Reducing power consumption for ble mesh sensor server node using LPN mode

[harid]

Hi, 

I am using nrf mesh sdk v5.0.0 and am using sensor server model example to build our own application on top of it. SOC we are using is  nRF52832.  I have enabled the LPN mode in the example and I am also able to establish friendship with a nearby friend node. And am also receiving messages intended to the LPN node when the LPN node polls its friend node. The purpose for LPN node is to reduce battery consumption by disabling the scanner. But the device is consuming a solid 5 - 8 mA after establishing friendship. Is it possible to reduce the battery consumption in the micro amperes range. Any guidance on how to achieve it would be really great. I am also interfacing an LED, I2C sensor and a switch with the SOC. Before and after establishing friendship, I am seeing same amount of current being consumed. 

[Hung Bui]

Hi Hariharan, 

Could you describe how did you do the test ? How did you do provisioning ? 

Have you tested with the LPN example with no modification ? In the example the power consumption should drop down to few uA after it provisioned and get a friendship. 

Which current do you see exactly after you establish friendship ? Have you verified that the CPU was not being kept awake by other modules ? 

[harid]

I am provisioning the sensor node using an ESP32(acting as a provisioner). Once the provisioning and model configuration is done, I am initiating the friendship establishment procedure. The current consumption goes as low as 150ua after establishing friendship. But it increases to 3ma after publishing data once. And it should return to low power consumption mode right? But its not. The sensor node is constantly consuming 3ma after publishing. I dont know why this is happening. Can you please guide me?

[Hung Bui]

Hi again, 
What I'm suspecting is that the CPU is stuck in a dead loop somewhere in the code. Besides high current consumption everything works ? 

Even at 400uA , it's high current consumption in my opinion. I don't know how you configure the node, have you checked if 400uA is the idle current or it's the average current ? 

Could you try doing I2C communication in the main loop (set a flag in the callback and execute the I2C activity in the main loop and go to sleep after that) and check if it make it high current consumption ? 
Could you provide the minimal code (for example modify the LPN example) so that we can test here ? 

[harid]

Hi,

Yes. Besides higher current consumption, everything else is working as expected.

Yes, it is a higher current consumption. Can you please tell me which node configuration you are referring to? When the CPU goes to sleep after friendship is established, the current goes down to around 400ua. When publishing it goes to upto 600-700ua and then back to 400. I am using multimeter to measure current consumed.

So you are suggesting me to do the i2c read in main loop instead of in the callback itself without deinitializing and reinitializing it?

Sure. Will provide one tomorrow. Its past 9 in the eve here.

[Hung Bui]

Hi Hariharan, 
I did a quick test here with the LPN example. What I found is that after LPN established friendship the current consumption should be around 16uA. What you have of 150uA or 700uA is still too high. 
Please try to test with the LPN example again. Did you test using our nRF52 DK ? 

Have you keep RTT logging when testing ? If you do please disconnect RTT or disable logging in the code. 

Do you have a PPK2 (power profiler kit) ? If you do, you can capture the current consumption , for example here is what I have : 

You can find the consumption is around 16uA with a peak every 2 seconds for polling friend node. 

The idle current consumption is about 9uA: 

If you see a peak of 100ms , it was because of RTT_INPUT_POLL_PERIOD_MS = 100ms. If you set RTT_INPUT_ENABLED = 0 in nrf_mesh_config_app.h you will not have this 100ms wake up period. 

So if you see anything above dozen of uA , there must be something wrong. If you don't have a PPK2 I would strongly suggest to get hold of one. 

[harid]

Hi,

Previously, I have written our application using senor_server example as our base application and integrated all the peripherals and low power node in the sensor_server example. Now, I was integrating the peripherals and sensor models with the low power node example as our base application. 

And it seems to be working so far. The device is consuming low current of 150ua (which is more than enough in our use case) when no peripherals were integrated. When the peripherals were integrated and initially in the unprovisioned state, the device was consuming around 1.8ma as a timer and LED is used to indicate the unprovisioned state. After provisioning, I disable the timer(I use timer's handler to toggle led - reason for higher current consumption) and the node goes to low power state immediately. 

