Bluetooth: Direction finding connectionless beacon

The direction finding connectionless beacon sample demonstrates Bluetooth LE direction finding transmission.


The sample supports the following development kits:

Hardware platforms


Board name

Build target

nRF52833 DK




The sample also requires an antenna matrix when operating in angle of departure mode. It can be a Nordic Semiconductor design 12 patch antenna matrix, or any other antenna matrix.


The direction finding connectionless beacon sample application uses Constant Tone Extension (CTE), that is transmitted with periodic advertising PDUs.

The sample supports two direction finding modes:

  • angle of arrival (AoA)

  • angle of departure (AoD)

By default, both modes are available in the sample.


See Configuring your application for information about how to permanently or temporarily change the configuration.

Angle of arrival mode

To build this sample with angle of arrival mode only, set OVERLAY_CONFIG to overlay-aoa.conf.

See Providing CMake options for instructions on how to add this option. For more information about using configuration overlay files, see Important Build System Variables in the Zephyr documentation.

Antenna matrix configuration for angle of departure mode

To use this sample when angle of departure mode is enabled, additional configuration of GPIOs is required to control the antenna array. Example of such configuration is provided in a devicetree overlay file nrf52833dk_nrf52833.overlay.

The overlay file provides the information about which GPIOs should be used by the Radio peripheral to switch between antenna patches during the CTE transmission in the AoD mode. At least two GPIOs must be provided to enable antenna switching.

The GPIOs are used by the Radio peripheral in order given by the dfegpio#-gpios properties. The order is important because it affects mapping of the antenna switching patterns to GPIOs (see Antenna patterns).

To successfully use the direction finding beacon when the AoD mode is enabled, provide the following data related to antenna matrix design:

  • Provide the GPIO pins to dfegpio#-gpios properties in nrf52833dk_nrf52833.overlay file

  • Provide the default antenna that will be used to transmit PDU dfe-pdu-antenna property in nrf52833dk_nrf52833.overlay file

  • Update the antenna switching patterns in ant_patterns array in main.c.

Antenna patterns

The antenna switching pattern is a binary number where each bit is applied to a particular antenna GPIO pin. For example, the pattern 0x3 means that antenna GPIOs at index 0,1 will be set, while the following are left unset.

This also means that, for example, when using four GPIOs, the pattern count cannot be greater than 16 and maximum allowed value is 15.

If the number of switch-sample periods is greater than the number of stored switching patterns, then the radio loops back to the first pattern.

The following table presents the patterns that you can use to switch antennas on the Nordic-designed antenna matrix:




0 (0b0000)


1 (0b0001)


2 (0b0010)


3 (0b0011)


4 (0b0100)


5 (0b0101)


6 (0b0110)


7 (0b0111)


8 (0b1000)


9 (0b1001)


10 (0b1010)


11 (0b1011)


12 (0b1100)


13 (0b1101)


14 (0b1110)


15 (0b1111)

Building and Running

This sample can be found under samples/bluetooth/direction_finding_connectionless_tx 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 development kit, test it by performing the following steps:

  1. Connect to the kit that runs this sample with a terminal emulator (for example, PuTTY). See How to connect with PuTTY for the required settings.

  2. In the terminal window, check for information similar to the following:

    Starting Connectionless Beacon Demo
    Bluetooth initialization...success
    Advertising set create...success
    Update CTE params...success
    Periodic advertising params set...success
    Enable CTE...success
    Periodic advertising enable...success
    Extended advertising enable...success
    Started extended advertising as XX:XX:XX:XX:XX:XX (random)


This sample uses the following Zephyr libraries:

  • include/zephyr/types.h

  • lib/libc/minimal/include/errno.h

  • include/sys/printk.h

  • include/sys/byteorder.h

  • include/sys/util.h

  • Bluetooth:

    • include/bluetooth/bluetooth.h

    • include/bluetooth/hci.h

    • include/bluetooth/direction.h

    • include/bluetooth/gatt.h