For the CO2 module, no attempt has been made yet to make it work with multiple types of CO2 sensors. The first CO2 sensor used was the MH-Z14, before it <indexentry content="modules, Building Management and Control (BMaC):CO2 module">switched to the more compact MH-Z19 sensor. Both of these use the same protocol on their universal asynchronous receiver/transmitter (UART) interface, however.
On the ESP8266 there are two UARTs, though only one is complete, with a receive (RX) and send (TX) line. The second UART only has a TX line. This essentially limits this MCU to a single UART and thus single UART-based sensor.
These sensors also have a single-wire interface in addition to the UART-based interface, where the sensor outputs the ...
