시리얼 통신과 디버깅 — PAI Lab

Why Serial Communication?

Arduino has no screen. The Serial Monitor (built into the IDE) is your primary debug window and the easiest way to inspect variable values while the sketch is running.

Under the hood, this uses UART — a two-wire asynchronous protocol on pins 0 (RX) and 1 (TX). Avoid using those pins for other purposes while Serial is active.

Basic Output

void setup() {
  Serial.begin(9600); // set baud rate — must match Serial Monitor setting
}

void loop() {
  int val = analogRead(A0);
  Serial.print("Raw ADC: ");
  Serial.println(val); // println adds newline
  delay(200);
}

Baud rate 9600 is safe for most purposes. Use 115200 when you need faster throughput.

Formatted Output

Serial.print("Temp: ");
Serial.print(temperature, 1); // 1 decimal place
Serial.println(" °C");

For multi-value debug lines, separate with commas (useful for the Serial Plotter):

Serial.print(sensor1); Serial.print(","); Serial.println(sensor2);

Reading from Serial

void loop() {
  if (Serial.available() > 0) {
    int brightness = Serial.parseInt(); // read next integer
    analogWrite(9, constrain(brightness, 0, 255));
    Serial.print("Set brightness: ");
    Serial.println(brightness);
  }
}

Serial.available() returns the number of bytes waiting in the buffer. Serial.parseInt() waits until a number is found (blocks briefly).

Debugging Tips

Print before and after suspect lines to isolate where code stalls
Include millis() to check timing: Serial.println(millis());
Use constrain() to catch out-of-range values
Comment out delay() calls and replace with millis()-based timing for non-blocking sketches

Exercises

Log pot + light sensor values to Serial Plotter; observe them live as graphs
Build a simple LED controller: type a brightness (0–255) in Serial Monitor to set it
Print “Loop time: Xms” every iteration to measure how long your loop takes