- Microcontroller: ATmega328P-PU
- Arduino Bootloader: Uno R3
- SDA and SCL pins near AREF pin
- Two pins near RESET pin- the IOREF: allows the shields to adapt to the voltage provided from the board (5V on the boards that use the AVR and 3.3V on Arduino Due). The other pin is not connected.
- Stronger RESET circuit.
- Atmega 16U2 replace the 8U2.
- Operating Voltage: 5V
- Input Voltage (recommended): 7-12V
- Input Voltage (limits) 6-20V
- Digital I/O Pins: 14 (including 6 for PWM output)
- Analog Input Pins: 6
- DC Current per I/O Pin: 40 mA
- DC Current for 3.3V Pin: 50 mA
- Flash Memory: 32 KB (including 0.5 KB used by bootloader)
- SRAM 2 KB
- EEPROM 1 KB (ATmega328)
- Clock Speed 16 MHz
Based on the ATmega328 with 14 digital i/o pins, 6 analog inputs, a 16 MHz ceramic resonator, a USB connection, a power jack, an ICSP header, and a reset button, UNO Rev3 contains everything needed to support the microcontroller. To get started, connect it to a computer with a USB cable or power it with a AC-to-DC adapter or battery.
The Uno clone does not use the FTDI USB-to-serial driver chip. Instead, it features the Atmega16U2 (Atmega8U2 up to version R2) programmed as a USB-to-serial converter.
The Uno and Arduino IDE version 1.0 are the reference versions and can use an Atmega8, 168, or 328. The pin configuration is identical on all three processors.
The Chineduino Uno can be powered via the USB connection or with an external power supply. The power source is selected automatically. External (non-USB) power can come either from an AC-to-DC adapter (wall-wart) or battery. The adapter can be connected by plugging a 2.1mm center-positive plug into the board’s power jack. Leads from a battery can be inserted in the GND and Vin pin headers on the board.
The board can operate on an external supply of 6 to 20 volts. If supplied with less than 7V, however, the 5V pin may supply less than five volts and the board may be unstable. Using more than 12V, may overheat the voltage regulator and damage the board. The recommended range is 7 to 12 volts.
The power pins are as follows:
VIN- The input voltage to the board when it’s using an external power source (as opposed to 5 volts from the USB connection or other regulated power source). You can supply voltage through this pin, or, if supplying voltage via the power jack, access it through this pin.
5V- This pin outputs a regulated 5V from the regulator on the board. The board can be supplied with power either from the DC power jack (7 – 12V), the USB connector (5V), or the VIN pin of the board (7-12V). Supplying voltage via the 5V or 3.3V pins bypasses the regulator, and can damage the board.
3V3- A 3.3 volt supply generated by the on-board regulator. Maximum current draw is 50 mA.
GND- Ground pins.
IOREF- This pin on the board provides the voltage reference with which the microcontroller operates. A properly configured shield can read the IOREF pin voltage and select the appropriate power source or enable voltage translators on the outputs for working with the 5V or 3.3V.
The ATmega328 has 32 KB (with 0.5 KB used for the bootloader). It also has 2 KB of SRAM and 1 KB of EEPROM (which can be read and written with the EEPROM library).
Each of the 14 digital pins on the Uno 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.
Some digital pins have specialized functions:
Serial- Pins 0 (RX) and 1 (TX). Used to receive (RX) and transmit (TX) TTL serial data. These pins are connected to the corresponding pins of the ATmega8U2 USB-to-TTL Serial chip.
External Interrupts- Pins 2 and 3. These pins can be configured to trigger an interrupt on a low value, a rising or falling edge, or a change in value by using the attachInterrupt() function.
PWM- Pins 3, 5, 6, 9, 10, and 11. Provide 8-bit PWM output with the analogWrite() function.
SPI- Pins 10 (SS), 11 (MOSI), 12 (MISO), and 13 (SCK). These pins support SPI communication using the SPI library.
LED- 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.
The Uno has 6 analog inputs, labeled A0 through A5, each of which provide 10 bits of resolution (i.e. 1024 different values). By default they measure from ground to 5 volts, though is it possible to change the upper end of their range using the AREF pin and the analogReference() function.
