Put BLE Mesh node in deep sleep

[Rajendra]

Hi,

We are working on BLE MESH using nRF52840. We are trying to put nRF52840 into deep sleep mode. The deep sleep current is about 210 micro Amp. Further, the current is continuously increasing approx. by 1 micro Amp after every 60 sec.

My setup:
nRF SDK ver : nRF5_SDK_17.0.2_d674dde
BLE MESH ver : nrf5_SDK_for_Mesh_v5.0.0
Hardware : BT840 based custom board

The functions used for putting the nRF52840 into deep sleep -
nrf_mesh_disable()
nrf_pwr_mgmt_shutdown(NRF_PWR_MGMT_SHUTDOWN_STAY_IN_SYSOFF);

We also tried sd_power_system_off() but result are no better.

We are able to achieve deep sleep current of 500 nano Amp on same hardware, using Thread protocol. We are not sure how to achieve it using BLE Mesh.

It would be a great help if you could suggest a solution or give us a direction.

Kind Regards,
Rajendra

[Elfving]

Hello Rajendra,

Well first of all, if you are developing a new product for Mesh I would recommend you to use the nRF Connect SDK. That is the SDK that will be worked on going forward. 

Secondly, even though Bluetooth 'low energy' is being used, Bluetooth Mesh isn't the most power efficient alternative. Continuous relaying and radio use is the backbone of Mesh, so for Bluetooth Mesh to pay off, you'd normally want at least one of the nodes being connected to the mains. Thread nodes can be configured to be very power efficient however, so its hard to compare Bluetooth Mesh and Thread.

You can however use what are called Low Power Nodes along with Friend nodes with Mesh, which can be very power efficient. Is this what you are trying to do? If so, see here.

Regards,

Elfving

[Rajendra]

Hi,

I am coming back to my original question on Mesh Leaf Node deep sleep current.

Using BLE Mesh Friend Functionality I am able to achieve Leaf node running with average current consumption around 235 microA. Without Friend Functionality it consumes average current around 11.6 mA. So there is some improvement on current consumption but not enough if we want to operate the device on battery. Even if the device is being put into deep sleep mode, the current consumption remains around 220 microA. Is there any limitation of BLE Mesh stack preventing the device from Deep Sleep mode?

What is the minimum possible achievable average current consumption with BLE Mesh Node? Are there any known examples/references I can refer to?

Note: For measuring "average current", the average current in 1 minute is considered.

Best Regards,
Rajendra

[tesc]

Hi,

The following is for the nRF Connect SDK. I am sorry for jumping in on the discussion before double checking SDK version, but will leave the answer standing in case it is still relevant for someone reading this in the future.

For saving power outside of friendship, you can enable the CONFIG_BT_MESH_LPN_ESTABLISHMENT. Normal nodes (and LPNs outside of friendship) will have RX enabled at all times, leading to high power consumption. With the above "LPN establishment" setting on, it will have around 10 % RX duty cycle instead.

When powering the LPN, it will act as a normal node for an initial period of time, controlled by the CONFIG_BT_MESH_LPN_AUTO_TIMEOUT setting. Decreasing it will shorten the "active" period after boot, more quickly entering the the "LPN establishment" state of 10 % RX duty cycle.

The serial drivers draw a lot of power. If you don't need them, you can usually save a lot by disabling CONFIG_SERIAL.

With these settings, I have measurements of around 700 uA while not in friendship, and around 20 to 30 uA while in friendship.

Regards,
Terje

[cgr]

Hi,

I am working the team of Rajendra.
The big question is if there is a chance with a leaf node to reach similar sleep currents then with thread. That means below 1 uA.  I mean to reach it with the NordIC SDK's.

As I understand are the leaf nodes in BLE mesh networks intended to run peripheral nodes on battery power. If we would like to run a node several years with the same battery, we need to reach that small sleep currents.

regards

Christoph Graf

[Hung Bui]

Hi Christoph,

I'm sorry for the late response. Håkon is travelling and I will take over the case. 

