A computer has only two things to work with: on and off, written as one and nought. Eight of them in a row make a number up to 255, and every letter has an agreed number. That is all text is, anywhere, ever.
Bacon got there three hundred years early with his A and B. The only difference is the name.
Two states, and nothing else
A switch is on or off. A hole is punched or not. A voltage is high or low. Every photograph, song and message you have ever seen arrives as a river of these two states, and the only reason it works is that two states are the easiest thing in the world for a machine to tell apart. Bacon got there in 1605 with A and B; the machines caught up three hundred years later.
Print this page and you get a worksheet: how the cipher works, where it came from, and the puzzles to crack, with the machine and the menus left off.
Print this page as a worksheet Its sheet in the pack Try the challengesLonger, harder and written for grown-ups. Worth a look when this page runs out.