Bluetooth: Peripheral UART

The Peripheral UART sample demonstrates how to use the Nordic UART Service (NUS). It uses the NUS service to send data back and forth between a UART connection and a Bluetooth LE connection, emulating a serial port over Bluetooth LE.


When connected, the sample forwards any data received on the RX pin of the UART 1 peripheral to the Bluetooth LE unit. On Nordic Semiconductor’s development kits, the UART 1 peripheral is typically gated through the SEGGER chip to a USB CDC virtual serial port.

Any data sent from the Bluetooth LE unit is sent out of the UART 1 peripheral’s TX pin.


In this sample, the UART console is used to send and read data over the NUS service. Debug messages are not displayed in this UART console. Instead, they are printed by the RTT logger.

If you want to view the debug messages, follow the procedure in Connecting via RTT.


The sample supports the following development kits:

Hardware platforms


Board name

Build target

nRF5340 DK





nRF52840 DK




nRF52833 DK




nRF52833 DK (emulating nRF52820)




nRF52 DK




The sample also requires a phone or tablet running a compatible application. The Testing instructions refer to nRF Connect for Mobile, but similar applications (for example, nRF Toolbox) can be used as well.

You can also test the application with the Bluetooth: Central UART sample. See the documentation for that sample for detailed instructions.

User interface

LED 1:
  • Blinks with a period of 2 seconds, duty cycle 50%, when the main loop is running (device is advertising).

LED 2:
  • On when connected.

Button 1:
  • Confirm the passkey value that is printed on the COM listener to pair/bond with the other device.

Button 2:
  • Reject the passkey value that is printed on the COM listener to prevent pairing/bonding with the other device.

Building and running

This sample can be found under samples/bluetooth/peripheral_uart in the nRF Connect SDK folder structure.

See Building and programming a sample application for information about how to build and program the application.


After programming the sample to your board, test it by performing the following steps:

  1. Connect the board to the computer using a USB cable. The board is assigned a COM port (Windows) or ttyACM device (Linux), which is visible in the Device Manager.

  2. Connect to the kit with a terminal emulator (for example, PuTTY). See How to connect with PuTTY for the required settings.

  3. Optionally, connect the RTT console to display debug messages. See Debugging.

  4. Reset the board.

  5. Observe that LED 1 is blinking and that the device is advertising with the device name that is configured in CONFIG_BT_DEVICE_NAME.

  6. Observe that the text “Starting Nordic UART service example” is printed on the COM listener running on the computer.

  7. Connect to the device using nRF Connect for Mobile. Observe that LED 2 is on.

  8. Optionally, pair/bond with the device with MITM protection. This requires RTT connection. To confirm pairing/bonding, press Button 1 on the device and accept the passkey value on the smartphone.

  9. In the app, observe that the services are shown in the connected device.

  10. Select the UART RX characteristic value in nRF Connect. You can write hexadecimal ASCII values to the UART RX and get the text displayed on the COM listener.

  11. Type ‘30 31 32 33 34 35 36 37 38 39’ (the hexadecimal value for the string “0123456789”) and tap write. Verify that the text “0123456789” is displayed on the COM listener.

  12. To send data from the device to your phone or tablet, enter any text, for example, “Hello”, and press Enter to see it on the COM listener. Observe that a notification with the corresponding ASCII values is sent to the peer on handle 0x12. For the string “Hello”, the notification is ‘48 65 6C 6C 6F’.

  13. Disconnect the device in nRF Connect. Observe that LED 2 turns off.


This sample uses the following nRF Connect SDK libraries:

In addition, it uses the following Zephyr libraries:

  • include/zephyr/types.h

  • boards/arm/nrf*/board.h

  • Kernel Services:

    • include/kernel.h

  • Peripherals:

    • incude/gpio.h

    • include/uart.h

  • Bluetooth:

    • include/bluetooth/bluetooth.h

    • include/bluetooth/gatt.h

    • include/bluetooth/hci.h

    • include/bluetooth/uuid.h