Analog

The real world isn't on/off — a knob turns gradually, light fades, temperature drifts. Analog handles the in-between.

Reading analog: analogRead()

The Uno's analog pins (A0–A5) measure voltage from 0 to 5V and report it as a number from 0 to 1023 (10-bit resolution):

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

void loop() {
  int value = analogRead(A0);   // 0 (0V) to 1023 (5V)
  Serial.println(value);
  delay(200);
}

Wire a potentiometer (knob): outer legs to 5V and GND, middle wiper to A0. Turn the knob, watch the numbers sweep 0–1023. That's a sensor reading — most analog sensors work exactly like this, presenting a voltage the Arduino measures.

Volts from the reading: volts = reading * 5.0 / 1023.0. The .0s matter — without them, C++ does integer division and your 0–5V becomes 0–4V of wrongness.

"Analog" output: PWM

Here's the catch: the Uno has no true analog output. It can't produce 2.5V. Instead, pins marked ~ (3, 5, 6, 9, 10, 11) do PWM — Pulse Width Modulation: they flicker between 0V and 5V hundreds of times per second, varying how long each pulse stays on. An LED (or motor) averages the flicker into "dimmer" or "slower":

const int LED_PIN = 9;   // a ~ PWM pin

void setup() {
  pinMode(LED_PIN, OUTPUT);
}

void loop() {
  int knob = analogRead(A0);          // 0–1023
  int brightness = map(knob, 0, 1023, 0, 255);
  analogWrite(LED_PIN, brightness);   // 0–255 duty cycle
  delay(10);
}

analogWrite(pin, value) takes 0 (fully off) to 255 (fully on). map() rescales one range to another — the translator between the 10-bit input world and the 8-bit output world.

Check: Turning the potentiometer fades the LED smoothly. If the LED only snaps on/off, you're on a non-PWM pin — move to one marked ~.

Honest limits: PWM at ~490Hz flickers visibly on camera and buzzes audibly through a speaker. It's "analog enough" for LEDs and motors, not for audio or precision instruments.

tone(): the bonus sound

Any digital pin can make noise with tone():

void setup() {
  tone(8, 440, 500);   // pin 8, 440Hz (A4), for 500ms
  delay(600);
  noTone(8);
}

void loop() {
}

Wire a piezo buzzer between pin 8 and GND. It's square-wave harsh, not musical — but doorbells and alarms don't need fidelity.

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