How did Stephen Hawking talk?

I am just too lazy to look this up but does anyone know how that machine worked? did he somehow just type it in or did it sync to his brain? I am just confused. Any ideas?

he typed it up through his keypad through his chair if I'm correct

dude, did u think how is the hard work to write down letter by letter to form 1 phase , we can speak lot of phases at one time, he dont

Facial recognition is crucial to the talking of stephen hawking as of what i have heard

A quick search came up with this : https://blog.swiftkey.com/swiftkey-revea...on-system/. Hope it helps.