Adafruit METRO 328

Overview

The Adafruit METRO 328 is a fully assembled Arduino-compatible development board based on the ATmega328P microcontroller running at 16 MHz. It ships with the Optiboot bootloader, making it immediately programmable via the Arduino IDE by selecting the "Arduino UNO" board target. Adafruit's implementation stays true to the Arduino UNO R3 reference design while adding their signature black PCB with gold-plated pads.

The board provides 20 digital I/O pins (6 PWM-capable), 6 analog inputs, and hardware UART/SPI/I2C interfaces. A 6-pin ICSP header is included for direct AVR programming. Connectivity comes via a micro USB port handled by the CP2104 USB-to-serial converter, plus a 2.1mm barrel jack with an on/off power switch accepting 7–9V DC.

Power regulation is handled by two onboard regulators: a 5V rail capable of 800mA peak and a 3.3V rail at 150mA. A solder jumper allows reconfiguring the logic level to 3.3V. Four indicator LEDs (power, RX, TX, and pin 13 status) provide instant visual feedback during development.

The METRO 328 is fully compatible with Adafruit's Classic and R3 shields and works with all standard Arduino libraries, making it an ideal drop-in replacement for the Arduino UNO in space-constrained or cost-sensitive projects.