BME680 strange behaviour on humidity and gas sensing

[LeonardoPapale]

Hi everyone! 

I am testing the BME680 sensor on a Adafruit Breakout board since few days now. I am using a STM32L073 Cortex M0+ processor, and i am still trying the iot examle BSEC code.  I didn't change anything in the code, just added the parts necessary for the integration. The initialization doesn't return any error. First of all i activated the sensor for around 40 minutes, then reseted it and activated another time for maybe 1 hour. Values are always quite strange: first of all iaq accuracy is always 0, (it can't be caused by a timing violation because when i debug it this error doesn't occur) i red that there is an activation time after that it should change (5 minutes in Low Power Mode that i am using) but this value never changes. (i don't know if i have to wait the "Burn In" Period to see changes in the iaq accuracy). But the most strange value is the RHumidity value, it is aways 100 or quite close (99.84 ecc...) that is absurd, i am also using an SHT31 from sensirion that reads normal value between 30/40 %. In debug mode i saw that the data obtained by the i2c trasmission seems to be actually 100 or similar, so it is not a software problem. Temperature and Pressure seem accurate. Here i show you some of the values recived:

Temperature: (23.64439) C, RHumidity:(100.0)
IAQ: (0) accuracy:(0), Pressure:(100213)
C02eq: (0.0) , BVocsEq:(0.0)
Temperature: (23.64439) C, RHumidity:(100.0)
IAQ: (0) accuracy:(0), Pressure:(100212)
C02eq: (0.0) , BVocsEq:(0.0)
Temperature: (23.64439) C, RHumidity:(100.0)
IAQ: (0) accuracy:(0), Pressure:(100213)
C02eq: (0.0) , BVocsEq:(0.0)
Temperature: (23.64439) C, RHumidity:(100.0)
IAQ: (0) accuracy:(0), Pressure:(100212)
C02eq: (0.0) , BVocsEq:(0.0)
Temperature: (23.64439) C, RHumidity:(100.0)
IAQ: (0) accuracy:(0), Pressure:(100213)
C02eq: (0.0) , BVocsEq:(0.0)

Temperature: (23.3396) C, RHumidity:(100.0)
IAQ: (0) accuracy:(0), Pressure:(100241)
C02eq: (0.0) , BVocsEq:(0.0)
Temperature: (23.3396) C, RHumidity:(100.0)
IAQ: (0) accuracy:(0), Pressure:(100245)
C02eq: (0.0) , BVocsEq:(0.0)
Temperature: (23.37862) C, RHumidity:(100.0)
IAQ: (0) accuracy:(0), Pressure:(100245)
C02eq: (0.0) , BVocsEq:(0.0)
Temperature: (23.37862) C, RHumidity:(100.0)
IAQ: (0) accuracy:(0), Pressure:(100245)
C02eq: (0.0) , BVocsEq:(0.0)
Temperature: (23.3396) C, RHumidity:(100.0)
IAQ: (0) accuracy:(0), Pressure:(100245)
C02eq: (0.0) , BVocsEq:(0.0)

From one side temperature and pressure are correct values, from the other side RH and gas are strange, I don't know how to solve this behaviour. Did anyone noticed something similar or has an idea about what is going on? Is it possible the problem is caused by bad soldering that dameged the component or similar reasons? 

Thank you for the help! 

[handytech]

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@AdamCarpenter wrote:

• The sensor is good, I tested it with RPI

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Could you please confirm what you mean by that? Does that mean that the same sensor/HW but connected to a RPI instead of STM32L071RBT will show valid humidity and gas outputs?

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@AdamCarpenter wrote:

• the read and write functions work well.

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Did you confirm this with an oscilloscope/logic analyzer? If so can you also confirm that your timings are valid (e.g . 3seconds between BSEC calls match the timestamp)?

[az2012]

I have th same problem! raspberry pi 3B raspbian 64 bits bme680. With library 1.4.7.2 and THE SAME PROGRAM  all works O K with library 2.5.2 humidity always set to 100%. Also I suspect the problem is insider config directory , the only difference between my two test!