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Arduino YÚN is a member of a new groundbreaking line of WiFi products combining the power of Linux with the ease of use of Arduino.
The Arduino Yún is a microcontroller board based on the ATmega32u4 (datasheet) and the Atheros AR9331. The Atheros processor supports a Linux distribution based on OpenWrt named Linino OS. The board has built-in Ethernet and WiFi support, a USB-A port, micro-SD card slot, 20 digital input/output pins (7 of them can be used as PWM outputs and 12 as analog inputs), a 16 MHz crystal oscillator, a micro USB connection, an ICSP header, and 3 reset buttons.
It is recommended to power the board via the micro-USB connection with 5VDC.
If you are powering the board though the Vin pin, you must supply a regulated 5VDC. There is no on-board voltage regulator for higher voltages, which will damage the board.
The Yún is also compatible with PoE power supply but in order to use this feature you need to mount a PoE module on the board or buy a preassembled board.
Warning: Arduino YÚN is only compatible with 5V PoE module, is not compatible with 12V PoE module.
The power pins are as follows:
The ATmega32u4 has 32 KB (with 4 KB used for the bootloader). It also has 2.5 KB of SRAM and 1 KB of EEPROM (which can be read and written with the EEPROM library).
The memory on the AR9331 is not embedded inside the processor. The RAM and the storage memory are externally connected. The Yún has 64 MB of DDR2 RAM and 16 MB of flash memory. The flash memory is preloaded in factory with a Linux distribution based on OpenWrt called Linino OS. You can change the content of the factory image, such as when you install a program or when you change a configuration file. You can return to the factory configuration by pressing the "WLAN RST" button for 30 seconds.
The Linino OS installation occupies around 9 MB of the 16 MB available of the internal flash memory. You can use a micro SD card if you need more disk space for installing applications.
Input and Output:
It is not possible to access the I/O pins of the Atheros AR9331. All I/O lines are tied to the ATmega32U4.
Each of the 20 digital i/o pins on the Yún can be used as an input or output, using pinMode(), digitalWrite(), and digitalRead() functions. They operate at 5 volts. Each pin can provide or receive a maximum of 40 mA and has an internal pull-up resistor (disconnected by default) of 20-50 kOhms. In addition, some pins have specialized functions:
The Yún has a number of facilities for communicating with a computer, another Arduino, or other microcontrollers. The ATmega32U4 provides a dedicated UART TTL (5V) serial communication. The 32U4 also allows for serial (CDC) communication over USB and appears as a virtual com port to software on the computer. The chip also acts as a full speed USB 2.0 device, using standard USB COM drivers. The Arduino software includes a serial monitor which allows simple textual data to be sent to and from the Arduino board. The RX and TX LEDs on the board will flash when data is being transmitted via the USB connection to the computer.
Digital pins 0 and 1 are used for serial communication between the 32U4 and the AR9331.
You can use Ciao library to communication between the processors.
Arduino Ciao is an easy-to-use and powerful technology that enables Arduino sketches to communicate intuitively with the "outside World". It aims to simplify interaction between microcontroller and Linino OS, allowing a variety of connections with most common protocols, third-party services and social networks.
Ciao has been designed and developed to be modular and easily configurable. Its goal is to support several connectors capable of interacting with the system resources (filesystem, console, memory) and to communicate with the most common and useful protocols (XMPP, HTTP, WebSocket, COAP, etc..) and applications (Jabber, WeChat, Twitter, Facebook, etc.).
Ciao Library is a lightweight library that can be used inside sketches for MCU to send and receive data, via serial communication, in a simple and intuitive way.
A SoftwareSerial library allows for serial communication on any of the Yún's digital pins. Pins 0 and 1 should be avoided as they are used by the Bridge library.
The ATmega32U4 also supports I2C (TWI) and SPI communication. The Arduino software includes a Wire library to simplify use of the I2C bus;. For SPI communication, use the SPI library.
The Yún appears as a generic keyboard and mouse, and can be programmed to control these input devices using the Keyboard and Mouse classes.
The onboard Ethernet and WiFi interfaces are exposed directly to the AR9331 processor. To send and receive data through them, use the Bridge library.
The Yún also has USB host capabilities through Linino OS. You can connect peripherals like USB flash devices for additional storage, keyboards, or webcams. You may need to download and install additional software for these devices to work.
The Yún can be programmed with the Arduino software (download). Select "Arduino Yún from the Tools > Board menu (according to the microcontroller on your board).
The ATmega32U4 on the Arduino Yún comes preburned with a bootloader that allows you to upload new code to it without the use of an external hardware programmer. It communicates using the AVR109 protocol.
You can also bypass the bootloader and program the microcontroller through the ICSP (In-Circuit Serial Programming) header using Arduino ISP or similar.
Automatic (Software) Reset:
Rather than requiring a physical press of the reset button before an upload, the Yún is designed in a way that allows it to be reset by software running on a connected computer. The reset is triggered when the Yún's virtual (CDC) serial / COM port is opened at 1200 baud and then closed. When this happens, the processor will reset, breaking the USB connection to the computer (meaning that the virtual serial / COM port will disappear). After the processor resets, the bootloader starts, remaining active for about 8 seconds. The bootloader can also be initiated by pressing the reset button on the Yún. Note that when the board first powers up, it will jump straight to the user sketch, if present, rather than initiating the bootloader.
Because of the way the Yún handles reset it's best to let the Arduino software try to initiate the reset before uploading, especially if you are in the habit of pressing the reset button before uploading on other boards. If the software can't reset the board you can always start the bootloader by pressing the reset button on the board.
USB Overcurrent Protection:
The Yún has a resettable polyfuse that protects your computer's USB ports from shorts and overcurrent. Although most computers provide their own internal protection, the fuse provides an extra layer of protection. If more than 500 mA is applied to the USB port, the fuse will automatically break the connection until the short or overload is removed.
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