QT Py (SAMD based)

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QTPy49 P18254-720px.jpg

QT Py 4600-06.jpg

Two Manufacturers (SAMD21)[edit]


  • ATSAMD21E18 32-bit Cortex M0+ version
    • 48 MHz, 32-bit processor
    • 256KB Flash
    • 32 KB RAM
  • Native USB supported by every OS
    • Can be used in Arduino or CircuitPython as USB serial console, MIDI, Keyboard/Mouse HID, even a little disk drive for storing Python scripts.
  • Built in RGB NeoPixel LED
  • 11 GPIO pins:
    • True analog output on one I/O pin
      • Can be used to play 10-bit quality audio clips in Arduino
        • CircuitPython does not have storage for audio clips
    • 9 x 12-bit analog inputs (SDA/SCL do not have analog inputs)
    • 1 x Optional AREF on A1
    • 9 x PWM outputs (A0 is analog out, A1 is not PWM capable)
    • Hardware I2C port with STEMMA QT plug-n-play connector
    • Hardware UART
    • Hardware SPI
    • Hardware I2S
    • 6 x Capacitive Touch with no additional components required
  • 3.3V regulator with AP2112, 600mA peak output
  • Reset switch for starting your project code over or entering bootloader mode
  • USB Type C connector

Optional External Flash (Adafruit QT Py Only)[edit]

  • Optional 2 MB SOIC-8 SPI Flash chip on bottom
    • Can't use castellated pins if Flash on bottom is installed
    • GD25Q16
  • Access the SPI flash in Arduino on SPI1 and chip select pin 17
  • In CircuitPython, a 'haxpress' version of the runtime will need to be installed, so it knows to look for the larger filesystem
    • There is more hardware support in the haxpress CircuitPython build because Adafruit added more code to the internal flash instead of using it for a filesystem
    • Built-in modules available: adafruit_pixelbuf, analogio, audiobusio, audiocore, audioio, board, busio, digitalio, displayio, errno, fontio, math, microcontroller, neopixel_write, nvm, onewireio, os, paralleldisplay, pulseio, pwmio, rainbowio, random, rotaryio, rtc, storage, struct, supervisor, terminalio, time, touchio, traceback, usb_cdc, usb_hid, usb_midi


Adafruit SAMD Pinout[edit]

(Click on image for larger file)

Adafruit products Adafruit QT Py SAMD21 pinout.png

Seeed Studio SAMD Pinout[edit]



  • Regulated output from the onboard regulator. You can draw 500mA


  • 5v out from the USB port.
  • Voltage input
    • Requires external diode
      • Schottky, signal, power
      • Between external power source and this pin
      • Cannot power the USB port by supplying 5V to this pin
        • There is a protection diode that prevents the 5V from reaching the USB connector.
        • This is to protect host computer USB ports, etc.

A0 / D0 - Digital/analog GPIO pin 0[edit]

  • Digital I/O 0
  • Analog In 0
  • True analog output with 10 bit precision
  • Does not have PWM
  • Capacitive touch input.

A1 / D1 - Digital/analog GPIO pin 1[edit]

  • Digital I/O 1
  • Analog In 1
  • Capacitive touch input
  • AREF pin.

A2 / D2 - Digital/analog GPIO pin 2[edit]

  • Digital I/O 2
  • Analog In 2
  • PWM
  • Capacitive touch input.

A3 / D3 - Digital/analog GPIO pin 3[edit]

  • Digital I/O 3
  • Analog In 3
  • PWM output
  • Capacitive touch input.

SDA / D4[edit]

  • Digital I/O 4
  • I2C SDA pin
  • PWM output
  • No analog on this pin
  • No pull up on this pin
  • When using with I2C requires an external 2.2K-10K pullup to 3.3V.

SCL / D5[edit]

  • Digital I/O 5
  • I2C SCL
  • No analog on this pin
  • No pull up on this pin
  • When using with I2C requires an external 2.2K-10K pullup to 3.3V.

