Bluetooth: nRF Distance Measurement with Bluetooth LE discovery

The nRF Distance Measurement sample demonstrates the functionality of the Distance Measurement subsystem. It shows how to use DM to measure the distance between devices. The Bluetooth® Direction and Distance Finding Service (DDFS) is running simultaneously.

Sample is configured to use Nordic’s SoftDevice link layer.

Note

The Distance Measurement support in the nRF Connect SDK is experimental. See Distance Measurement for details.

Requirements

The sample supports the following development kits:

Hardware platforms	PCA	Board name	Build target
nRF5340 DK	PCA10095	nrf5340dk_nrf5340	nrf5340dk_nrf5340_cpuapp
nRF52 DK	PCA10040	nrf52dk_nrf52832	nrf52dk_nrf52832
nRF52840 DK	PCA10056	nrf52840dk_nrf52840	nrf52840dk_nrf52840
nRF52833 DK	PCA10100	nrf52833dk_nrf52833	nrf52833dk_nrf52833

Overview

The sample initializes and performs distance measurements between devices. The procedure for distance measurement on both devices must be synchronized.

The synchronization step has two goals:

• Detect peers that support the ranging procedure.

• Provide synchronization for the ranging step.

This sample synchronizes devices using the scan and advertising facilities of the Bluetooth LE. Anchoring occurs after the exchange of SCAN_REQ and SCAN_RSP packets.

The chart shows the sequence of the synchronization process.

Both devices act as an advertiser and a scanner. Device B receives advertising from Device A and scans it. Device A sends a scan response that contains Manufacturer Specific Data. This message contains the following fields:

• Company Identifier Code.

• Identifier indicating that the device supports distance measurement.

• The access address used for measurement.

This scanner/advertiser interaction is used as a synchronization point. After a configurable delay, Device A and Device B try to range each other.

• If a Device acts as an advertiser in synchronization, it will act as the reflector in the ranging procedure.

• If a Device acts as a scanner in synchronization, it will act as the initiator in the ranging procedure.

The synchronization will be performed cyclically.

Based on the SCAN_RSP response, the device recognizes peers that support the distance measurement functionality within its coverage. The addresses of these devices are stored in a list. When a device does not respond within a certain period of time, it is removed from the list. Also the last measurement results with the peers are stored in this list.

User interface

LED 1:

Indicates the measured distance for MCPD (Multi-carrier phase difference) method. The shorter the distance, the brighter the light.

LED 2:

Blinks every two seconds with the duty cycle set to 50% when the main loop is running and the device is advertising.

LED 3:

On when connected.

Building and running

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

To build the sample with Visual Studio Code, follow the steps listed on the How to build an application page in the nRF Connect for VS Code extension documentation. See Building and programming an application for other building and programming scenarios and Testing and debugging an application for general information about testing and debugging in the nRF Connect SDK.

Testing

After programming the sample to development kits, 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. Reset the kit.

3. Program the other development kit with the same sample and reset it.

4. Wait until the devices identify themselves and synchronize.

5. Observe that the received measurement results are output in the terminal window.

Sample output

The result should look similar to the following output:

• The MCPD method:

  *** Booting Zephyr OS build v2.6.99-ncs1  ***
  Starting Distance Measurement example
  I: SoftDevice Controller build revision:
  I: 3f 47 70 8e 81 95 4e 86 |?Gp...N.
  I: 9d d3 a2 95 88 f6 30 0a |......0.
  I: 7f 53 49 fd             |.SI.
  I: HW Platform: Nordic Semiconductor (0x0002)
  I: HW Variant: nRF52x (0x0002)
  I: Firmware: Standard Bluetooth controller (0x00) Version 63.28743 Build 1318420878
  I: Identity: C4:90:D5:4E:C2:20 (random)
  I: HCI: version 5.2 (0x0b) revision 0x125b, manufacturer 0x0059
  I: LMP: version 5.2 (0x0b) subver 0x125b
  DM Bluetooth LE Synchronization initialization
  
  Measurement result:
        Addr DB:49:E9:62:DF:6D (random)
        Quality ok
        Distance estimates: mcpd: ifft=0.29 phase_slope=0.28 rssi_openspace=0.28 best=0.29
  
  Measurement result:
        Addr CF:4E:38:D5:C0:ED (random)
        Quality ok
        Distance estimates: mcpd: ifft=0.94 phase_slope=1.10 rssi_openspace=0.22 best=0.94
  
  Measurement result:
        Addr CF:4E:38:D5:C0:ED (random)
        Quality ok
        Distance estimates: mcpd: ifft=0.79 phase_slope=1.08 rssi_openspace=0.25 best=0.79
  

• The RTT method:

  *** Booting Zephyr OS build v2.6.99-ncs1  ***
  Starting Distance Measurement example
  I: SoftDevice Controller build revision:
  I: 3f 47 70 8e 81 95 4e 86 |?Gp...N.
  I: 9d d3 a2 95 88 f6 30 0a |......0.
  I: 7f 53 49 fd             |.SI.
  I: HW Platform: Nordic Semiconductor (0x0002)
  I: HW Variant: nRF52x (0x0002)
  I: Firmware: Standard Bluetooth controller (0x00) Version 63.28743 Build 1318420878
  I: Identity: C4:90:D5:4E:C2:20 (random)
  I: HCI: version 5.2 (0x0b) revision 0x125b, manufacturer 0x0059
  I: LMP: version 5.2 (0x0b) subver 0x125b
  DM Bluetooth LE Synchronization initialization
  
  Measurement result:
        Addr CF:4E:38:D5:C0:ED (random)
        Quality ok
        Distance estimates: rtt: rtt=1.75
  
  Measurement result:
        Addr CF:4E:38:D5:C0:ED (random)
        Quality ok
        Distance estimates: rtt: rtt=1.70
  
  Measurement result:
        Addr DB:49:E9:62:DF:6D (random)
        Quality ok
        Distance estimates: rtt: rtt=2.75
  

Dependencies

This sample uses the following nRF Connect SDK subsystems:

• Direction and Distance Finding Service (DDFS)

• DK Buttons and LEDs

This sample uses the following sdk-nrfxlib library:

• Nordic Distance Measurement library

In addition, it uses the following Zephyr libraries:

• Kernel Services:

  • include/kernel.h

• PWM:

  • drivers/pwm.h

• include/sys/printk.h

• include/sys/byteorder.h

• include/random/rand32.h

• Bluetooth APIs:

  • include/bluetooth/bluetooth.h

  • include/bluetooth/scan.h

• ext/hal/nordic/nrfx/hal/nrf_radio.h