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Getting Started with Seeed Studio XIAO nRF52840 (Sense)

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As the first wireless product in the Seeed Studio XIAO family, Seeed Studio XIAO nRF52840 is equipped with a powerful Nordic nRF52840 MCU which integrates Bluetooth 5.0 connectivity. Meanwhile, it has a small and exquisite form-factor which can be used for wearable devices and Internet of Things projects. The single-sided surface-mountable design and the onboard Bluetooth antenna can greatly facilitate the rapid deployment of IoT projects.

In addition, there is an advanced version of this board, Seeed Studio XIAO nRF52840 Sense. It is integrated with two extra onboard sensors. One of them is a Pulse Density Modulation (PDM) Digital Microphone. It can receive audio data in real-time which allows it to be used for audio recognition. The other one is a 6-axis Inertial Measurement Unit (IMU), this IMU can be very useful in TinyML projects like gesture recognition. These onboard sensors provide a great convenience for users while the board is ultra-small.

Compared to Seeed Studio XIAO RP2040, Seeed Studio XIAO nRF52840 contains richer interfaces. The first thing to note is that the Near Field Communication (NFC) interface is functional on the board. Secondly, there is a tiny reset button on the side of the Type-C interface. On the other side, there is a 3-in-one LED (User LED) along with a Charge LED to indicate the charging status when a battery is connected. There are 11 digital I/O that can be used as PWM pins and 6 analog I/O that can be used as ADC pins. It supports all three common serial interfaces such as UART, I2C, and SPI. Same as Seeed Studio XIAO RP2040, it has an onboard 2 MB flash which means it can also be programmed using Arduino, MicroPython, CircuitPython, or other programming languages.

Seeed Studio XIAO nRF52840 Sense is compatible to the Seeed Studio XIAO expansion board.

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Features​

  • Powerful wireless capabilities: Bluetooth 5.0 with onboard antenna
  • Powerful CPU: Nordic nRF52840, ARM® Cortex®-M4 32-bit processor with FPU, 64 MHz
  • Ultra-Low Power: Standby power consumption is less than 5μA
  • Battery charging chip: Supports lithium battery charge and discharge management
  • Onboard 2 MB flash
  • Onboard PDM microphone (only in Seeed Studio XIAO nRF52840 Sense)
  • Onboard 6-axis LSM6DS3TR-C IMU (only in Seeed Studio XIAO nRF52840 Sense)
  • Ultra Small Size: 20 x 17.5mm, Seeed Studio XIAO series classic form-factor for wearable devices
  • Rich interfaces: 1xUART, 1xI2C, 1xSPI, 1xNFC, 1xSWD, 11xGPIO(PWM), 6xADC
  • Single-sided components, surface mounting design

Specifications comparison​

ItemSeeed Studio XIAO SAMD21Seeed Seeed Studio XIAO RP2040Seeed Seeed Studio XIAO nRF52840Seeed Seeed Studio XIAO nRF52840 Sense
ProcessorSAMD21 M0+@48MHzRP2040 Dual-core M0+@133MhznRF52840 M4F@64MHznRF52840 M4F@64MHz
Wireless ConnectivityN/AN/ABluetooth 5.0/BLE/NFCBluetooth 5.0/BLE/NFC
Memory32 KB SRAM 256KB FLASH264 KB SRAM 2MB onboard Flash256 KB RAM, 1MB Flash 2MB onboard Flash256 KB RAM,1MB Flash 2MB onboard Flash
Built-in SensorsN/AN/AN/A6 DOF IMU (LSM6DS3TR-C), PDM Microphone
InterfacesI2C/UART/SPII2C/UART/SPII2C/UART/SPII2C/UART/SPI
PWM/Analog Pins11/1111/411/611/6
Onboard ButtonsN/AReset/ Boot ButtonReset ButtonReset Button
Onboard LEDsN/AFull-color RGB/ 3-in-one LED3-in-one LED/ Charge LED3-in-one LED/ Charge LED
Battery Charge ChipN/AN/ABQ25101BQ25101
Programming LanguagesArduino/ CircuitPythonArduino/ MicroPython/ CircuitPythonArduino/ MicroPython/ CircuitPythonArduino/ MicroPython/ CircuitPython

Hardware overview​

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Two Arduino Libraries​

Seeed Studio XIAO nRF52840 assembles many functions in one tiny board and sometimes may not perform the best of them. Hence, Seeed has published two Arduino libraries to let it maximum the power of each function. Therefore:

  • It is recommanded to use the Seeed nRF52 Boards library if you want to apply Bluetooth function and "Low Energy Cost Function".
  • It is recommanded to use the Seeed nRF52 mbed-enabled Boards library if you want to use it in embedded Machine Learning Applications or apply "IMU & PDM advanced function".
  • Both libraries support very well when it comes to the basic usage, such as LED, Digital, Analog, Serial, I2C, SPI.

The Pin definition supported by these two libraries might be a little different and Seeed will keep update the wiki until it is clear.

Getting started​

First, we are going to connect the Seeed Studio XIAO nRF52840 (Sense) to the computer and upload a simple code from Arduino IDE to check whether the board is functioning well.

