BME688, can I switch between basic IAQ and 4 gas recognition mode on the go?

[andrisigaunis]

Hello, all! 

Our company is developing a battery-powered device for air quality analysis. We have already been extensively working with BME680 in the past, and it was great. Now we want to use BME688 to analyze the air and only alert us if a specific gas is present, to cross out "false positives" in IAQ when a benign smell is present. 

BME688 is just as great using generic IAQ profile in ULP mode with measurements every 300s, where each measurement takes only around 2s, so our average current is even lower than the one specified in datasheet. Using a 3.3V power source and a Buck converter to 1.8V, the source "sees" only 56uA average current including MCU current, which is great. 

What is not as great is the power consumption in gas recognition mode. I have adapted your Hand Sanitizer example, and in that mode the sensor does 5x scans in a row, each scan being ~10 seconds, and consuming between 3mA and 10mA; that is 50s total in active mode. Then it sleeps for some 100s. So the average current is around 2.6mA, and that is, of course, not "low energy" (I am using Silicon Labs WSTK dev kit for current measurements and profiling). 

Therefore I have some questions, answers to which I could not really find in the code examples, AI-studio or datasheets: 

1) Can the sensor be realistically used in a "10 year battery life" application in gas recognition mode? Using a standard D-size Li-SOCl2 primary battery with capacity of 19Ah, our 10-year average current budget is only 200uA at best, but since battery will derate due to temperature and TX current, realistically it is around 100-150uA from 3.6V side, or 300-400uA on 1.8V rail. 

2) Can I do just 1 scan per 5-10 minutes? Where in the code is it defined to do 5 scans in a row, with just 100s pause? It looks to me that it is coded in the serialized configuration blob... 

3) Is it possible to use the sensor in simple, low power IAQ mode, and then, when IAQ goes high, switch to the more power hungry gas recognition mode? Does the algorithm need some "warm up time" when switching between modes (i.e., changes in serialized configuration)? How can I "gently" change serialized configuration from generic IAQ to gas recognizer and back, without the sensor (or actually BSEC2) restarting everything completely? 

Best regards, 

Andris Igaunis

SIA KOLOS MEDIA

[BSTRobin]

Hi andrisigaunis, For "Now we want to use BME688 to analyze the air and only alert us if a specific gas is present, to cross out "false positives" in IAQ when a benign smell is present. ", do you mean you generate config file with BME AI Studio, and setup software code in your project? If yes, could we get your soft code file and check it? To understand how you use it.

[BSTRobin · Accepted solution]

Hi andrisigaunis,

BME680/688 pass qualification test according to valid JEDEC standard for consumer electronics components, and the JEDEC standard including accelerate aging test which simulate the lifetime of the sensor.

"5 scans in a row" is defined in the configbody ( parameter: dutyCycleProfiles). For measurement accuracy, we don't recommend scanning per 5-minutes (individual opinion).

[BSTRobin]

Hi andrisigaunis,

We didn't recommend switching between modes without restarting.