XIAO C3 knob

// Knob: a potentiometer on D0 sets the brightness of an LED on D10.
//
// D0 is A0, which is GPIO 2 and ADC1 channel 2. The converter is twelve bits,
// 0 to 4095, and at its default 11 dB attenuation the count is not a straight
// line to 3.3 V (a C3 reads 4095 from about 2.9 V), so the sketch asks the core
// for calibrated millivolts rather than scaling the count itself.
// D3 is labelled A3 on the board too, but it is on ADC2, which Mokxi does not
// model, so use D0, D1 or D2 for anything analogue.

const int KNOB = A0;
const int LED = D10;

unsigned long lastReport = 0;

void setup() {
  Serial.begin(115200);
  pinMode(LED, OUTPUT);
}

void loop() {
  int raw = analogRead(KNOB);
  analogWrite(LED, raw >> 4);

  unsigned long now = millis();
  if (now - lastReport >= 200) {
    lastReport = now;
    long mv = (long)analogReadMilliVolts(KNOB);
    Serial.print("D0 ");
    Serial.print(mv);
    Serial.println(" mV");
  }
  delay(10);
}