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Microcontroller
Adafruit Metro M4 Express
A SAMD51 Arduino-compatible board in the UNO shield footprint, with much higher performance and CircuitPython storage.
Processor
Microchip ATSAMD51J19 Arm Cortex-M4F
Logic
3.3 V GPIO
Power
USB, barrel jack, VIN
Format
UNO-compatible Metro layout
Check before wiring
- Despite the UNO-like shape, GPIO is 3.3 V only.
- Legacy 5 V shields may require level shifting.
- SPI is primarily on the ICSP header for shield compatibility.
Interfaces
GPIOI2CSPIUARTADCDACPWMUSB
Source-backed connector
Interactive pin map
Pin map
Connector
Arduino Uno R3 shield headers
Signals grouped by function — schematic layout, not to physical scale
Dense header — open Full view for a roomier, fully-labelled diagram.
Simplified diagram, grouped by function — not to physical scale. Pin data is source-backed; verify against the linked documentation.
Hover, tap, or focus a pad to inspect a pin. Use arrow keys to move between pins.
- ATSAMD51J19 at 120 MHz; pinout from the official Adafruit Metro M4 Express learn guide.
- GPIO is 3.3 V only — 5 V shields need level shifting.
- SPI is on the ICSP 2×3 header and shared with D11/D12/D13 pads.
- A0 is also DAC0; A1 is also DAC1.
All 34 pins (table)
| # | Signal | Role | Net | Also / notes |
|---|---|---|---|---|
| Digital (D0–D13) | ||||
| 1 | UART | UART | ||
| 2 | UART | UART | ||
| 3 | GPIO | |||
| 4 | PWM | |||
| 5 | GPIO | |||
| 6 | PWM | |||
| 7 | PWM | |||
| 8 | GPIO | |||
| 9 | GPIO | |||
| 10 | PWM | |||
| 11 | GPIO | |||
| 12 | SPI | SPI | ||
| 13 | SPI | SPI | ||
| 14 | SPI | SPI | ||
| Analog (A0–A5 + AREF) | ||||
| 15 | DAC | Also DAC0. | ||
| 16 | DAC | Also DAC1. | ||
| 17 | ADC | |||
| 18 | ADC | |||
| 19 | I2C | I2C | ||
| 20 | I2C | I2C | ||
| 21 | ADC | Analog reference; leave unconnected or tie to 3.3 V. | ||
| Power header | ||||
| 22 | Power | VIN | ||
| 23 | Ground | GND | ||
| 24 | Ground | GND | ||
| 25 | Power | 5V | ||
| 26 | Power | 3V3 | ||
| 27 | System | |||
| 28 | System | |||
| SPI / ICSP header | ||||
| 29 | SPI | SPI | ||
| 30 | SPI | SPI | ||
| 31 | SPI | SPI | ||
| 32 | System | |||
| 33 | Power | VCC | ||
| 34 | Ground | GND | ||
Why it matters
- Official pinout explains 3.3 V Metro shield compatibility.
- QSPI flash enables CircuitPython filesystems.
- Good for projects that need UNO ergonomics with more CPU headroom.
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