Some analog pins have specialized functions:
TWI- Pins A4 (SDA) and A5 (SCL). Support TWI communication using the Wire library.
AREF- Reference voltage for the analog inputs. Used with analogReference().
Reset- Bring this line LOW to reset the microcontroller. Typically used to add a reset button to shields which block the one on the board.
The Uno has a number of facilities for communicating with a computer, another Arduino compatible board, or other microcontrollers. The ATmega328 provides UART TTL (5V) serial communication, which is available on digital pins 0 (RX) and 1 (TX). An ATmega16U2 on the board channels this serial communication over USB and appears as a virtual com port to software on the computer. The ATmega16U2 firmware uses the standard USB COM drivers, and no external driver is needed. However, on Windows, a .inf file is required. The Arduino software includes a serial monitor which allows simple textual data to be sent to and from the board. The RX and TX LEDs on the board will flash when data is being transmitted via the USB-to-serial chip and USB connection to the computer (but not for serial communication on pins 0 and 1).
A SoftwareSerial library allows for serial communication on any of the Uno’s digital pins.
The ATmega328 also supports I2C (TWI) and SPI communication. The Arduino software includes a Wire library to simplify use of the I2C bus and SPI library for SPI communication.
The Uno can be programmed with the Arduino software. Select “Arduino Uno from the Tools > Board menu (according to the microcontroller on your board). The ATmega328 on the Uno comes preburned with a bootloader that allows upload of new code to it without the use of an external hardware programmer. It communicates using the original STK500 protocol. It is also possible to bypass the bootloader and program the microcontroller through the ICSP (In-Circuit Serial Programming) header.
The ATmega16U2/8U2 is loaded with a DFU bootloader, which can be activated by:
On Rev1 boards: connecting the solder jumper on the back of the board (near the map of Italy) and then resetting the 8U2.
On Rev2 or later boards: there is a resistor that pulling the 8U2/16U2 HWB line to ground, making it easier to put into DFU mode.
Use Atmel’s FLIP software (Windows) or the DFU programmer (Mac OS X and Linux) to load a new firmware. Or the ISP header with an external programmer (overwriting the DFU bootloader).
Automatic (Software) Reset
Rather than requiring a physical press of the reset button before an upload, the Uno is designed in a way that allows it to be reset by software running on a connected computer. One of the hardware flow control lines (DTR) of the ATmega8U2/16U2 is connected to the reset line of the ATmega328 via a 100 nanofarad capacitor. When this line is taken low, the reset line drops long enough to reset the chip. The Arduino software uses this capability to allow upload of code by simply pressing the upload button in the Arduino environment. This means that the bootloader can have a shorter timeout, as the lowering of DTR can be well-coordinated with the start of the upload.
However, when the Uno is connected to either a computer running Mac OS X or Linux, it resets each time a connection is made to it from software (via USB). For the following half-second or so, the bootloader is running on the Uno. While it is programmed to ignore malformed data (i.e. anything besides an upload of new code), it will intercept the first few bytes of data sent to the board after a connection is opened. If a sketch running on the board receives one-time configuration or other data when it first starts, make sure that the software with which it communicates waits a second after opening the connection and before sending this data.
The Uno contains a trace that can be cut to disable the auto-reset. The pads on either side of the trace can be soldered together to re-enable it. It’s labeled “RESET-EN”. You may also be able to disable the auto-reset by connecting a 110 ohm resistor from 5V to the reset line.
USB Overcurrent Protection
The Uno 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.
The maximum length and width of the Uno PCB are 2.7 and 2.1 inches respectively, with the USB connector and power jack extending beyond the former dimension. Four screw holes allow the board to be attached to a surface or case. Note that the distance between digital pins 7 and 8 is 160 mil (0.16″), not an even multiple of the 100 mil spacing of the other pins.
For Schematic & Reference Design [Link]
Arduino Software [Link]
Possible Application Areas
This board can be used with any sensor or motor that conforms to the voltage and current range of the board. If a sensor or motor needs an external power source, it is usually prefer to create a common GND between the secondary power source and the Uno. Some application ideas are:
1. Motion Detection Security [Link].
2. Self Watering Plant System [Link].
3. Object Detecting Robot [Link].
Did you create a project using this product? Leave details/links below!