Metro is our series of microcontroller boards for use with the Arduino IDE. This new Metro M0 Express board looks a whole lot like our original Metro 328, but with a huge upgrade. Instead of the ATmega328, this Metro features a ATSAMD21G18 chip, an ARM Cortex M0+.
Primary board power input over Micro USB; source states about 5 V at 500 mA, with temporary fuse shutoff above about 1000 mA.
5.5 mm / 2.1 mm centre-positive DC input; source states provide about 6 V to 12 V to power the Metro.
Output from the 3.3 V regulator; source states it can supply 500 mA peak.
5 V rail from the regulator when DC jack is used, or from USB; source states about 500 mA peak from USB and 800 mA peak from DC.
Common ground for all power and logic.
Higher of the DC jack or USB voltage; source gives 9 V example for DC input and 5 V when only USB is connected.
GPIO 0 and Serial1 hardware UART receive input.
GPIO 1 and Serial1 hardware UART transmit output.
General-purpose GPIO pins; source states most pins can do PWM output and all except D4 can be interrupt inputs.
GPIO 13, connected to the red LED marked L next to the USB jack.
I2C Wire data pin; source notes no default pull-up, so an external 2.2 kΩ to 10 kΩ pull-up may be needed.
I2C Wire clock pin; source notes no default pull-up, so an external 2.2 kΩ to 10 kΩ pull-up may be needed.
Analogue input A0 and true analogue output via DAC; source states output can be set from 0 V to 3.3 V.
Analogue input pins that can also be used as digital I/O.
Hardware SPI clock pin, also connected to the 2x3 SPI header.
Hardware SPI MOSI pin, also connected to the 2x3 SPI header.
Hardware SPI MISO pin, also connected to the 2x3 SPI header.
Reset pin; tie to ground to manually reset the ATSAMD21 and launch the bootloader manually.
External analogue reference input; source states it cannot go higher than 3.3 V.
Digital reference voltage pin; source states it is the same as the 3.3 V logic voltage and cannot be changed.
2x5 0.05 inch SWD debug interface for trace debugging, external programming, or non-bootloader development.
| Pin | Position | Type | Function | Voltage |
|---|---|---|---|---|
| Micro USB | power | Primary board power input over Micro USB; source states about 5 V at 500 mA, with temporary fuse shutoff above about 1000 mA. | 5V USB input | |
| DC jack | power | 5.5 mm / 2.1 mm centre-positive DC input; source states provide about 6 V to 12 V to power the Metro. | 6V-12V input | |
| 3V | power | Output from the 3.3 V regulator; source states it can supply 500 mA peak. | 3.3V output | |
| 5V | power | 5 V rail from the regulator when DC jack is used, or from USB; source states about 500 mA peak from USB and 800 mA peak from DC. |
UART · I2C · Analog · 5V USB input · 6V-12V input
Confirm the data interface matches your host board.
Module pins: Micro USB, DC jack, 3V, 5V, Vin, IORef, GND, #0 / RX. Schematik maps them to your board in the app.
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| 5V output |
| GND | ground | Common ground for all power and logic. | 0V |
| Vin | power | Higher of the DC jack or USB voltage; source gives 9 V example for DC input and 5 V when only USB is connected. | USB/DC input rail |
| #0 / RX | signal | GPIO 0 and Serial1 hardware UART receive input. | 3.3V logic |
| #1 / TX | signal | GPIO 1 and Serial1 hardware UART transmit output. | 3.3V logic |
| #2-#12 | signal | General-purpose GPIO pins; source states most pins can do PWM output and all except D4 can be interrupt inputs. | 3.3V logic |
| #13 / L | signal | GPIO 13, connected to the red LED marked L next to the USB jack. | 3.3V logic |
| SDA | signal | I2C Wire data pin; source notes no default pull-up, so an external 2.2 kΩ to 10 kΩ pull-up may be needed. | 3.3V logic |
| SCL | signal | I2C Wire clock pin; source notes no default pull-up, so an external 2.2 kΩ to 10 kΩ pull-up may be needed. | 3.3V logic |
| A0 | analog | Analogue input A0 and true analogue output via DAC; source states output can be set from 0 V to 3.3 V. | 0V-3.3V analogue |
| A1-A5 | analog | Analogue input pins that can also be used as digital I/O. | 3.3V logic / analogue input |
| SCK | signal | Hardware SPI clock pin, also connected to the 2x3 SPI header. | 3.3V logic |
| MOSI | signal | Hardware SPI MOSI pin, also connected to the 2x3 SPI header. | 3.3V logic |
| MISO | signal | Hardware SPI MISO pin, also connected to the 2x3 SPI header. | 3.3V logic |
| RST | control | Reset pin; tie to ground to manually reset the ATSAMD21 and launch the bootloader manually. | 3.3V logic |
| ARef | analog | External analogue reference input; source states it cannot go higher than 3.3 V. | <=3.3V reference |
| IORef | power | Digital reference voltage pin; source states it is the same as the 3.3 V logic voltage and cannot be changed. | 3.3V reference |
| SWD header | programming | 2x5 0.05 inch SWD debug interface for trace debugging, external programming, or non-bootloader development. | 3.3V logic |