With the current passing of Don Lancaster, I took a minute to mirror on how far issues have are available in a fairly quick time period. Should you someway acquired a pc within the early Seventies, it was most likely some discarded DEC, HP, or Knowledge Normal machine. Just a few folks constructed their very own, however that was a stout mission 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 pc” swelled — comparatively talking — and it left a serious drawback: What sort of enter/output system might you employ?
At work, you may need TeleType. Most of these had been leased, and the value 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 usually nicely over $1,500, though Lear Siegler launched one on the $1,000 worth, and it turned wildly profitable. Snagging a used terminal was not very probably, and surplus TeleType gear was probably of the 5-bit Baudot selection — not unusable, however not the terminal you actually wished.
A variety of the price of a video terminal was the display screen. But almost 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 pc and spawned a profitable package for an organization referred to 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 Unhealthy
After all, the largest promoting level was the fee. Should you had been a thrifty shopper or had a well-stocked junk field, you may most likely spend much less. It used your TV, which additionally helped hold the fee down.
However there have been unhealthy issues, too. The TV Typewriter 2 confirmed 16 traces of 32 uppercase-only characters. Outdated TVs aren’t made to indicate digital information, and several other issues — notably the 4.5 MHz sound lure and the rejection of the colour subcarrier at 3.58 MHz — restrict how briskly you possibly can push dots into the TV. A premium TV may need a bandwidth of three MHz to three.5 MHz, however virtually, even that may be a stretch. That’s why the decision was so poor. Later variations supplied totally different codecs, together with 32 traces by 64 characters, however good luck getting that into a traditional 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, for those who had the money, you may get a devoted monitor.
There have been different minor points. Southwest Technical Merchandise turned the design right into a package and paid Don royalties. It wasn’t very succesful by at this time’s requirements. Nonetheless, it was the perfect factor on the town on the time. As soon as folks began constructing them, in addition they began hacking on them. The TV Typewriter matured right into a usable terminal.
The Books
Don wrote a number of books and lots of journal articles based mostly on the TV typewriter design. Most individuals knew about it from a complete Radio Electronics article. (The PDF obtain is definitely the “information” you needed to ship away for, nevertheless it consists of 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! The whole lot needed to be printed.
The TV Typewriter Cookbook was a highly regarded guide. (PDF) My copy is co-branded with Radio Shack and price all of $3.95. The guide coated the TVT-1, which used shift register reminiscence, the TVT-2, which was primarily what you bought from Southwest Technical Merchandise as a package, and the TVT-3, which was CMOS and could possibly be wired to a microcontroller through DMA.
Again then, you couldn’t go “Google” for extra info, so books had a bit extra of a normal to stay as much as. Additionally, again then, the standard hacker didn’t know as a lot about computer systems as a faculty child does at this time. So there’s quite a lot of info upfront about ASCII codes and what a UART is. In these days, a guide like this needed to clarify flip flops and different belongings you’d just about assume folks know at this time.
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 through a pc requires a keyboard and a serial interface. That’s all within the guide, too. The tail finish of the guide provides some notes on how you may do shade show — an enormous deal again then.
Trying Again
Trying again, it appears fairly simple. Generate sync pulses and hold time for every line, pushing the sign in some way for every dot. Trivial with a microcontroller or an FPGA. However when Don confirmed us how to do that, these applied sciences had been primarily unobtainable. The guide is an incredible mixture of analog, digital, and sensible computing. Don’s title was synonymous with TV Typewriter for a technology.
Don wrote loads of different issues. Lots. However none of them had the super affect of the TV Typewriter Cookbook. The [Tech Time Traveller] has a great video that reveals a few of the classic {hardware} and even offers a bit context of a $1,000 TeleType while you most likely made lower than $8,000 a yr. Should you make it to the 20 minute mark, you possibly can see the insides of a reproduction unit and dig these old-style PCBs.
You hear quite a lot of names when the dialog turns to the early days of private computing. By our reckoning, you must hear Don Lancaster’s extra usually. We sometimes see issues that had been clearly influenced by the TV Typewriter. Particularly for retrocomputer tasks.
Banner picture: TV Typewriter by Marcin Wichary, of Don’s personal prototype from the Pc Historical past Museum