London’s Transport for London has a wonderful service called Countdown that can give live bus arrival times. For example, here’s a page showing live buses passing No. 10 Downing St. Underlying this is a simple JSON API that, while not public, seems to be usable by the average programmer as long as I’m not abusive. So with its details deciphered (hardly hard since the web site uses the API) I set about building an ambient bus monitor into a model London bus. The idea is that I can glance at the bus and see the times of up to the next two buses that I’m likely to want to catch and know when to leave the house.