The oldest form of television used a spinning disk with a progression of holes — a Nipkow disk — to slice the image into lines for display. They’re surprisingly simple machines and capable of unexpectedly high-quality images despite their relatively low resolution. Even better, in an age of microcontrollers and bright LEDs, making one that works is not the chore it might once have been. [Markus Mierse] has created one that uses an Arduino Mega and a set of 3D printed parts, so there’s no excuse for not having a spinning disk TV on your shelf.
The Arduino Mega is chosen because it has enough lines to drive three six-bit DACs for each of red, green, and blue. The disk is driven by a PWM motor controller, and synchronization is taken care of by a piece of reflective tape and an IR proximity sensor. Images and video are read from an SD card and displayed on the screen in glorious 32-line colour. The full build process can be seen in the video below the break.
A surprise when viewing mechanical TV is that its quality is much better than the meager resolution would have you believe, and this one with its colour display is much better than the usual monochrome devices. It’s hardly HDTV, but it acquits itself well and would provide an excellent talking point.
If you’re curious about Nipkow disks, they’re a subject we’ve examined in the past.
I wonder if an addressable RGB LED could have been used for this project, some of them will refresh at 800KHz or faster.
I’m not familiar with addressable RGBs that refresh that quickly.
depends on the size of the array and the controller. i have a controller and strips in my garage that can refresh plenty fast. can map the array right on the soc with built in live debugging. im no good at programming it, but it works and the pixels flip fast enough to perform this in a smaller array. the more pixels you add the slower they can be addressed. i think i had 600 pixels on there and there was not a noticable difference in refresh rate, even though the onboard fps counter obviously drops down.
It’s not a 800kHz refresh rate, but it’s the datarate. But (the right) APA102 RGB LEDs (aka dotstar) can be driven with an 20kHz refresh rate with the fastled library, that should be sufficient for this application. HD107 LEDs support even higher refresh rates.
but they probably won’t be bright enough to get a viewable picture…
There are spi based DotStar pixels that have very fast internal PWM rates and can be updated over SPI at 5MHz. They can be used in persistence of vision experiments where the unclocked pixels cannot because their internal PWM is slow and the update rate is only a few KHz.
I think he could have used the WS2811 coupled with a high power driver. You can actually get these as modules that can drive the same sized RGB led used in this project.
http://nbtv.org is an association in the UK, a good place to learn about early television, I think Malcolm Baird is president or such, I built one about ten years ago, very interesting project.
Yes, that’s correct johnrpm. The website is a great resource and I’d encourage anyone interested in narrow bandwidth TV to consider joining. The expertise and experience in the association is unparalleled.
In the 1920s they didn’t need such fancy electronics. Actually, it didn’t exist. I’ve read itwas a neon bulb behind the spinning disk.
Yeah, you hit the nail. That’s why the Nipkow disc had failed back then. The light source. Normal lamps weren’t strong enough to provide a picture with a good contrast. That’s why it’s creator was so down when, I suppose.
There were several reasons why it eventually failed:
The resolution could not be made as high as CRT resolutions. I think it topped out at 180 lines. The more lines, the smaller the picture. So you’d have to increase disk size, but still end up with a small picture.
The picture size was severely limited. A larger and larger disk was needed for larger pictures, but the larger you make them, the higher the edge speed, causing trouble with thin disks flexing. The device itself would also be obnoxiously large.
And brightness, indeed, was a problem. Though the early CRTs weren’t that much better than the Nipkow based TVs.
However, in a Nipkow disk TV, the amount of light coming from the lamp is blocked by all but the tinyest hole in the disk. Eventually CRTs would handle more brightness, while even with a bright lamp behind the disk you’d lose 98ish percent of the light.
J.L. Baird did eventually make a color version of his disk based TV, by the way. Afaik it was the first color TV system ever. It used multiple disks, with color filters in them. I don’t know the type of lamp he used. It was his final hurrah. It was scheduled to be shown to some important people, but it was destroyed in the war before he was able to show the color TV. That was a major blow to the guy, and i can understand that…
Well that was one of the issues yeah, but the other issue was that the picture was always going to be tiny relative to the size of the disk. So it wouldn’t ever really have been that feasible, but it’s a neat piece of technological history.
With each rotation being one frame, the disc has to spin at 30 revolutions per second to get 30 frames per second. 1800 revolutions per minute.
What I’d try is laser cut the disc to have the holes with closer radial spacing, and make two sets of them, each going halfway around the disc, and one set offset halfway between the others.
Same 1800 RPM now makes a higher resolution, 60 fields per second, interlaced image.
A bigger image requires a larger diameter disc, so drop to a PAL style 25 frame, 50 field per second picture at 1500 RPM.
Why do all of these put the image to the side and use “vertical” lines? I’d put it at the top to use “horizontal” lines.
Standards.
The original baird standard was 30 lines, the NBTV Association made it 32 lines for reasons unknown to me (but undoubtedly you can find it somewhere, there is some thinking behind it). Both vertically scanned. Most NBTV material you find on the internet is the NBTVA standard, so that’s what most people make their TVs for.
Furthermore, increasing the frame/field rate and resolution means you might have a bigger bandwidth necessary than the average CD player or sound card (typically the signal sources for NBTV) can handle.
