Knob (potentiometer)

A blue knob, a potentiometer, with three legs: two on one side, the middle leg on the other

A potentiometer has three legs. The two outer legs go to + and −; the middle leg gives a voltage between them, depending on where you turn the knob.

Middle leg to an analog pin: the program reads 0 (turned fully one way) to 1023 (fully the other way).

More: reading it, and map

An analog pin measures a voltage instead of only on and off. map turns the number 0 to 1023 into any range you need, for example 0 to 359 for a colour on the colour wheel, or 0 to 180 for a servo angle.

The same in Python

def on_forever():
    led.plot_bar_graph(pins.analog_read_pin(AnalogPin.P2), 1023)
basic.forever(on_forever)

On the Micro:bit, pins 0, 1 and 2 can read analog values.

void setup() {
  Serial.begin(9600);
}

void loop() {
  int value = analogRead(A0);              // 0 to 1023
  int angle = map(value, 0, 1023, 0, 180); // into 0 to 180
  Serial.println(angle);                   // see it in the Serial Monitor
  delay(100);
}