220uA when in sleep current is not normal. 

We will need to take a look to see if it's the mesh stack causing the issue or it's the hardware on your custom board making that issue. 

I would suggest to do the following: 

- Test the same software on a Nordic Dev Kit and measure the current consumption as the reference. 

- Test a very simple software on your board that put the device to  sleep mode and measure the current consumption. This is to rule out the issue with the mesh stack. You can try the rtc example in nRF5 SDK v17.1 . The current consumption should be around 3-4 uA. 

The mesh lpn example when in sleep mode shouldn't consume more current than what you see in the rtc example. When in sleep mode it just puts the CPU and all peripherals to sleep and only keeps RTC running. 

[cgr]

Thank you for the information. I will discuss it with the Harman team next week.

[Rajendra]

Hi,

We have migrated from nrf5_SDK_for_Mesh_v5.0.0 to nRF Connect SDK v2.1.2. We are referring to samples -
nrf\samples\bluetooth\mesh\light_switch
nrf\samples\bluetooth\mesh\light

Using light_switch we are trying to produce DEEP SLEEP scenario. 225 uA is the lowest current value we are able to achieve. We tried following things.
Trial 1: Try to make Friendship between light_switch and light server using friendship configuration settings.
    In light_switch
        CONFIG_BT_MESH_LPN_ESTABLISHMENT=y
        CONFIG_BT_MESH_LOW_POWER=y
        CONFIG_BT_MESH_LPN_AUTO=y
In light
        No change
Check the current on light_switch node. Average current observed = 6.4 mA (Too high)

Trial 2: Put light_switch in deep sleep using power configuration settings and power management calls. There is NO Friendship between light_switch and light.
    light_switch prj.conf
        CONFIG_UART_CONSOLE=n
        CONFIG_GPIO=n
        CONFIG_LOG=n
        CONFIG_SERIAL=n
        CONFIG_PM=y
        CONFIG_PM_DEVICE=y
    light_switch main.c
        bt_mesh_prov_disable(BT_MESH_PROV_GATT | BT_MESH_PROV_ADV);
        bt_mesh_suspend();
        nrf_power_system_off(NRF_POWER);

In light
        No change
Check the current on light_switch node. Average current observed = 225 uA (Still High)

Trial 3: Combination of trial 1 and 2. (We are not much confident about this trial).
Put light_switch in deep sleep using power settings and power management calls.
Try to make Friendship between light_switch and light server using friendship configuration settings.
    light_switch prj.conf
        CONFIG_UART_CONSOLE=n
        CONFIG_GPIO=n
        CONFIG_LOG=n
        CONFIG_SERIAL=n
        CONFIG_PM=y
        CONFIG_PM_DEVICE=y

    light_switch main.c
        bt_mesh_prov_disable(BT_MESH_PROV_GATT | BT_MESH_PROV_ADV);
        bt_mesh_suspend();
        nrf_power_system_off(NRF_POWER);

In light
        No change
Check the current on light_switch node. Average current observed =  225 uA (High)

Trial 4: We used blinky app to check and verify the current consumption. We used following calls in main.c.
    In main.c
        nrf_power_system_off(NRF_POWER);
Using blinky and power management call Average current observed = 660nA

light_switch and blinky use same hardware settings on our BT840F based custom hardware.

So from above trials it seems that BLE Mesh Node current consumption always higher even in DEEP sleep and is 221 uA. We are expecting much lower value. Can you please verify above settings and let us now if we are missing anything?

Best Regards,
Rajendra

[Hung Bui]

Hi Rajendra, 

Before you test with any mesh sample, please follow my suggestion in my last reply: 

- Test a very simple software on your board that put the device to  sleep mode and measure the current consumption. In NCS SDK please try testing with the nrf\samples\boards\nrf\system_off sample. The current consumption should go down to ~1uA when the log says "Entering system off; press BUTTON1 to restart"

- If you still see high current consumption, please test the same software on a Nordic Dev Kit and measure the current consumption as the reference.