Alarm system with sensor and buzzer in Arduino - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to set the sensor pin as input.

Arduino

const int sensorPin = 2;
void setup() {
  pinMode([1], INPUT);
}
void loop() {}

Drag options to blanks, or click blank then click option'

A13

BOUTPUT

CbuzzerPin

DsensorPin

Attempts:

3 left

💡 Hint

Common Mistakes

Using the buzzer pin instead of the sensor pin.

Setting the pin mode to OUTPUT instead of INPUT.

The sensor pin must be set as input to read sensor data.

2fill in blank

medium

Complete the code to read the sensor value inside the loop.

Arduino

const int sensorPin = 2;
int sensorValue;
void setup() {
  pinMode(sensorPin, INPUT);
}
void loop() {
  sensorValue = [1](sensorPin);
}

Drag options to blanks, or click blank then click option'

AanalogRead

BdigitalWrite

CdigitalRead

DanalogWrite

Attempts:

3 left

💡 Hint

Common Mistakes

Using digitalWrite() instead of digitalRead().

Using analogRead() for a digital sensor.

Use digitalRead() to read a digital sensor value from the sensor pin.

3fill in blank

hard

Fix the error in the code to turn on the buzzer when the sensor is triggered.

Arduino

const int sensorPin = 2;
const int buzzerPin = 8;
void setup() {
  pinMode(sensorPin, INPUT);
  pinMode(buzzerPin, OUTPUT);
}
void loop() {
  if (digitalRead(sensorPin) == [1]) {
    digitalWrite(buzzerPin, HIGH);
  } else {
    digitalWrite(buzzerPin, LOW);
  }
}

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AHIGH

BLOW

CINPUT

DOUTPUT

Attempts:

3 left

💡 Hint

Common Mistakes

Comparing sensor reading to LOW instead of HIGH.

Using pin modes instead of HIGH/LOW values.

The buzzer should turn on when the sensor reads HIGH (triggered).

4fill in blank

hard

Fill both blanks to make the buzzer beep for 1 second when triggered.

Arduino

const int sensorPin = 3;
const int buzzerPin = 9;
void setup() {
  pinMode(sensorPin, INPUT);
  pinMode(buzzerPin, OUTPUT);
}
void loop() {
  if (digitalRead(sensorPin) == [1]) {
    digitalWrite(buzzerPin, HIGH);
    delay([2]);
    digitalWrite(buzzerPin, LOW);
  }
}

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AHIGH

BLOW

C1000

D500

Attempts:

3 left

💡 Hint

Common Mistakes

Using LOW instead of HIGH for sensor trigger.

Using 500 ms delay instead of 1000 ms.

The buzzer should turn on when sensor reads HIGH and delay 1000 milliseconds (1 second).

5fill in blank

hard

Fill all three blanks to create a dictionary-like structure that maps sensor states to buzzer actions.

Arduino

const int sensorPin = 4;
const int buzzerPin = 10;
void setup() {
  pinMode(sensorPin, INPUT);
  pinMode(buzzerPin, OUTPUT);
}
void loop() {
  int state = digitalRead(sensorPin);
  switch(state) {
    case [1]:
      digitalWrite(buzzerPin, [2]);
      break;
    case [3]:
      digitalWrite(buzzerPin, LOW);
      break;
  }
}

Drag options to blanks, or click blank then click option'

AHIGH

BLOW

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up HIGH and LOW values in cases.

Using pin modes instead of HIGH/LOW values.

When sensor state is HIGH, buzzer turns HIGH; when LOW, buzzer turns LOW.

Practice

1. What does the digitalRead(sensorPin) function do in an Arduino alarm system?

easy

A. It turns on the buzzer connected to sensorPin.

B. It sets the sensorPin to HIGH to activate the sensor.

C. It reads the current state (HIGH or LOW) of the sensor connected to sensorPin.

D. It resets the Arduino board.

Solution

1. Step 1: Understand digitalRead function

   The function digitalRead(pin) checks the electrical state of the given pin, returning HIGH or LOW.

2. Step 2: Apply to sensorPin

   When used with sensorPin, it reads if the sensor is triggered (HIGH) or not (LOW).

3. Final Answer:

   It reads the current state (HIGH or LOW) of the sensor connected to sensorPin. -> Option C

4. Quick Check:

   digitalRead(sensorPin) = sensor state [OK]

Hint: digitalRead reads input pin state, not output [OK]

Common Mistakes:

• Confusing digitalRead with digitalWrite
• Thinking digitalRead sets pin state
• Assuming digitalRead controls buzzer

2. Which of the following is the correct way to turn ON a buzzer connected to pin 9 in Arduino?

easy

A. digitalWrite(9, HIGH);

B. pinMode(9, INPUT);

C. digitalRead(9);

D. analogWrite(9, LOW);

Solution

1. Step 1: Identify function to set pin output

   digitalWrite(pin, HIGH) sets the pin to HIGH voltage, turning ON devices like buzzers.

