Uno R4 knob

// Analog: a knob on A0 sets the brightness of an LED on D9.
//
// Wire a 10 k potentiometer between 5V and GND with its wiper on A0, and an
// LED and a 220 ohm resistor from D9 to GND. With nothing wired, A0 floats and
// the reading means nothing, which is the honest answer rather than an
// invented one.
//
// Two things about this board are worth knowing while you turn the knob:
//
//   * The converter is **fourteen bits**, but analogRead returns **ten**
//     (0 to 1023) because that is what the Arduino core does and what every
//     sketch written for an Uno expects. analogReadResolution(14) below asks
//     for the rest, and the report prints both.
//   * Full scale is 5 V, not 3.3. An Uno R4 runs its analogue supply at 5 V,
//     which is why a sensor written for an Uno moves across without a divider.
//
// analogWrite on D9 is a GPT channel at 490 Hz, the same rate an Uno's
// phase-correct pins run at. Which GPT channel D9 is, is this model's belief
// and is marked unverified in docs/uno-r4.md section 7.

const int KNOB = A0;
const int LED = 9;

unsigned long lastReport = 0;

void setup() {
  Serial.begin(115200);
  pinMode(LED, OUTPUT);
  Serial.println("Mokxi Arduino Uno R4 Minima: analog example");
  Serial.println("A0 in counts, D9 in duty. Turn the knob.");
}

void loop() {
  int counts = analogRead(KNOB);          // ten bits by default: 0..1023
  int duty = (counts * 255) / 1023;       // analogWrite takes 0..255

  analogWrite(LED, duty);

  unsigned long now = millis();
  if (now - lastReport >= 500) {
    lastReport = now;

    Serial.print("A0 = ");
    Serial.print(counts);
    Serial.print(" of 1023, duty ");
    Serial.print(duty);

    // The same pin at the converter's own width, to show what the ten-bit
    // default is hiding.
    analogReadResolution(14);
    Serial.print(", raw ");
    Serial.print(analogRead(KNOB));
    Serial.println(" of 16383");
    analogReadResolution(10);
  }
}