Low Power UART

The Low Power UART sample demonstrates the capabilities of the Low power UART driver module.


The sample implements a simple loopback using a single UART instance. It has console and logging disabled by default, to demonstrate low power consumption while having UART active.


The sample supports the following development kits:

Hardware platforms


Board name

Build target

nRF9160 DK




nRF52840 DK




nRF52833 DK




nRF52 DK




nRF5340 DK




nRF21540 DK




The sample also requires the following pins to be shorted:

  • TX (Arduino Digital Pin 10 (4 on nRF21540 DK)) with RX (Arduino Digital Pin 11 (5 on nRF21540 DK))

  • Request Pin (Arduino Digital Pin 12 (6 on nRF21540 DK)) with Response Pin (Arduino Digital Pin 13 (7 on nRF21540 DK))

Additionally, it requires a logic analyzer.


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

FEM support

You can add support for the nRF21540 front-end module to this sample by using one of the following options, depending on your hardware:

  • Build the sample for one board that contains the nRF21540 FEM, such as nrf21540dk_nrf52840.

  • Manually create a devicetree overlay file that describes how FEM is connected to the nRF5 SoC in your device. See Set devicetree overlays for different ways of adding the overlay file.

  • Provide nRF21540 FEM capabilities by using a shield, for example the nRF21540 EK shield that is available in the nRF Connect SDK. In this case, build the project for a board connected to the shield you are using with an appropriate variable included in the build command. This variable instructs the build system to append the appropriate devicetree overlay file. For example, to build the sample from the command line for an nRF52833 DK with the nRF21540 EK attached, use the following command within the sample directory:

    west build -b nrf52833dk_nrf52833 -- -DSHIELD=nrf21540_ek

    This command builds the application firmware. See Programming nRF21540 EK for information about how to program when you are using a board with a network core, for example nRF5340 DK.

Each of these options adds the description of the nRF21540 FEM to the devicetree. See Radio front-end module (FEM) support for more information about FEM in the nRF Connect SDK.

To add support for other front-end modules, add the respective devicetree file entries to the board devicetree file or the devicetree overlay file.

Building and running

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

See Building and programming an 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 the logic analyzer to the shorted pins, to confirm UART activity.

  2. Measure the current to confirm that the power consumption indicates that high-frequency clock is disabled during the idle stage. During the idle stage, the UART receiver is ready to start reception, as the request pin wakes it up.


This sample uses the following nRF Connect SDK driver:

In addition, it uses the following Zephyr libraries: