Design of a high-precision exhaled breath detection circuit for 24-channel gas concentration sampling

A circuit capable of achieving 24-channel multiplexed exhaled gas collection, detection, and heating has been designed in this paper. A significant advantage is the use of a multiplexer to multiplex the limited ADC interfaces on a microcontroller. This multiplexing circuit makes rational use of a first-level 1-to-4 multiplexer to quickly multiplex 6 ADC channels into 24 channels at once, striking a balance between circuit complexity and control complexity. It not only multiplexes the port lines but also does not significantly increase the number of sampling rounds. In addition, this circuit has other advantages, such as reducing the number of constant current source circuits required to drive sensors. Similarly, the heating circuit for gas sensors has also been multiplexed using a pass-through method, with 3 port lines being used to multiplex 24 heating control lines, thus greatly conserving the microcontroller's port lines. The collected sensor voltage is visually displayed through a serial port screen, and finally, the collected data values are transmitted to a server via the WiFi of the ESP32, with the data being stored on a web page.