Click Generate to generate a QR code. Use the size variable to adjust the size of a normal QR code. Use the Code Type variable to change between normal codes and Mii codes. 25x25 is the standard web URL size, so you might have better luck with that.
Just a little something I whipped up for fun. Technically, all the codes you generate could be legitimate, but you'd be hard-pressed to find one that actually leads somewhere (or that gives you a Mii). You can still try though!