Feature: Processors and MCUs


Enabled MCUs for simple, low-cost infrared communications By Graeme Clark, Principal Engineer, Renesas


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nfrared (IR) technology was one of the first technologies that was commonly available to enable true wireless communications between embedded devices, long before the advent of modern low power


radio frequency (RF) protocols. Tis technology has a long history in embedded applications, with consumer electronics being among the first adopters.


A short history of IR technology In the late 1970s, television manufacturers needed an easier and more reliable way to control their sets than the early generations of ultrasonic and wired remote controls. Early IR remote control systems used basic pulse-position modulation to send simple commands to the TV. A microcontroller inside the TV set decoded these light pulses into commands to change channels or turn the TV on and off. In the early 1980s, Philips developed


RC-5, a semi-proprietary consumer IR remote control communications protocol. It used a UART-like data frame, with start and stop bits, which could be easily created by a standard microcontroller UART. Tis was then used to create a Manchester


encoded bitstream, modulating a 36kHz or 38kHz carrier that could then be transmitted over an IR link. Tese frequencies were chosen to eliminate interference from ambient sunlight and household lighting. Tis development resulted in the same basic architecture still used today: a microcontroller, an infrared LED transmitter and a filtered photodiode receiver. Tere are many other protocols for data


transmission over an IR link, based around different encoding methods. Among them are pulse distance encoding used by the NEC protocol, pulse width coding used by Sony, and protocols using pulse burst and space encoding. Each of these is an appropriate solution for a specific type of application. In 1990s, the explosion of portable


computers and personal digital assistants called for high-speed wireless data transfers between devices. In 1993, the Infrared Data Association (IrDA) was founded by several major tech companies that included Hewlett-Packard, IBM and Sharp. Teir goal was to create a secure, interoperable, point-to-point wireless data standard using IR, which would enable easy, short-distance IR communication between devices. In 1995, Microsoſt announced that’s


IrDA would be supported in Windows 95, accelerating its adoption. IrDA introduced a structured protocol


Figure1: Microcontroller IrDA peripheral


stack for embedded microcontrollers. Te physical layer evolved from Serial Infrared (SIR) at 115.2kbps to Fast Infrared (FIR) at 4Mbps. IrDA modules were integrated into many products including mobile phones, tablets and laptops, enabling users to sync calendars, print documents and share contacts without cables. However, IrDA had strict constraints.


26 October 2026 www.electronicsworld.co.uk


It required direct line-of-sight and precise alignment between devices, and the operational range was typically limited to one metre. Over time, many consumer


mobile devices shiſted away from IR communications protocols, due to low power radio technologies, like Bluetooth Low Energy, becoming cost effective. Today, some products still maintain IR functionality and some embedded applications like utility meters, consumer remote controls and various data collection devices still use IR communications as one of their interfaces. Tis is because IR connectivity still provides many advantages, including ultra-low power consumption and zero licensing fees. Te short-range line-of-sight signal requirements and immunity to RF interference mean the connection is typically robust and secure. Using IR also reduces physical wear on connectors and keeps the electronics sealed against moisture and dirt.


MCUs with IR communications Many of today’s microcontrollers include peripheral modules that support IR communications. Several Renesas microcontrollers contain a dedicated IrDA peripheral module that encodes and decodes waveforms compliant with the IrDA Standard version 1.0. Tese can be integrated with the microcontroller’s internal UART for generating and receiving the signals; see Figure 1. IR transceivers are available from many


suppliers, including Vishay who provides transceivers that conform to IrDA 1.0, with versions supporting both the SIR and FIR. Te contents of the encoded messages are then based on the receiving device’s command specifications.


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