Now, I want to integrate the sensor models into the application. When I tried to initialize the sensor models in the low power node example with the API - "app_sensor_init(&m_sensor_server_0, APP_SENSOR_ELEMENT_INDEX);" , the return code which I am getting is 4 (which corresponds to NRF_ERROR_NO_MEM). Can you help me troubleshoot this issue?

And we don't have a PPK2 with us.

[Hung Bui]

Hi Hariharan,

Could you please test with the unmodified LPN example ? As I mentioned in the last reply, 150uA is too high, you should see around 16uA. 

Even if you don't have a PPK or a oscilloscope to measure the current/voltage drop , you can use a simple multiple meter and should see the similar average current. 

If you don't there must be something wrong with your board. Please try to compare the current consumption on a Dev Kit and check why there is a difference. 150uA without doing any activity (except for polling the friend node) is not normal. 
Even if you use a timer (RTC not the TIMER) 150uA is high. If you use a timer (RTC) the current should increase only a few uA and the timer (RTC) is already used by the mesh 

Regarding your issue of NRF_ERROR_NO_MEM, if you read the description of the function , you can find this: 

You may want to increase ACCESS_MODEL_COUNT or ACCESS_SUBSCRIPTION_LIST_COUNT. Please try to debug if you see an error, you can step into the code and check why the function throws an error. 

[harid]

Yes, I have found the reason why it was giving me NRF_ERROR_NO_MEM error code. Sensor model example had 4 models in an element and low power had only three. Modified it in the nrf_mesh_config_app.h and the issue was resolved.

Seems to be there an issue with the board. I will report this issue to my hardware team. I ran the unmodified lpn example in our board and got the same 150ua. The reason for 150ua is that am powering the board through a 5v to 3v3 regulator which consumes half of that current. So, the soc actually consumes only 60-70ua. 

Is reading I2C data and ADC data inside sensor model's periodic callback to publish data a wrong idea? Because that seems to make the CPU consume higher current around 3ma.

[Hung Bui]

Hi Hariharan, 
If you have any activity that take longer time you should put it into thread context (main context). 
Also , after the activity is finished (reading ADC for example) the CPU should go to sleep and you should see the current consumption goes down. If you don't see that there must be something wrong and the CPU was stuck. 

I would suggest to use DCDC instead of LDO converter to save more current consumption. But still at 60-70uA it's high current consumption. You may want to try testing some very simple application that only put the CPU to sleep (try the RTC example) and check if you can achieve a few uA current consumption. This is to verify that your board doesn't have any fault. 

[harid]

After reading once using I2C and SAADC, the current consumption is not going down. CPU is not going back to sleep but the application is running smoothly as expected with only current consumption being a big concern for us. 

I have created a separate tickets for I2C and SAADC separately, wherein I would have attached the code routines I use for initializing, deinitializing and reading data from the desired peripheral. 

I tried reading ADC voltage and data from I2C sensor in thread context but didnt see the current consumption dropping back to 70ua after the peripherals are deinitialized. As of now, 70ua is sufficiently low current for us. Please refer to the tickets I have attached below for the code routines and kindly let me know your thoughts. 

And yes, I have enabled DCDC in both sdk_config.h, and in the code too using the below function. 

    ERROR_CHECK(sd_power_dcdc_mode_set(NRF_POWER_DCDC_ENABLE));

SAADC - https://devzone.nordicsemi.com/f/nordic-q-a/95473/nrf52832-constantly-consuming-higher-current-of-3-4ma-after-reading-adc-value-using-using-saadc-in-blocking-mode

I2C - https://devzone.nordicsemi.com/f/nordic-q-a/95472/nrf52832-staying-in-400ua-current-consumption-after-single-write-and-read-from-i2c

[Hung Bui]

Hi Hariharan, 
I would suggest to continue on the other cases. It's important that you narrow down the issue to see where the current is from. Please try to test the code without mesh and see if you can achieve lower current. So that we know if it has anything to do with mesh or not. And to know which exact peripheral causing the problem. 

[harid]

Hi hung,

I was able to reduce the current consumption to upto 20ua. The current consumption was due to some known errata. Once the workaround is implemented, it was resolved. Thank you so much for your time and quick responses. Appreciate it much!