Serial Monitor

What is the Serial Monitor?

The Serial Monitor is a communication channel between your Arduino and computer. It lets you:

• Print debug messages
• Display sensor values
• Send commands to the Arduino
• Monitor program flow

Setup

void setup() {
  Serial.begin(9600);  // Start at 9600 baud
}

The number (9600) is the baud rate, which is the speed of communication. Both sides must match.

Printing

Serial.print("Hello ");     // Print without newline
Serial.println("World!");   // Print with newline
Serial.println(42);         // Print a number
Serial.println(3.14);       // Print a float
Serial.println(val, HEX);  // Print in hexadecimal

Formatting Output

Serial.print("Temp: ");
Serial.print(temperature);
Serial.print("°C | Light: ");
Serial.print(lightLevel);
Serial.println("%");
// Output: "Temp: 22.5°C | Light: 67%"

Reading Input

if (Serial.available() > 0) {
  char incoming = Serial.read();
  // or
  String message = Serial.readStringUntil('\n');
}

Common Baud Rates

| Rate | Use | |------|-----| | 9600 | Default, most common | | 115200 | Fast, for lots of data |

Tips

• Open the Serial Monitor with Ctrl+Shift+M (or the magnifying glass icon)
• Make sure the baud rate in the monitor matches Serial.begin()
• Use Serial.print() liberally while debugging, then remove when done
• Don't use pins 0 and 1 for I/O when using Serial (they're TX/RX)