Horizontally scanned nipkow TVs existed back in the 30s (usually german and 60 lines), but the vertical one has been the most common one.
The disks with two sets of holes, shifted halfway across the disc also existed.
The smaller you make the holes (to increase the resolution) the dimmer the little dot of light gets. With today’s super bright LEDs perhaps not that much of an issue, but definitely something that has significant inflluence on picture brightness.
The reason for 32 lines was to make production of the early NBTV discs easier by using a compass to sub divide the disc for making the disks manualy . No CAD or 3D in the early seventies.
You wouldn’t steal a TV!
But, I’d download one…
There’s a small, but fine and dedicated community that experiments with both mechanical SSTV and NBTV – Narrow band television.
There’s even software for it, for Windows/Mac OS X.
Albeit for the latter, perhaps it’s good to still have a Power PC or Intel Mac with OS 10.4. 11 to 10.6.8 might be required, no M1 Mac.
Example:
https://antiqueradios.com/forums/viewtopic.php?f=3&t=184353
Software:
https://tinyurl.com/yc873haw
https://tinyurl.com/2p8kryty
Why he not use pwm for led ? is it necessary using tons of resistors ?
I’m not entirely sure, but maybe it’s a timing problem.
Eretidely, PWM caused a high CPU usage.
A resistor network, a Covox Speech Thing, essentially, causes less usage.
It’s operating on 8-Bit values rather (usually), which are sent group wise in parallel fashion.
There were games and demos that could play real sound on a 4,77MHz PC through PC speaker, but the PWM was so demanding that the PC wasn’t able to do much else.
Here’s the nameknown Magic Mushroom demo, as a likething:
https://www.youtube.com/watch?v=J42iN3HMB68
Have fun! 😁
The IEEE article linked above implies that pre-war Germany TV broadcasts used mechanical Nipkow disc technology, but after a bit of searching the only reference I was able to find is that the german broadcast centre was named after Nipkow.
According to the wikipedia articles the german system was electronic with 180 lines at 25 frames/second. Curious if anyone knows for sure whether Nipkow discs were actually used in Germany previously, or was it always electronic?
I first recall reading about german wartime television in Walter Dornberger’s book ‘V-2’ where he mentions a roving television camera crew turned up for a live broadcast of a V-2 launch. Incidentally this fascinating book was reviewed here on Hackaday a few years ago.
Official TV in Germany started with 180/25p, mechanical (Nipkow) flying spot scanners for studio use and intermediate film for outdoor. In 1936, electronic cameras were already good enough for live outdoor events like the Olympic Games in Berlin (with “PAL-guy” Walter Bruch as camera operator). Soon after, the TV standard was upgraded to 441/50i. Receiving sets were CRT-based right from the start, except some early experimental sets and projection equipment.
In addition to that, the Deutsche Reichspost offered cable-based video telephony services between major cities.
Video calling in the 1930s? That’s cool. Do you have any more info on this, or some keywords? The closest I could find with a quick web search was this old picture, which may or may not be real: https://www.alamy.com/stock-photo-technics-telephone-visual-telephone-deutsche-reichspost-berlin-germany-17976473.html
replace disk with drum and you could get rid of that trapazoidal frame for something a little flatter (at least sort of like a trinitron). or perhaps some kind of tape reel.
I’ve had the idea for a long time of a mechanical TV using a belt system that has the holes in it. You could increase the resolution by making the belt wider.
I’ve often wondered if it was possible to use the nipkow image to project a larger picture. It would me much more useful as a text terminal if the disc displayed a single ascii character and then another device scanned in a 80×25 grid.
maybe someone could combine this with a pov led globe. different eras of technologies, but with the possibility to create a great display.
Hmm, what if you build a 2nd, identical but mirror image device, and position it so its tiny picture is right next to the first one’s tiny picture, and then arrange some lenses so you can lean right in close and look at both images at the same time, one image per eye. Wouldn’t that make for *3D* color TV?
Come to think of it, the slight bendy-ness of the lines being in opposite directions might make things .. interesting. Well, maybe it would turn out to be a “4D” color migraine machine, idk. Quickly, Ginger, to the laboratory!
Just a point of clarification — The IEEE article and project are by Markus Mierse, the illustrations are by James Provost.
Thanks, fixed.
The other fun thing about these Nipkow disk TVs is that they also with backwards. Put a light sensor in place of the lamp, amplify the signal, feed it into the lamp of another disk and you can recreate the image.
You see the samething with electronic tv.
A flying spot scanner has a photomultiplier tube in front of a tv screen. Put a picture between the two, obviously opaque, and you get the image. Donewith both ntsc and sstv.
I just wonder whether 3D printing ist really the best way to make a disc with holes in it, especially if your intention is to spin it fast.
That’s a good question. Another type of 3D printer, say, based on a laser or a high-pressure water beam would be handy:
Instead of a plastic roll, maybe it would melt top-down through a block of plastic or some fluid/polymere/gel in a container?
But since the wheel\disc is flat, a CNC machine or a modified plotter (cutter) could be used, as well. Those laser-based engraving machines are a possibility, too, once modified.
Why two sets of holes? The rpm would go down but the edge of the disc would have the same speed. Also the disc has to be double the size.
The two sets of holes crate two interlaced fields to help reduce flicker. CRT based television used the same principle.