Datasheet

I connected a trimpot from ground (left pin) to 3.3V (right pin) and conneted the wiper (center pin) to ADC1

For pins that don't have anything connected, such as ADC2 and ADC3 you'll notice the values flicker around a lot. If

you don't like this, just tie the pins to GND and it will keep the values 'steady'

The values of the ADC range from -32512 to 32512 but note that they correspond to ~1.8V to ~0.9V. You can map the

raw values to an approx voltage using

Which will convert the raw adc value into volt in units of millivolts

volt = map(adc, -32512, 32512, 1800, 900);