The Arduino Yśn Mini is a breadboard PCB developed with an ATmega32U4 MCU and a Qualcomm Atheros AR9331 MIPS 24K SoC CPU operating at up to 400 MHz. The Atheros CPU supports a Linux distribution based on OpenWRT named Linino. The board has built-in WiFi (IEEE 802.11b/g/n operation up to 150Mbps 1x1 2.4 GHz), supports 20 digital input/output pins (of which seven can be used as PWM outputs and 12 as analog inputs), a 16 MHz crystal oscillator, a micro-USB connector, an ICSP header, two reset buttons and one user button.
The Bridge Library facilitates communication between the two processors, giving Arduino sketches the ability to run shell scripts, communicate with network interfaces, and receive information from the AR9331 processor. The USB Host, network interfaces and SD card are not connected to the 32U4, but to the AR9331; the Bridge library also enables the Arduino to use those peripherals.
This module was based on the Linino ONE. It's a stripped-down version of the full-sized Arduino Yśn for applications that don't require all of the Yśn's built-in connectors or the larger Arduino shield form factor.
The Yśn is similar to the Leonardo in that the ATmega32U4 has built-in USB communication, eliminating the need for a secondary processor. This allows the Yśn to appear to a connected computer as a mouse and keyboard, in addition to a virtual (CDC) serial / COM port.
Arduino Yśn Mini Features The features relating to the two different processors are listed separately.
|AVR Arduino microcontroller |
|Operating Voltage||5V |
|Input Voltage||5V |
|Digital I/O Pins||20 |
|PWM Channels||7 |
|Analog Input Channels||12 |
|DC Current per I/O Pin||40 mA |
|DC Current for 3.3V Pin||50 mA |
|Flash Memory||32 KB (of which 4 KB is used by bootloader) |
|SRAM||2.5 KB |
|EEPROM||1 KB |
|Clock Speed||16 MHz |
|Linux microprocessor |
|Processor||Atheros AR9331 |
|Architecture||MIPS 24K @ up to 400 MHz |
|Operating Voltage||3.3V @ typ. 380mA (113-570mA) |
|Input Voltage||4.75V to 5.25V @ 1A |
|WiFi||IEEE 802.11b/g/n |
|RAM||64 MB DDR2 |
|Flash Memory||16 MB |
You can add Ethernet, USB and SD Card interfaces by plugging in either or both of the Linino ONE Accessories boards that you can add to your order using the option checkbox at the bottom of this page. The accessories kit consists of two boards: dogRJ45 with an RJ45 port and Ethernet switch, and dogUSB with a Type A USB connector with 2.0 transceiver and a microSD connector.
Powering the Board It is recommended to power the Yśn via the micro-USB connection with 5V DC.
If you power the board though the Vin pin, you must supply a regulated 5V DC. Unlike other Arduino boards, the Yśn Mini does not have an on-board voltage regulator; applying more than 5V will damage the board. You may want to pick up the MIKROE-192 voltage regulator/rectifier board.
The power pins are as follows:
- VIN The input voltage to the Arduino board. Unlike other Arduino boards, if you are going to provide power to the board through this pin, you must provide a regulated 5V.
- 5V The power supply used to power the microcontrollers and other components on the board. This can come either from VIN or be supplied by USB.
- 3V3 A 3.3-volt supply generated by the on-board regulator. Maximum current draw is 50 mA.
- GND Ground pins.
- IOREF The voltage at which the I/O pins of the board are operating (i.e. VCC for the board). This is 5V on the Yśn Mini.
- VCC_GT A 2.1V supply generated by the on-board regulator (designed for optional dogRJ45 module)
Memory The ATmega32U4 has 32KB (with 4KB used for the bootloader). It also has 2.5KB of SRAM and 1KB 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 connected externally. The Yśn Mini has 64MB of DDR2 RAM and 16MB of Flash memory. The Flash memory is preloaded with a Linux distribution based on OpenWRT called Linino. 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 6MB of the 16MB internal Flash memory. You can use optional dogUSB module with a microSD card if you need more disk space for installing applications.
Input and Output Now it is possible to have access to the I/O pins of the Atheros AR9331 together with the I/O pins of the ATmega32U4.
Atheros AR9331 pins Each of these pins can be used by the Linino OS side as peripherals of the Linux Kernel. In addition, some pins have specialized functions:
- USB+ and USB- Used to connect USB MIPS with external USB devices. The optional dogUSB module is recommended.
- AR_GP7 and AR_GP6 These are General-Purpose Input/Output commanded through the the Linino OS distribution. They operate at 5V.
- RD+, RD-, TD+, TD- Used to connect the MIPS Ethernet PHY with the optional dogRJ45 module to provide an Ethernet interface.
AVR ATmega32U4 pins Each of the 20 digital I/O pins on the Yśn Mini can be used as an input or an output, using pinMode(), digitalWrite(), and digitalRead() functions. They operate at 5V. Each pin can provide or receive a maximum of 40mA and has an internal pull-up resistor (disconnected by default) of 20-50 kOhms. In addition, some pins have specialized functions:
There are three reset buttons with different functions on the board:
- Serial: 0→RX and 1←TX Used to receive (RX) and transmit (TX) TTL serial data using the ATmega32U4 hardware serial capability. Note that on the Yśn Mini, the Serial class refers to USB (CDC) communication; for TTL serial on pins 0 and 1, use the Serial1 class. The hardware serials of the ATmega32U4 and the AR9331 on the Yśn Mini are connected together and are used to communicate between the two processors. As is common in Linux systems, the console for access to the system is exposed on the serial port of the AR9331. This means that you can have access to the programs and tools offered by Linux from your sketch.
- TWI: 2 (SDA) and 3 (SCL) Support TWI communication using the Wire Library.
