Making A Cassette Mass Storage Interface

If you are of the generation who were lucky enough to use the first 8-bit home computers in your youth, you will be familiar with their use of cassette tapes as mass storage. Serial data would be converted to a sequence of tones which could then be recorded using a standard domestic cassette recorder, this recording could then be played back into the machine’s decoder and loaded into memory as a complete piece of software. Larger programs could take a while to load, but though it was rather clunky it was a masterful piece of making the best of what was at hand.

[Mike Kohn] was working with some microcontroller infra-red communication projects when he saw that the same techniques could be used to produce a tape interface like those on the home computers of old.

Over the years he has returned to the project a couple of times, and his original Atmel processor has been supplanted by a W65C265SXB development board based on the 16-bit derivative of the 6502. This made generating the tones as straightforward using his processor’s built-in tone generator, but decoding still presented a challenge. His earlier attempts used an LM2917 frequency to voltage converter to decode tones to logic levels, but on further consideration he decided to move to the LM567 tone decoder. This chip is designed specifically for an on-off logic output rather than the 2917’s analogue voltage output.

His recording device was originally a hi-fi separate cassette deck after experimenting with microcassettes, but eventually he used a data recorder designed for a Radio Shack TRS-80. All his code can be found in his GitHub repository.

It’s probably true to say that [Mike] has made a better cassette interface than the one you could have found on your home computer back in the day. We’ve featured a few data cassette hacks over the years, including this Commodore tape deck with an LED counter, and a tape deck emulator capable of holding an entire software archive.

Onde Magnetique Will Wow And Flutter Your Ears

[Scott Campbell] built a cassette-based synthesizer that sounds exactly like everything you’ve heard before. The sound generation comes straight off cassettes, but the brainbox of this synth varies the volume and pitch. It’s called the Onde Magnetique, and it is what you would get if you combined a Mellotron and Ondes Martenot.

The key component for the Onde Magnetique is a Sony cassette recorder that conveniently and inexplicably comes with a ‘tape speed input’ mini jack. By varying the voltage sent to this input jack, the speed of the tape, and thus the pitch of the sound being played, is changed. Build a box with a touch-sensitive button for volume, and a few tact switches for different speeds, and you have an electromechanical bastard child of a Mellotron and an Ondes Martenot.

By itself, the Onde Magnetique produces no sound – it only controls the pitch and volume of whatever is on the cassette. [Scott] produced a few single-note cassettes for his instrument, with ‘voice patches’ including a flute, choir, and a synth. With the CV and Gate input, these sounds can be sequenced with outboard gear, producing the wonderful sounds heard in the video after the break.

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Fisher Price Bluetooth Speaker Hack

A good hacker hates to throw away electronics. We think [Matt Gruskin] must be a good hacker because where a regular guy would see a junky old 1980’s vintage Fisher Price cassette player, [Matt] saw a retro stylish Bluetooth speaker. His hack took equal parts of electronics and mechanics. It even required some custom 3D printing.

You might think converting a piece of old tech to Bluetooth would be a major technical challenge, but thanks to the availability of highly integrated modules, the electronics worked out to be fairly straightforward. [Matt] selected an off the shelf Bluetooth module and another ready-to-go audio amplifier board. He built a custom board to convert the stereo output to mono and hold the rotary encoder he used for the volume control. An Arduino (what else?) reads the encoder and also provides 3.3V to some of the other electronics.

The really interesting part of the hack is the mechanics. [Matt] managed to modify the existing mechanical buttons to drive the electronics using wire and hot glue. He also added a hidden power switch that doesn’t change the device’s vintage look. Speaking of mechanics, there’s also a custom 3D printed PCB holder allowing for the new board to fit in the original holder. This allows [Matt] to keep the volume control in its original location

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Microcassette Recorders Become A Tape Delay

Long before audio engineers had fancy digital delays, or even crappy analog delays, there were tape delays. Running a tape around in a loop with a record and play head is the basis of the Echoplex and Space Echo, and both of these machines are incredible pieces of engineering.

Microcassette recorders are not, in general, incredible pieces of engineering. They do, however, have a strip of magnetic tape, a record head, and a play head. Put two of them together, and you can build your own tape delay.

The basic principle of a tape delay is simple enough – just run a loop of tape round in a circle, through a record and playback head, record some audio, and send the output to an amplifier. In practice, it’s not that simple. [dogenigt] had to manufacture his own tape loop from microcassettes, a process that took far too long and was far too finicky.

For a control circuit, [dogenigt] is using four audio pots and one linear pot for speed control. The audio pots are responsible for input gain, feedback, the amplitude of the clean signal, and the output of the signal after it’s been run through the delay.

Apart from being one of those builds that’s very dependent on the mechanical skill of the builder, it’s a pretty simple delay unit, with all the electronics already designed for a stripboard layout. You can hear an example of what it sounds like below.

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Bringing a Century Stereo into the 21st Century

Way back in the previous century, people used to use magnetized strips of tape to play music. It might be hard to believe in today’s digital world, but these “cassette” tapes were once all the rage. [Steve] aka [pinter75] recently found a Bang & Olufsen stereo with this exact type of antequated audio playback device, and decided to upgrade it with something a little more modern.

Once the unit arrived from eBay and got an electronic tune-up, [pinter75] grabbed a Galaxy S3 out of his parts drawer and got to work installing it in the old cassette deck location. He used a laser cutter to make a faceplate for the phone so it could be easily installed (and removed if he decides to put the tape deck back in the future).

The next step was wiring up power and soldering the audio output directly to the AUX pins on the stereo. Once everything was buttoned up [pinter75] found that everything worked perfectly, and mounted the stereo prominently on his wall. It’s always great when equipment like this is upgraded and repaired rather than thrown out.

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.