Description

At Adafruit, they love the ATmega328, and they use it a lot for their own projects. The processor has many GPIO inputs, analog inputs, UART SPI and I2C, timer and PWM inputs in abundance - just enough for most simple projects. When they need a small size, they use a Pro Trinket 3V or 5V, but when the size is not as large, and a USB-to-serial converter is needed, they prefer a METRO Adafruit.

This is the METRO Adafruit with connectors.  It comes with welded connectors.  It is a fully assembled and tested board with through hole conncectors.

METRO is the culmination of years with AVRs: we wanted to make a development map that was easy to use and user-friendly for hackers. The core is an ATmega328P, with 32KB of flash and 2KB of RAM, running at 16 MHz

• Power the METRO with a polarity-protected 7-9V DC power supply or via the micro USB connector from any 5V USB source. The 2.1 mm DC plug has an on/off switch next to the DC plug, so you can easily turn off your configuration. The METRO switches automatically between USB and DC.
• METRO has 19 GPIO pins, of which 6 are Analog and 2 are reserved for the USB serial converter. There are also 6 PWM available on 3 timers (1 x 16 bits, 2 x 8 bits). There is a hardware SPI port, a hardware I2C port and a UART port from hardware to USB. The logic level is 5V, but by cutting and soldering a jumper closed, you can easily convert it to 3.3V logic
• USB to Serial Converter, there is a USB to Serial converter that can be used by any computer to listen/send data to METRO, and can also be used to launch and update code via bootloader
• Four LEDs on the front edge of the card for easy debugging. One green power LED, two RX/TX LEDs for the UART and one red LED connected to pin PB5
• Easy reprogramming, delivered preloaded with Optiboot bootloader, which is supported by avrdude and uses only 512 bytes.
• Works with all Adafruit shield!

We also provide 4 rubber pads to prevent it from slipping off your desk.

Mac and Windows! Don't forget to install the FTDI FTDI VCP drivers so that the COM/Serial port is displayed correctly! Default drivers do not support this FTDI chip!

Features

• ATmega328 microcontroller with Optiboot (UNO) Bootloader
• USB Programming and debugging via the well-supported genuine FTDI FT231X
• Input voltage: 7-9V (a 9VDC power supply is recommended)
• 5V regulator can supply peak ~800mA as long as the die temp of the regulator does not exceed 150*C
• 3.3V regulator can supply peak ~150mA as long as the die temp of the regulator does not exceed 150*C
• 5V logic with 3.3V compatible inputs, can be converted to 3.3V logic operation
• 20 Digital I/O Pins: 6 are also PWM outputs and 6 are also Analog Inputs
• 6-pin ICSP Header for reprogramming
• 32KB Flash Memory - 0.5K for bootloader, 31.5KB available after bootloading
• 16MHz Clock Speed
• Compatible with "Classic" and "R3" Shields
• Adafruit Black PCB with gold plate on pads
• 53mm x 71mm / 2.1" x 2.8"
• Height (w/ barrel jack): 13mm / 0.5"
• Weight: 19g
• Derivative of "Arduino UNO R3 Reference design" 
• Open source hardware files on github!