TV Typewriter Remembered

With the recent passing of Don Lancaster, I took a minute to reflect on how far things have come in a pretty short period of time. If you somehow acquired a computer in the early 1970s, it was probably some discarded DEC, HP, or Data General machine. A few people built their own, but that was a stout project with no microprocessor chips readily available. When machines like the Mark-8 and, more famously, the Altair appeared, the number of people with a “home computer” swelled — relatively speaking — and it left a major problem: What kind of input/output device could you use?

An ad from Kilobaud offered you a ready-to-go, surely refurbished, ASR33 for $840

At work, you might have TeleType. Most of those were leased, and the price tag of a new one was somewhere around $1,000. Remember, too, that $1,000 in 1975 was a small fortune. Really lucky people had video terminals, but those were often well over $1,500, although Lear Siegler introduced one at the $1,000 price, and it became wildly successful. Snagging a used terminal was not very likely, and surplus TeleType equipment was likely of the 5-bit Baudot variety — not unusable, but not the terminal you really wanted.

A lot of the cost of a video terminal was the screen. Yet nearly everyone had a TV, and used TVs have always been fairly cheap, too. That’s where Don Lancaster came in. His TV Typewriter Cookbook was the bible for homebrew video displays. The design influenced the Apple 1 computer and spawned a successful kit for a company known as Southwest Technical Products. For around $300 or so, you could have a terminal that uses your TV for output.

The Good and The Bad

A 1975 ad for the SWTP “terminal system”

Of course, the biggest selling point was the cost. If you were a thrifty shopper or had a well-stocked junk box, you could probably spend less. It used your TV, which also helped keep the cost down.

But there were bad things, too. The TV Typewriter 2 showed 16 lines of 32 uppercase-only characters. Old TVs aren’t made to show digital data, and several things — notably the 4.5 MHz sound trap and the rejection of the color subcarrier at 3.58 MHz — limit how fast you can push dots into the TV. A premium TV might have a bandwidth of 3 MHz to 3.5 MHz, but practically, even that is a stretch. That’s why the resolution was so poor. Later versions offered different formats, including 32 lines by 64 characters, but good luck getting that into a normal TV set. There were ways to modify your TV for dedicated service as a monitor, but that required figuring out your specific brand of TV. Or, if you had the cash, you could get a dedicated monitor.

There were other minor issues. Southwest Technical Products turned the design into a kit and paid Don royalties. It wasn’t very capable by today’s standards. Still, it was the best thing in town at the time. Once people started building them, they also started hacking on them. The TV Typewriter matured into a usable terminal.

The Books

Don wrote several books and many magazine articles based on the TV typewriter design. Most people knew about it from a comprehensive Radio Electronics article. (The PDF download is actually the “guide” you had to send away for, but it includes the article and errata, too.) No need to download the schematics or the printed circuit artwork — there was nowhere to download them from in those days! Everything had to be printed.

The TV Typewriter Cookbook was a very popular book. (PDF) My copy is co-branded with Radio Shack and cost all of $3.95. The book covered the TVT-1, which used shift register memory, the TVT-2, which was essentially what you got from Southwest Technical Products as a kit, and the TVT-3, which was CMOS and could be wired to a microcontroller via DMA.

One of the output stages you could pick out of the cookbook

Back then, you couldn’t go “Google” for more information, so books had a bit more of a standard to live up to. Also, back then, the typical hacker didn’t know as much about computers as a school kid does today. So there’s a lot of information upfront about ASCII codes and what a UART is. In those days, a book like this had to explain flip flops and other things you’d pretty much assume people know today.

By Chapter 3, though, the discussion moves to memory. A TV typewriter that doesn’t use a microprocessor needs both RAM to store characters and ROM to map characters into dot patterns. Of course, you also need to know how an analog TV signal works. Even things like how to draw the cursor in hardware bear discussion.

The original typewriter was mostly made to put text on a TV screen and nothing more. Using it for input or controlling it via a computer requires a keyboard and a serial interface. That’s all in the book, too. The tail end of the book gives some notes on how you could do color display — a big deal back then.

Looking Back

Looking back, it seems pretty easy. Generate sync pulses and keep time for each line, pushing the signal one way or the other for each dot. Trivial with a microcontroller or an FPGA. But when Don showed us how to do this, those technologies were essentially unobtainable. The book is an amazing mix of analog, digital, and practical computing. Don’s name was synonymous with TV Typewriter for a generation.

Don wrote plenty of other things. Plenty. But none of them had the tremendous impact of the TV Typewriter Cookbook. The [Tech Time Traveller] has a good video that shows some of the vintage hardware and even provides a little context of a $1,000 TeleType when you probably made less than $8,000 a year. If you make it to the 20 minute mark, you can see the insides of a replica unit and dig those old-style PCBs.

You hear a lot of names when the conversation turns to the early days of personal computing. By our reckoning, you should hear Don Lancaster’s more often. We occasionally see things that were clearly influenced by the TV Typewriter. Especially for retrocomputer projects.

Banner image: TV Typewriter by Marcin Wichary, of Don’s own prototype from the Computer History Museum

22 thoughts on “TV Typewriter Remembered

  1. I’m bought school, 3 of us built one.

    We etched the double sided board, but didn’t have a way to plate through the holes. I soldered sockets on both sides.

