Adafruit METRO 328

Adafruit METRO 328 is easy to use and hacker-friendly. It has an ATmega328 at the heart with 32KB of flash and 2KB of RAM running at 16MHz. Versions of the METRO 328 come as a fully assembled and tested development board with or without headers attached. Four rubber bumpers are included to keep it from slipping off a desk.


  • ATmega328 brains: 32KB of flash (1/2K reserved for the bootloader), 2KB of RAM, clocked at 16MHz.
  • Power the METRO with 7-9V polarity protected DC or the micro USB connector to any 5V USB source. The 2.1mm DC jack has an on/off switch and the METRO will automatically switch between USB and DC.
  • METRO has 20 GPIO pins, 6 of which are Analog, 2 are reserved for the USB-serial converter. 6 PWMs are available on 3 timers (1x16-bit, 2x8-bit). There's a hardware SPI port, hardware I2C port, and hardware UART to USB.
  • GPIO Logic level is 5V but by cutting and soldering closed a jumper, you can easily convert it to 3.3V logic.
  • USB to Serial converter can be used by any computer to listen/send data to the METRO and can launch and update code via the bootloader.
  • Four indicator LEDs, on the front edge of the PCB, for easy debugging. A green power LED, 2 RX/TX LEDs for the UART, and a red LED connected to pin PB.
  • Easy reprogramming, comes preloaded with the Optiboot bootloader, supported by avrdude, and only uses 512 bytes.
  • Beautiful styling by PaintYourDragon and Bruce Yan, in Adafruit Black with gold, plated pads. Works with all Adafruit designed shields.

Technical Information

  • 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 logic with 3.3V compatible inputs can be converted to a 3.3V logic operation
  • 20 Digital I/O Pins: 6 are also PWM outputs and 6 are also Analog Inputs
  • 32KB Flash Memory - 0.5K for bootloader, 31.5KB available after bootloading
  • 6-pin ICSP Header for reprogramming
  • 16MHz Clock Speed
  • Compatible with "Classic" and "R3" Shields
  • Adafruit Black PCB with gold plate on pads
  • 53x68.5mm / 2.1x2.7"
  • Height (w/ barrel jack): 13mm / 0.5"
  • Weight: 16.5g
  • Derivative of "Arduino UNO R3 Reference design"
  • Open-source hardware files on Github

METRO Mini 328

Adafruit METRO 328

Adafruit METRO Mini 328 has USB-to-serial built-in and is used for smaller projects. The METRO Mini 328 is a tiny, breadboard-friendly development board that is easy to use and hacker-friendly. Metro Mini can be programmed with the Arduino IDE.

​The Metro Mini comes as a fully assembled and tested board, with bootloader burned in and also a stick of 0.1" header. Some light soldering is required if you'd like to plug it into a breadboard, or you can solder wires or header directly to the breakout pads. Once headers are installed they can be fitted into 0.6" wide sockets.

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Published: 2015-08-19 | Updated: 2022-10-03