BME280 wrong values from humidity sensor

[DeFina]

We use your sensor BME280 for one of our products. We have made a hardware modification to our product and produced a prototype series with the adapted PCB . With the first 10 pieces everything works, except that the sensor returns wrong humidity values. But the temperature and the air pressure have realistic normal values. With the exact same software on the old PCB I get the correct humidity values. The scheme is identical for both versions.
Can you explain this? We have already replaced the supposedly defective sensors and got the same result again.

Best Regards

Loris De Fina

[FAE_CA1]

Hi,

Thanks for the informaiton. Please provide us with your email address through private message. Our local FAE will contact you and support you.

Thanks.

[handytech]

While looking for different solutions, we could offer to review the current output of the API/compensation formulas. For that we would be interested in the current sensor settings, your sensor specific trimming parameters (in hex/from the register map) and raw ADC values (at least temperature and humidity are needed for the humidity output).

Do you know which soldering process was used to solder the parts? Can you confirm that the BME280's HSMI guidelines were followed? Have you already or could you please try to follow the reconditioning procedure found in the datasheet or HSMI manual?

[DeFina · Accepted solution]

I've compared the registers from the working and non working version. In the non working version I am to early with writing the registers but in the working version I have the same sensor and schematic but there the registers are written. I put a delay after poweron and befor I configure the registers of the BME280. This solved my problem. But why is the same software working with one batch of sensors and did not work with another batch? 

Best regards 

Loris De Fina

[Vincent]

After sensor power on, we need a start up time which is 2 ms listed in datasheet.   Only after this time, our sensor is able to respond to the read / write on bus communication.

Maybe you can check with your logic analyzer on non working board and working board to see if the delay after power on is same on both boards or not.