- External Interrupts: 3 (interrupt 0), 2 (interrupt 1), 0 (interrupt 2), 1 (interrupt 3) and 7 (interrupt 4) These pins can be configured to trigger an interrupt on a Low value, a rising or falling edge, or a change in value. See the attachInterrupt() function for details. Is not recommended to use pins 0 and 1 as interrupts because they are the also the hardware serial port used to talk with the Linux processor. Pin 7 is connected to the AR9331 processor and it may be used as handshake signal in the future. Is recommended to be careful of possible conflicts if you intend to use it as an interrupt.
- PWM: 3, 5, 6, 9, 10, 11, and 13 Provide 8-bit PWM output with the analogWrite() function.
- SPI: MISO, SCK, MOSI, RXLED/SS These pins support SPI communication using the SPI Library. Note that the SPI pins are not connected to any of the digital I/O pins as they are on the Uno. The SPI pins are also connected to the AR9331 GPIO pins, where SPI has been implemented in software. This means that the ATMega32U4 and the AR9331 can also communicate using the SPI protocol.
- LED: 13 (Pin 13) There is a built-in LED connected to digital pin 13. When the pin is High value, the LED is on; when the pin is Low, it's off. There are several other status LEDs on the Yśn Mini, indicating power, WLAN connection, ETH connection and USER functions.
- Analog Inputs: A0 - A5, A6 - A11 (on digital pins 4, 6, 8, 9, 10, and 12) The Yśn Mini has 12 analog inputs, labeled A0 through A11, all of which can also be used as digital I/O. Pins A0-A5 appear on dedicated pins; inputs A6-A11 are on digital I/O pins 4, 6, 8, 9, 10, and 12 respectively. Each analog input provides 10 bits of resolution (i.e. 1024 different values). By default, the analog inputs measure from ground to 5V, though is it possible to change the upper end of their range using the AREF pin and the analogReference() function.
- AREF Reference voltage for the analog inputs. Used with analogReference().
See also the mapping between Arduino pins and ATmega32U4 ports.
- Yśn Mini RST Bring this line Low to reset the AR9331 microprocessor. Resetting the AR9331 will cause the reboot of the Linux system. All the data stored in RAM will be lost and all the programs that are running will be terminated.
- 32U4 RST Bring this line Low to reset the ATmega32U4 microcontroller. Typically used to add a reset button to add-on modules which block the one on the board.
- WLAN RST This button has two functions. Primarly it serves to restore the WiFi to its factory configuration. The factory configuration consists of putting the WiFi of the Yśn Mini in access-point mode (AP) and assign to it the default IP address of 192.168.240.1; in this condition you can connect your computer to the WiFi network that appears with the SSID name Linino-XXXXXXXXXXXX, where the twelve X's are the MAC address of your Yśn Mini. Once connected, you can reach the web panel of the Yśn Mini with a browser at the 192.168.240.1 or http://linino.local address. Note that restoring the WiFi configuration will cause a reboot of the Linux environment. To restore your WiFi configuration, you have to press and hold the WLAN RST button for five seconds. When you press the button, the WLAN blue LED will start to blink and will keep blinking when you release the button after five seconds, indicating that the WiFi restore procedure has been recorded. The second function of the WLAN RST button is to restore the Linux image to the default factory image. To restore the Linux environment, you must press the button for 30 seconds. Note that restoring the factory image means you will lose all the files saved and all software installed on the on-board Flash memory connected to the AR9331.
Communication The Yśn Mini 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 USB2.0 device, using standard USB COM drivers. The Arduino software includes a serial monitor which allows simple text data to be sent to and from the Arduino board. The RX and TX LEDs on the board will flash when data are 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. Communication between the processors is handled by the Bridge Library.
A SoftwareSerial Library allows for serial communication on any of the Yśn Mini's digital pins except for pins 0 and 1 which 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; see that link for details. For SPI communication, use the SPI Library.
The Yśn Mini appears as a generic keyboard and mouse, and can be programmed to control these input devices using the Keyboard and Mouse classes.
The on-board WiFi interface is exposed directly to the AR9331 processor. To send and receive data through WiFi (or Ethernet if using the optional dogRJ45 module), use the Bridge Library. To configure the interfaces, you can access the network control panel as described in the getting started page.
The Yśn Mini also has USB Host capabilities through the 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. For information on adding software to the AR9331, refer to the notes on the Deep Knowledge of Arduino Yun page (its diagrams show the full-sized Arduino Yśn, but the text is relevant to the Yśn Mini).
Programming The Yśn Mini can be programmed with the Arduino software. Select Arduino Yśn Mini from the Tools → Board menu. For details, see the Arduino Reference and Basic Concepts.
The ATmega32U4 on the Arduino Yśn Mini comes pre-burned with a bootloader that allows you to upload new code to it without the use of an external hardware programmer via the Arduino Development Environment. It communicates using the STK500 protocol.
It is possible to bypass the bootloader and program the microcontroller through the SPI signals that are available on the pin headers. See these instructions for details.
Automatic (Software) Reset and Bootloader Initiation Rather than requiring a physical press of the reset button before an upload, the Yśn Mini is designed in a way that allows it to be reset by software running on a connected computer. The reset is triggered when the Yśn Mini'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 eight seconds. The bootloader also can be initiated by pressing the reset button on the Yśn Mini. 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 Yśn Mini 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.
Physical Characteristics The maximum length and width of the Yśn Mini PCB are 71.12 and 22.86 mm respectively, with the micrp-USB connector extending slightly. The board weighs 16 grams.
Other Arduino Yśn Mini Resources The various links above on this page can be found also from the the starting points listed below.
Note: The board does not have a connection for an external WiFi antenna. What looks like a U.FL connector on board is in fact an SWF microwave switch used in testing.
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