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 0 peripheral to the Bluetooth LE unit. On Nordic Semiconductor’s development kits, the UART 0 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 0 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.


On Thingy:53 debug logs are provided over the USB CDC ACM class serial port, instead of using RTT.


The sample supports the following development kits:

Hardware platforms


Board name

Build target

nRF5340 DK





nRF52840 DK




nRF52840 DK (emulating nRF52811)




nRF52833 DK




nRF52833 DK (emulating nRF52820)




nRF52 DK




nRF52 DK (emulating nRF52810)









  • To build this sample for nrf52dk_nrf52810, nrf52840dk_nrf52811 or nrf52833dk_nrf52820, use the Minimal build approach.

  • When used with Thingy:53, the sample supports the MCUboot bootloader with serial recovery and SMP DFU over Bluetooth. Thingy:53 has no built-in SEGGER chip, so the UART 0 peripheral is not gated to a USB CDC virtual serial port.

The sample also requires a smartphone or tablet running a compatible application. The Testing instructions refer to nRF Connect for Mobile, but you can also use other similar applications (for example, nRF Blinky or nRF Toolbox).

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

User interface

The user interface of the sample depends on the hardware platform you are using.

Development kits

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 in the debug logs to pair/bond with the other device.

Button 2:

Reject the passkey value that is printed in the debug logs to prevent pairing/bonding with the other device.



The RGB LED channels are used independently to display the following information:

  • Red channel blinks with a period of 2 seconds, duty cycle 50%, when the main loop is running (device is advertising).

  • Green channel displays if device is connected.


Confirm the passkey value that is printed in the debug logs to pair/bond with the other device. Thingy:53 has only one button, therefore the passkey value cannot be rejected by pressing a button.

Building and running

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

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

Minimal build

You can build the sample with a minimum configuration as a demonstration of how to reduce code size and RAM usage. To build the minimum configuration, use the following command:

west build samples/bluetooth/peripheral_uart -- -DCONF_FILE='prj_minimal.conf'


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

  1. Connect the device to the computer to access UART 0. If you use a development kit, UART 0 is forwarded as a COM port (Windows) or ttyACM device (Linux) after you connect the development kit over USB. If you use Thingy:53, you must attach the debug board and connect an external USB to UART converter to it.

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

  3. Optionally, you can display debug messages. See Debugging for details.

  4. Reset the kit.

  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 or bond with the device with MITM protection. This requires using the passkey value displayed in debug messages. See Debugging for details on how to access debug messages. To confirm pairing or bonding, press Button 1 on the device and accept the passkey value on the smartphone.

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

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

  11. Type ‘0123456789’ and tap SEND. 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 is sent to the peer.

  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