qr code

54 Articles

Archiving Data On Paper Using 2D Images

September 15, 2024 by 44 Comments

It seems like only yesterday we covered a project using QR codes to archive data on paper (OK, it was last Thursday), so here’s another way to do it, this time with a dedicated codec using the full page. Optar or OPTical ARchiver is a project capable of squeezing a whopping 200 Kb of data onto a single A4 sheet of paper, with writing and reading achieved with a standard laser printer and a scanner. It’s a bit harder than you might think to get that much data on the page, given that even a 600 DPI printer can’t reliably place every dot each time. Additionally, paper is rarely uniform at the microscopic scale, so Optar utilizes a forward error-correcting coding scheme to cater for a little irregularity in both printing and scanning.

The error-correcting scheme selected was an Extended Golay code (24, 12, 8),  which, interestingly, was also used for image transmission by the NASA Voyager 1 and 2 missions. In information theory terms, this scheme has a minimum Hamming Distance of 8, giving detection of up to seven bit errors. This Golay code implementation is capable of correcting three-bit errors in each 24-bit block, with 12 bits available for payload. That’s what the numbers in those brackets mean.

Another interesting problem is paper stretch during printing. A laser printer works by feeding the paper around rollers, some of which are heated. As a printer wears or gets dirty, the friction coefficient along the rollers can vary, leading to twisting and stretching of the paper during the printing process. Water absorbed by the paper can also lead to distortion. To compensate for these effects, Optar regularly inserts calibration targets throughout the bit image, which are used to locally resynchronize the decoding process as the image is processed. This is roughly similar to how the alignment patterns work within larger QR codes. Finally, similar to the position detection targets (those square bits) in QR codes, Optar uses a two-pixel-wide border around the bit image. The border is used to align to the corners well enough to locate the rows of bits to be decoded.

In the distant past of last week, we covered a similar project that uses QR codes. This got us thinking about how QR codes work, and even if encoding capacity can be increased using more colors than just black and white?

Thanks to [Petr] for the tip!

Back Up Your Data On Paper With Lots Of QR Codes

September 12, 2024 by 55 Comments

QR codes are used just about everywhere now, for checking into venues, ordering food, or just plain old advertising. But what about data storage? It’s hardly efficient, but if you want to store your files in a ridiculous paper format—there’s a way to do that, too!

QR-Backup was developed by [za3k], and is currently available as a command-line Linux tool only. It takes a file or files, and turns them into a “paper backup”—a black-and white PDF file full of QR codes that’s ready to print. That’s legitimately the whole deal—you run the code, generate the PDF, then print the file. That piece of paper is now your backup. Naturally, qr-backup works in reverse, too. You can use a scanner or webcam to recover your files from the printed page.

Currently, it achieves a storage density of 3KB/page, and [za3k] says backups of text in the single-digit megabyte range are “practical.” You can alternatively print smaller, denser codes for up to 130 KB/page.

Is it something you’ll ever likely need? No. Is it super neat and kind of funny? Yes, very much so.

We’ve seen some other neat uses for QR codes before, too—like this printer that turns digital menus into paper ones. If you’ve got your own nifty uses for these attractive squares, let us know!

OpenSCAD Library Creates QR Codes On The Fly

September 4, 2024 by 18 Comments

If you’ve been reading Hackaday for awhile, you’ll know we’re big fans of OpenSCAD around these parts. There’s a number of reasons it’s a tool we often reach for, but certainly one of the most important ones is its parametric nature. Since you’re already describing the object you want to generate with code and variables, it’s easy to do things like generate an arbitrary number of cloned objects by using a for loop.

There are a number of fantastic OpenSCAD libraries that explore this blurred line between code and physical objects, and one that recently caught our eye is scadqr from [xypwn]. The description says it lets you “Effortlessly generate QR codes directly in OpenSCAD”, and after playing around with it for a bit, we have to agree.

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Play Giant Tetris On Second-Floor Window

May 28, 2024 by 11 Comments

Sometimes it seems like ideas for projects spring out of nothingness from a serendipitous set of circumstances. [Maarten] found himself in just such a situation, with a combination of his existing Tetris novelty lamp and an awkwardly-sized window on a second-floor apartment, he was gifted with the perfect platform for a giant playable Tetris game built into that window.

To make the giant Tetris game easily playable by people walking by on the street, [Maarten] is building as much of this as possible in the browser. Starting with the controller, he designed a NES-inspired controller in JavaScript that can be used on anything with a touch screen. A simulator display was also built in the browser so he could verify that everything worked without needing the giant display at first. From there it was on to building the actual window-sized Tetris display which is constructed from addressable LEDs arranged in an array that matches the size of the original game.

There were some issues to iron out, as would be expected for a project with this much complexity, but the main thorn in [Maarten]’s side was getting his controller to work in Safari on iPhones. That seems to be mostly settled and there were some other gameplay issues to solve, but the unit is now working in his window and ready to be played by any passers-by, accessed by a conveniently-located QR code. Tetris has been around long enough that there are plenty of unique takes on the game, like this project from 2011 that uses Dance Dance Revolution pads for controllers.

