Storing Image Data As Analog Audio

Ham radio operators may be familiar with slow-scan television (SSTV) where an image is sent out over the airwaves to be received, decoded, and displayed on a computer monitor by other radio operators. It’s a niche mode that isn’t as popular as modern digital modes like FT8, but it still has its proponents. SSTV isn’t only confined to the radio, though. [BLANCHARD Jordan] used this encoding method to store digital images on a cassette tape in a custom-built tape deck for future playback and viewing.

The self-contained device first uses an ESP32 and its associated camera module to take a picture, with a screen that shows the current view of the camera as the picture is being taken. In this way it’s fairly similar to any semi-modern digital camera. From there, though, it starts to diverge from a typical digital camera. The digital image is converted first to analog and then stored as audio on a standard cassette tape, which is included in the module in lieu of something like an SD card.

To view the saved images, the tape is played back and the audio signal captured by an RP2040. It employs a number of methods to ensure that the reconstructed image is faithful to the original, but the final image displays the classic SSTV look that these images tend to have as a result of the analog media. As a bonus feature, the camera can use a serial connection to another computer to offload this final processing step.

We’ve been seeing a number of digital-to-analog projects lately, and whether that’s as a result of nostalgia for the 80s and 90s, as pushback against an increasingly invasive digital world, or simply an ongoing trend in the maker space, we’re here for it. Some of our favorites are this tape deck that streams from a Bluetooth source, applying that classic cassette sound, and this musical instrument which uses a cassette tape to generate all of its sounds.

Streaming Music To Cassette

In almost every measurable way, a lossless digital audio file is superior to any analog media. This doesn’t mean that analog audio isn’t valuable though; plenty of people appreciate the compression, ambiance, and other side-effects of listening to a vinyl record or a cassette tape despite the technical limitations. To combine the audio technology of the modern world with these pleasant effects of old analog media, [Julius] built a cassette-based media streamer.

The music playback device takes input from a Bluetooth stream of some sort, converts the digital stream to analog, combines the stereo signal into a mono signal, and then records it to a cassette tape. The tape is then looped through to a playback device which outputs the sound to a single speaker. This has the effect of functioning as a tape delay device, and [Julius] did add input and output jacks to use it as such, but in its default state it has the effect of taking modern streaming through a real analog device and adding the compression and saturation that cassette tapes are known for.

The design of the device is impressive as well, showing off the tape loop and cassette front-and-center with a fluorescent vu meter on the side and a metal case. Getting all of this to work well together wasn’t entirely smooth, either, as [Julius] had to sort out a number of issues with the electronics to keep various electric noises out of the audio signal. Retro analog music players are having a bit of a resurgence right now, whether that’s as a revolt against licensed streaming services or as a way to experience music in unique ways, and our own [Kristina Panos] recently went down an interesting rabbit hole with one specific type of retro audio player.

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FPGA Brings UNIX V1 To The DEC J-11

If you’ve never used a PDP-11 before it’s probably because you simply weren’t around in the 70s and 80s. Although they started as expensive machines only in research labs and industry, they eventually became much more accessible. They’re a bit of a landmark in computing history, too, being largely responsible for the development of things like UNIX and the C programming language. [ryomuk] is using an FPGA in combination with an original DEC J-11 to bring us a new take on this machine. (Google Translate from Japanese)

The FPGA used in this build is a Tang Nano 20k, notable for its relatively low cost. The FPGA emulates the memory system and UART of a PDP-11 system down to the instruction set, while the original, unmodified DEC chip is left to its own devices. After some initial testing [ryomuk] built a PC11 paper tape emulator to ensure the system was working which runs a version of BASIC from the era. The next thing up was to emulate some disk drives and co-processors so that the machine can run the first version of UNIX. 

[ryomuk] also developed a PCB for the DEC microprocessor and the FPGA to sit on together, and it includes all of the jumpers and wiring needed to allow the computer to run UNIX, as well as handling other miscellaneous tasks like power. It’s an interesting build that gets to the heart of the early days of computer science. PDP-11 computers did eventually get smaller and more accessible, and if you want to build a modern version this build fits a complete system into an ATX case.

Thanks to [RetepV] for the tip!

Bar of conductive filament with leds and a battery

Putting Conductive TPU To The Test

Ever pried apart an LCD? If so, you’ve likely stumbled at the unassuming zebra strip — the pliable connector that makes bridging PCB pads to glass traces look effortless. [Chuck] recently set out to test if he could hack together his own zebra strip using conductive TPU and a 3D printer.

