IrDA
This article is a technical history of free-space optical communications that traces how infrared links evolved from niche laser networking and satellite experiments into short-range device interconnects such as HP calculator peripherals and, ultimately, IrDA. It explains that Hewlett-Packard’s early “RedEye” link was effectively a UART carried over an IR LED and photodiode pair for wireless printing, then expanded into HP SIR, a bidirectional serial infrared protocol that behaved much like RS-232 over light. The piece highlights the engineering constraints that shaped these designs, especially half-duplex operation because an active transmitter can blind its own receiver, along with the power and component limitations of late-1980s portable hardware. While not a vulnerability write-up, it provides useful protocol and physical-layer context for anyone studying how short-range optical communications were implemented and why IR networking remained a specialized technology.