The article Home Computers Behind the Iron Curtain sparked a lot of interest, which made me very happy. Therefore, I decided to introduce more computer curiosities from the Iron Curtain period, especially from the former Czechoslovakia (CSSR).

As I mentioned in the previous article, the lack of spare parts, literature and technology in Czechoslovakia forced geeks to solve it themselves: by improvisation and what we would today call “hacking.” Hobbyist projects of one person or a small party was eventually taken over by a state-owned enterprise, which then began to manufacture and deliver to stores with some minor modifications. These projects most often involved a variety of peripherals that could only be found in the Czechoslovakia with great difficulty.

Much like the production of components, the production of peripherals was also distributed throughout the eastern block so that each country was specializing in certain types of peripherals. For example, East Germany produced matrix printers, and Bulgaria made floppy disks drives. This meant industrial enterprises had to wait for vital computer parts, because the production in another country was not sufficient to cover even the local requirements, let alone the home user.

BT-100

If you had brought a computer like a Spectrum or Atari from the west without a printer, you had almost no chance to get one in the CSSR. You would manage to scavenge some discarded matrix printer through your network of friends, but then you stumbled upon the need of connecting it through non-standard interfaces and coding drivers for it. You would consider yourself lucky when the printer used a Centronics interface and standard Epson control codes. Therefore, various attempts arose to build a printer at home. You think that’s impossible?

In larger cities, clubs s formed, covered officially by the only national youth organization, but they were mostly free of any ideology. They congregated modelers, electrical engineers, computer enthusiasts and other tech lovers. These clubs often had better ways to obtain some of the technology or more expensive devices. In one such a club, the one-dot printer Centrum T85 was born. After several modifications to the mechanical parts and electronics, Tesla (an electronics manufacturer mentioned in the previous article) began its production under the name of BT-100.

The BT-100 was a very simple printer, which consisted of two motors and one relay. One motor rotated a pinch roller and pushed the sheet of paper, the other one pushed a trolley with a print head which had an electromagnetically controlled blunt tip. The tip rode across the paper left and right and clicked into the paper to print a dot. The printer also had two wheels with notches which generated synchronization pulses.

The printer did not use any ribbons. Printing was achieved by placing a sheet of paper along with the carbon copy paper under the rollers. An imprint was made on the paper where the print tip clicked. This printing technology has given rise to a fitting nickname “runaway nail”.

The internal wiring of the printer was really primitive: 3 motors drives, excitation coil for pulling of the print tip and optoelectronic sensors to offset the paper, carriage and range. The interface used four input signals (carriage left, carriage right, paper feed and tip pulling) and four output signals (signal range, offset paper pulse sensor and two pulse head movement sensors). The interface truly was extremely simple and all of the work was offloaded to the control program.

The printer could print unidirectionally or bidirectionally (it took about 10 minutes to print one A4 paper, or 20 minutes with unidirectional printing). Even though the printer itself was a technological hack, it was modified even further by its users. They increased the speed of head movement, added notches to increase the printing accuracy (without these adjustments it had a resolution of 480 dots per line, therefore approximately 60 DPI) and made other adjustments to increase the speed and print quality. As a curiosity I will mention a program which had spread over Czechoslovakia – it was able to elicit a simple melody from the printer by using precisely timed controlling.

This printer certainly was not the best tool to print a source code or any documentation. It managed to print just a few pages at a time, and even that took tens of minutes:

A similar printer called Gamacentrum 01 used a slightly different design. It was equipped with two printing tips (two “nails”) on one print head, spaced at a distance of half a page between each other. During printing, each tip printed a half of the page. The print quality was only slightly higher than that of BT-100, while the printer still cost three times as much.

Alfi

Around 1925 in the former Czechoslovak Republic a kit for children was created, based on connecting perforated metal sheets with screws and nuts. This kit was called Merkur. Later in the 60s it was being exported throughout the Europe and several generations (without exaggeration) of children in Czechoslovakia had grown up with it. The kit is easily accessible, while allowing to assemble almost anything with a plenty of imagination. The inventor of contact lenses [Otto Wichterle] created his first prototypes on a centrifuge, which was made from this kit.

