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.
Continue reading “3D Print A Colour TV”
Its safe to say that colour television is taken for granted nowadays. Consumed by the modern marketing jargon of colour dynamic range, colour space accuracy and depth, it is easy to overlook the humble beginnings of image reproduction when simply reconstructing an image with the slightest hint of colour required some serious ingenuity and earned you a well deserved pat on the back!
[anfractuosus] revisited an old gem of a technique, first patented in 1903 and used it to successful make an old monochrome TV produce a colour image. The idea in essence, is actually similar to what cheap image sensors and LCDs still use today. Rather than relying on true RGB colour generation by individually integrating colour sources as AMOLED does, we take an easier route: Produce a simpler monochrome image where each colour pixel is physically represented by four monochrome sub-pixels, one for each colour component. Now light up each of the sub-pixels according to the colour information of your image and rely on an external colour filter array to combine and spit out the correct colours.
He first used some image processing to convert a standard colour video into the aforementioned monochrome sub-pixel representation. Next, a Bayer colour filter array was printed on some acetate sheets using an inkjet printer (the original inventors used potato starch!), which when overlaid on top of the monochrome monitor, magically result in colour output.
There are some problems associated with this technique, mainly to do with the difficulty in measuring the size of the TV pixels and then producing and perfectly aligning a filter sheet for it. You should check out how [anfractuosus] went about solving those issues.
So now you know a bit more about colour image generation, but how about colour TV transmission? Check out an earlier piece to learn more.
Continue reading “Trick From 1903 Makes An Old Monochrome TV Spit Some Colours”
By the time colour TV came to the United Kingdom, it was old news to Americans. Most of the viewing public on the Western side of the Atlantic had had the opportunity to see more than black-and-white images for years when in 1967 the BBC started transmitting its first colour channel, BBC2.
For Americans and continental Europeans, the arrival of colour TV had been an incremental process, in which the colour subcarrier had been added to their existing transmission standard. Marketed as “compatible color” to Americans, this ensured that their existing black-and-white TV sets had no need for replacement as the new transmissions started.
The United Kingdom by contrast had been one of the first countries in the world to adopt a television standard in the 1930s, so its VHF 405-line positive-modulation black-and-white services stood alone and looked extremely dated three decades later. The BBC had performed experiments using modified round-CRT American sets to test the feasibility of inserting an NTSC colour subcarrier into a 405-line signal, but had eventually admitted defeat and opted for the Continental 625-line system with the German PAL colour encoding. This delivered colour TV at visibly better quality than the American NTSC system, but at the expense of a 15-year process of switching off all 405-line transmitters, replacing all 405-line sets, and installing new antennas for all viewers for the new UHF transmissions.
Such a significant upgrade must have placed a burden upon the TV repair and maintenance trade, because as part of the roll-out of the new standard the BBC produced and transmitted a series of short instructional animated films about the unfamiliar technology, which we’ve placed below the break. The engineer is taken through the signal problems affecting UHF transmissions, during which we’re reminded just how narrow bandwidth those early UHF Yagis must have been, then we are introduced to the shadowmask tube and all its faults. The dreaded convergence is introduced, as these were the days before precision pre-aligned CRTs, and we briefly see an early version of the iconic Test Card F. Finally we are shown the basic procedure for achieving the correct white balance. There is a passing reference to dual-standard sets, as if convergence for colour transmissions wasn’t enough of a nightmare a lot of the early colour sets incorporated a bank of switches on their PCB to select 405-line or 625-line modes. The hapless engineer would have to set up the convergence for both signals, something that must have tried their patience.
The final sequence looks at the hand-over of the new set to the customer. In an era in which we are used to consumer electronics with fantastic reliability we would not be happy at all with a PAL set from 1967. They were as new to the manufacturers as they were to the consumers, so the first generation of appliances could hardly have been described as reliable. The smiling woman in the animated film would certainly have needed to call the engineer again more than once to fix her new status symbol.
Continue reading “Retrotechtacular: Information From The Days When Colour TV Was New”
In a lifetime of working with electronics we see a lot of technologies arrive, become mighty, then disappear as though they had never been. The germanium transistor for instance, thermionic valves (“tubes”), helical-scan video tape, or the CRT display. Along the way we pick up a trove of general knowledge and special skills associated with working on the devices, which become redundant once the world has moved on, and are suitable only reminiscing about times gone by.
When I think about my now-redundant special skills, there is one that comes to the fore through both the complexity and skill required, and its complete irrelevance today. I’m talking about convergence of the delta-gun shadow mask colour CRTs that were the height of television technology until the 1970s, and which were still readily available for tinkering purposes by a teenager in the 1980s.
Continue reading “My Most Obsolete Skill: Delta-Gun Convergence”
Black and white NTSC is simple – it can, and was, done with vacuum tubes for a long, long time. Color is just weird, though. It runs at 29.976 frames per second, uses different phases of the carrier for different colors, and generally takes a while to wrap your head around. [Sagar] is doing a series on the intricacies of NTSC, and the latest post deals with color and progressive scanning versus interlacing, or as it is better known, how classic game consoles and home computers generate video.
The test bed for [Sagar]’s video experimentations is a circuit containing an ATMega16, a 4-bit shift register, and a 14.31818 MHz clock. This clock is much faster than the 3.579545 MHz clock in an NTSC carrier frequency – exactly four times as fast – allowing the shift register to output four different phases of the carrier frequency a 0°, 90°. 180°, and 270°. Playing with some of the pins on the ATMega in the circuit results in a palette being generated on any old TV.
NTSC requires interlaced scanning, or sending an entire screen of even lines, then an entire screen of odd lines, at around 60 fields per second. The Nintendos and Segas of yesteryear didn’t bother with this, instead opting to send half the vertical resolution at double the frame rate. This is known as a progressive scan. [Sagar] found that this resulted in some image artifacts when displayed on a modern LCD, and moving back to an interlaced mode fixed the problem. All the code and files are up on the gits. If you’re feeling adventurous, this is exactly how projects like the Uzebox have created homebrew game consoles using little more than the ATMega found in [Sagar]’s build.