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    BME688 -- Bad Gas Resist Results

    amitr
    New Poster

    BME688 -- Bad Gas Resist Results

    I am using 4 BME688 on a board we designed for the ESP32. The sensors are read using SPI.

    My software is based on the Bosch Parallel-mode example -- measuring 10 steps with a wait time of 6 seconds per each step.

    2 of my sensors perform well. The remaining 2 return a fixed Gas-resist value of 5684.8 for ALL of the steps. One of those sensors also returns a bad pressure result.

    I have this similar phenomemnon on several of these boards. I also have boards where all 4 sensors perform well -- so this is not a board-design issue.

    I also had a phenomemnon were a specific sensor seemed to perform well and then in some instances, sporadically (no rule to it), also gave me this same 5684.8 Gas-resist value in one or more steps.

    I couldn't find anything about this in the data sheet.

    Has anybody else seen this phenomenon?

    Can anyone provide an explanation -- or suggestion what can be done to fix this?

    I attach a sample measurement of the 4 sensors, labeled BME0 - BME3:

    First 2 sensors are good:

            BME:0,ADP:4:    Step:0  Target-Temp:75 for:6[secs]    Measured Temp:30.0 Pressure:1006.3 Humidity:50.2 GasResist:1718120.8 Stat:b0 Idx:0
            BME:0,ADP:4:    Step:1  Target-Temp:200 for:6[secs]   Measured Temp:31.1 Pressure:1006.3 Humidity:47.9 GasResist:100549.9 Stat:b0 Idx:1
            BME:0,ADP:4:    Step:2  Target-Temp:100 for:6[secs]   Measured Temp:30.1 Pressure:1006.3 Humidity:48.1 GasResist:645039.4 Stat:b0 Idx:2
            BME:0,ADP:4:    Step:3  Target-Temp:225 for:6[secs]   Measured Temp:30.9 Pressure:1006.3 Humidity:47.5 GasResist:76646.7 Stat:b0 Idx:3
            BME:0,ADP:4:    Step:4  Target-Temp:125 for:6[secs]   Measured Temp:30.1 Pressure:1006.3 Humidity:48.1 GasResist:364932.3 Stat:b0 Idx:4
            BME:0,ADP:4:    Step:5  Target-Temp:275 for:6[secs]   Measured Temp:30.9 Pressure:1006.3 Humidity:47.6 GasResist:88581.3 Stat:b0 Idx:5
            BME:0,ADP:4:    Step:6  Target-Temp:150 for:6[secs]   Measured Temp:30.1 Pressure:1006.3 Humidity:48.3 GasResist:458678.6 Stat:b0 Idx:6
            BME:0,ADP:4:    Step:7  Target-Temp:325 for:6[secs]   Measured Temp:30.9 Pressure:1006.3 Humidity:47.8 GasResist:141241.4 Stat:b0 Idx:7
            BME:0,ADP:4:    Step:8  Target-Temp:175 for:6[secs]   Measured Temp:30.2 Pressure:1006.3 Humidity:48.1 GasResist:558494.7 Stat:b0 Idx:8
            BME:0,ADP:4:    Step:9  Target-Temp:375 for:6[secs]   Measured Temp:31.0 Pressure:1006.3 Humidity:47.6 GasResist:175703.5 Stat:b0 Idx:9

            BME:1,ADP:4:    Step:0  Target-Temp:75 for:6[secs]    Measured Temp:29.0 Pressure:1006.3 Humidity:52.7 GasResist:2684141.5 Stat:b0 Idx:0
            BME:1,ADP:4:    Step:1  Target-Temp:200 for:6[secs]   Measured Temp:30.2 Pressure:1006.3 Humidity:49.9 GasResist:103664.7 Stat:b0 Idx:1
            BME:1,ADP:4:    Step:2  Target-Temp:100 for:6[secs]   Measured Temp:29.4 Pressure:1006.4 Humidity:49.6 GasResist:769057.4 Stat:b0 Idx:2
            BME:1,ADP:4:    Step:3  Target-Temp:225 for:6[secs]   Measured Temp:30.4 Pressure:1006.3 Humidity:48.7 GasResist:98918.1 Stat:b0 Idx:3
            BME:1,ADP:4:    Step:4  Target-Temp:125 for:6[secs]   Measured Temp:29.7 Pressure:1006.3 Humidity:48.7 GasResist:601291.8 Stat:b0 Idx:4
            BME:1,ADP:4:    Step:5  Target-Temp:275 for:6[secs]   Measured Temp:30.7 Pressure:1006.4 Humidity:48.0 GasResist:123195.4 Stat:b0 Idx:5
            BME:1,ADP:4:    Step:6  Target-Temp:150 for:6[secs]   Measured Temp:30.0 Pressure:1006.3 Humidity:48.1 GasResist:762614.1 Stat:b0 Idx:6
            BME:1,ADP:4:    Step:7  Target-Temp:325 for:6[secs]   Measured Temp:30.9 Pressure:1006.4 Humidity:47.4 GasResist:192048.0 Stat:b0 Idx:7
            BME:1,ADP:4:    Step:8  Target-Temp:175 for:6[secs]   Measured Temp:30.3 Pressure:1006.3 Humidity:47.5 GasResist:879536.2 Stat:b0 Idx:8
            BME:1,ADP:4:    Step:9  Target-Temp:375 for:6[secs]   Measured Temp:31.1 Pressure:1006.4 Humidity:46.9 GasResist:191832.1 Stat:b0 Idx:9
     
