utilizing mechanical computers, I wondered if their most limiting attribute wouldn't be the display monitor. You could meet the basic expectations of suspension-of-disbelief with a pocket-watch sized computer (the small watch gears, densely packed and spring driven, whirring away inside. Let's not worry about heat.). But what would I be looking at?

When my eyes were younger, I could comfortably read 6-point Times New Roman text. Printing a wheel with minimum inter-character spacing having 26 letters, 10 numbers, and maybe 10 punctuation marks (including the space), means a wheel with 46 minimally-spaced characters. The diameter of the wheel would limit actual character spacing on the "display" (the space between the characters I read would be equal to the diameter of the wheel). I could reduce that by half if I'm willing to live with letters that jump up and down, allowing me to interdigitate the wheels.

But, in the end, there's simply no efficient way to display text in this manner. I could use something like the old 1970s-era bedside clocks that flipped panels. But 46 characters would require 23 panels, which feels mechanically yucky (and so very 1970s...).

Idea: I propose for a steampunk universe a very small cylinder, it's height equal to its diameter. The cylinder is painted in five1 shades of white (creating a spectrum from white to black). Kinda like this:

The mechanics would spin this sucker around at a thousand miles per hour, pausing briefly whenever a color must be displayed. My pocket watch may have a "display" of 30x30 small spindles, allowing text to appear to scroll across the screen.2

Clarification: in pixelated displays, everything is a graphic image. True, in the early days of computing dedicated hardware converted the concept of the letter "A" into the picture of the letter "A," but the distinction is one of advancement, not discovery. If the make-or-break point for the believably of the idea is moving pictures and not simply scrolling text, moving pictures are an easily dispensed with concept.

Due to the spinning, the background color of the "monitor" would be the average of the colors on the spindle (which argues against using an odd number of colors) or 50% black.3

Theoretically, the cylinder can be made of a small enough diameter to produce a reasonably smooth, if rough to look at (you'll be wishing for that 8-color TRS-80) pixel display.

Clarification: using a modern reference for pocket watch sizes, the largest watch is about 16mm or 2.3 inches. Accounting for the glass size, let's assume 1.5 inches with a 30x30 pixel display for 20 dpi. Technically, the letter "H" could be made 4 pixels wide (including white space for the next letter) and 3 pixels high, but it's not the most complicated letter. Ignoring whether or not the display could believably scale text, let's assume 8-pixel-tall letters in three rows separated by some pixels for legibility. Remember, however, that as a pixelated display, it's only limited by the technology driving it. This question is more about the believably of the display than it is whether or not you can make a purely mechanical graphics card.

Ignorance:

• Ignore the fact that 99% of the mechanics in a pocket watch and far too much of a "table top" mechanical computer would be given over to interpreting and processing display information and the control of the display.4

• Ignore the fact that such a solution would last a very short time before breaking.

• Ignore the fact that you'd need ear muffs to (literally) muffle the sound.

• Ignore the fact that the gearing itself may take too much space to permit a comfortably dense display.

• Ignore the size of the spring required to drive this. At the moment, it's being stored in an attached pocket universe and you'd need a modern power drill to wind it up.

Question: For a steampunk story, would the presented display appear too modern, out of place, to too mechanically unsound — or would it fit neatly into the "modern conveniences in a steam-driven society" that is the steampunk world?

Clarification: If you're familiar with the American TV show, The Wild, Wild West (the original TV show, not the horrible movie), then imagine Artemus Gordon flipping this watch open to help Jim West save the day with some critical piece of info from Washington D.C.

1Frankly, you could paint 256 colors. The problem is that you need a wide enough mark on the cylinder to be visually discernible during use while keeping the diameter of the cylinder to an absolute minimum for maximum "screen resolution." I'm having trouble convincing myself that even 8 colors would work. 5 might be a stretch.

2Part of my inspiration was an episode of the Murdoch Mysteries that used grayscale to transmit a photograph of a mystery woman to the constabulary. If only they had this device....

3You could change the behavior to "park" on white or black and only "spin" to the color that's needed in any given moment, but that's a lot harder than "pausing" while spinning. Ultra-high-speed printers in the 70s and 80s used a drum filed with spirals of characters that constantly spun with hammers that struck the paper against the drum to print. It's fast and efficient — but not quiet.

4If you don't believe this, please take the time to look up the processing requirements to convert "computer-speak" (electronically: binary) into the beautiful letters and pictures you see on your monitors today. The actual electronics involved in that process is substantial. Doing it mechanically may be DaVinci-esque and cool — but I'd hate to be the one to design and build it.

• It's not the same question, but some of the discussion in answers to my old question How could I have modern computers without GUIs? may be of interest. – a CVn Jan 20 at 18:09
• @aCVn, There's a trove of info there! Thanks for the link. I especially like the answer that breaks down the learner types. It got me thinking that sound in my context would be a series of chimes, harking back to the good old days of single-tone-based computer sound, doorbells, and pinball machines. – JBH Jan 20 at 18:30
• Which kind of dynamic performances are you looking for? Text only, or moving images? – L.Dutch Jan 20 at 19:00
• Could you give some actual measurements? What is the size of one of those painted rectangles? What is the size of a letter 'H' for example. How many characters on the screen? Do you want graphics - what sort? Can we project the image onto a screen? – chasly from UK Jan 20 at 19:03
• @L.Dutch, Moving pictures. I mention in the Q that the text is allowed to scroll across the screen. I'll make that more clear. Note that once you move to pixelated displays, text is just another picture. – JBH Jan 20 at 19:06

Mechanical displays have been invented, and are in regular, day-to-day use. There are two dominating variants:

You could see your rotating cylinders as an advanced version of a flip-disk display: They are turning around like the flip disks to display a pixel, but they have more than two sides, so they can display more colors.

