ESP8266 ADC - IS IT 1V or 3.3V?


ESP8266 on PCB

I recently encountered what I thought was a problem with the on-board ADC on an ESP8266. It was producing low values that had me checking other parts of my circuit. In the end I realised that the value was about ⅓ of what I was expecting and this led me to check the ADC analogue range. It turned out that although the ESP chip has a 0-1V ADC the breakout board on which it was mounted had voltage dividing circuitry to allow up to 3.3V on the exposed A0 pin.