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Hi CircuitDojo Community,

I’m working on the nrf9160 to be used as a remote device to enable/disable other power systems and is connected to a small battery. When testing current draw using the configuration and following the instructions here (https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/nrf/app_power_opt.html) the device draw an average of 7.65ma when running the blinky script, rather than the 600 µA suggested. Turning off serial logging also had a negligible effect on the current draw. Following your other “low power” scripts also seemed to have no effect and the current remained around 7.65ma.

Currently, I do not have the external development chip and so am flashing the chip with CONFIG_BOOTLOADER_MCUBOOT=y using the terminal command “newtmgr -c serial image upload build/zephyr/app_update.bin”.

Any suggestions as to why this is occurring or what to test/investigate would be much appreciated.
Jesse

CMakeLists.txt:

# SPDX-License-Identifier: Apache-2.0

cmake_minimum_required(VERSION 3.13.1)

# Adding custom overlay to add settings that aren't included in the SDK (yet) for the nRF9160 Feather
if(${BOARD} STREQUAL circuitdojo_feather_nrf9160ns)
message(STATUS "Adding .overlay for mcuboot.")
list(APPEND mcuboot_DTC_OVERLAY_FILE
  "${CMAKE_CURRENT_LIST_DIR}/conf/mcuboot/circuitdojo_feather_nrf9160ns.overlay"
  )
endif()

find_package(Zephyr HINTS $ENV{ZEPHYR_BASE})
project(blinky)

target_sources(app PRIVATE src/main.c)

prj.conf:

CONFIG_GPIO=y

# Enable Zephyr application to be booted by MCUboot
CONFIG_BOOTLOADER_MCUBOOT=y

overlay

/ {
	aliases {
		bootloader-led0 = &blue_led;
    };
};

// Full speed ahead
&uart0 {
	status = "okay";
	current-speed = <1000000>;
	tx-pin = <6>;
	rx-pin = <5>;
};

src/main.c -> the default blinky main

    Hey jessemorris

    What version of the board do you have?

    One thing you can do is disable the rx-pin if you’re not using bidirectional logging. Any time you leave the receiver on for a UART it draws about 1mA (per UART). You can also disable it in software using the power management API.

        jaredwolff

        Hey Jared, the board version is: BRD-0015-02.
        Another question - what should the power draw of the feather be in low power mode in an ideal, optimized state?

            Hello Mr. Morris,
            Your post caught my eye as I am facing nearly the same issue on an nRF9160 based custom board. I posted an initial set of questions on this issue here at CicruitDojo Forum a few weeks ago, and Jared helped me with some run-time code which, in an nRF9160 + Zephyr RTOS context puts UART devices into a suspend mode. This is a low power mode which disables the high frequency clock of the 9160’s ARM application core, the Cortex-M33.
            In my firmware project I have been able to reduce average current draw down to about 85uA, by suspending the two UARTs which would normally be in use while the product’s firmware is running in a functionally active state. We’re battery powered also, and are relying / hoping/ praying to reach the nRF9160’s specified 1.4uA lowest current consumption. I will be posting a new set of questions here shortly as I’m running into a couple of brick walls to drawing lower current than I can presently reach.
            In case it is of interest to you, here is a code snippet where I declare a local pointer to a Zephyr device, in this case Zephyr’s chosen console UART, and then call a Zephyr API function to manage its power state:

            const struct device *console;
            console = device_get_binding(DT_LABEL(DT_CHOSEN(uart0)));
            rstatus = pm_device_state_set(console, PM_DEVICE_STATE_SUSPEND, NULL, NULL);

            On review here I have neglected to check whether my pointer *console is null or not, and that would likely be a best practice. But I have confirmed in a Nordic Devzone post reply dated 2022-03-21 that I am successfully suspending the UARTs on my hardware. Otherwise Devzone engineer tells me I would measure about 500 microamps or higher, not 85 microamps.
            A final note, I am sure you have turned off any LEDs in your low power firmware tests (you mention running a “blinky script”). In our hardware, even the red LED draws about 1mA current when on. I believe blue LEDs draw more.
            I’ll bookmark your post so I may follow along and see what solution you find. I hope we can get to the bottom of each of our mystery power consumption issues in our nRF9160 designs!

            • Ted

              jessemorris while you can get lower, the older boards only support low current shutdown using the external RTC. The latest boards should active sleep < 100uA.

              tedhavelka66 thanks for adding those tips. 😀

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