Arduino Yún

Overview

The Arduino Yún (meaning "cloud" in Chinese) is a unique board that combines two processors: an ATmega32U4 Arduino microcontroller and a Atheros AR9331 MIPS-based Linux SoC running OpenWrt. This dual-processor architecture allows developers to write standard Arduino sketches on the 32U4 side while leveraging a full Linux environment for web services, network connectivity, and complex processing on the Linux side.

The ATmega32U4 runs at 16 MHz with 32KB flash and 2.5KB SRAM, providing familiar Arduino compatibility for hardware interfacing. The AR9331 runs at up to 400 MHz with 64MB DDR2 RAM and 16MB SPI flash, hosting an OpenWrt Linux system that provides WiFi (802.11bgn with AP/router capability), Ethernet via PoE, USB 2.0 host, and microSD card support.

The two processors communicate via a Bridge library, allowing Arduino sketches to invoke Linux commands, read web APIs, and publish data to cloud services. The board can be programmed wirelessly over WiFi using Arduino IDE 1.5.4+, eliminating the need for a physical USB cable in deployed installations.

The Yún was a pioneering board for IoT development at a time when WiFi-enabled microcontrollers were uncommon, enabling projects like weather stations, security cameras, and smart home controllers that required both real-time hardware control and internet connectivity.