Make a tilt alarm with a buzzer

A tilt switch contains a tiny metal ball. When the switch tilts, the ball rolls and opens or closes the contact. Combine it with a buzzer and you have an alarm for your desk drawer or treasure box.

What you'll learn

• How to read a digital input
• What a pull-up resistor does
• How to drive an active buzzer

What you need

• UNO R3 board (or any Arduino-compatible board) and USB cable
• Tilt switch module from the 45-in-1 kit
• Buzzer module (the active one, which beeps on its own) from the kit
• 6 jumper wires

Wiring

The UNO has only one 5V pin, so use the breadboard's power rails to share 5V and GND between the two modules.

Step 1: Find the "tilted" value

void setup() {
  Serial.begin(9600);
  pinMode(2, INPUT_PULLUP);
}

void loop() {
  Serial.println(digitalRead(2));
  delay(200);
}

Open the Serial Monitor. Note whether the value is 0 or 1 when the module stands upright, and what it changes to when you tilt it.

Step 2: The alarm

Set TILTED to the value you saw when the module was tilted.

const int TILT_PIN = 2;
const int BUZZER_PIN = 8;
const int TILTED = LOW; // the value you saw when tilted

void setup() {
  pinMode(TILT_PIN, INPUT_PULLUP);
  pinMode(BUZZER_PIN, OUTPUT);
}

void loop() {
  if (digitalRead(TILT_PIN) == TILTED) {
    // beep three times
    for (int i = 0; i < 3; i++) {
      digitalWrite(BUZZER_PIN, HIGH);
      delay(150);
      digitalWrite(BUZZER_PIN, LOW);
      delay(150);
    }
  }
  delay(50);
}

How it works

INPUT_PULLUP turns on a resistor inside the UNO that holds the pin at 5 V (HIGH) until the switch connects it to ground. Without it, an unconnected pin "floats" and reads random values. The active buzzer has its own oscillator, so a simple HIGH is enough to make it sound.

Try this next

• Make the alarm keep beeping until you press the button module from the kit.
• Swap the tilt switch for the shock switch or the knock sensor. They work the same way.

Troubleshooting

• The buzzer beeps all the time: some buzzer modules turn on with LOW. Swap HIGH and LOW in the beep loop.
• The buzzer only clicks: you're using the passive buzzer. Use the active one, or use tone(BUZZER_PIN, 1000) and noTone(BUZZER_PIN).