qr code

59 Articles

Compress Links For Optimal QR Codes

August 18, 2026 by 21 Comments

Link shorteners have been a staple of the online world for over two decades now, but they’ve got some issues– for one thing, it’s totally non-transparent where the link actually goes, leaving you open to all sorts of shenanigans, of which RickRolling is probably the best case. For two, your traffic is going through an external service who may have their own nefarious intent. [PortalRunner] had an idea: don’t shorten the link, but compress it.

You see, a traditional URL shortener like tinyurl just generates a random code and associates that with your original link in its database. That’s fine, but you’re relying on a third party database. The alternative is to take the URL, encode it in some way, and apply some compression algorithm to the data. If the encoding and compression are open-source– which [Portal ]’s absolutely are— then you can check yourself before following the link, and/or self-host the whole thing for piece of mind. As a bonus [Portal]’s Ha.mr– that’s pronounced Hammer– also gives you a QR code optimized for easy scanning. QR codes have a specific alphanumeric character set built in, and it isn’t the full UTF-8– if you naively use random text, you’re in byte mode, which needs a lot more QR real estate. Or inverting that, the fewer bits it has to store, the easier a qr code is to scan at the same size. The text version of the compressed links can use UTF-8– including emoticons– but they don’t have to.

The whole project has a “why isn’t everyone doing it this way” vibe about it. We’d probably want to self-host this if we were using it seriously– [Portal] put this together on a lark and makes no promises it will be online forever–but again, this is open source, so we can. [Portal] is using normal compression algorithms here, but if you really want to squeeze text, use a neural net. 

Continue reading “Compress Links For Optimal QR Codes” →

Store Tunes On Paper And Stream Them Over LoRA

August 18, 2026 by 37 Comments

Some projects seem too good to be true until you dig into it and find the secret magic that makes it all work. Take Paper Tunes by [Makestreame], a project which purports to store a song on a single sheet of paper via QR code and transmit the data over LoRA. If it was a MIDI sequence, maybe. But the promise of Paper Tunes is to take any MP3 and give it this treatment, and that just seems like an impossible level of compression at first glance.

The music is heavily compressed, make no doubt about that. There’s samples in the Instructables link above and in the video below, but it sounds far better than it has any right to. The secret is Meta’s EnCodec neural codec, which like you’d guess uses neural nets to squeeze the absolute minimum information needed to reconstruct a sample. With it [Makestreame] is able to get a 2.9 MB MP3 file down to just 21.44 kB.

Of course, that’s still not going to fit in a 3.3 kB QR code. But by simply making eight of them, [Makestreame] is able to fit the song onto the front and back of a piece of paper. Yes, each song has an “A” and a “B” side — and you thought flipping a record halfway through got old fast. Having to scan eight codes to get one song may strike some as a bit silly, but we do enjoy some silly things here.

The same EnCodec compression that gets the song so tiny as to fit in a brace of QR codes is obviously also what enables its transmission over LoRA. While it’s got far lower bandwidth than something like WiFi, 21 kB is well within its limits. It’s often said that LoRA isn’t suitable for audio, but this project is another example that one person’s “unsuitable” is another person’s “challenge accepted”.

We’ve seen other LoRA audio projects before. Speaking of things not suitable for audio, we once featured an entire album crammed onto a floppy disk. Continue reading “Store Tunes On Paper And Stream Them Over LoRA” →

Worst Clock Ever Teaches You QR Codes

September 18, 2025 by 11 Comments

[WhiskeyTangoHotel] wrote in with his newest clock build — and he did warn us that it was minimalist and maybe less than useful. Indeed, it is nothing more than a super-cheap ESP32-C3 breakout board with an OLED screen and some code. Worse, you can’t even tell the time on it without pointing your cell phone at the QR code it generates. Plot twist: you skip the QR code and check the time on your phone.

But then we got to thinking, and there is actually a lot to learn from here on the software side. This thing pulls the time down from an NTP server, formats it into a nice human-readable string using strftime, throws that string into a QR code that’s generated on the fly, and then pushes the bits out to the screen. All in a handful of lines of code.

As always, the secret is in the libraries and how you use them, and we wanted to check out the QR code generator, but we couldn’t find an exact match for QRCodeGenerator.h. Probably the most popular library is the Arduino QRCode library by [ricmoo]. It’s bundled with Arduino, but labelled version 0.0.1, which we find a little bit modest given how widely it’s used. It also hasn’t been updated in eight years: proof that it just works?

That library drew from [nayuki]’s fantastically documented multi-language QR-Code-generator library, which should have you covered on any platform you can imagine, with additional third-party ports to languages you haven’t even heard of. That’s where we’d go for a non-Arduino project.

What library did [WTH] use? We hope to find out soon, but at least we found a couple good candidates, and it appears to be a version of one or the other.

We’ve seen a lot of projects where the hacker generates a QR code using some online tool, packs the bits into a C header array, and displays that. That’s fine when you only need a single static QR code, but absolutely limiting when you want to make something dynamic. You know, like an unreadable clock.

You will not be surprised to know that this isn’t the first unreadable QR-code clock we’ve featured here. But it’s definitely the smallest and most instructive.

Continue reading “Worst Clock Ever Teaches You QR Codes” →

Studying QR Code Degradation

May 13, 2025 by 31 Comments

It’s fair to say that QR codes are a technology that has finally come of age. A decade or more ago they were a little over-hyped and sometimes used in inappropriate or pointless ways, but now they are an accepted and useful part of life.

They’re not without their faults though, one of which is that despite four increasingly redundant levels of error correction, there comes a point at which a degraded QR code can no longer be read. [HumanQR] is soliciting these broken QR codes for research purposes and inclusion in an eventual open-source database, and they’ll even have a shot at repairing your submissions for you.

It’s a problem inherent to all digital media, that once the limit of whatever error correction they contain has been reached, they arrive at a cliff-edge at which they go immediately from readability to non readability. The example given in the linked article is a locator tag on a stray cat, it had been rubbed away in part. Improving its contrast, sharply defining its edges, and improving the definition of its fiducials was able to revive it, we hope leading to the cat being returned home.

The idea is that by studying enough damaged codes it should be possible to identify the means by which they become degraded, and perhaps come up with a way to inform some repair software. Meanwhile if you are interested, you might want to learn more about how they work, the hard way.

This QR Code Leads To Two Websites, But How?

January 23, 2025 by 47 Comments

QR codes are designed with alignment and scaling features, not to mention checksums and significant redundancy. They have to be, because you’re taking photos of them with your potato-camera while moving, in the dark, and it’s on a curved sticker on a phone pole.  So it came as a complete surprise to us that [Christian Walther] succeeded in making an ambiguous QR code.

Nerd-sniped by [Guy Dupont], who made them using those lenticular lens overlays, [Christian] made a QR code that resolves to two websites depending on the angle at which it’s viewed. The trick is to identify the cells that are different between the two URLs, for instance, and split them in half vertically and horizontally: making them into a tiny checkerboard. It appears that some QR decoders sample in the center of each target square, and the center will be in one side or the other depending on the tilt of the QR code.

Figuring out the minimal-difference QR code encoding between two arbitrary URLs would make a neat programming exercise. How long before we see these in popular use, like back in the old days when embedding images was fresh? QR codes are fun!

Whether it works is probably phone- and/or algorithm-dependent, so try this out, and let us know in the comments if they work for you.

Thanks [Lacey] for the tip!

 

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 59 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!