Hardware setup​

You need to prepare the following:

提示

Some USB cables can only supply power and cannot transfer data. If you don't have a USB cable or don't know if your USB cable can transmit data, you can check Seeed USB Type-C support USB 3.1.

Connect the Seeed Studio XIAO nRF52840 (Sense) to your computer via a USB Type-C cable.

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Software setup​

  • Step 1. Download and Install the latest version of Arduino IDE according to your operating system

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  • Step 2. Launch the Arduino application

  • Step 3. Add Seeed Studio XIAO nRF52840 (Sense) board package to your Arduino IDE

Navigate to File > Preferences, and fill "Additional Boards Manager URLs" with the url below: https://files.seeedstudio.com/arduino/package_seeeduino_boards_index.json

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Navigate to Tools > Board > Boards Manager..., type the keyword "seeed nrf52" in the search box, select the latest version of the board you want, and install it. You can install both.

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  • Step 4. Select your board and port

Board

After installing the board package, navigate to Tools > Board and choose the board you want, continue to select "Seeed XIAO nRF52840 Sense". Now we have finished setting up the Seeed Studio XIAO nRF52840 (Sense) for Arduino IDE.

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Port

Navigate to Tools > Port and select the serial port name of the connected Seeed Studio XIAO nRF52840 (Sense). This is likely to be COM3 or higher (COM1 and COM2 are usually reserved for hardware serial ports). The serial port of the connected Seeed Studio XIAO nRF52840 (Sense) usually contains parentheses that are written Seeed Studio XIAO nRF52840 for Seeed Studio XIAO nRF52840 or Seeed Studio XIAO nRF52840 Sense for Seeed Studio XIAO nRF52840 Sense.

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  • Step 5. Navigate to File > Examples > 01.Basics > Blink to open Blink example

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  • Step 6. Click the Upload button to upload the Blink example code to the board

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Once uploaded, you will see the built-in red LED blinking with a 1-second delay between each blink. This means the connection is successful and now you can explore more projects with the Seeed Studio XIAO nRF52840 (Sense)!

Playing with the built-in 3-in-one LED​

Seeed Studio XIAO nRF52840 (Sense) has an onboard 3-in-one LED which is user-programmable. Now you will learn how to control the RGB colors one-by-one using Arduino!

You first have to understand that the behavior of this LED is not as usual when controlled by the code. The LED turns ON when we give a LOW signal and it turns OFF when we give a HIGH signal. This is because this LED is controlled by a common anode and will light up only with a low-level signal.

An example code would be:

void setup() {
  pinMode(LED_BUILTIN, OUTPUT);
}

void loop() {
  digitalWrite(LED_BUILTIN, HIGH);   
}

Here, even though HIGH is used, the LED will be OFF. You need to replace HIGH with LOW to turn ON the LED.

Refer to the following pin mappings of the LEDs and use them in your codes:

  • Red LED - LED_BUILTIN or LEDR
  • Green LED - LEDG
  • Blue LED - LEDB

Power Consumption Verification​

The Seeed Studio XIAO nRF52840 is low power consumption and here we provide a method to verify. It is highly recommend to use the Seeed nRF52 Boards library here.

  • Step 1. Use JLink Downloader to flash the bootloader firmware for Seeed Studio XIAO nRF52840 (Sense).
备注

If you are using the factory firmware of the Seeed Studio XIAO nRF52840 or have never made changes to the firmware of the Seeed Studio XIAO nRF52840, you can skip this step.

  • Step 2. Use theSeeed nRF52 Boards library here.

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  • Step 3. Upload the deep_sleep demo here and run it with Arduino

  • Step 4. Adjust the voltage of the digital source meter to 3.6V constant voltage

  • Step 5. Touch the red test pen to BAT+ and black test pen to BAT-

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  • Step 6. The output shows the current is at about 3 μA

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Battery Charging current​

The battery charging current is selectable as 50mA or 100mA, where you can set Pin13 as high or low to change it to 50mA or 100mA. The low current charging current is at the input model set up as HIGH LEVEL and the high current charging current is at the output model set up as LOW LEVEL.

Low Charging Current

void setup(){
pinMode P0_13, OUTPUT);
}
void loop() {
digitalWrite(P0_13, HIGH);
}

High Charging Current

void setup(){
pinMode P0_13, OUTPUT);
}
void loop() {
digitalWrite(P0_13, LOW);
}

Access the SWD Pins for Debugging and Reflashing Bootloader​

Hardware Required

Software Required

It is required to download the Segger software from the website.

  • Step 1. Use Jlink to connect pins below:

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  • Step 2. Start the J-Flash and serach nRF52840, creating a new project:

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  • Step 3. Click "Target" and then select "Connect".

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  • Step 4. Draw the bin or hex file to software. Then press F4 and F5 in that order. The reflashing is done.

FAQ​

Q1: My Arduino IDE is stuck when uploading code to the board​

You can first try to reset the board by clicking the "Reset Button" once. If that does not work, rapidly click it twice to enter bootloader mode. If that also doesn't work, disconnect the board from the PC, and connect the board again.

Q2: My board is not showing up as a serial device on Arduino IDE​

You can first try to reset the board by clicking the "Reset Button" once. If that does not work, rapidly click it twice to enter bootloader mode.

Resources​

Tech support​

Please do not hesitate to submit the issue into our forum.


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