Note
If the analog input pin is not connected to anything, the value returned by analogRead() will fluctuate based on a number of factors (e.g. the values of the other analog inputs, how close your hand is to the board, etc.).
However, please note that here the ADC-CH4 of ESP32 is 12 bits and the return value will be 0 to 4096. For more details, please refer to the related link in the original article and the ESP32 manual.
