The gas sensor (U9) monitors indoor air quality and can detect a wide range of Volatile Organic Compounds (VOCs).
It provides a TVOC value or equivalent CO2 (eCO2) as output over the I2C bus (slave address 0x5A). To improve current consumption when the gas sensor is not used, the power, I2C lines, and the interrupt line are routed through an analog switch (U10). When the gas sensor is not in use, the GPIO used for the interrupt signal can be accessed on test point TP2.
Figure 1. Gas sensor schematic
