The Word of Notch. Index page - Minecraft Forums. Redstone circuits. A redstone circuit is a structure that can be built to activate or control mechanisms.
Circuits can be designed to act in response to player activation, or to operate autonomously—either on a loop, or in response to non-player activity such as mob movement, item drops, plant growth, etc. The mechanisms that can be controlled by redstone circuits range from simple devices such as automatic doors and light switches, to complex devices such as elevators, automatic farms, or even in-game computers. Understanding how to build and use redstone circuits and the mechanisms they can control will greatly increase the range of things that can be accomplished in Minecraft.