DIY · Card 73 · Computing · Electronics
A computer the size of a stick of gum, a screen made of electric ink, and a case of grey bricks. Build a working one-third-scale Macintosh and discover how two colours can paint a whole picture.
01The brief
A real computer, in bricks, with a screen that remembers.
1:3
roughly the scale: a 2.7-inch screen for the Mac’s 9-inch one
264×176
pixels on the e-paper, half the original Mac’s in each direction
0 W
needed to keep the picture on the screen once it is drawn
In 2017 Jannis Hermanns, a programmer in Berlin, was playing LEGO with his son and decided to rebuild one of the first computers he had used: a Macintosh Classic. He hid a Raspberry Pi Zero inside a case of grey bricks and gave it a real screen made of electronic paper.
You can do the same. The case is pure LEGO; the computer costs about the same as a book; and the screen behaves like no other. It holds its picture without power, and it can only show black or white, just like the 1984 original. It pairs well with the conveyor-belt cinema and the moiré patterns.
02Kit
A tiny computer, a tiny screen and a box of bricks.
Tick off what you have
0 of 5 ready
03Method
Get the screen working first, then build the case around it.
Step 1 of 8 · Day 1
You need a Raspberry Pi Zero W, a 2.7-inch e-paper display module (264 × 176 pixels) made to fit the Pi’s pin header, a microSD card, a micro-USB power supply, a computer to set it up, and a pile of light grey and white LEGO bricks and plates.
The screen stays blank.
Why
The SPI interface is switched off, or the display is on the wrong pins.
Fix
Turn on SPI in the Pi’s configuration tool, reboot, and check the module is seated on the correct end of the header.
Old pictures ghost through new ones.
Why
Partial updates leave some particles half-way.
Fix
Do a full refresh, which flashes the screen black and white, every few updates.
The window doesn’t line up with the screen.
Why
The height is off by a fraction of a brick.
Fix
Swap a brick for three plates, or one plate, to move the window in 3.2 mm steps.
04Ink and dots
An e-paper screen has no light inside. Each pixel is a thin layer of microscopic capsules, each holding white and black particles with opposite electric charges in clear oil. A voltage pulls one colour to the front, and there it stays.
Paint with the capsules and send the pulse:
Tap capsules to plan a new picture, then send the voltage pulse.
what you see from the front
Power right now
0
Capsules flipped
0
Picture held without power
yes
A positive voltage on the front electrode pushes the positive white particles to the back and pulls the negative black ones to the front; reverse it and the colours swap. Once they have moved they stay put, so the screen uses power only while the picture changes. A phone screen, by contrast, must be lit and redrawn many times a second just to stand still.
Black or white is all each pixel can do. To show a shaded picture, the trick is in how you arrange them:
Pixels
264 × 176
Colours
2
White pixels
46 %
Bill Atkinson’s recipe for the early Macintosh passes only three-quarters of the error on, an eighth to each of six neighbours. Highlights and shadows stay crisp: the classic Mac look.
05The big idea
Two colours
are enough.
Your eye averages what it can’t resolve. Mix one black dot with three white ones and, from arm’s length, you see a pale grey. Every shade is just a proportion.
The art is in where you put the dots. Error diffusion keeps a running tally: whenever a pixel is rounded to black or white, the mistake is handed to its neighbours, so that every small patch comes out with the right average.
06The math
1 · Sharpness
ppi = √(w² + h²) ⁄ d
Pixels along the diagonal per inch of diagonal.
2 · Memory
bytes = w × h ⁄ 8
One bit per pixel, eight bits to a byte.
3 · Atkinson
6 neighbours × e ⁄ 8
Error e shared out; the other quarter is dropped.
The e-paper has √(264² + 176²) ≈ 317 pixels along a 2.7-inch diagonal: about 117 pixels per inch, sharper than the original Mac’s 615.7 ⁄ 9 ≈ 68 across its 9-inch tube. One screen takes 264 × 176 ⁄ 8 = 5,808 bytes. The 1984 Mac’s 512 × 342 screen needed 21,888: a sixth of its 128 KB of memory, just for the picture.
Atkinson’s dithering passes on only 6 ⁄ 8 of each pixel’s error. Losing the last quarter makes very light and very dark areas snap to pure white or black, which is why his pictures look crisper and higher in contrast than Floyd–Steinberg’s, which pass on all 16 ⁄ 16.
