NEW PRODUCT – Adafruit METRO 328 without Headers – ATmega328


NEW PRODUCT – Adafruit METRO 328 without Headers – ATmega328

We sure love the ATmega328 here at Adafruit, and we use them a lot for our 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 we need to go small, we use a Pro Trinket 3V or 5V, but when size isn’t as much of a concern, and an USB-serial converter is required, we reach for an Adafruit METRO.


METRO is the culmination of years of playing with AVRs: we wanted to make a development board that is easy to use and is hacker friendly.


  • 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 7-20V 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 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.


Features & more at a glance:

  • ATmega328 microcontroller with Optiboot (UNO) Bootloader
  • USB Programming and debugging via the well-supported genuine FTDI FT231X
  • Input voltage: 7-20V
  • 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
  • Derivative of “Arduino UNO R3 Reference design
  • Open source hardware files on github!

In stock and shipping now!

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