This thing will generate a QR code from the supplied text. It is a native OpenSCAD program, so you don't need to download any third-party app to use it.

Code has been updated to remove the unprintability bug. It now has a small gap between each square.

Enter your string, set the minimum error correction level, choose a mask and away you go...

I've only got the data pre-set to generate QR codes up to version 6, which means there is a character limit of 134/106/74/58 (depending on your error correction level).