[Chuck] started by printing alternating bands of conductive and non-conductive TPU, aiming to mimic the compressible, striped conductor. Despite careful tuning and slow prints, the results were mixed to say the least. The conductive TPU measured a whopping 16 megaohms, barely touching the definition of conductivity! LEDs stayed dark, multimeters sulked, and frustration mounted. Not one to give up, [Chuck] took to his trusty Proto-pasta conductive PLA, and got bright, blinky success. It left no room for flexibility, though.

It would appear that conductive TPU still isn’t quite ready for prime time in fine-pitch interconnects. But if you find a better filament – or fancy prototyping your own zebra strip – jump in! We’d love to hear about your attempts in the comments.

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Newspaper clipping with words 'speaking personally' and a photo

A Fast Rewind To The Era Of Tapesponding

Imagine a time before Discord servers and cheap long-distance calls. Back in the 1950s, a curious and crafty group of enthusiasts invented their own global social network: on reels of magnetic tape. They called it tapesponding (short for tape corresponding), and it was a booming hobby for thousands of radio hams, tinkerers, and audio geeks. Here’s the original video on this analog marvel.

These folks weren’t just swapping mixtapes. They crafted personal audio letters, beamed across the globe on 3-inch reels. DIY clubs emerged everywhere: World Tape Pals (Texas-based, naturally) clocked 5,000 members from “every Free Nation” – which frames it in a world in terms of East vs. West. Some groups even pooled funds to buy shared tape decks in poorer regions – pure hacker spirit. The tech behind it: Speeds of 3¾ IPS, half-track mono, round-robin reels, and rigorous trust networks to avoid ghosters. Honestly, it makes IRC net ops look soft. Tapesponding wasn’t just for chatty types. It fostered deep friendships, even marriages. It was social engineering before that term was coined. The video is below the break.

What are your thoughts on this nostalgic way of long-distance communication? The warm whirring of a spinning tape reel? The waiting time before your echo is returned? Or are have you skipped all the analog mechanics and shouted out into the LoRaWAN void long ago?

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An image showing an original grey and blue Sony Walkman with the text "1970" below it, and an arrow pointing to the right of it at a much smaller blue Walkman with the text "2000" underneath it, and a final arrow pointing to the right to a bright orange cassette player by We Are Rewind in a man's hand with the text "now" beneath it.

Why Are Cassette And CD Players So Big Now?

The early 2000s were the halcyon days of physical media. While not as svelte as MP3 players became, why are those early 2000s machines smaller than all the new models popping up amidst the retro audio craze?

We’ve bemoaned the end of the electromechanical era before, and the Verge recently interviewed the people at We Are Rewind and Filo to get the skinny on just why these newer cassette and CD players aren’t as small as their predecessors. It turns out that all currently produced cassette players use the same mechanism with some small tweaks in materials (like metal flywheels in these higher quality models) because the engineering required to design a smaller and better sounding alternative isn’t warranted by the niche nature of the cassette resurgence.

A similar fate has befallen the laser head of CD mechanisms, which is why we don’t have those smooth, rounded players anymore. Economies of scale in the early 2000s mean that even a cheap player from that era can outperform a lot of the newer ones, although you won’t have newer features like Bluetooth to scandalize your audiophile friends. A new Minidisc player is certainly out of the question, although production of discs only ended this February.

If you’re looking to get back into cassettes, this masterclass is a good place to start. If you don’t fancy any of the players the Verge looked at, how about rolling your own incarnation with the guts from a vintage machine or just going for the aesthetic if cassettes aren’t your jam?

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Copying Commodore Data Tapes, 40 Years Late

Unless you handle the backups for a large corporation, bank, or government entity, you likely haven’t stored much data to tape recently. But magnetic storage used to be fairly mainstream back in the 1980s for all kinds of computer programs. Plenty of computers used standard cassette tapes for this too but you couldn’t just copy them with standard audio equipment. You’d need something like this 1560 datasette from [Jan].

The core problem with using Hi-Fi equipment to copy tapes storing data instead of audio is that data tapes need to be much more precise in order to avoid losses that might not be noticeable in an audio recording. In the 80s computer companies like Commodore built tape drives specifically for their computers, so [Jan]’s project uses two of these 1530 drives to build this “1560” datasette. (No working 1530 hardware was harmed in this build.) An inverter circuit in one tape deck is used to provide the signal to write the data to the other tape, reliably copying data from these data tapes in a way Hi-Fi never could.

[Jan] does lament not having something like this back in the 80s when the Commodore was in its heyday, but there’s still a dedicated retrocomputing scene for these machines that will get plenty of use out of projects like this. If you need to go the other direction in time, there are also interfaces that allow data tapes from old Commodores to be read by modern computers with USB.

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