    After we put in chips, many of the sockets were removed and the chip soldered on both sides.

    It worked, but it was months of troubleshooting

  2. The TV limitations are true fir NTSC/PAL, maybe.
    But monochrome video doesn’t have that limitation. It has a bigger bandwidth, too. And no screen mask (good).
    RS-170 and CCIR are the underlying standards to NTSC and PAL.
    They can do 80×25 just fine. That’s why, say, green monitors were being used in professional applications and as PC monitors. These video monitors used the same “Composite” connection as broadcast monitors used, minus the nasty colour signal.

    1. True for monochrome as well…standard TV receiver IF amplifiers don’t have the bandwidth needed for 80 character display. It might work if you could tap into the baseband vidoe amp. That’s the difference between TV sets and video monitors.

      Source: worked on an early CRT terminal.

      1. Video monitors don’t have a tuner.
        And modified (hacked) b/w TV sets from the 70s had their tuner bypassed.
        Monochrome Composite, or rather VBS, is the signal that’s being used natively by a CRT with a single tube. It’s their equivalent to an RGB input, more or less.

      2. Before color became common, good B&W televisions had a video bandwidth of up to 5 MHz. Allowing 10% for retrace and 6 dots for 5×7 characters plus space,

        (5e6 / 15.75e3) x 2 x 0.9 / 6 = 95 characters.

        Quality would not be good. Detuning the IF to optimize for transient response instead of selectivity could slightly reduce horizontal blur.

        After color became common, some cheap B&W TVs would not bother to trap the color carrier, making wide bandwidth possible for them also.

  3. I was a CS student at WPI when the Radio Electronics article came out. I also had a part-time job working for a large software development firm (Applied Data Research, eventually absorbed into Computer Associates). They loaned me a TI Silent 700 terminal/modem (which fit in a briefcase) so I could develop software that ran on this thing called ARPAnet, which required dialing into a Terminal Interface Processor (TIP) located at MIT and using Telnet to get to our system. They wouldn’t pay for a phone line in my dorm room, so I split the cost with a EE student named Ron who lived on the floor below. Now Ron was a true hardware hacker, we used to drive to the Honeywell Data Systems surplus store in nearby Framingham and pick up all sorts of electronics esoterica which he would make working stuff out of. He built an elaborate switching system to enable sharing the line with status lights, intercom capability, etc. When the RE TV Typewriter article came out, we made a trip to the surplus store to acquire a busted 300 baud modem, some wire wrap boards, a bunch of 74xx logic chips and the necessary static RAM, most of which had to be desoldered from PCBs. He got the thing working in a month or so, after fixing a few apparent logic errors that made it into the original article.

    Later on I found out he had rigged things so his TV Typewriter could transparently connect to the shared phone line while I was logged into the TIP. He had all of my passwords, so he and some of my other friends would go out on ARPAnet and hack various systems (except mine, thankfully) while I was sleeping or in class. Ron graduated a year later, got his dream job at Data General designing CPUs, but died shortly thereafter from kidney failure while sleeping. RIP Ron!

  4. I remember finding a copy at a public library in White Plains NY, and reading it cover to cover, and even though I owned an Apple 2E I wanted to build an RO (receive only) version of the design, he included that as an option for just displaying text on a screen. Then years later found a copy here in Queens NY, and wanted to do that again. Now the copy I own is from the same vintage as the Queens NY one. I also donated to the Infoage museum two spares of his Cheap Video Cookbook ones.

    1. There also were books about electron tubes and relays logic, btw. My father has them in his book shelves. The relay books are from about the 1970s, I think. They’re very interesting. Ring counters, flip-flops, AND/NAND gates, electronic locks, delay circuits etc. All with simple electro mechanical relays running at about 5 to 24V. No integrated circuits needed.

  5. Back in the late ’70s I had most of Don’s books, but before I built a TV Typrewriter I got lucky and found a broken green-screen terminal at a hamfest that wasn’t too hard to get working again. I used it with a Signetics 2650 evaluation board with a home-bult memory expansion board. I used it until I got a VIC 20 and then a C64. Both Commodores were a step down from the 80 columns on the green-screen, but better in every other way.

  6. Many of the above comments are mostly true regarding the bandwidth of the earlier TV’s. The true part was if you had spent lots of money on your TV. Run of the mill TV’s, (monochrome included), did not have the necessary bandwidth for higher density display. TV’s were made VERY cost consciously to appeal as much as possible to the general consumer for which they were intended. So, the TV typewrite was designed for as broadly as possible to work with the most available televisions. I cut my teeth on the i4004/8008 and then graduated to the CDP1802. Now that was a computer….lol. I was only a teenager at the time of those devices and when Don Lancaster’s TV Typewriter came out, I read everything possible on it , but could not afford to build one…… I ate up everything Mr. Lancaster wrote….. what a man!!!

  7. Aw man, I missed the note that he’d passed.

    I still have my copy of the TV Typewriter Cookbook. It taught me almost everything I needed to build an external video system for my TRS-80 Model I. I never could’ve even started the project without Don’s books.

    He was one of the best technical communicators I’ve ever read. I’m glad we had him.

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