BME680 ultra low power profile

[NicoBosch]

Good morning,

I'm integrating your BME680 in my custom board (esp32 and lora board).

We wanto to use the sensor in the following two configurations using I2c in order to acquire T/H pressure and IAQ:

1) ULP : 300 seconds . How can I know the sensor has finished to acquire data and is ready to be polled by the master (esp32) ? How is the pseudo state machine (FSM)  in this configuration? I see 100uA of consumption, this mean the sensor is always active and ready to be polled ?

2) the sensor will be switched on every 20 minutes by the esp32  and then has to acquire data for the necessary time. How much is this time in order to get the internal heater working and having a goos measurements? when I have switched on the sensor which is the FSM for this configuration to get proper measurements?

Hope you can help,  thanks in advance for support

Nico

[handytech]

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@NicoBosch wrote:

Could you please tell me how much seconds t takes for TPGH in force mode considering also the heater time to be ready  and the total average current in this time window?

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In Ultra-Low-Power mode (ULP), the TPHG measurement takes ~2s with a current of ~12mA then the sensor remains in sleep mode for the remaining ~298s, so the total average current over the 300s cycle is ~0.09mA.

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@NicoBosch wrote:

ULP:

What do you mean about BSEC. Is it a fw library supplied by bosch?

From what I know since I understood the sensor is still active in sleep mode, my MCU has simply to send a request every about 5 minuts but what you mean with :

"BSEC uses timestamps as input/output which tells you when the next measurement is needed"

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Yes, BSEC is a SW library that you can find here. The library doesn't run in the sensor but in an external controller, typically the MCU connected to the sensor (the ESP32 is supported in the default package). This library processes the raw BME680 data over time and converts raw sensor signals into the IAQ index, etc. You need to pass a timestamp to BSEC together with the raw sensor data, and together with the outputs you have enabled it will return the timestamp it wants for the next sample.

[NicoBosch]

Hi HandyTech and thanks for info,

From what you say I will not able to do this:

Mcuu Sleep every -20 minute -----> read a TPGH ----->MCU sleep for other 20 minutes

From what you say every time I go to sleep with my MCU I will also Know when I can wake up for a new good sample form BME680, right ?

In this way the sleep time of my MCU is related to the sensor and this situation could get worse my power budget because I have to wake up the MCU exactly when I have to read the BME which could be less than 20 minutes: is possible to skip measurements in order to get them every about 20 minutes.

Awaiting your kind reply.

Thanks

Nicola

[handytech · Accepted solution]

Your understanding seems correct.

The sensing technology of the BME680 requires the sensor to stabilize to its environment. This equilibrium depends a little on the environmental conditions, but mostly on the operation of the gas sensor (ON/OFF time duty-cycle and temperature). Extending the sleep duration could slightly change the behavior of the sensor or require different gas sensor settings to perform optimally. Therefore with the ULP mode (5 minutes), we try to offer an optimal ratio between sampling rate, current consumption and performance of the BME680.

[NicoBosch]

It's clear, 

I will wakeup the MCU every 5min and I will read just the BME680 . Then after 20 minutes I will send the last 4 samples readings

Thanks a lot for support.

Nicola