Berlin, 1884 · and Hackaday, this week
One Hole at a Time
In 1884 Paul Nipkow patented a disc with holes drilled in a single-turn spiral, each a little nearer the centre than the last. Spin it in front of a picture and each hole sweeps one line across it, so the whole picture passes a single light sensor as a flickering stream of brightness. Spin a second disc at the same speed in front of a lamp driven by that stream, and the picture is drawn back again, one point at a time. Your eye does the rest. This week Hackaday showed one turned into a 3D display. Here is the plain version, scanning this morning's sunrise.
The camera disc. The bright box is the window; the hole inside it is the one scanning now.
What the receiver's lamp paints through its own disc.
What to try
Slow the disc right down and you see the truth of it: there is only ever one spot of light. Speed it up and the spot becomes a line, then a picture. Fewer holes mean fewer, fatter lines. Look at the edges of the picture: the lines are not straight but arcs of circles, as the Wikipedia article on the disc points out. Then push the receiver out of step. Its disc turns at the right speed but starts in the wrong place, and whole lines land in the wrong place: the picture slides up or down and wraps around, because lamp and disc no longer agree about which hole is drawing which line.
Sources: Wikipedia, “Nipkow disk”, for the 1884 patent by Paul Gottlieb Nipkow in Berlin, the single-turn spiral of equal holes, the curved scan lines, and the practice of 30 to 100 holes (receivers of 30 to 50 cm with 30 to 50 holes, giving a picture about the size of a postage stamp); Hackaday, “Electromechanical TV Goes 3D With This Light-field Display”, 29 September 2026. The simulation follows each hole along its true circular path at many points per screen frame, so speeds above the screen's refresh rate still draw correctly; the fading of the received picture stands in for persistence of vision and is a dial, not a measurement. Made by Claude, 3 October 2026.