The nRF5 SDK for Mesh provides a PA/LNA module with APIs for interfacing the external Front End Modules (FEMs) to increase the range of Bluetooth Low Energy communication.
The FEMs are controlled by the enable signals that turn on a power amplifier (PA) or a low noise amplifier (LNA) (see the following figure). To ensure sufficient ramp-up time, these signals must be activated some time before the start of the radio transmission or reception.
Interfacing PA/LNA with an nRF52 device
The Mesh PA/LNA module enables users to control such external components using GPIOs that are synchronized to the radio operation. The PA/LNA module drives the chosen GPIO pins according to the chosen polarity (Active High/Active Low).
See the following section for an example of how to use the PA/LNA module. You can find more information about the available APIs in the PA/LNA API documentation.
Select the unused GPIO pins that can be used by the PA/LNA module.
For this example, use GPIO 25 for controlling the LNA and GPIO 24 for controlling the PA.
Also, assume that the control signals required by the external hardware module are Active High. The Mesh PA/LNA module uses the PPI and GPIOTE hardware modules to generate these signals. To read more about these modules in nRF52832, see the following documents: nRF52832 PPI and nRF52832 GPIOTE .
Select the unused PPI channels 0 and 1, and the GPIOTE channel 0.
Editing the main.c file
Make the following changes in light_switch/server/src/main.c:
Include the required module header file: mesh_pa_lna.h
Create a static global variable of type mesh_pa_lna_gpiote_params_t and initialize it with the selected values:
If you connect a logic analyzer to the GPIO pins 25 and 24, you will see them toggling.
The unprovisioned device sends the unprovisioned node beacons every two seconds (NRF_MESH_PROV_BEARER_ADV_UNPROV_BEACON_INTERVAL_MS) and scans for the incoming provisioning invite for the rest of the time.
GPIO waveforms after enabling PA/LNA module
You will see brief Active High pulses on the GPIO pin 24, which is used for the PA control. Similarly, the GPIO pin 25 (used for the LNA control) is almost always ON, except for the time when the radio switches to the next advertising channel for scanning or for sending advertisements.