PIR motion sensor in Arduino - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to set the PIR sensor pin as input.

Arduino

const int pirPin = 7;

void setup() {
  pinMode([1], INPUT);
}

void loop() {
  // Your code here
}

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

ApirPin

B7

COUTPUT

DLED_BUILTIN

Attempts:

3 left

💡 Hint

Common Mistakes

Using the pin number directly instead of the variable.

Setting the pin mode to OUTPUT instead of INPUT.

You need to set the PIR sensor pin as input using pinMode(pirPin, INPUT); where pirPin is the variable holding the pin number.

2fill in blank

medium

Complete the code to read the PIR sensor value.

Arduino

int sensorValue = digitalRead([1]);

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

AINPUT

BpirPin

CLED_BUILTIN

D8

Attempts:

3 left

💡 Hint

Common Mistakes

Using a wrong pin number.

Passing INPUT instead of a pin number.

To read the PIR sensor value, use digitalRead(pirPin); where pirPin is the pin connected to the sensor.

3fill in blank

hard

Fix the error in the code to turn on the built-in LED when motion is detected.

Arduino

if (sensorValue == [1]) {
  digitalWrite(LED_BUILTIN, HIGH);
} else {
  digitalWrite(LED_BUILTIN, LOW);
}

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

ALOW

B0

CHIGH

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Checking for LOW or 0 instead of HIGH or 1.

Using the wrong constant for comparison.

The PIR sensor outputs HIGH (1) when motion is detected, so the condition should check for 1.

4fill in blank

hard

Fill both blanks to create a dictionary that maps sensor states to messages.

Arduino

const char* messages[] = {"No motion", [1];

void loop() {
  int state = digitalRead(pirPin);
  Serial.println(messages[[2]]);
}

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

A"Motion detected"

Bstate

CsensorValue

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong message string.

Using a constant like 1 instead of the state variable.

The array holds messages for states 0 and 1. Use "Motion detected" for {{BLANK_1}} and state for {{BLANK_2}} to print the correct message based on the sensor state.

5fill in blank

hard

Fill all three blanks to complete the code that initializes serial communication, reads the PIR sensor, and prints the status.

Arduino

void setup() {
  Serial.[1](9600);
  pinMode(pirPin, INPUT);
}

void loop() {
  int [2] = digitalRead(pirPin);
  Serial.println([3] == 1 ? "Motion detected" : "No motion");
  delay(500);
}

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

Abegin

BsensorState

Dprint

Attempts:

3 left

💡 Hint

Common Mistakes

Using print instead of begin to start serial.

Using different variable names for reading and printing.

Use Serial.begin(9600); to start serial communication. Read the sensor into sensorState and print the message based on its value.

Practice

1. What does a PIR motion sensor detect in an Arduino project?

easy

A. Light intensity changes

B. Sound levels in the environment

C. Movement by sensing infrared changes

D. Temperature variations

Solution

1. Step 1: Understand PIR sensor function

   A PIR sensor detects motion by sensing changes in infrared radiation emitted by objects.

2. Step 2: Compare with other options

   Sound, temperature, and light sensors detect different things, not motion via infrared.

3. Final Answer:

   Movement by sensing infrared changes -> Option C

4. Quick Check:

   PIR sensor = Motion detection [OK]

Hint: PIR sensors detect heat movement, not sound or light [OK]

Common Mistakes:

• Confusing PIR with sound or light sensors
• Thinking PIR detects temperature directly

2. Which Arduino code line correctly reads the PIR sensor connected to digital pin 7?

easy

A. int motion = digitalWrite(7);

B. int motion = digitalRead(7);

C. int motion = analogRead(7);

D. int motion = pinMode(7, INPUT);

Solution

1. Step 1: Identify correct function to read digital input

   digitalRead(pin) reads the digital value from a pin, suitable for PIR sensor output.

2. Step 2: Eliminate incorrect functions

   analogRead reads analog pins, digitalWrite sets output, pinMode sets pin mode but does not read value.

