BME 680 Using without BSEC Library

[o_o]

Hi Ruslan,

I can only give you a partial answer :
Gas resistance vs data rate
According to our expertise the gas resistance value is impacted by the data rate, this is why we selected 2 different fixed data rate for BSEC : 1/3 hz and 1/300 hz. Your data rate of 1/1800 hz is not the same supported by our algorithm.

With such a low data rate, it would take quite some time for the pollutants to reach an equilibrium when the sensor is heated. The working mode has to be carefully tuned, so that there isn't an accumulation of pollutants on the sensor due to the extended low temperature phase.

My advice would be to use the RTC ram to batch the the raw data(temp, humidity, gas) every 5min, then every 30min you can run BSEC (by adding the correct timestamps) and save the state to NVM.

[Ruslan]

Hi,
so if I will decide to use bsec lib I must use bsec_init and bsec_loop functions and in bsec_loop I write ...ULP mode. Then I go to standby mode(!!! all clocks off and system after wackining will reset all mcu and ram) for 299sec and after wackining up how I can take measurement if mcu was in that mode(as without power)?

[o_o]

Hi Ruslan,

For BSEC to work, you have to use the sensor settings dictated by the library, and sample at the rate of the working mode you are using. For ULP that would be every 300sec. However, this sensor configuration is always the same. (It only dynamically changes in ULP+ mode). Your host MCU can indeed wake up every 300sec and sample the BME680 data.

However the BSEC library needs data buffers to keep the state of the library. If you MCU loses the RAM contect at every sample, this gives you 2 options:
1- Save the BSEC state to NVM
2- Send the raw data to another processor, which would then run the BSEC library (e.g. a server running in the cloud)

o_o

[Ruslan]

I have only 32pcs of  16-bit registers of RTC memory. BSEC needs:  #define BSEC_MAX_STATE_BLOB_SIZE (139) /*!< Maximum size (in bytes) of the data blobs returned by bsec_get_state()*/ . If I change 139 to 64 will BSEC work properly? And I must save state after every measurement and then go to deep sleep?

[o_o]

This would unfortunately not work. The entire state needs to be saved for BSEC to work.