TX / A6 / D6[edit]

  • Digital I/O 6
  • Transmit (output) for Serial1
  • Analog 6
  • PWM output
  • Capacitive touch input

RX / A7 / D7[edit]

  • Digital I/O 7
  • Receive (input) for Serial1
  • Analog 7
  • PWM output
  • Capacitive touch input

SCK / A8 / D8[edit]

  • Digital I/O 8
  • SPI SCK pin
  • Analog 8
  • PWM output

MISO / A9 / D9[edit]

  • Digital I/O 8
  • SPI MISO pin
  • Analog 8
  • PWM output

MOSI / A10 / D10[edit]

  • Digital I/O 10
  • SPI MOSI pin
  • Analog 10
  • PWM output

NeoPixel (Adafruit SAMD)[edit]

  • The XAIO does not have a NeoPixel on-board
  • The Adafruit QT Py SAMD board does not have an individual
  • NeoPixel Blink sketch (Arduino)
  • Neopixel sketch (Arduino)
  • Connected to digital pin 11 for signal
  • Set pin 12 low for low power usage
  • By default pin 12 is set high by Arduino/CircuitPython
  • Python code example
import board
import neopixel

pixels = neopixel.NeoPixel(board.NEOPIXEL, 1)
# fill((rVal, gVal, bVal))
# rVal, gVal, bVal = red/green/blue values (0-255)
pixels.fill((255, 0, 0))  # Note double parens

LED (XAIO)[edit]

  • On-board LED


  • The SAMD on the QT Py and XIAO cards can be programmed using
    • C/C++
    • CircuitPython
    • MicroPython


  • Different Arduino installs for QT Py and XIAO

C/C++ QT Py[edit]

  • Arduino QT Py IDE Setup
  • Requires Arduino IDE version 1.8 or higher
  • Add to Preferences Additional Boards Manager URLs

C/C++ Seeeduino XIAO[edit]

  • Tools-> Board-> Boards Manager..., search for "Seeeduino XIAO"
  • Tools-> Board, find "Seeeduino XIAO M0"
  • Select the serial device of the Arduino board from the Tools | Serial Port menu


Adafruit CircuitPython[edit]

import gc
Updating CircuitPython[edit]
  • Save the contents of CIRCUITPY, just in case
  • Double-click the reset button to show the BOOT drive
  • Drag the update-bootloader.uf2 file to the BOOT drive
  • Wait a few tens of seconds for the bootloader to update; the BOOT drive will reappear
  • Check INFO_UF2.TXT to verify that the bootloader version has been updated. Then you will need to reload CircuitPython.
  • Update mpy files

SeeedStudio CircuitPython for SAMD[edit]

Land Boards CircuitPython Code[edit]

I2CIO-8 (MCP23008) Drivers[edit]
SWLEDX8-I2C (MCP23017) Drivers[edit]
PROTO16-I2C (MCP23017) Drivers[edit]

Digital I/O Example[edit]

import board
import digitalio
import time

led = digitalio.DigitalInOut(board.D13)
led.direction = digitalio.Direction.OUTPUT

while True:
    led.value = True
    led.value = False

Flash EEPROM 2 MB[edit]

QT Py 4600-07.jpg

QT Py Breakout Board[edit]

QT Py Breakout P18212-720px.jpg

  • Built onto GRID49 card
  • Socket for QT Py
  • QT Py pins brought to header strips
  • 3.3V power distribution on 2x8 header

Pins (CCW direction)[edit]

  • S12 = A0
  • R12 = A1
  • Q12 = A2
  • P12 = A3
  • N12 = SDA
  • M12 = SCL
  • L12 = TX
  • L1 = RX
  • M1 = SCK
  • N1 = MI
  • P1 = MO
  • Q1 = 3.3V
  • R1 = GND
  • S1 = 5V
  • A6=B6=C6=D6=E6=F6=G6=H6 = GND
  • A7=B7=C7=D7=E7=F7=G7=H7 = 3.3V

QTPy49 Board[edit]

QTPY P18242-720pxV.jpg