blogmywiki dives into the mystery that is generating NTSC video from a BBC micro:bit (version 1):
It had been bugging me for years that it must be possible to get composite video out of a BBC micro:bit the same way as on the Arduino and IchigonJam. And it is, and someone has already done it. Welcome, IchigonQuest! It’s a very quirky, very Japanese way of coding microcontrollers in something a bit like BASIC. There’s a whole ecosystem around it, and as they’re not shipping to the UK at the moment I put it out of my mind.
Then I found there’s a micro:bit port of it. And I got it working. I have no idea what I’m doing, but it works! The micro:bit becomes a self-contained computer with its own keyboard and screen that you can program on its own.