3. Final Answer:

   int motion = digitalRead(7); -> Option B

4. Quick Check:

   Use digitalRead for digital sensor input [OK]

Hint: Use digitalRead to get sensor state from digital pins [OK]

Common Mistakes:

• Using analogRead on digital pin
• Using digitalWrite instead of digitalRead
• Confusing pinMode with reading value

3. What will be the output on the Serial Monitor when the following Arduino code runs and the PIR sensor detects motion?

const int pirPin = 8;
void setup() {
  pinMode(pirPin, INPUT);
  Serial.begin(9600);
}
void loop() {
  int motion = digitalRead(pirPin);
  if (motion == HIGH) {
    Serial.println("Motion detected!");
  } else {
    Serial.println("No motion.");
  }
  delay(1000);
}

medium

A. Motion detected! printed every second when motion is present

B. No output because Serial.begin is missing

C. Motion detected! printed once and then stops

D. Syntax error due to missing semicolon

Solution

1. Step 1: Analyze the loop behavior

   The loop reads the PIR sensor pin every second and prints "Motion detected!" if motion is HIGH, else "No motion.".

2. Step 2: Check Serial setup and output

   Serial.begin(9600) is correctly called in setup, so output will appear on Serial Monitor continuously.

3. Final Answer:

   Motion detected! printed every second when motion is present -> Option A

4. Quick Check:

   Serial prints motion status each second [OK]

Hint: Loop prints sensor state every second with delay(1000) [OK]

Common Mistakes:

• Thinking Serial.begin is missing
• Assuming output prints only once
• Confusing syntax errors

4. Identify the error in this Arduino code snippet using a PIR sensor on pin 9:

void setup() {
  pinMode(9, OUTPUT);
  Serial.begin(9600);
}
void loop() {
  int motion = digitalRead(9);
  if (motion == HIGH) {
    Serial.println("Motion detected");
  }
  delay(500);
}

medium

A. Pin 9 should be set as INPUT, not OUTPUT

B. Serial.begin should be in loop()

C. digitalRead cannot be used on pin 9

D. Missing semicolon after Serial.println

Solution

1. Step 1: Check pinMode for sensor input

   PIR sensor output is digital input, so pin 9 must be set as INPUT, not OUTPUT.

2. Step 2: Verify other code parts

   Serial.begin is correctly in setup, digitalRead works on pin 9, and semicolon is present.

3. Final Answer:

   Pin 9 should be set as INPUT, not OUTPUT -> Option A

4. Quick Check:

   Input pins must use pinMode(INPUT) [OK]

Hint: Set sensor pins as INPUT, not OUTPUT [OK]

Common Mistakes:

• Setting sensor pin as OUTPUT
• Moving Serial.begin to loop
• Ignoring pinMode settings

5. You want to turn on an LED connected to pin 13 only when the PIR sensor on pin 2 detects motion. Which Arduino code snippet correctly implements this behavior?

hard

A. pinMode(2, INPUT);
pinMode(13, OUTPUT);
if (digitalRead(2) == LOW) {
digitalWrite(13, HIGH);
}

B. pinMode(2, OUTPUT);
pinMode(13, INPUT);
if (digitalRead(13) == HIGH) {
digitalWrite(2, HIGH);
}

C. pinMode(2, INPUT);
pinMode(13, OUTPUT);
if (digitalRead(2) == HIGH) {
digitalWrite(13, HIGH);
}

D. pinMode(2, INPUT);
pinMode(13, OUTPUT);
digitalWrite(13, digitalRead(2));

Solution

1. Step 1: Set correct pin modes

   Pin 2 is sensor input, so INPUT; pin 13 is LED output, so OUTPUT.

2. Step 2: Use digitalRead to control LED

   digitalWrite(13, digitalRead(2)) sets LED HIGH when sensor reads HIGH, LOW otherwise.

3. Step 3: Eliminate other options

   pinMode(2, OUTPUT); pinMode(13, INPUT); if (digitalRead(13) == HIGH) { digitalWrite(2, HIGH); } has wrong pin modes and logic. pinMode(2, INPUT); pinMode(13, OUTPUT); if (digitalRead(2) == HIGH) { digitalWrite(13, HIGH); } turns LED on for motion but lacks else clause to turn off when no motion. pinMode(2, INPUT); pinMode(13, OUTPUT); if (digitalRead(2) == LOW) { digitalWrite(13, HIGH); } reverses logic.

4. Final Answer:

   pinMode(2, INPUT); pinMode(13, OUTPUT); digitalWrite(13, digitalRead(2)); -> Option D

5. Quick Check:

   LED state = PIR sensor state [OK]

Hint: Write LED pin to sensor pin state directly for simplicity [OK]

Common Mistakes:

• Setting sensor pin as OUTPUT
• Reversing HIGH/LOW logic
• Confusing input/output pin modes
• Omitting else clause to turn off LED