Bosch BME680/688

Overview of the Bosch BME680/688 Sensor

The BME680 sensor measures temperature, humidity, barometric pressure and produces a Volatile Organic Compound gas resistance and communicates these readings over an I2C bus interface.

Bosch uses the ISO16000-29 standard “Test methods for VOC detectors” to calibrate the BME680 sensors.

Bosch produces a library called BSEC that implements an algorithm to provide the combination of the input measurements as an Indoor Air Quality (IAQ) value. The index ranges from 0 – 500 to indicate or quantify the quality of the air in the immediate environment where measurements are taking place.

The IAQ scale ranges from 0 (clean air) to 500 (heavily polluted air).

Of particular interest in the BSEC algorithm, is the unusual correlation between IAQ value and CO2 concentrations, because somewhat counter-intuitively, as CO2 levels rise, the IAQ index falls!

The following graphs show the BME680 IAQ over 24-hours together with a Sensiron SCD41 measurement of CO2 over the same time base, note the clear correlation between CO2 levels measured by the precision SCD41 sensor and the BME680 sensor:

BME680 IAQ variation

SCD41 CO2 variation

it is clearly discernible that as CO2 levels rise the Bosch IAQ index falls, so when concentrations of CO2 are high indicating a polluted environment the BSEC IAQ index improves!