Just in case someone else runs across this: As per this post on github: https://github.com/espressif/arduino-esp32/issues/102 ADC1 pins can be used at the same time as WiFi. ADC2 pins cannot work when WiFi is in use - not sure about BLE. ADC1 GPIO pins: 32, 34 through to 39 ADC2 GPIO pins: 6, 7, 8, ...