Project Overview

A keyless, biometric door-lock that opens via:

• Android phone's fingerprint sensor

• Bluetooth connection (HC-05) to an Arduino

• Solenoid door lock mechanism

No traditional fingerprint module on the lock itself—everything rides on your phone’s fingerprint scanner.

Hardware Components

1. Arduino Nano / Uno – central control unit

2. HC-05 Bluetooth module – wireless link between phone and Arduino

3. Relay module – toggles power to the solenoid lock

4. 12 V solenoid lock – actual locking mechanism

5. 5 V regulator (e.g. 7805) – to power Arduino & Bluetooth

6. Buzzer / LED indicators – optional status alerts

Typical wiring:

• Relay input → Arduino digital pin (e.g. D13)

• HC-05 TX/RX ↔ Arduino RX/TX (or software serial pins D2/D3)

• 12 V rail powers both solenoid + 7805 (which steps down to 5 V)

• 5 V line feeds Arduino & HC-05 module

Software & Android App

• Custom Android APK/App built with tools like MIT App Inventor or Kodular

• App flow:

  • Connect via Bluetooth to HC-05

  • Prompt for fingerprint authentication

  • Send a specific command (e.g. integer “1”) to Arduino if authorized

• Arduino sketch listens over serial:

Operational Flow

1. Phone connects to HC-05 via app

2. User scans fingerprint on phone

3. If verified, app sends unlock code (e.g. "1")

4. Arduino receives code and energizes relay

5. Relay powers solenoid, unlocking door for defined time

6. After delay, Arduino opens circuit to relock

Design Decisions & Advantages

• No dedicated fingerprint sensor hardware—uses the AD phone's biometric scanner

• Reduces cost, complexity, wiring, and programming effort

• Solenoid lock delivers 12 V latch movement

• Relay module interfaces between Arduino and solenoid

• Custom app ensures only authorized users can unlock

• Wiring is kept straightforward with minimal components

Performance

Though this exact build doesn’t include timings, similar research shows:

• Fingerprint recognition on embedded modules ≈1.2 s beep respons

Expect a total delay of ~2–3 seconds from fingerprint scan to lock activation.

Wiring Block Diagram (Simplified)

(Plus optional LED/Buzzer connected to Arduino for feedback)

Step-by-Step Summary

1. Assemble hardware

   • Connect Arduino, HC-05, relay, and solenoid per diagram

   • Add power relations: 12 V supply → solenoid + 7805 regulator → Arduino/HC-05

2. Program Arduino

   • Write serial listening code

   • Test unlocking relay logic

3. Build Android app

   • Use BiometricPrompt API or MIT App Inventor fingerprint blocks

   • Send fixed code upon successful scan

4. Test entire chain

   • Pair app with HC-05

   • Authenticate, receive unlock signal, observe lock action

5. Enclose in casing (optional 3D printed for a clean look)

Pros & Cons

Variations & Enhancements

• Add Wi-Fi or GSM modules for remote unlocking

• Integrate time-based or multi-user fingerprint access

• Include logging or notifications via smartphone or cloud

• Deploy solenoid and relay in a secure, tamper-resistant casing

More References

• ResearchGate project (Arduino UNO, solenoid, fingerprint, HC-05)

• ElectronicClinic article (Arduino Nano + relay + Android Biometric app)

• IoTDesignPro stepwise walkthrough (components, code, wiring)

In Summary

This project connects an Android phone’s fingerprint sensor to a simple Arduino-relay-solenoid setup, all via Bluetooth. You only need a smartphone for biometric authentication—cutting down on hardware needs. It’s a modular, educational entry into smart-lock systems.