Peripherals Behind The Iron Curtain

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.

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Transferring Audio to an AVR at 12kbps

Back in the bad ‘ol days of computing, hard drives cost as much as a car, and floppy drives were incredibly expensive. The solution to this data storage problem offered by all the manufacturers was simple – an audio cassette. It’s an elegant solution to a storage problem, and something that has applications today.

[Jari] was working on a wearable message badge with an 8-pin ATTiny. To get data onto this device, he looked at his options and couldn’t find anything good; USB needs two pins and the firmware takes up 1/4 of the Flash, UART isn’t available on every computer, and Bluetooth and WiFi are expensive and complicated. This left using audio to send digital data as the simplest solution.

[Jari] went through a ton of Wikipedia articles to figure out the best modulation scheme for transferring data with audio. What he came up with is very simple: just a square wave that’s changed by turning a pin off and on. When the audio is three samples long without crossing zero, the data is 0. When it’s five samples long without crossing zero, the data is 1. There’s a 17-sample long sync pulse, and with a small circuit that acts as a zero crossing detector, [Jari] had a simple circuit that would transfer data easily and cheaply.

All the code for this extremely cheap modem is available on GitHub.

The Cassette MP3 Player

1994 was twenty years ago. There are people eligible to vote who vaguely remember only one Bush presidency. You can have a conversation with someone born after the millennium, and they think a 3.5 inch disk is called a save icon. Starting to feel old? Don’t worry, all the trinkets of your youth have now become shells for MP3 players, the cassette tape included.

[Britt] is aware you can pick up one of these cassette tape MP3 players through the usual channels, but she wanted her build to be a little different. She’s using ar real, vintage cassette tape for starters, and from the outside, looks pretty much like any other cassette tape: there’s a thin strip of tape at the bottom, and the clear plastic window shows the tape is at the beginning of side A.

Outside appearances are just that; inside, there is a small, repurposed MP3 player, with tact switches wired up to the old buttons, actuated by moving the spools back and forth. Yes, you actually play, pause, rewind and fast forward by sticking a pencil in the spool and moving it back and forth. Amazing.

It’s a great build, and considering both cassette tapes and cheap MP3 players can be found in the trash these days, it’s something that should be hard to replicate.

The Entire Commodore 64 Library In Your Pocket

Monty

[sweetlilmre] is just beginning his adventures in retrocomputing, and after realizing there were places besides eBay to buy old computers, quickly snagged a few of the Amigas he lusted after in his youth. One of the machines that didn’t make it into his collection until recently was a Commodore 64 with Datasette and 1541 drive. With no tapes and a 1541 disk drive that required significant restoration, he looked at other devices to load programs onto his C64.

These devices, clever cartridge implementations of SD cards and Flash memory, cost more than anyone should spend on a C64. Realizing there’s still a cassette port on the C64, [sweetlilmre] created Tapuino, the $20 Commodore tape emulator

The hardware used to load games through the Datasette connector included an Arduino Nano, a microSD breakout board, a 16×2 LCD, some resistors, buttons, and a little bit of wire. The firmware part of the build – available here on the Git – reads the .TAP files off the SD card and loads them into the C64.

[sweetlilmre] posted a very complete build post of the entire device constructed on a piece of protoboard, Pop that thing in a 3D printed case, and he can have the entire C64 library in his pocket.

Tape delay made from recycled cassette decks

Professional tape delay units are great fun, but often expensive. You’d think that with so many derelict cassette decks filling the world’s dumpsters someone must have figured out a way to make a cheap tape delay… not only in the interest of saving money (sometimes quality is worth paying for) but also in the interest of re-using otherwise wasted resources.

Forosdeelectronica forum user [Dano] has made just such a device from used cassette decks and miscellaneous parts (translated). First he investigated the operation of the playback, erase, and record mechanisms and broke out the tape heads. The playback head is on a plastic rail so that the delay time can be changed, while the record head is fixed. [Dano] encountered some difficulties in ensuring good quality for the recording and erasure, which is an important consideration when working with magnetic tape.

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Cassette case cameraphone tripod

We see a lot of comments on shaky video asking why that person didn’t use a tripod. [Aatif Sumar] wants to use one when taking pictures and video with his phone but the threaded mounting hole you’d find in most cameras doesn’t come as a feature on smart phones. That didn’t deter him, he used an old cassette case for this phone tripod. The build started with a cheap flexible camera tripod. [Aatif] used a soldering iron to melt a hole in a plastic cassette case. We’re apprehensive about relying on the plastic’s ability to hold threads so we’re recommend epoxy to reinforce the joint. A bit more melting with the iron and he had a cradle on legs with a hole for the camera lens. It’s nothing fancy, but it also cost him next-to-nothing.

More car audio input hacking

[Dave] pulled the head unit out of his dashboard to add an iPod input. He took a much more invasive route than the other hack we saw a few days ago. He actually patched into the audio lines going from the Dolby reader head chip to the amplifier.

The first step was to trick the deck into thinking it had a cassette inserted. He scoped an enable pin on one of the chips to discover the timing and emulated that signal using a PIC microprocessor. From there he popped off the chip that reads the tape data, patching directly into the audio out traces. This presented some noise issues when charging the iPod but [Dave] fixed that with some decoupling capacitors.