07Real life
From e-readers and supermarket shelves to Seurat’s canvases.
E-readers
Amazon’s first Kindle, in 2007, used an E Ink screen. Because the page only draws power when it turns, an e-reader can last weeks on one charge and is as easy to read in sunshine as paper.
Shelf labels
Many supermarkets now show prices on small e-paper labels. Head office can change thousands at once by radio, and each label runs for years on a coin battery.
Newspaper halftones
From the late 1800s, newspapers printed photographs as grids of black dots of different sizes. Look closely at an old newspaper picture with a magnifying glass and the greys break into dots.
Pointillism
Georges Seurat painted A Sunday on La Grande Jatte, in the 1880s, from countless small dots of pure colour that blend in the eye: dithering with a paintbrush, a century before computers.
Icons in a grid
Susan Kare designed the original Macintosh icons and fonts on graph paper, one square per pixel. With only 32 × 32 black or white squares, every dot had to count.
The LEGO grid
LEGO patented its modern brick in 1958. Studs sit 8 mm apart and a brick is 9.6 mm tall, three plates of 3.2 mm, so every model is really a three-dimensional grid of pixels.
1984
When the Macintosh went on sale in January 1984, its 9-inch screen could show only black and white. Yet its pictures looked startlingly rich, thanks largely to Bill Atkinson, who wrote QuickDraw, the Mac’s drawing engine, and MacPaint.
To turn scanned photographs into something the screen could show, Atkinson devised his own error-diffusion recipe, sharing three-quarters of each pixel’s error among six neighbours. Four decades later his dithering is still used to make crisp black-and-white pictures, including on e-paper screens like this one.
08Is and isn’t
E-paper screens light up.
They don’t make any light. Like ink on paper, they reflect it, which is why they’re easy to read in sunshine and invisible in the dark without a lamp.
You need greys to show a photograph.
Black and white dots, mixed in the right proportions, are enough. Newspapers did it for a century and the first Macintosh did it in software.
Dithering is a modern trick.
Ordered dithering was described by Bryce Bayer in 1973 and error diffusion by Robert Floyd and Louis Steinberg in 1976, years before the Mac.
A LEGO Mac is just a model.
With a Raspberry Pi inside it is a real Linux computer that you can program, connected to the internet over Wi-Fi.
09Go further
A
A daily quote
Write a short script that shows a new quotation, joke or maths fact every morning.
B
Dither by hand
On squared paper, shade a sphere using only filled and empty squares. Can you make it look round?
C
Weather station
Fetch the forecast over Wi-Fi and draw it in pixel-art icons: a sun, a cloud, raindrops.
D
A LEGO TV
Use the same screen to build another classic: a tiny television, a radio or an arcade cabinet.
E
Count the bytes
Work out how much memory one screen of your display needs at one bit per pixel, and compare it with a colour photo.
10Questions
Put a Raspberry Pi Zero W and a 2.7-inch e-paper display inside a case built from light grey LEGO, with a window for the screen and a dark tile for the floppy slot. Set the Pi up over Wi-Fi, install the display’s driver, and send it black-and-white pictures.
Jannis Hermanns, a programmer in Berlin, built one in 2017 while playing LEGO with his son. It used a Raspberry Pi Zero W and a 2.7-inch e-paper panel, cost a little over $100, and he shared how he made it online.
Each pixel holds tiny capsules of clear fluid with white particles carrying one electric charge and black particles carrying the other. A voltage across the capsule pulls one colour to the front. Once moved, the particles stay put, so the picture remains with the power off.
A way of showing shades of grey on a screen that can only show black and white, by mixing black and white dots in the right proportions. Seen from a distance, the eye blends them. Error-diffusion methods like Floyd–Steinberg and Atkinson pass each pixel’s rounding error on to its neighbours.
512 × 342 pixels on a 9-inch black-and-white screen, when the Macintosh launched in January 1984. Storing one full screen took 21,888 bytes, about a sixth of the 128 KB of memory in the first model.
Safety · Always unplug the Pi before connecting or moving the display. Use a proper USB power supply, handle the thin glass panel gently, and keep small LEGO pieces away from children under three.
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