🎯 Security Surveillance Turret

Interrupt-Driven PIR Wake-Up + Ultrasonic Target Tracking · Arduino Uno

An energy-efficient embedded surveillance system that stays fully idle until a PIR motion sensor detects presence — then wakes up, sweeps a servo-mounted ultrasonic sensor across 180°, locks onto any target within range, and renders a live radar display on a connected PC.

Built as part of an Embedded Systems & Design course. Documented to IEEE project report standards.

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Processing radar display showing active target detection (red dots) alongside the physical build: servo-mounted HC-SR04, Arduino Uno, and wiring. Tested in an electronics lab environment.

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System Overview

         IDLE ──[PIR triggers]──► SCANNING ──[object < 50cm]──► ALERT
           ▲                          │                            │
           └──────[sweep done]────────┘◄──────[dwell 2s]──────────┘

Radar visualization runs live in Processing on the host PC, showing the sweep arc, detected target position, and distance readout in real time.

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Features

• PIR-triggered wake-up — system draws near-zero active power at idle; servo and ultrasonic only activate on motion detection
• 180° servo sweep — bidirectional scan in 5° increments with HC-SR04 ranging at each step
• Target lock — servo halts and LED triggers when object detected within configurable threshold (default 50 cm)
• Live radar display — Processing sketch renders a sonar-style sweep with plotted hit points and distance labels
• Serial data protocol — lightweight text-based protocol (angle,distance) streams data to host at 9600 baud
• Finite State Machine architecture — clean IDLE → SCANNING → ALERT state model with defined transitions

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Hardware Requirements

Component	Model	Role
Microcontroller	Arduino Uno (ATmega328P)	Main controller
Motion Sensor	HW-416-B (HC-SR501 based PIR)	Wake-up trigger
Ranging Sensor	HC-SR04 Ultrasonic	Distance measurement
Actuator	SG90 Micro Servo (9g)	180° pan sweep
Indicator	5mm LED + 330Ω resistor	Alert output
Host PC	Any OS	Radar visualization (Processing)

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Wiring

Component	Pin	Arduino Pin
HC-SR04	VCC	5V
HC-SR04	GND	GND
HC-SR04	TRIG	D10
HC-SR04	ECHO	D11
SG90 Servo	Red (VCC)	5V
SG90 Servo	Brown/Black (GND)	GND
SG90 Servo	Orange/Yellow (Signal)	D9
HW-416-B PIR	VCC	5V
HW-416-B PIR	GND	GND
HW-416-B PIR	OUT	D7
LED (long leg +)	via 330Ω resistor	D6
LED (short leg −)	—	GND

Note: Mount the HC-SR04 on top of the SG90 servo horn using double-sided tape, with the two sensor "eyes" facing forward. Leave enough wire slack for a full 180° rotation.

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Getting Started

Prerequisites

• Arduino IDE (v1.8+ or v2.x)
• Processing (v4.x recommended)
• No external Arduino libraries required — Servo.h is bundled with the IDE

1. Clone the repository

git clone https://github.com/HeyFang/security-turret.git
cd security-turret

2. Upload the Arduino sketch

1. Open arduino/turret.ino in the Arduino IDE
2. Go to Tools → Board → select Arduino Uno
3. Go to Tools → Port → select your COM port (e.g. COM3 on Windows, /dev/cu.usbmodem... on Mac)
4. Click Verify (✓) to compile — confirm no errors
5. Click Upload (→) to flash the sketch

3. Run the radar display

Close the Arduino IDE Serial Monitor before this step. Both cannot use the serial port simultaneously.

1. Open processing/radar.pde in the Processing IDE
2. Run the sketch once — the console will print a list of available serial ports
3. Find the index of your Arduino's port in that list
4. In radar.pde, update line:

   port = new Serial(this, Serial.list()[0], 9600);
   //                                      ↑ change this index if needed

5. Run again — the radar window should appear and animate on PIR trigger

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Repository Structure

security-turret/
│
├── arduino/
│   └── turret.ino          # Main Arduino sketch (FSM + sensor control)
│
├── processing/
│   └── radar.pde           # Host-side radar visualization
│
├── docs/
│   └── report.pdf          # Full IEEE-format project report
│
├── assets/
│   └── model.jpeg          # Build photo (used in README)
│
└── README.md

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Configuration

The following constants at the top of turret.ino can be adjusted without touching any other logic:

#define MAX_RANGE   50    // Alert threshold in cm (default: 50)
#define SCAN_STEP    5    // Degrees per servo step (default: 5°)
#define STEP_DELAY  80    // Milliseconds between steps (default: 80ms)

Decrease SCAN_STEP for finer angular resolution (slower sweep). Increase MAX_RANGE for a longer detection zone.