However, for full gray scale, I would recommend cylinders with just two colors on them. One side is painted white, the other side is black. Adjust the orientation of these cylinders such that the visible amounts of the black and the white side matches the intended gray scale value.

I.e. To display a black pixel, just show the black side. For a white pixel, rotate by 180°. To display 50% gray, rotate by just 90°. For 25% dark gray, you need a 60° rotation, 75% is at 120°, and so on.

Text displays will only ever use pure black and white, of course. But a large display viewed from afar may easily provide the impression of true gray scale.

If you want to improve gray scale display, you can use three sides of the cylinder, allowing only 1/3 of its surface to be seen by means of a mask. The third sector would be painted middle gray, of course, and light gray would be displayed by displaying a portion of the white and gray sectors. I don't think that more than three sectors make any sense, as any further sectoring of the cylinder will force a reduction of the switchable pixel surface, and having grays displayed as a combination of a gray and a black/white sub-pixel doesn't seem too bad to me.

• I dismissed the split-flap display in the paragraph beginning But, in the end, there's simply no efficient way.... With so many characters, it would be too bulky for the size of the intended application and not look much like a modern display screen. I'd forgotten about flip-disk displays - but they're a 2-color (binary) system and I wanted more (5 shades). Is there an example of a split-disk system that has more colors and/or shades? – JBH Jan 20 at 22:23
• @JBH As I said in my answer: 1) Your cylinders are basically 5-sided flip-disks. 2) You can get any gray value between two adjacent faces of your cylinder by making the cylinder round and turning it so that parts of two adjacent sectors are shown at the same time. This gives you any gray scale value possible. 3) Best performance is achieved either with two sides (black and white, and any angle in between), or three sides (avoids showing sharp line between black and white sub-pixels when showing gray). This is just reuse of basic idea, not reuse of existing design. – cmaster Jan 20 at 22:58
• @JBH: why not use split flaps, but with coloured squares instead of characters? It adds a touch of complexity but keeps the display flat, and you can add as many colours as you have space for flaps... – Joe Bloggs Jan 21 at 11:15
• @JoeBloggs Split flaps work great as long as there is only a single row to display (because the drum with the flabs is quite a bit taler than the displayable area), and the display is correctly oriented in gravity. You simply cannot turn a split flap display to the side, or upside down, or even put it flat on a table. The rotating cylinders do not have either of these problems: The binary version only needs a safety distance to the next cylinder, and the three-sided version uses $\frac{\sqrt{3}}{2} = 86\%$ of the cylinders width as display area. And it fully ignores gravity. – cmaster Jan 21 at 19:18

Your mechanism is way too complicated, error prone and uses much too much power for displaying just 5 colors.

Why not settle for 4 colors and build the "pixels" out of cubes with a different color on each side?

• No power consumption and noise when the display is not being refreshed. The cubes simply lock into their current position.
• Reliable technology. The colors are created by moving one side of the cube to the front, not by pulsing a constant rotation.
• You could have more colors than black, white and grey.

• The pixels must have margins between each other to be able to move.
• Neighboring pixels must move one after another to avoid collisions (or the margins would have to be even bigger). The refresh rate is halved, since every odd pixel can move first and every even pixel after that.

If you opted for 3 or 2 colors, you could even get rid of most of the margins. Use 2-colored tiles or 3-colored prisms instead of cubes, like a three-messages-billboard mechanism. Unlike a cube, these objects don't need more space to spin than they need to display their color, so all of them can refresh at the same time without collision.

• Am I still rotating the cubes? Doesn't this require the cube to be set back away from the watch face for the same reason they can't be too close together? It's a pocket watch - with a glass face. You couldn't let a grain of dirt into this system. curious, though. – JBH Jan 20 at 19:25
• @JBH You're right, the glass needs the same margin as between each cube. The cubes only rotate when they are being refreshed / their color changes. Once the right side faces front, they lock into that position. – Elmy Jan 20 at 19:28
• Note that you don't need a margin if rotating triangular prisms rather than cubes - like a three-messages-billboard mechanism. – G0BLiN Jan 20 at 19:51
• @G0BLiN, you've made a point. It removes the space needed between "pixels," but still requires the space between the "pixel" and the glass. Good catch! – JBH Jan 20 at 22:53

I have an alternative for you...

Each pixel is a small white-painted metal square on the end of a slender rod. For argument's sake let's say there is a "mask" with holes in it for each pixel. The square is perpendicular to the rod. They can be "plucked" to vibrate (think thumb piano) by a hidden mechanism. The "further" they vibrate, the less time they spend visible (because the mask obscures them) so due to persistence of vision an arbitrary greyscale colour can be displayed.

The main issue is the amount of blank space between the pixels. The mask could simply be in interlaced strips, or tiny holes in a checkerboard pattern. Maybe that would actually make it look more steampunk-y.

[Re]-watch Man of Steel: https://en.wikipedia.org/wiki/Man_of_Steel_(film) and then see if you could do it better. You are not "bound" by any laws of physics in SF, but just keep the "laws" that you introduce consistent.

• Welcome Konstantin! Your anwer would be improved if you brought informaton from that link into your answer. Links change and the opportunity to understand what you're talking about lost. Cheers! – JBH Jan 21 at 1:54
• Could you clarify just how this is relevant to the question asked? – nzaman Jan 21 at 12:45