🔐 Embedded Sentry

A gesture-based hardware lock built with an Arduino + MPU6050 accelerometer

Wave your hand. Unlock the world. Record a secret 3-move gesture sequence; the device only unlocks when that exact motion is repeated.

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🎯 What it does

Embedded Sentry is a wearable security primitive: a microcontroller reads a 3-axis accelerometer, classifies each flick of the wrist into one of six discrete directions (← → ↑ ↓ forward backward), and uses a finite-state machine to:

1. Record a secret sequence of N gestures.
2. Arm itself and wait for someone to repeat it.
3. Drive an unlock signal (an LED on Pin 13 — easily swapped for a relay) for 3 seconds when the sequence matches.

It's tiny, hardware-only, and needs no internet, no companion app, and no key fob.

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✨ Try it in your browser

There's a fully interactive web simulator in web-demo/ that runs the same finite-state machine as the firmware — no hardware needed.

# from the repo root
cd web-demo && python3 -m http.server 5000
# then open http://localhost:5000

The simulator implements the same finite-state machine as the firmware (record → arm → unlock), with a live accelerometer readout, animated tilting device, and real-time serial log. Click the directional buttons or use the arrow keys + W / S to flick the device — the firmware classifies gestures from raw accelerometer samples; the demo skips that step and feeds discrete directions straight into the FSM.

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🧠 How it works

Finite-state machine

       ┌──────────────┐  N gestures   ┌────────────┐  match all  ┌────────────┐
 ────► │   RECORD     │ ────────────► │   ARMED    │ ──────────► │  UNLOCKED  │
       │  (capture)   │               │  (verify)  │             │ (LED HIGH) │
       └──────────────┘               └─────┬──────┘             └──────┬─────┘
                                            │ wrong move                │ 3 s
                                            ▼                           │
                                       (reset attempt) ◄────────────────┘

Direction classification

The MPU6050 reports linear acceleration in m/s² on three axes. At rest the device reads (0, 0, 9.81) — pure gravity. A flick of the wrist briefly pushes one axis past a threshold:

Gesture	Condition
Right	x < -4
Left	x > 4
Up	z > 13
Down	z < 7
Forward	y < -3 and |x| < 2
Backward	y > 3 and |x| < 2

A 500 ms debounce ensures one physical flick maps to exactly one symbol.

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📂 Repository layout

.
├── firmware/
│   └── SentryLock.ino                ← clean, table-driven implementation (recommended)
├── web-demo/
│   ├── index.html                    ← interactive in-browser simulator
│   ├── styles.css
│   └── app.js                        ← same FSM, in JavaScript
├── docs/
│   └── WIRING.md                     ← hardware bill of materials + pinout
├── Project_with_keyboard.ino         ← original NYU submission (kept for history)
├── Project_with_no_keyboard.ino      ← original NYU submission (kept for history)
└── LICENSE

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🔌 Hardware

Part	Notes
ATmega328p	Arduino Uno / Nano
MPU6050	I²C, address 0x68 (SDA=A4, SCL=A5)
LED + 220 Ω	On D13 — swap for a relay to drive a real lock

Full wiring diagram and pin map: docs/WIRING.md.

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🚀 Flashing the firmware

1. Install the Arduino IDE (or arduino-cli).
2. Add the Adafruit MPU6050 library via the Library Manager (it pulls Adafruit_Sensor automatically).
3. Open firmware/SentryLock.ino, select your board + port, and click Upload.
4. Open the Serial Monitor at 115200 baud to see the FSM transitions.

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🛠 Tuning

All thresholds are constexpr at the top of SentryLock.ino:

constexpr uint8_t  SEQ_LEN     = 3;     // length of the secret
constexpr uint16_t DEBOUNCE_MS = 500;   // delay between gestures
constexpr uint16_t UNLOCK_MS   = 3000;  // how long the LED stays on
constexpr float    TH_LR       = 4.0f;  // accel threshold for left/right
// ...

Want a 5-move sequence? Change SEQ_LEN. Want a more sensitive flick? Lower the thresholds.

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📜 License

MIT — built originally for NYU's Embedded Systems course (Spring 2020).

_{Made by Mohammad Asfour · NYU Tandon}