Alarm system with sensor and buzzer in Arduino - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Arduino alarm system code?

Consider this Arduino code snippet for an alarm system using a sensor and buzzer. What will the buzzer do when the sensor reads a value above 500?

Arduino

const int sensorPin = A0;
const int buzzerPin = 9;

void setup() {
  pinMode(buzzerPin, OUTPUT);
  Serial.begin(9600);
}

void loop() {
  int sensorValue = analogRead(sensorPin);
  Serial.println(sensorValue);
  if (sensorValue > 500) {
    digitalWrite(buzzerPin, HIGH);
  } else {
    digitalWrite(buzzerPin, LOW);
  }
  delay(1000);
}

A The buzzer will never sound because pinMode for buzzerPin is missing.

B The buzzer will beep once every second regardless of sensor value.

C The buzzer will sound only once when sensor value first goes above 500, then stay silent.

D The buzzer will sound continuously when sensor value is above 500, and be silent otherwise.

💡 Hint

Look at how digitalWrite is used inside the if condition.

The buzzer pin is set to HIGH whenever the sensor value is above 500, making the buzzer sound continuously during that time. When the value is 500 or below, the buzzer is turned off.

🧠 Conceptual

intermediate

Which component is responsible for detecting the environment change in this alarm system?

In an alarm system with a sensor and buzzer, which part detects changes like motion or light?

A The sensor

B The buzzer

C The Arduino board

D The power supply

💡 Hint

Think about which part senses something outside.

The sensor detects changes in the environment, such as motion or light, and sends signals to the Arduino.

🔧 Debug

advanced

What error will this Arduino code cause?

Examine this code snippet for an alarm system. What error will occur when compiling?

Arduino

const int sensorPin = A0;
const int buzzerPin = 9;

void setup() {
  pinMode(buzzerPin, OUTPUT);
}

void loop() {
  int sensorValue = analogRead(sensorPin);
  if (sensorValue > 400) {
    digitalWrite(buzzerPin, HIGH);
  } else {
    digitalWrite(buzzerPin, LOW);
  }
  delay(500);
}

A LogicalError: buzzer never turns off

B RuntimeError: buzzerPin not initialized

C SyntaxError: Missing semicolon after buzzerPin declaration

D No error, code compiles and runs fine

💡 Hint

Check the line where buzzerPin is declared.

The line const int buzzerPin = 9 is missing a semicolon at the end, causing a syntax error.

📝 Syntax

advanced

Which option correctly initializes the buzzer pin as output?

Choose the correct Arduino code line to set the buzzer pin as an output in setup().

A pinMode(buzzerPin, INPUT);

B pinMode(buzzerPin, OUTPUT);

C digitalWrite(buzzerPin, OUTPUT);

D digitalWrite(buzzerPin, HIGH);

💡 Hint

Remember, pinMode sets pin direction.

To configure a pin as output, use pinMode(pin, OUTPUT);. Other options either set input mode or write values.

🚀 Application

expert

How many times will the buzzer beep in this code?

Given this Arduino code, how many times will the buzzer beep during the loop() execution?

Arduino

const int sensorPin = A0;
const int buzzerPin = 9;

void setup() {
  pinMode(buzzerPin, OUTPUT);
}

void loop() {
  int sensorValue = analogRead(sensorPin);
  if (sensorValue > 600) {
    for (int i = 0; i < 3; i++) {
      digitalWrite(buzzerPin, HIGH);
      delay(200);
      digitalWrite(buzzerPin, LOW);
      delay(200);
    }
  }
  delay(1000);
}

A 3 times

B Continuously without stopping

C 1 time

D 0 times

💡 Hint

Look at the for loop inside the if condition.

The buzzer beeps 3 times because the for loop runs 3 iterations, each turning the buzzer on and off once.