This example shows the implementation of a device supporting the Low Power node (LPN) feature. It emulates an occupancy sensor device through button presses and a timer.

You can use this example as the starting point for adding the LPN feature to your device, as it demonstrates all the required changes to the application.

When configured to interact with a device with a Generic OnOff Server model, the device running this example turns on the LED on the light switch server device upon a button press, which emulates triggering the occupancy sensor. It also sends an off message to the light switch server device after five seconds to emulate inactivity.

This example uses GATT for provisioning, and instantiates a Generic OnOff Client model that can be used to control light switch servers.

You can read more about the Low Power Node feature in Low Power node feature and Integrating Low Power node feature.

Table of contents

Prerequisites

Running this example requires three PCA10040 Development Kits:

One development kit for the LPN device running the Low Power Node example.
One development kit for thr Friend device running mesh firmware with the Friend feature enabled.
One development kit for the light switch server device running the light switch server example.

As the Friend feature is not supported by this version of the nRF5 SDK for Mesh, use a precompiled version of the Friend node from the Zephyr RTOS to fulfill the Friend device role. The precompiled Friend node hex files are available at <InstallFolder>/examples/experimental_lpn/bin. See Zephyr RTOS binaries for additional information on how they were built.

You also need to download and install nRF Mesh mobile app (available for iOS and Android) for Provisioning and configuration.

Setup

You can find the source code and the project file of the example in the following folder: <InstallFolder>/examples\experimental_lpn

To set up the example:

Build the Low Power node example and Light switch server example. To build the example, follow the instructions in Building the mesh stack. Refer to the Running examples using nrfjprog section on the Running examples page for the commands required to program a device using nrfjprog.
Program the examples onto two development kits.
Choose the Friend node hex file appropriate for your hardware platform from examples/experimental_lpn/bin/, and program it to the third development kit using nrfjprog:

nrfjprog --program <path-to-hex-file> --chiperase -r

Note: The Zephyr Friend node hex file does not require a SoftDevice, so it will start running immediately after nrfjprog finshes execution.

All three devices are now running Bluetooth Mesh enabled firmware.

Button assignments

These assignments refer to the LPN device only.

Button 1: Send the on message.
Button 2: Send the off message.
Button 3: Establish or terminate friendship.
Button 4: Reset the device (erase all mesh data).

LED assignments

These assignments refer to the LPN device only.

LED 1: Reacts to pressing button 1 (turns on) and button 2 (turns off). Can be off for other reasons, for example when joining the network.
LED 2: Friendship established.
LED 2 and 3 blinking: Device identification active.
All LEDs blinking four times: Provisioning complete.
All LEDs flashing instensively: An error occurred. See the RTT log for details.

Running the example

To send messages between the LPN device and the light switch server device, complete the following steps:

Provisioning and configuration

Before a friendship can be established between the LPN device and the Friend device, they both must be provisioned to the same mesh network. As the Low Power node example only supports the PB-GATT bearer for provisioning, use nRF Mesh mobile app (for iOS or Android) to provision and configure all three devices.

Configuring light switch server device

The light switch server device shows up in the nRF Mesh App as "nRF5x Mesh Light".

Provision the light switch server device with the nRF Mesh App.
Give the light switch server device Application key 1 through its configuration menu, if it doesn't already have it. This application key will represent the light switch application. The key will be used by the Generic OnOff client on the LPN device and the Generic OnOff server to communicate.
Open the Generic OnOff Server model's configuration menu, and bind Application key 1 to a Generic OnOff Server model that the light switch server device instantiates in its first element.
Disconnect from the light switch server device, and go back to the scanner screen.
Take note of the light switch server device's unicast address, as it is needed for the configuration of the LPN device.

The light switch server is now a part of the mesh network, and is ready to receive messages from the LPN device.

Configuring the LPN device

The LPN device shows up in the nRF Mesh App as "nRF5x Mesh LPN".

Provision the LPN device with the nRF Mesh App.
Give the LPN device Application key 1 through its configuration menu, if it doesn't already have it. The key has the same role and usage as in the case of the light switch server device.
Open the Generic OnOff Client model's configuration menu, and bind Application key 1 to a Generic OnOff Client model that the LPN device instantiates in its first element.
Open the Generic OnOff Client model's publication settings.
Set the Publish Address to the unicast address of the light switch server that you took note of.
Disconnect from the LPN device, and go back to the scanner screen.

The LPN device is now part of the mesh network and can control the LEDs of the light switch server device. It has not entered the low power mode yet, as it needs a Friend device to accept its Friend requests.

Provisioning the Friend device

The Friend shows up in the nRF Mesh App as "Zephyr". Provision the Friend device with the nRF Mesh App. No additional configuration is needed.

Establishing the friendship

After the configuration, the LPN device enters the idle state.

To start the friendship establishment process, press button 3 on the LPN device. The device starts searching for an appropriate Friend in the mesh network.

The LPN example always accepts the first friendship it's offered. Establishing a friendship normally takes less than a second. If the LPN device cannot find a Friend after 5-10 seconds, all LEDs will blink intensively. You have to press button 3 again to retry.

Once the friendship is established, LED 2 turns on and stays lit throughout the friendship.

Note: Pressing button 3 again while the LPN is in a friendship causes it to terminate the friendship and go back to the normal power mode.

Sending messages

You can send on and off messages by pressing buttons 1 and 2, respectively. These buttons also control the LED 1 of the light switch server through the Generic OnOff client model.

Pressing button 1 turns on the LED 1 on the LPN device and sends message to the light switch server. This message turns on the LED 1 on the light switch server.
Pressing button 2 turns off the LED 1 on the LPN device and sends message to the light switch server. This message turns off the LED 1 on the light switch server.

This behavior is identical to the one in the light switch client example.

Resetting the device

Pressing button 4 resets and unprovisions the LPN device.