Alarm system with sensor and buzzer in Arduino - Step-by-Step Execution

Concept Flow - Alarm system with sensor and buzzer

Start

↓

Initialize pins

↓

Read sensor value

↓

Is sensor triggered?

No→Wait and read again

Yes↓

Turn buzzer ON

↓

Keep buzzer ON for a moment

↓

Turn buzzer OFF

↓

Repeat loop

The system starts by setting up pins, then continuously reads the sensor. If triggered, it turns the buzzer on briefly, then off, and repeats.

Execution Sample

Arduino

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

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

void loop() {
  int sensorValue = digitalRead(sensorPin);
  if (sensorValue == HIGH) {
    digitalWrite(buzzerPin, HIGH);
    delay(1000);
    digitalWrite(buzzerPin, LOW);
  }
}

This code reads a sensor on pin 2; if triggered (HIGH), it turns on a buzzer on pin 9 for 1 second.

Execution Table

Step	Action	Sensor Value	Condition (sensorValue == HIGH)	Buzzer State	Delay/Wait
1	Setup pins	N/A	N/A	Buzzer OFF	N/A
2	Read sensor	LOW	False	Buzzer OFF	N/A
3	Loop again	N/A	N/A	Buzzer OFF	N/A
4	Read sensor	HIGH	True	Buzzer ON	Start 1000ms delay
5	During delay	HIGH	True	Buzzer ON	Continuing delay
6	After delay	HIGH	True	Buzzer OFF	Delay ended
7	Loop again	N/A	N/A	Buzzer OFF	N/A

💡 The loop never exits; it continuously reads sensor and controls buzzer accordingly.

Variable Tracker

Variable	Start	After Step 2	After Step 4	After Step 6	Final
sensorValue	N/A	LOW	HIGH	HIGH	Depends on sensor
buzzerPin state	OFF	OFF	ON	OFF	OFF or ON depending on sensor

Key Moments - 3 Insights

Why does the buzzer turn on only when sensorValue is HIGH?

Because the condition in the if statement (sensorValue == HIGH) is true only when the sensor detects something, as shown in execution_table row 4.

What happens during the delay(1000) call?

The program pauses for 1000 milliseconds (1 second) while the buzzer stays ON, as seen in execution_table rows 4 and 5.

Why does the loop keep running forever?

Because Arduino's loop() function repeats endlessly, continuously checking the sensor and controlling the buzzer, as shown by the repeated steps in the execution_table.

Visual Quiz - 3 Questions

Look at the execution_table, what is the buzzer state at Step 5 during the delay?

A Buzzer OFF

B Buzzer ON

C Buzzer blinking

D Buzzer disconnected

💡 Hint

Check the 'Buzzer State' column at Step 5 in the execution_table.

At which step does the sensorValue first become HIGH?

A Step 4

B Step 6

C Step 2

D Step 7

💡 Hint

Look at the 'Sensor Value' column in the execution_table to find when it changes to HIGH.

If the sensor never detects anything (always LOW), what will the buzzer state be after Step 3?

A Blinking

B ON

C OFF

D Random

💡 Hint

Refer to the 'Buzzer State' column in execution_table rows 2 and 3.

Concept Snapshot

Arduino alarm system:
- Setup sensor pin as INPUT
- Setup buzzer pin as OUTPUT
- In loop, read sensor
- If sensor HIGH, turn buzzer ON
- Keep buzzer ON for 1 second
- Then turn buzzer OFF
- Repeat forever

Full Transcript

This Arduino alarm system code starts by setting the sensor pin as input and the buzzer pin as output. In the loop, it reads the sensor value. If the sensor detects something (sensorValue is HIGH), it turns the buzzer on for one second, then turns it off. The loop repeats endlessly, continuously checking the sensor and controlling the buzzer. The execution table shows each step: reading sensor, checking condition, turning buzzer on or off, and waiting during delay. Variables like sensorValue and buzzer state change accordingly. Key points include understanding the if condition, the delay pause, and the infinite loop behavior.