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How It Works

The system runs a three-state Finite State Machine:

IDLE — PIR pin is polled continuously. Servo and ultrasonic are inactive. Minimal power draw.

SCANNING — Triggered by PIR HIGH. Servo steps from 0° to 180° bidirectionally. At each step, the HC-SR04 fires a 10 μs trigger pulse and measures the echo return time. Distance is computed as:

distance (cm) = pulseIn duration (μs) / 58

Each reading is serialized as angle,distance\n and sent over UART at 9600 baud to the Processing display. If a full sweep completes with no detection and PIR has gone LOW, system returns to IDLE.

ALERT — Triggered when distance < MAX_RANGE. Servo halts at detection angle, LED turns on, and ALERT,angle,distance\n is transmitted. System holds for 2 seconds then resumes scanning.

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Serial Protocol

The Arduino outputs a simple newline-delimited text protocol:

Message	Meaning
WAKE	PIR triggered, scan starting
45,82	Servo at 45°, object at 82 cm
ALERT,45,28	Object detected at 45°, 28 cm
IDLE	Sweep complete, returning to standby

This makes the data easy to parse, log, or redirect to any serial terminal or custom application.

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Real-Time Design Notes

This project runs bare-metal (no RTOS). Key design decisions:

• PIR as wake-up: Polling is adequate here — PIR output stays HIGH for 2–3 seconds, so no events are missed. Avoids ISR complexity on a single-threaded system.
• PWM on D9 (Timer 1): Hardware PWM pin selected deliberately for jitter-free servo control, independent of software loop timing.
• pulseIn() timeout: Set to 30 ms — slightly above the round-trip time for 400 cm range — to prevent indefinite blocking on no-return echoes.
• Step delay of 80 ms: Chosen to allow full mechanical servo settling before ultrasonic trigger fires. Values below ~50 ms cause missed readings.

Primary limitation: pulseIn() is blocking, meaning no other processing occurs during echo measurement. An ISR-based timing approach (or RTOS migration to ESP32/FreeRTOS) would eliminate this constraint.

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Testing

Test	Method	Result
Ultrasonic accuracy	Measured at 10, 30, 50 cm with ruler	±2 cm variance — within datasheet spec
PIR reliability	Triggered after 60s warmup in static room	Consistent HIGH on motion, LOW at rest
Servo settling	Logged ultrasonic readings at 50ms vs 80ms delay	80ms required for consistent readings
Serial throughput	Frame size ~12 bytes at 9600 baud	~12.5ms/frame — well within 80ms step window
Full sweep time	Timed 36-step sweep (0°–180°)	~3.96s worst-case (30ms timeout × 36 steps)

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Known Limitations

• PIR sensor requires ~60 seconds of warmup after power-on before reliable detection
• Blocking pulseIn() call prevents response to new PIR events mid-reading
• Single horizontal axis only — no vertical (tilt) coverage
• Requires tethered PC for radar display — no standalone screen support in current version
• HC-SR04 beam angle (~15°) limits angular discrimination at longer ranges

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Future Improvements

• Migrate to ESP32 + FreeRTOS for true multitasking and non-blocking echo measurement
• Add pan-tilt second axis (vertical servo) for hemispheric coverage
• Replace Processing display with onboard SSD1306 OLED for standalone operation
• Add Wi-Fi alert via ESP8266 (push notification on detection)
• Integrate OV2640 camera module (ESP32-CAM) for image capture on alert
• TinyML motion classification to filter false positives (human vs animal vs environmental)

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License

This project is licensed under the MIT License — see LICENSE for details.

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Author

Aryan Shete
LinkedIn · GitHub

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Built for an Embedded Systems & Design course project. Documented to IEEE report standards.