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Kit purchase

Looking for parts? Check out our all-in-one kits below — packed with components, beginner-friendly guides, and tons of fun.

Name	Includes Arduino board	PURCHASE LINK
Ultimate Sensor Kit	Arduino Uno R4 Minima	BUY
Elite Explorer Kit	Arduino Uno R4 WiFi	BUY
3 in 1 Ultimate Starter Kit	Arduino Uno R4 Minima	BUY
Universal Maker Sensor Kit	×	BUY

Course Introduction

In this lesson, you will learn how to use an Arduino UNO R4 WiFi with six LEDs, a button, and a passive buzzer to create a police light and siren simulator.

Press the button to start the effect. The red and blue LEDs will flash alternately while the buzzer produces a sweeping police siren sound. Press the button again to stop the lights and siren.

Note

If this is your first time working with an Arduino project, we recommend downloading and reviewing the basic materials first.

• 1.1 Install Arduino IDE(Important)

• 1.2 Introduce of Arduino IDE

Required Components

In this project, we need the following components:

SN	COMPONENT INTRODUCTION	QUANTITY	PURCHASE LINK
1	Arduino UNO R4 Minima	1	BUY
2	USB Type-C cable	1
3	Breadboard	1	BUY
4	Wires	Several	BUY
5	220 resistor	Several	BUY
6	Button	1	BUY
7	LED	Several	BUY
8	Passive Buzzer	1

Wiring

Common Connections:

• LED

  • Connect the LEDs cathode to the negative power bus on the breadboard, and the LEDs anode to a 220Ω resistor then to 2 to 7 on the Arduino.

• Button

  • Connect to breadboard’s negative power bus.

  • Connect to 10 on the Arduino.

• Passive Buzzer

  • ＋: Connect to 9 on the Arduino.

  • －: Connect to breadboard’s negative power bus.

Writing the Code

Note

• You can copy this code into Arduino IDE.

• Don’t forget to select the board(Arduino UNO R4 Minima/WIFI) and the correct port before clicking the Upload button.

/*
  Police Light and Siren Project
  Board: Arduino UNO R4 WiFi

  Components:
  - 3 red LEDs
  - 3 blue LEDs
  - 1 passive buzzer
  - 1 push button

  Operation:
  - Press the button once to start the lights and siren.
  - Press it again to stop everything.
*/

// ==================== Pin settings ====================

// Red LEDs
const byte RED_LED_1_PIN = 2;
const byte RED_LED_2_PIN = 3;
const byte RED_LED_3_PIN = 4;

// Blue LEDs
const byte BLUE_LED_1_PIN = 5;
const byte BLUE_LED_2_PIN = 6;
const byte BLUE_LED_3_PIN = 7;

// Passive buzzer
const byte BUZZER_PIN = 9;

// Button
const byte BUTTON_PIN = 10;

// ==================== Timing settings ====================

// Time between red and blue light changes
const unsigned long LIGHT_INTERVAL = 180;

// Button debounce time
const unsigned long DEBOUNCE_DELAY = 40;

// Siren frequency update interval
const unsigned long SIREN_INTERVAL = 8;

// Siren frequency range
const int MIN_SIREN_FREQUENCY = 650;
const int MAX_SIREN_FREQUENCY = 1300;

// Amount the frequency changes each step
const int SIREN_STEP = 10;

// ==================== State variables ====================

// True when the police effect is running
bool policeEffectRunning = false;

// Current light state
bool redLightsOn = true;

// Light timing
unsigned long lastLightUpdate = 0;

// Siren timing
unsigned long lastSirenUpdate = 0;

// Current siren frequency
int sirenFrequency = MIN_SIREN_FREQUENCY;

// 1 means rising pitch, -1 means falling pitch
int sirenDirection = 1;

// ==================== Button variables ====================

bool lastButtonReading = HIGH;
bool stableButtonState = HIGH;

unsigned long lastDebounceTime = 0;