    Here Pressure value is bad and Gas is fixed at 5684.8 -- sometimes the stat is 0xa0 and sometimes 0xb0
            BME:2,ADP:4:    Step:0  Target-Temp:75 for:6[secs]    Measured Temp:29.9 Pressure:689.6 Humidity:51.1 GasResist:5684.8 Stat:b0 Idx:0
            BME:2,ADP:4:    Step:1  Target-Temp:200 for:6[secs]   Measured Temp:31.2 Pressure:690.9 Humidity:47.4 GasResist:5684.8 Stat:a0 Idx:1
            BME:2,ADP:4:    Step:2  Target-Temp:100 for:6[secs]   Measured Temp:30.4 Pressure:690.1 Humidity:46.6 GasResist:5684.8 Stat:b0 Idx:2
            BME:2,ADP:4:    Step:3  Target-Temp:225 for:6[secs]   Measured Temp:31.5 Pressure:691.3 Humidity:45.5 GasResist:5684.8 Stat:a0 Idx:3
            BME:2,ADP:4:    Step:4  Target-Temp:125 for:6[secs]   Measured Temp:30.9 Pressure:690.6 Humidity:45.3 GasResist:5684.8 Stat:b0 Idx:4
            BME:2,ADP:4:    Step:5  Target-Temp:275 for:6[secs]   Measured Temp:31.9 Pressure:691.7 Humidity:44.4 GasResist:5684.8 Stat:a0 Idx:5
            BME:2,ADP:4:    Step:6  Target-Temp:150 for:6[secs]   Measured Temp:31.3 Pressure:691.1 Humidity:44.3 GasResist:5684.8 Stat:b0 Idx:6
            BME:2,ADP:4:    Step:7  Target-Temp:325 for:6[secs]   Measured Temp:32.3 Pressure:692.1 Humidity:43.6 GasResist:5684.8 Stat:a0 Idx:7
            BME:2,ADP:4:    Step:8  Target-Temp:175 for:6[secs]   Measured Temp:31.6 Pressure:691.4 Humidity:43.5 GasResist:5684.8 Stat:b0 Idx:8
            BME:2,ADP:4:    Step:9  Target-Temp:375 for:6[secs]   Measured Temp:32.6 Pressure:692.5 Humidity:42.9 GasResist:5684.8 Stat:a0 Idx:9
     
    Here Pressure is good but Gas is fixed at 5684.8
            BME:3,ADP:4:    Step:0  Target-Temp:75 for:6[secs]    Measured Temp:30.0 Pressure:1006.3 Humidity:53.0 GasResist:5684.8 Stat:b0 Idx:0
            BME:3,ADP:4:    Step:1  Target-Temp:200 for:6[secs]   Measured Temp:31.4 Pressure:1006.3 Humidity:49.7 GasResist:5684.8 Stat:b0 Idx:1
            BME:3,ADP:4:    Step:2  Target-Temp:100 for:6[secs]   Measured Temp:30.7 Pressure:1006.3 Humidity:48.9 GasResist:5684.8 Stat:b0 Idx:2
            BME:3,ADP:4:    Step:3  Target-Temp:225 for:6[secs]   Measured Temp:31.8 Pressure:1006.3 Humidity:47.2 GasResist:5684.8 Stat:b0 Idx:3
            BME:3,ADP:4:    Step:4  Target-Temp:125 for:6[secs]   Measured Temp:31.0 Pressure:1006.3 Humidity:46.7 GasResist:5684.8 Stat:b0 Idx:4
            BME:3,ADP:4:    Step:5  Target-Temp:275 for:6[secs]   Measured Temp:32.0 Pressure:1006.3 Humidity:45.3 GasResist:5684.8 Stat:b0 Idx:5
            BME:3,ADP:4:    Step:6  Target-Temp:150 for:6[secs]   Measured Temp:31.3 Pressure:1006.3 Humidity:45.1 GasResist:5684.8 Stat:b0 Idx:6
            BME:3,ADP:4:    Step:7  Target-Temp:325 for:6[secs]   Measured Temp:32.3 Pressure:1006.3 Humidity:44.4 GasResist:5684.8 Stat:b0 Idx:7
            BME:3,ADP:4:    Step:8  Target-Temp:175 for:6[secs]   Measured Temp:31.5 Pressure:1006.3 Humidity:44.2 GasResist:5684.8 Stat:b0 Idx:8
            BME:3,ADP:4:    Step:9  Target-Temp:375 for:6[secs]   Measured Temp:32.4 Pressure:1006.3 Humidity:43.3 GasResist:5684.8 Stat:b0 Idx:9
    Tags (3)
    1 REPLY 1
    BSTRobin
    Community Moderator

    Re: BME688 -- Bad Gas Resist Results

    Hi amitr,

    You can run the force mode example first to access a single sensor, such as "BME: 2" or "BME: 3". If the pressure and resistance values are normal, then the hardware is OK, and you need to check the software code.

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