IremitterSans writes “The cheapest way to remotely control a device within a visible range is via Infra-Red light. Almost all audio and video equipment can be controlled this way nowadays. Due to this wide spread use the required components are quite cheap, thus making it ideal for us hobbyists to use IR control for our own projects. This part of my knowledge base will explain the theory of operation of IR remote control, and some of the protocols that are in use in consumer electronics.” Link.