RCx

The RCX, short for Robotic Command eXplorer, is the programmable brick at the heart of LEGO Mindstorms. It was released in 1998 as part of the LEGO Mindstorms Robotics Invention System and became the core controller for subsequent Mindstorms kits. The brick provides three sensor input ports and three actuator output ports, a built-in infrared receiver, a small display, and power from a detachable battery pack or external supply. It is designed to operate standalone or as part of a larger robot built with LEGO elements.

Programming the RCX is done through LEGO's Mindstorms software, a graphical environment that allows users to assemble programs by arranging blocks and setting conditions. The programs are stored on the brick and executed sequentially or in response to sensor input. In addition to the official software, third-party languages such as Not Quite C (NQC) enable more advanced coding with a text-based syntax.

The RCX played a pivotal role in popularizing educational robotics and remains a favorite among hobbyists and educators. It is considered legacy hardware of LEGO Mindstorms, having been succeeded by the LEGO Mindstorms NXT system in 2006, which introduced more capable hardware and a different programming paradigm. Nevertheless, RCX-based projects and their software libraries continue to be documented and discussed within the robotics community. Related topics include LEGO Mindstorms, the RCX's successor NXT, and the Not Quite C language.