Using an esp8266, how can I create a circuit to measure 2 different analog inputs (not simultaneously) with only one ADC pin available (A0)
There's two basic solutions, both of which require the addition of an external chip:


Use an analog multiplexer to select the different devices to connect to the ADC input
Use an external (I2C or SPI) ADC chip. These can give you higher resolutions than the internal ADC and many more inputs (depending on the chip you choose).


My recommended solution would be to get an external ADC chip.