// ==================== Setup ====================

void setup() {
  // Configure LED pins
  pinMode(RED_LED_1_PIN, OUTPUT);
  pinMode(RED_LED_2_PIN, OUTPUT);
  pinMode(RED_LED_3_PIN, OUTPUT);

  pinMode(BLUE_LED_1_PIN, OUTPUT);
  pinMode(BLUE_LED_2_PIN, OUTPUT);
  pinMode(BLUE_LED_3_PIN, OUTPUT);

  // Configure buzzer
  pinMode(BUZZER_PIN, OUTPUT);

  // Use the Arduino internal pull-up resistor
  pinMode(BUTTON_PIN, INPUT_PULLUP);

  // Start with everything turned off
  stopPoliceEffect();
}

// ==================== Main loop ====================

void loop() {
  handleButton();

  if (policeEffectRunning) {
    updatePoliceLights();
    updateSiren();
  }
}

// ==================== Button handling ====================

void handleButton() {
  bool currentReading = digitalRead(BUTTON_PIN);

  // Restart the debounce timer when the reading changes
  if (currentReading != lastButtonReading) {
    lastDebounceTime = millis();
  }

  // Accept the reading after it remains stable
  if (
    millis() - lastDebounceTime >= DEBOUNCE_DELAY
  ) {
    if (currentReading != stableButtonState) {
      stableButtonState = currentReading;

      // INPUT_PULLUP means LOW is pressed
      if (stableButtonState == LOW) {
        policeEffectRunning = !policeEffectRunning;

        if (policeEffectRunning) {
          startPoliceEffect();
        } else {
          stopPoliceEffect();
        }
      }
    }
  }

  lastButtonReading = currentReading;
}

// ==================== Effect control ====================

void startPoliceEffect() {
  policeEffectRunning = true;

  redLightsOn = true;

  sirenFrequency = MIN_SIREN_FREQUENCY;
  sirenDirection = 1;

  lastLightUpdate = millis();
  lastSirenUpdate = millis();

  // Start with red LEDs on
  setRedLights(true);
  setBlueLights(false);

  tone(BUZZER_PIN, sirenFrequency);
}

void stopPoliceEffect() {
  policeEffectRunning = false;

  setRedLights(false);
  setBlueLights(false);

  noTone(BUZZER_PIN);
}

// ==================== LED functions ====================

void updatePoliceLights() {
  unsigned long currentTime = millis();

  if (
    currentTime - lastLightUpdate >=
    LIGHT_INTERVAL
  ) {
    lastLightUpdate = currentTime;

    redLightsOn = !redLightsOn;

    setRedLights(redLightsOn);
    setBlueLights(!redLightsOn);
  }
}

void setRedLights(bool state) {
  digitalWrite(
    RED_LED_1_PIN,
    state ? HIGH : LOW
  );

  digitalWrite(
    RED_LED_2_PIN,
    state ? HIGH : LOW
  );

  digitalWrite(
    RED_LED_3_PIN,
    state ? HIGH : LOW
  );
}

void setBlueLights(bool state) {
  digitalWrite(
    BLUE_LED_1_PIN,
    state ? HIGH : LOW
  );

  digitalWrite(
    BLUE_LED_2_PIN,
    state ? HIGH : LOW
  );

  digitalWrite(
    BLUE_LED_3_PIN,
    state ? HIGH : LOW
  );
}

// ==================== Siren function ====================

void updateSiren() {
  unsigned long currentTime = millis();

  if (
    currentTime - lastSirenUpdate >=
    SIREN_INTERVAL
  ) {
    lastSirenUpdate = currentTime;

    // Increase or decrease the siren pitch
    sirenFrequency +=
      SIREN_STEP * sirenDirection;

    // Reverse direction at the upper limit
    if (
      sirenFrequency >=
      MAX_SIREN_FREQUENCY
    ) {
      sirenFrequency =
        MAX_SIREN_FREQUENCY;

      sirenDirection = -1;
    }

    // Reverse direction at the lower limit
    if (
      sirenFrequency <=
      MIN_SIREN_FREQUENCY
    ) {
      sirenFrequency =
        MIN_SIREN_FREQUENCY;

      sirenDirection = 1;
    }

    tone(
      BUZZER_PIN,
      sirenFrequency
    );
  }
}