SAMD21 MINI / Wemos D1 SAMD21 M0 Mini Development Board Sells for $7 and Up

Microchip / Atmel SAMD21 Arm Cortex-M0+ microcontroller has been around for several years, and we covered various boards based on the MCU include the official Arduino Zero launched in 2014, Arduino Tian, and the tiny SAM 15×15 or Exen Proto boards among others.

Another SAMD21 development board has now shown up on Electrodragon website: SAMD21 Mini Development Board sold for $14.50 on the website, but you’ll also find it, under the RobotDyn or Wemos brand on Aliexpress for $7.05 and up.

SAMD21 Mini Board / WeMos D1 SAMD21 M0 Mini

SAMD21 Mini Development Board


  • MCU – Microchip ATSAMD21G18 Arm Cortex-M0+ microcontroller @ 48 MHz with 32KB data RAM, 256KB flash
  • USB – 1x micro USB port for power and programming
  • Expansion
    • 2x 14-pin headers with 19x digital I/O (including 12x PWM), 6x Analog I/O
    • 3.3V logic level
  • Programming – 6-pin ISCP connector
  • Misc – Power, Tx and Rx LED’s, button
  • Power Supply
    • Input – 5V via micro USB port or VIN
    • Output – 3.3V-800mA (However, it reads 3.3V/180mA on the silkscreen)
    • Consumption – 3.3V @ 220mA
  • Dimensions – 56.5 x 18 mm
  • Temperature Range – -40°С – +85°С

Wemos D1 SAMD21 M0 Mini

Both Wemos D1 SAMD21 M0 Mini and RobotDyn SAMD21 Mini boards appear to be identical except for the branding on the bottom of the board. There’s not an awful lot of documentation made available from any of the sellers but luckily, BLavery tested the board late last year and documented his experience with Arduino and CircuitPython on Github.

Thanks to Zoobab for the tip.

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2 Replies to “SAMD21 MINI / Wemos D1 SAMD21 M0 Mini Development Board Sells for $7 and Up”

  1. Regarding the Robotdyn and Wemos boards you have mentioned, there are some minor points to take into account. I am currently using both the Wemos and the Robotdyn versions of the board and the choice of which module I order is primarily determined by delivery time. One the boards I have received, there are a few differences, the voltage regulators used are different between two with the Robotdyn units having both a higher current rating and a lower quiescent current. Neither module is capable of supplying any where near the 800mA shown in the specification section. Having said that, in my testing the current consumption at 3.3 volts for these modules is about 20mA without using sleep leaving a lot of headway for driving external devices from the 3,3 volt regulator.

    They have different bootloaders installed on them, I could not program the Robotdyn modules via the Arduino IDE until I installed a new bootloader.

    The Robodyn modules include the FET for driving the LED on D13 whereas the Memos branded variant the the FET pads empty.

    The ISP connector is not actually an ISP connector because the SAMD21 does not support the ISP mechanism.

    The design of the module is flawed. The quiescent current for both modules is 4mA when the processor is in sleep mode. It is supposed to be in the microamps range. There is a design error on the board with the USB interfaces, It appears that U5, the smaller of the two 5 pin packages near the USB connector, was intended to control the ability for the module to support OTG USB interfaces by enabling the module to power external USB devices. However the implementation of this function is flawed, and is the reason for the high quiescent current consumption when the CPU is sleeping.

  2. Mine is labelled HW-799 and Arduino IDE recognizes device ATSAMD21G18A

    Blinky needed to toggle 25

    First Arduino IDE host machine could not upload via USB. 2nd no problem.

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