PIR motion sensor in Arduino - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does a PIR motion sensor detect?

A PIR (Passive Infrared) motion sensor detects changes in infrared radiation, which usually means it senses movement of warm objects like humans or animals.

beginner

How do you connect a PIR sensor to an Arduino?

Connect the PIR sensor's VCC pin to 5V on Arduino, GND to ground, and the output pin to a digital input pin on the Arduino (e.g., pin 2).

beginner

What Arduino function reads the PIR sensor output?

Use the digitalRead() function on the Arduino pin connected to the PIR sensor output to check if motion is detected (HIGH) or not (LOW).

intermediate

Why is it important to add a delay after detecting motion with a PIR sensor?

Adding a delay helps prevent multiple rapid triggers and gives the sensor time to stabilize before detecting new motion.

beginner

What is the typical output signal of a PIR sensor when motion is detected?

The PIR sensor output goes HIGH (usually 3.3V or 5V) when motion is detected, and LOW when no motion is present.

What type of signal does a PIR sensor output to the Arduino when motion is detected?

A Digital HIGH signal

B Analog voltage proportional to distance

C PWM signal

D No signal

The PIR sensor outputs a digital HIGH signal when it detects motion.

Which Arduino function is used to read the PIR sensor's output pin?

A pulseIn()

B analogRead()

C digitalWrite()

D digitalRead()

digitalRead() reads the digital signal from the PIR sensor output pin.

Why should you add a delay after detecting motion with a PIR sensor?

A To increase sensor sensitivity

B To reset the Arduino

C To prevent multiple rapid triggers

D To save power

Adding a delay prevents multiple rapid triggers and allows the sensor to stabilize.

What voltage is typically used to power a PIR sensor with Arduino?

A 5V

B 3.3V only

C 12V

D 1.5V

Most PIR sensors work well with 5V power from the Arduino.

What does PIR stand for in PIR motion sensor?

A Proximity Infrared

B Passive Infrared

C Power Infrared

D Pulse Infrared

PIR stands for Passive Infrared, meaning it detects infrared radiation passively.

Explain how a PIR motion sensor works with an Arduino to detect movement.

Think about how the sensor senses heat changes and how Arduino reads that.

Describe the steps to connect and program a PIR sensor with Arduino for a simple motion detection project.

Start from wiring, then how to read and respond to sensor signals.

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