Streaming Deck Removes Need For Dedicated Hardware

February 25, 2024 by 11 Comments

Streaming content online has never been more popular than it is now, from YouTube to Twitch there are all kinds of creators around with interesting streams across a wide spectrum of interests. With that gold rush comes plenty of people selling figurative shovels as well, with audio mixing gear, high-quality web cams, and dedicated devices for controlling all of this technology. Often these devices take the form of a tablet-like device, but [Lenochxd] thinks that any tablet ought to be able to perform this task without needing dedicated, often proprietary, hardware.

The solution offered here is called WebDeck, an application written in Flask that turns essentially any device with a broswer into a stream control device. Of course it helps to have a touch screen as well, but an abundance of tablets and smartphones in the world makes this a non-issue. With the software running on the host computer, the streamer can control various aspects of that computer remotely by scanning a QR code which opens a browser window with all of the controls accessible from within. It has support for VLC, OBS Studio, and Spotify as well which covers the bases for plenty of streaming needs.

Currently the host software only runs on Windows, but [Lenochxd] hopes to have MacOS and Linux versions available soon. We’re always in favor of any device that uses existing technology and also avoids proprietary hardware and software. Hopefully that’s a recipe to avoid planned obsolescence and unnecessary production. If you prefer a version with a little bit of tactile feedback, though, we’ve seen other decks which add physical buttons for quick control of the stream.

Unlimited Cloud Storage YouTube Style

February 22, 2024 by 76 Comments

[Adam Conway] wanted to store files in the cloud. However, if you haven’t noticed, unlimited free storage is hard to find. We aren’t sure if he wants to use the tool he built seriously, but he decided that if he could encode data in a video format, he could store his files on YouTube. Does it work? It does, and you can find the code on GitHub.

Of course, the efficiency isn’t very good. A 7 K image, for example, yielded a 9-megabyte video. If we were going to store files on YouTube, we’d encrypt them, too, making it even worse.

The first attempt was to break the file into pieces and encode them as QR codes. Makes sense, but it didn’t work out. To get enough data into each frame, the modules (think pixels) in the QR code were small. Combined with video compression, the system was unreliable.

Simplicity rules. Each frame is 1920×1080 and uses a black pixel as a one and a white pixel as a zero. In theory, this gives about 259 kbytes per frame. However, to help avoid problems decoding due to video compression, the real bits use a 5×5 pixel block, so that means you get about 10 kbytes of data per frame.

The code isn’t perfect. It can add things to the end of a file, for example, but that would be easy to fix. The protocol could use error correction and compression. You might even build encryption into it or store more data — old school cassette-style — using the audio channel. Still, as a proof of concept, it is pretty neat.

This might sound like a new idea, but people way back in the early home computer days could back up data to VCRs. This isn’t even the first time we’ve seen it done with YouTube.

Recreating The Quadrophonic Sound Of The 70s

February 6, 2024 by 23 Comments

For plenty of media center PCs, home theaters, and people with a simple TV and a decent audio system, the standard speaker setup now is 5.1 surround sound. Left and right speakers in the front and back, with a center speaker and a subwoofer. But the 5.1 setup wasn’t always the standard (and still isn’t the only standard); after stereo was adopted mid-century, audio engineers wanted more than just two channels and briefly attempted a four-channel system called quadrophonic sound. There’s still some media from the 70s that can be found that is built for this system, such as [Alan]’s collection of 8-track tapes. These tapes are getting along in years, so he built a quadrophonic 8-track replica to keep the experience alive.

The first thing needed for a replica system like this is digital quadrophonic audio files themselves. Since the format died in the late 70s, there’s not a lot available in modern times so [Alan] has a dedicated 8-track player connected to a four-channel audio-to-USB device to digitize his own collection of quadrophonic 8-track tapes. This process is destructive for the decades-old tapes so it is very much necessary.

With the audio files captured, he now needs something to play them back with. A Raspberry Pi is put to the task, but it needs a special sound card in order to play back the four channels simultaneously. To preserve the feel of an antique 8-track player he’s cannibalized parts from three broken players to keep the cassette loading mechanism and track indicator display along with four VU meters for each of the channels. A QR code reader inside the device reads a QR code on the replica 8-track cassettes when they are inserted which prompts the Pi to play the correct audio file, and a series of buttons along with a screen on the front can be used to fast forward, rewind and pause. A solenoid inside the device preserves the “clunk” sound typical of real 8-track players.

As a replica, this player goes to great lengths to preserve the essence of not only the 8-track era, but the brief quadrophonic frenzy of the early and mid 70s. There’s not a lot of activity around quadrophonic sound anymore, but 8-tracks are popular targets for builds and restorations, and a few that go beyond audio including this project that uses one for computer memory instead.

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