Adafruit METRO 328 without Headers - ATmega328

A board inspired by Arduino designed by Adafruit

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23,40 € incl. tax

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Adafruit sure love the ATmega328, and it is used a lot for their own projects. The processor has plenty of GPIO, Analog inputs, hardware UART SPI and I2C, timers and PWM galore - just enough for most simple projects. When it is needed to go small, we use a Pro Trinket 3V or 5V, but when size isn't as much of a concern, and a USB-serial converter is required, let's reach for an Adafruit METRO.


METRO is the culmination of years of playing with AVRs: Adafruit wanted to make a development board that is easy to use and is hacker friendly. It is a derivative of "Arduino UNO R3 Reference design".


ATmega328 brains - This popular chip has 32KB of flash (1/2 K is 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 next to it so you can turn off your setup easily. The METRO will automagically switch between USB and DC.

METRO has 20 GPIO pins, 6 of which are Analog in as well, and 2 of which are reserved for the USB-serial converter. There's also 6 PWMs available on 3 timers (1 x 16-bit, 2 x 8-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, there's a hardware USB to Serial converter that can be used by any computer to listen/send data to the METRO, and can also be used to launch and update code via the bootloader

Four indicator LEDs, on the front edge of the PCB, for easy debugging. One green power LED, two RX/TX LEDs for the UART, and a red LED connected to pin PB5

Easy reprogramming, comes pre-loaded with the Optiboot bootloader, which is 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 or Snootlab designed shields!


This version of the METRO 328 comes as a fully assembled and tested development board but without any headers attached. We do include some through-hole headers that you can solder on if you like, or you can solder wires or header directly to the breakout pads. We also include 4 rubber bumpers to keep it from slipping off your desk.




  • 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)
  • On/Off switch on DC power supply
  • 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 68.5mm / 2.1" x 2.7"
  • Height (w/ barrel jack): 13mm / 0.5"
  • Weight: 16.5g


All the informations are available on the official website here.


Soldering kit comes in a reusable zip ESD packaging.

Like all our products, this kit is RoHS.

Logo RoHS

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