There have been a few projects to get double height characters on LCD displays, but none that I found particularly easy to use. I’ve created two libraries which hopefully make this easy.
One library, BigCrystal is for LCDs connected directly to an Arduino, whilst the other, BigCrystalTWI is for LCDs connected via I2C. The code is based on the original fonts and code written by Michael Pilcher, documented in an old forum post.
I’ve put additional documentation on my blog.
I no longer have an I2C backpack for my LCD, so couldn’t test the BigCrystalTWI library. I’d appreciate it if someone with one handy can give the library a quick test and confirm it all works.