21cm
A knowledge progression game by
Play With Your Mind
Solving all parts of this puzzle will reveal a secret code, which can be used in the game 1420MHz upon release to unlock exclusive content.
Choose between Just Logic or Research modes below.
If you want to skip past the research part of this puzzle, click on the icon above for a summary of the relevant information.
Everything you need to solve this puzzle can be found on the Wikipedia page for QR Codes. You got this!
What is a QR Code?
A QR Code is a structured image that computers can translate into data, often a URL. You likely used a QR Code to get to this website!Creating a QR Code by hand involves a fair bit of math, but you don't need any of that to solve this puzzle.
Modules
QR Codes are made up of a grid of squares. Each square is called a module. They can be either black or white, corresponding to 1s and 0s.
◼︎ ◼︎
Finder Pattern
All QR Codes have at least one Finder Pattern, usually three. It looks like this:
The Finder Pattern needs a Separator of one ◼︎ module all around it, even on the corners. No ◼︎ modules are allowed to touch the Finder Patterns.
Fixed Patterns
QR Codes come in different sizes. Each one is called a version, and there are 40 standard versions, plus some other less standard ones. Each version has specified fixed patterns of ◼︎ and ◼︎ modules that are the same for all QR Codes of that version.
The alternating ◼︎ and ◼︎ modules are call the Timing Patterns.The single ◼︎ just above and to the right of the bottom left Finder Pattern is called the "Dark Module", and it is always black.The white area all around the entire QR Code is call the "Quiet Zone", and it must be 4 modules wide and high.QR codes of Version 2 or bigger have Alignment Patterns. They look similar to Finder Patterns, but smaller, and do not require Separator modules (◼︎ modules can touch them).
Formatting Pattern
In order for your device to be able to decode the data, it needs to know how it was encoded and what masking pattern was used. The Formatting and Version Patterns provide that information, and they are near the Finder Patterns.
In the images above, the Formatting Pattern has been marked as ◼︎, the Version Information Pattern has been marked with ◼︎, and the Data Bit Stream has been marked with ◼︎.Only QR Codes of Version 7 or above have Version Patterns. The smaller QR Codes do not need this information.
Formatting Pattern Encoding
The Formatting Pattern contains two copies of the formatting information for redundancy.
The Formatting Pattern contains two pieces of information: the Error Correction Level (2 bits), and the Encoding Mode (3 bits). The remaining 10 bits are for error correction on the Formatting Pattern itself.
The image above shows an example of how a "mask pattern" is applied to the raw Formatting Information to get the final Formatting Pattern. The details of this calculation are not necessary for this puzzle.
Encoding Mode & Masks
The Encoding Mode of the QR code is stored in the first four bits of data, which are stored in the bottom right corner of the QR code. However, the data is transformed by a "data mask pattern" to help with machine readability. The details of the masking patterns are not necessary for this puzzle.
In the image above, the Formatting Pattern has been marked as ◼︎, the and the Encoding Mode data location has been marked with ◼︎.
This QR Code uses Alphanumeric encoding, so we can calculate what the data encoding pattern will look like for each Data Mask Pattern. In the image above, the Encoding Mode bits that correspond to each Data Mask Pattern have been pre-calculated.
More Info
There is a lot more to QR Codes than was covered here, but this is all you need to solve this puzzle.If this puzzle seems fun to you, check out 1420MHz, a knowledge progression game about deciphering an alien message from space.