In the 80s an engineer Vladimír Doval built a simple plotter from this kit and called it Alfi. Its structure was somewhat more sophisticated than the above-mentioned BT-100. The author used two stepper motors (one for paper feed, the other to move the pen) and electromagnetically controlled lowering of the pen. Assembly instructions were then published in a magazine of “Science and technology for youth” (VTM), and shortly after these plotters began to appear on the of tables Czechoslovak computer enthusiasts who rummaged through their attics, looking for dusty boxes with their childhood kit. A simple interface was used to connect the plotter, built mostly with a 8255 circuit.

Alfi was not confined to the drawing pen – some even used home-built optical pens and created primitive scanners. Alfi was indeed very simple, as it was again fully reliant on computer software, but the quality was very decent – speed of 50 mm per second and minimum step of 0.15 mm.

Alfi plotter lives to this day, as you can see in this video: https://www.youtube.com/watch?v=LBip6q0qjDk

If you did not want to build a plotter yourself, you had several options at the end of the 80s. You could, for example, buy a plotter Minigraf 0507 (manufactured by Aritma) or series XY41xx plotters (manufactured by Laboratory equipment). They offered more or less the same performance as Alfi, and the top model XY4160 contained its own processor and understood the HPGL language.

SP210T

In the previous article I already mentioned that floppy disks weren’t among the usual stock in a socialist market. Floppy drives were produced mainly in Bulgaria and their production was definitely not enough to meet demand. In Czechoslovakia they largely belonged to industrial computers and the “home” computer category had to settle for an ordinary cassette tape.

Despite this, many diverse floppy drives emerged. For example, a school computer IQ-151 was assembled with a 8″ floppy drive (aka “teacher’s computer”) and a network of several other computers (“student’s computers”) were connected to it. They had a clone of CP/M on them, along with WordStar text editor and a Pascal compiler. Later, after the regime fell and imports from the world were permitted and renewed, a mass-produced drives as well as other computers were created.

Only some of the lucky ones brought a floppy drive (usually Commodore) from the West countries for their computers. The others obtained or built a Spectrum Betadisk. Its custom interface was not much of a problem, because instructions got published in the magazines, but the drive itself was hard to get a hold of, you would need an acquaintance or bring it from abroad yourself.

The most common peripheral remained a cassette recorder for a long time, and a lot of those among the people have various provenance and quality, ranging from weird plastic experiments to almost professional pieces. Tesla could show off their own cassette deck SM260, which had a surprisingly decent design and that was certainly an exception for Czechoslovak electronic devices at that time. Tesla then modified their cassette deck, removed power parts of the amplifier, and the result was a “data recorder” SP210. It had the same structure, but a slightly different design: the front part received speakers, the tape recorder contained a microphone through which you could make a preamble of the recording, and it was even possible to receive control from a computer directly using a simple TTL interface, including rewinding and recording. There was even a module which allowed the computer SAPI-1 to use SP210 as a recording device for CP/M.

And since the removal of the audio bits left a relatively large space unused inside, the creator thought to incorporate the previously mentioned printer BT-100 into that space. Thus a model SP-210T was created.

Tesla created a very surreal hybrid between a cassette tape SP210 and the BT-100 printer, and called it SP210T. The SP210T had a recording device and printer combined into one device. What the West would consider a curiosity was in Czechoslovakia a serious product. This printer had been gradually connected to nearly every computer in Czechoslovakia, ranging from ZX Spectrum and Atari to the Czechoslovak PMD-85 computer.

But the SP210T was not the last word in technology with the same design: In 1990, production began on a floppy drive PMD-32 (as the name suggests, it was a peripheral of the PMD-85) – again, in the same box as the SP-210T. It contained two 5.25” drives, controller based on FDC i8227 and DMA i8257 and a control circuit, where all the work was taken care of by a 8080 processor. The PMD computer communicated using an interface based on 8255 circuit.

