Project made by Ghita Anita-Raluca, 334CB.

A brief overview of the project:

• This project detects motion using a PIR sensor and alerts the user through LEDs and an LCD display.
• The purpose is to simulate a simple, cheap and effective motion-activated silent alarm.
• It’s useful for personal learning and practical applications like basic surveillance.

Block diagram:

Block diagram description:

• PIR Sensor (GPIO): Detects motion and sends digital signal to Arduino.
• Arduino UNO R3: Central controller that reads the sensor and drives the outputs.
• Potentiometer (ADC): Sets the alert duration and the time before it checks again.
• LEDs (GPIO): Green = idle, Red = motion detected.
• LCD 16×2 (I2C): Displays status messages via I2C.

• D2 – PIR sensor input: receives the digital signal from the sensor (HIGH = motion detected).
• D3 – Red LED output: lights up when motion is detected.
• D4 – Green LED output: stays ON when system is idle (no motion).
• A0 – Potentiometer: analog input to set delay duration for alert (LED ON time).
• A4 (SDA) and A5 (SCL) – I2C communication for the LCD 1602 module.

The system uses an Arduino UNO R3 board connected with several components to detect motion and respond visually.

• The PIR motion sensor detects movement and sends a HIGH signal to pin D2.
• The red LED (D3) turns ON when motion is detected.
• The green LED (D4) indicates idle state.
• A potentiometer connected to A0 adjusts how long the green LED stays ON (between 1 and 9 seconds).
• The LCD (connected via I2C to A4 and A5) displays real-time status messages.

All components are powered via the Arduino’s 5V and GND pins, using a breadboard and jumper wires for interconnection.

Schematics:

Using the Arduino IDE

• Wire.h – for I²C communication with the 16×2 LCD.
• LiquidCrystal_I2C.h – for displaying messages on the LCD screen.
• No additional libraries are required for the PIR sensor, LEDs, or the potentiometer – native digital and analog pins are used.

Structures:

• Global variables for system state: `motionDetected`, `alertStartTime`.
• `int alertDuration` – alert duration in milliseconds, calculated from the potentiometer reading.
• `bool ledState` – tracks the state of the red LED.

Algorithms:

• PIR motion detection: when motion is detected, the PIR sensor sends a HIGH signal to a digital input pin.
• Timing with millis(): the moment of detection is stored using `alertStartTime = millis()`, and the red LED remains ON until `millis() - alertStartTime > alertDuration`.
• LCD display update: messages such as “No motion” or “Motion detected” are dynamically updated using functions from the LiquidCrystal_I2C library.
• Potentiometer reading: analogRead is used to obtain a value between 0–1023, which is mapped to a duration range (e.g., 0–10000 ms).
• LED control logic: the green LED indicates idle mode, the red LED is ON when motion is detected.

• `setup()` – initializes the LCD, I/O pins, and performs initial readings from the PIR sensor and potentiometer.
• `loop()` –
  1. Reads the PIR sensor signal
  2. Controls LEDs based on motion detection
  3. Verifies timeout using `millis()`
  4. Updates LCD messages
  5. Reads potentiometer and updates `alertDuration`

Source code: https://github.com/anitaraluca/proiectPM/blob/main/code