[SOLVED]Example BME650 CubeCell Board BUG for value GAS

#1

Hello,

while testing the BME650 i found that the Third Party Sensor Example “BME650test” by ARND@SV-Zanshin shows every time the same value for GAS.

The same hardware testet with the Adafruit Library (Arduino Mega) shows valid values:

Temperature = 23.94 *C
Pressure = 1008.65 hPa
Humidity = 36.11 %
Gas = 134.76 KOhms
Approx. Altitude = 38.54 m

The Adarfuit Library could not be compiled with the CubeCell-Board:
error: redefinition of ‘class SPIClass’

Has sameone solved the problem?

Greetings

E_T

#2

What you see is normal if you power down the bme680 between measurements.
You have to save the baseline after the reading and restore it after repower.

You can take a look in the LoRaWAN Multisensor example for the functions used for stpring and restoring the baseline.

When i have time tomorrow i will upload a new bme680 example with baseline storing

1 Like
#3

Hello WASN,

thank yor for the quick response! :grinning:

E_T

#4

So, i have testet it with the Arduino core 0.0.6, there ist no change.

The example “BME_test” in the Folder Example\ Third Party Sensor Examples doesn’t work for the value gas. There ist every time the same value, and there ist no sleep during measurement.

Copyright @ 2019 Heltec Automation.All rights reserved.
Starting I2CDemo example program for BME680

  • Initializing BME680 sensor
  • Setting 16x oversampling for all sensors
  • Setting IIR filter to a value of 4 samples
  • Setting gas measurement to 320°C for 150ms

24.54°C 38.92%Hum 1010.40hPa 23.76m 8083.70mOhm
26.00°C 36.28%Hum 1010.32hPa 24.42m 8083.70mOhm
25.99°C 36.26%Hum 1010.34hPa 24.26m 8083.70mOhm
25.99°C 36.33%Hum 1010.34hPa 24.26m 8083.70mOhm
25.97°C 36.60%Hum 1010.32hPa 24.42m 8083.70mOhm
25.97°C 36.95%Hum 1010.34hPa 24.26m 8083.70mOhm
25.99°C 37.30%Hum 1010.34hPa 24.26m 8083.70mOhm
25.98°C 37.62%Hum 1010.34hPa 24.26m 8083.70mOhm
25.98°C 37.88%Hum 1010.34hPa 24.26m 8083.70mOhm

Greetings

E_T

#5

Forget my last post. Baseline us only important for the css811 sensor.
Had no time to test. Hope to find some time next week

#6

@ernst.schulz
i have uploaded a new BME680 library version to the Heltec Github repository.

the gas value read failure should be fixed by that

1 Like
#7

Thank you very much!

E_T

#8

perhaps you are interested in caculating the IAQ:

float CalculateIAQ(float gas, float humidity)
{
  float hum_weighting = 0.25; // so hum effect is 25% of the total air quality score
  float gas_weighting = 0.75; // so gas effect is 75% of the total air quality score
  float hum_score, gas_score;
  float gas_reference = gas;
  float hum_reference = 40;
  int getgasreference_count = 0;

  //Calculate humidity contribution to IAQ index

  if (humidity >= 38 && humidity <= 42)
    hum_score = 0.25 * 100; // Humidity +/-5% around optimum
  else
  { //sub-optimal
    if (humidity < 38)
      hum_score = 0.25 / hum_reference * humidity * 100;
    else
    {
      hum_score = ((-0.25 / (100 - hum_reference) * humidity) + 0.416666) * 100;
    }
  }

  //Calculate gas contribution to IAQ index

  float gas_lower_limit = 10000;  // Bad air quality limit
  float gas_upper_limit = 100000; // Good air quality limit

  if (gas_reference > gas_upper_limit)
    gas_reference = gas_upper_limit;
  if (gas_reference < gas_lower_limit)
    gas_reference = gas_lower_limit;

  gas_score = (0.75 / (gas_upper_limit - gas_lower_limit) * gas_reference - (gas_lower_limit * (0.75 / (gas_upper_limit - gas_lower_limit)))) * 100;

  //Combine results for the final IAQ index value (0-100% where 100% is good quality air)

  float air_quality_score = hum_score + gas_score;

  return air_quality_score;
}
2 Likes
#9

Thank you!

Great, that would have been my next task

Kind regards
E_T

#10

Hello WASN,

i tested the code, but for me the values ar not plausible.

The IAQ-value is a number between 1 and 500, described in the datasheet BME680.

Here the result:
-13556.46 IAQ
24.28°C 32.70%Hum 1014.33hPa -9.15m 624.87mOhm
-13538.76 IAQ
24.28°C 32.67%Hum 1014.33hPa -9.15m 635.78mOhm
-13526.60 IAQ
24.29°C 32.65%Hum 1014.35hPa -8.99m 647.08mOhm
-13515.24 IAQ
24.29°C 32.62%Hum 1014.35hPa -8.99m 652.62mOhm
-13505.62 IAQ
24.29°C 32.60%Hum 1014.35hPa -8.99m 664.53mOhm
-13495.46 IAQ
24.29°C 32.57%Hum 1014.35hPa -8.99m 672.00mOhm
-13482.75 IAQ
24.29°C 32.56%Hum 1014.33hPa -8.82m 682.96mOhm
-13475.17 IAQ
24.29°C 32.54%Hum 1014.33hPa -8.99m 693.71mOhm

Kind regards
E_T

#11

the function i posted does the calculation not like bosh do it.

it will give a range of 0-100% 100% for perfect air (see source)

but you have to change this for your usage:L

float gas_lower_limit = 10000;  // Bad air quality limit
float gas_upper_limit = 100000; // Good air quality limit
#12

Hello WASN, thank you for the quick answer.

I will play with the values.

Kind regards
E_T