TV Typewriter Remembered | Hackaday
With the recent passing of Don Lancaster, I took a minute to replicate on how far issues have are available a reasonably brief time period. If you happen to someway acquired a pc within the early Seventies, it was in all probability some discarded DEC, HP, or Information Common machine. A couple of folks constructed their very own, however that was a stout challenge with no microprocessor chips available. When machines just like the Mark-8 and, extra famously, the Altair appeared, the variety of folks with a “residence laptop” swelled — comparatively talking — and it left a serious drawback: What sort of enter/output machine might you utilize?
At work, you might need TeleType. Most of these had been leased, and the worth tag of a brand new one was someplace round $1,000. Keep in mind, too, that $1,000 in 1975 was a small fortune. Actually fortunate folks had video terminals, however these had been typically effectively over $1,500, though Lear Siegler launched one on the $1,000 worth, and it grew to become wildly profitable. Snagging a used terminal was not very possible, and surplus TeleType tools was possible of the 5-bit Baudot selection — not unusable, however not the terminal you actually wished.
A whole lot of the price of a video terminal was the display screen. But practically everybody had a TV, and used TVs have at all times been pretty low-cost, too. That’s the place Don Lancaster got here in. His TV Typewriter Cookbook was the bible for homebrew video shows. The design influenced the Apple 1 laptop and spawned a profitable equipment for a corporation often known as Southwest Technical Merchandise. For round $300 or so, you may have a terminal that makes use of your TV for output.
The Good and The Dangerous
After all, the largest promoting level was the fee. If you happen to had been a thrifty shopper or had a well-stocked junk field, you may in all probability spend much less. It used your TV, which additionally helped preserve the fee down.
However there have been unhealthy issues, too. The TV Typewriter 2 confirmed 16 traces of 32 uppercase-only characters. Previous TVs aren’t made to point out digital knowledge, and a number of other issues — notably the 4.5 MHz sound lure and the rejection of the colour subcarrier at 3.58 MHz — restrict how briskly you may push dots into the TV. A premium TV might need a bandwidth of three MHz to three.5 MHz, however virtually, even that could be a stretch. That’s why the decision was so poor. Later variations provided completely different codecs, together with 32 traces by 64 characters, however good luck getting that into a standard TV set. There have been methods to switch your TV for devoted service as a monitor, however that required determining your particular model of TV. Or, in case you had the money, you may get a devoted monitor.
There have been different minor points. Southwest Technical Merchandise turned the design right into a equipment and paid Don royalties. It wasn’t very succesful by right now’s requirements. Nonetheless, it was the most effective factor on the town on the time. As soon as folks began constructing them, additionally they began hacking on them. The TV Typewriter matured right into a usable terminal.
The Books
Don wrote a number of books and plenty of journal articles based mostly on the TV typewriter design. Most individuals knew about it from a comprehensive Radio Electronics article. (The PDF obtain is definitely the “information” you needed to ship away for, however it contains the article and errata, too.) No must obtain the schematics or the printed circuit art work — there was nowhere to obtain them from in these days! All the things needed to be printed.
The TV Typewriter Cookbook was a highly regarded e book. (PDF) My copy is co-branded with Radio Shack and price all of $3.95. The e book lined the TVT-1, which used shift register reminiscence, the TVT-2, which was basically what you bought from Southwest Technical Merchandise as a equipment, and the TVT-3, which was CMOS and may very well be wired to a microcontroller by way of DMA.
Again then, you couldn’t go “Google” for extra info, so books had a bit extra of a typical to reside as much as. Additionally, again then, the everyday hacker didn’t know as a lot about computer systems as a faculty child does right now. So there’s loads of info upfront about ASCII codes and what a UART is. In these days, a e book like this needed to clarify flip flops and different belongings you’d just about assume folks know right now.
By Chapter 3, although, the dialogue strikes to reminiscence. A TV typewriter that doesn’t use a microprocessor wants each RAM to retailer characters and ROM to map characters into dot patterns. After all, you additionally must know the way an analog TV sign works. Even issues like how to attract the cursor in {hardware} bear dialogue.
The unique typewriter was largely made to place textual content on a TV display screen and nothing extra. Utilizing it for enter or controlling it by way of a pc requires a keyboard and a serial interface. That’s all within the e book, too. The tail finish of the e book provides some notes on how you may do coloration show — an enormous deal again then.
Wanting Again
Wanting again, it appears fairly simple. Generate sync pulses and preserve time for every line, pushing the sign by hook or by crook for every dot. Trivial with a microcontroller or an FPGA. However when Don confirmed us how to do that, these applied sciences had been basically unobtainable. The e book is an incredible mixture of analog, digital, and sensible computing. Don’s identify was synonymous with TV Typewriter for a era.
Don wrote loads of different issues. Loads. However none of them had the super influence of the TV Typewriter Cookbook. The [Tech Time Traveller] has an excellent video that reveals among the classic {hardware} and even supplies a little bit context of a $1,000 TeleType once you in all probability made lower than $8,000 a 12 months. If you happen to make it to the 20 minute mark, you may see the insides of a reproduction unit and dig these old-style PCBs.
You hear loads of names when the dialog turns to the early days of non-public computing. By our reckoning, it’s best to hear Don Lancaster’s extra typically. We sometimes see issues that had been clearly influenced by the TV Typewriter. Particularly for retrocomputer projects.
Banner picture: TV Typewriter by Marcin Wichary, of Don’s personal prototype from the Computer History Museum