Computer Mouse

The creators of this homebrew computer mouse rightly thought that the mouse is nothing too difficult. It’s just a ball that transmits its movement to vertical rollers, and this movement somehow gets measured. They sat down and put together their own mouse, which kind of resembles a feverish handyman’s dream. Judge for yourself:

As housing for the mouse they used plastic kitchen spice can. Inside the can they placed a circuit board on which were two mutually perpendicular metal rollers. On both rollers there was a jagged aperture made from a thick paper. Its position was read using a LED and a pair of phototransistors. There were two buttons at the front. Each button was created from a cap screw and a pair of shortened and bent safety pins. (Why? Well, because micro switches were unobtainable for a long time in Czechoslovakia!) The ball, an important part of the mouse, was replaced by a ping-pong ball. The cable was made as an interweaving of eight wires.

All of this was manufactured and supplied as a kit. You could buy it in the store and then assemble at home. Here is a construction manual (PDF, in Czech).

The most serious enthusiasts used ingenious ways to fill the ping-pong ball with heavy ballast for better fit and movement transmission.

This peripheral was very simple and acceded to some parallel interface. The rest had to be taken care by the software. The proprietary driver, a program that has been supplied with this kit used interrupts for determining the positions of apertures. And since interrupts on the Spectrum had a frequency of 50 Hz, it meant that the scanning was imprecise during faster mouse movements. Therefore, the authors suggested the use of a certain diagram, which increased the frequency of interruptions.

There have been perhaps 5000 of these kits created, which is a huge number in the Czechoslovak situation where computer accessories for small computers were produced in a series of several hundred.

I got my mouse in a little curious way: Sometime in 1988, the Czechoslovak authorities have decided to support young people working with computers, and so the idea of an international game was born. A text game City Of Robots was made, which was then ported to several platforms (Spectrum, PMD-85, IQ-151, Sharp MZ-800 and Ondra) and was distributed to interested parties on tape. To make sure everyone had the same conditions, the game required a password, which was to be announced at a specified date in the main news broadcast on a state television.

Unfortunately, due to authors mistake, the password could be read in a binary file, so it has spread throughout Czechoslovakia before the game even started. And on that particular day in the news the announcer said this unfortunate password (it was “konvalinka”, or “lily” in English) and added “for those who do not know it yet”. And because there weren’t even conditions for everyone, the winners were drawn, and I received the mouse kit as a prize.

Czechoslovakia also manufactured computer mice, of course, at the very end of 80’s, like 3WN16605/16607.

In Conclusion

Creating peripherals for home 8-bit computers and their small batch production in Czechoslovakia after the fall of the Iron Curtain lasted until the early 90s. With the collapse of socialism it was possible to produce these accessories legally, so new manufacturers seized the opportunity and began to supply larger series of universal interfaces with an Intel 8255 or audio peripherals such as the General Instrument AY-3-8912 or the Philips SAA-1099. But the opening of the border also meant an invasion of PCs, tech enthusiasts switched to Amiga, and eight-bit era slowly ended…

I certainly did not describe all former peripherals that were made or homemade in Czechoslovakia. We can introduce other computer curiosities of the “socialist bloc” some other time – from the joystick built from doorbell buttons to the clone of ZX Spectrum, where the circuit ULA was replaced by several dozen of standard TTL 74xx series chips…

About The Author

[Martin Malý] works as a media technology consultant and team leader of developers for some Czech newspapers. He has experience from startups and did a lot of web projects (e.g. was a Lead developer, Programmer, Administrator, Manager and Ideologist for a cutting edge Czech blogging system called Bloguje.cz).

His biggest hobby, beside programming, is microelectronics and old computers. He did some task programming on railroad engines, based on microcontrollers (8051 family, AVR, Microchip) and some “homebrew” gadgets, computers etc. He joined his two hobbies together in ASM80.com – an online IDE and assembler for 8bit CPUs.

[Martin] is an Evangelist and Teacher of New Web Technologies (OpenID, OAuth, cloud computing, HTML5, Node.js, Coffeescript and other stuff) as well as Evangelist of HTML5 development for mobile devices.

He does quite a bit of writing – starting with some juvenile textperiments, continuing through a series of blogs and online magazines, and he ended up as an Editor-in-Chief of zdrojak.cz – an online mag about web technologies.