Adafruit METRO 328 without Headers [ATmega328]

The Adafruit METRO 328 without Headers is a fully assembled, Arduino UNO R3-compatible development board powered by the ATmega328P running at 16 MHz. It's shape and pin-compatible with Arduino UNO R3 shields, and works directly with the Arduino IDE by selecting "Arduino UNO" in the Boards menu. This version ships without headers pre-soldered, giving you flexibility to solder your own headers, wires, or connectors as needed. If you'd prefer headers already attached, see the METRO 328 with Headers.

The METRO is designed to be both easy to use and hacker-friendly, featuring an on-board USB-to-serial converter, polarity-protected DC jack with power switch, and the Optiboot bootloader pre-loaded.

Key Features

• ATmega328P @ 16 MHz – 32 KB flash, 2 KB RAM with Optiboot bootloader pre-installed
• Arduino UNO R3 Compatible – Works with UNO shields and the Arduino IDE (desktop and cloud)
• 20 GPIO Pins – Including 6 analogue inputs and 6 PWM outputs across 3 timers
• Hardware SPI, I2C & UART – Full serial communication support
• USB-to-Serial Converter – On-board chip for programming and serial monitoring
• Flexible Power – USB or 7–9V DC with polarity protection and auto-switching
• On/Off Switch – Conveniently located next to the DC jack
• 5V Logic (3.3V Optional) – Cut and solder a jumper to switch to 3.3V logic
• Four Indicator LEDs – Power (green), RX/TX (yellow), and pin 13 (red)
• No Headers – Solder your own headers, wires, or connectors for maximum flexibility

Ideal For

• Projects where a slim profile or custom wiring is preferred
• Permanent installations where headers aren't needed
• Arduino projects requiring UNO R3 shield compatibility
• Prototyping with the Arduino ecosystem

Package Contents

• 1× Adafruit METRO 328 board (without headers)
• 1× Through-hole header set (unsoldered)
• 4× Rubber bumper feet

Resources

• Optiboot Bootloader (GitHub)