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The Adafruit METRO 328 is a fully assembled, Arduino UNO R3-compatible development board powered by the ATmega328P running at 16 MHz. It's shape and pin-comp...

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The Adafruit METRO 328 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 comes with through-hole headers pre-soldered — for a slimmer profile, see the METRO 328 without Headers.

The METRO is the result of years of AVR development experience, designed to be both easy to use and hacker-friendly. It features an on-board USB-to-serial converter, polarity-protected DC jack with power switch, and comes pre-loaded with the Optiboot bootloader.

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)
  • 19 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 CP2104 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)

Ideal For

  • Arduino projects requiring UNO R3 shield compatibility
  • Beginners learning microcontroller programming
  • Prototyping with the Arduino ecosystem
  • Projects needing a reliable, well-documented ATmega328P platform

Package Contents

  • 1× Adafruit METRO 328 board (with headers pre-soldered)
  • 4× Rubber bumper feet
Tip: Need something smaller? Check out the Metro Mini 328 V2 for a compact breadboard-friendly option, or the Trinket M0 for a tiny CircuitPython-compatible board.
Note: Mac and Windows users may need to install the CP2104 VCP drivers from Silicon Labs for the serial port to appear correctly.

Resources

Jargon buster

Plain-language definitions for the technical terms used above.

ATmega328P
An 8-bit microcontroller chip used on many Arduino Uno-compatible boards. Knowing the controller uses an ATmega328P helps you understand its memory, speed, pin compatibility, and the Arduino sketches it can run.
AVR
AVR is a family of 8-bit microcontrollers used in many classic Arduino-style boards. If a USB host library mentions AVR support, it suggests the examples or compatibility may be aimed at those older microcontroller boards.
Bootloader
Small starter software on a microcontroller that lets new code be uploaded before the main program runs. Knowing how to enter bootloader mode matters when you need to program the board or recover it after a faulty sketch.
CircuitPython
A beginner-friendly version of Python designed to run directly on microcontroller boards. If a product supports CircuitPython, you can often program it by copying code files onto the board rather than setting up a more complex toolchain.
GPIO
General-purpose input/output pins are microcontroller pins you can set in software to read signals, switch devices on and off, or connect to peripherals. The number of GPIO pins matters because it limits how many buttons, LEDs, sensors, and other parts you can wire directly to the board.
Headers
Rows of metal pins used to plug a module into a breadboard or connect it with jumper wires. Pre-soldered headers make the module easier to use straight away without needing to solder the pins yourself.
I2C
I2C is a two-wire communication bus used by many sensors and small modules. It matters because several I2C devices can share the same two wires, but each device needs a compatible address and your controller must support I2C.
IDE
Short for Integrated Development Environment, a program used to write, run and manage code. It matters because some learners prefer a traditional coding workspace instead of a guided notebook-style lesson.
microcontroller
A microcontroller is a small computer on a chip that runs your program and controls connected inputs and outputs. For this product, it is the part that reads buttons and sensors, drives the display and speaker, and communicates over Bluetooth.
PWM
Pulse Width Modulation is a way for a digital pin to simulate variable output power by switching on and off very quickly. It matters for controlling things like LED brightness, motor speed, or servo-style signals from a microcontroller pin.
RAM
RAM is temporary memory used while a device is running, and its contents are lost when power is removed. A “Run in RAM” mode is useful for testing settings without permanently programming the module, but it may not support every feature.
Shield
An add-on board that plugs into a main controller board to give it extra features such as sensing, motor control or communication. Knowing a product supports shields helps you judge whether it can connect neatly into an existing maker-board setup.
SPI
A fast serial communication bus often used for displays, memory cards, and sensors. It matters because SPI devices need specific pins for clock and data, plus a separate chip-select line for each device.
UART
UART is a simple serial connection that sends data over separate transmit and receive wires, often labelled TX and RX. It matters because this module is designed to replace a wired UART cable with a wireless link while keeping the same serial data format.
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