Hi:
The choice of ADC reference voltage depends on the voltage input of the O2 sensor. If O2 sensor’s supply is 5V, Vref is 5V. Otherwise Vref is 3.3V.
We just use Seeeduino’s adc that can get sensor’s data. I use a Seeeduino V4.2 to test it, and can get right data. But the wiki makes a mistakes. It connects O2 sensor to A0, but in the demo code it use A5 pin. I have told wiki manager to check it, maybe it has been checked now.