Analog I/O: Sensors and PWM Output

10비트 ADC로 아날로그 센서값을 읽고 PWM으로 아날로그 출력을 생성하는 방법.

Analog Input (ADC)

The Uno/Nano has a 10-bit ADC on pins A0–A5. analogRead(pin) returns a value from 0 (0V) to 1023 (5V reference voltage).

int val = analogRead(A0); // 0–1023
float voltage = val * (5.0 / 1023.0); // convert to volts

Common analog sensors: potentiometers, LDRs (light-dependent resistors), thermistors, flex sensors.

Reading a Potentiometer

Wire a 10kΩ pot: outer pins to 5V and GND, wiper to A0.

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

void loop() {
  int raw = analogRead(A0);         // 0–1023
  Serial.println(raw);
  delay(100);
}

Open the Serial Monitor and turn the knob — you should see the number change.

PWM Output

PWM (Pulse Width Modulation) simulates analog voltage by switching a pin ON/OFF very fast. Duty cycle (0–255 → 0%–100%) determines the effective average voltage.

PWM pins on Uno/Nano: 3, 5, 6, 9, 10, 11 (marked with ~ on the board).

analogWrite(9, 128); // 50% duty cycle ≈ 2.5V effective

Controlling LED Brightness with a Sensor

const int LDR_PIN = A0;
const int LED_PIN = 9;  // must be PWM pin

void setup() { /* nothing needed */ }

void loop() {
  int light = analogRead(LDR_PIN);          // bright = high value
  int brightness = map(light, 0, 1023, 255, 0); // invert: dark → bright LED
  analogWrite(LED_PIN, brightness);
  delay(20);
}

map(value, fromLow, fromHigh, toLow, toHigh) linearly scales a value between ranges.

Exercises

1. Print pot value as a bar of # characters to Serial Monitor
2. Build a “dimmer” that maps a pot to LED brightness smoothly
3. Add a threshold: if light < 300, turn LED fully on; otherwise dim proportionally