2. Step 2: Check pin number and value

   Pin 9 is correct, and HIGH turns the buzzer ON.

3. Final Answer:

   digitalWrite(9, HIGH); -> Option A

4. Quick Check:

   digitalWrite(pin, HIGH) = turn ON output [OK]

Hint: Use digitalWrite(pin, HIGH) to turn ON output devices [OK]

Common Mistakes:

• Using digitalRead instead of digitalWrite
• Setting pinMode to INPUT to turn ON buzzer
• Using analogWrite with LOW to turn ON buzzer

3. What will be the output behavior of this Arduino code snippet?

const int sensorPin = 2;
const int buzzerPin = 9;

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

void loop() {
  int sensorState = digitalRead(sensorPin);
  if (sensorState == HIGH) {
    digitalWrite(buzzerPin, HIGH);
  } else {
    digitalWrite(buzzerPin, LOW);
  }
}

medium

A. The buzzer will sound only when the sensor detects HIGH signal.

B. The buzzer will always be ON regardless of sensor state.

C. The buzzer will never turn ON.

D. The code will cause a compilation error.

Solution

1. Step 1: Analyze sensor reading

   The code reads sensorPin state; if HIGH, it triggers the buzzer.

2. Step 2: Check buzzer control logic

   If sensorState is HIGH, buzzerPin is set HIGH (ON), else LOW (OFF).

3. Final Answer:

   The buzzer will sound only when the sensor detects HIGH signal. -> Option A

4. Quick Check:

   sensor HIGH -> buzzer ON, else OFF [OK]

Hint: If sensor reads HIGH, buzzer turns ON [OK]

Common Mistakes:

• Assuming buzzer is always ON
• Thinking code has syntax errors
• Confusing sensor input with buzzer output

4. Identify the error in this Arduino alarm code snippet:

const int sensorPin = 3;
const int buzzerPin = 8;

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

void loop() {
  if (digitalRead(sensorPin) == HIGH) {
    digitalWrite(buzzerPin, HIGH);
  } else {
    digitalWrite(buzzerPin, LOW);
  }
}

medium

A. digitalWrite should use LOW to turn buzzer ON.

B. sensorPin should be set as INPUT, not OUTPUT.

C. digitalRead cannot be used on sensorPin.

D. buzzerPin should be set as INPUT, not OUTPUT.

Solution

1. Step 1: Check pinMode for sensorPin

   sensorPin reads sensor input, so it must be INPUT, not OUTPUT.

2. Step 2: Verify buzzerPin mode

   buzzerPin controls buzzer output, so OUTPUT is correct.

3. Final Answer:

   sensorPin should be set as INPUT, not OUTPUT. -> Option B

4. Quick Check:

   Input pins need pinMode(INPUT) [OK]

Hint: Set sensor pins as INPUT, buzzer pins as OUTPUT [OK]

Common Mistakes:

• Setting sensorPin as OUTPUT
• Confusing input and output pin modes
• Misusing digitalWrite for sensor reading

5. You want to modify an Arduino alarm system so the buzzer sounds only if the sensor detects HIGH for 3 seconds continuously. Which code change correctly implements this?

hard

A. Add a delay(3000) after detecting HIGH before turning buzzer ON.

B. Set sensorPin as OUTPUT and buzzerPin as INPUT to control timing.

C. Turn buzzer ON immediately when sensorPin is HIGH, then delay 3000 ms.

D. Use a timer to check if sensorPin stays HIGH for 3000 ms before activating buzzer.

Solution

1. Step 1: Understand requirement for continuous HIGH detection

   We need to confirm sensorPin stays HIGH for 3 seconds before buzzer sounds.

2. Step 2: Evaluate options for timing logic

   Using a timer to measure continuous HIGH duration is correct; delay alone pauses code and is insufficient.

3. Final Answer:

   Use a timer to check if sensorPin stays HIGH for 3000 ms before activating buzzer. -> Option D

4. Quick Check:

   Continuous HIGH detection needs timer logic [OK]

Hint: Use timer logic, not delay, for continuous sensor check [OK]

Common Mistakes:

• Using delay which blocks code execution
• Switching pin modes incorrectly
• Turning buzzer ON immediately without timing