Bluetooth-Based Keyless Entry System

by Arun Kumar Varadarajan, Clemson Automotive Engineering Graduate Student

Introduction

The keyless entry system allows or denies access to a vehicle using signals from a hand-held key fob. Most current systems operate by transmitting radio waves at a frequency of 315 MHz or 434 MHz. The system is primarily comprised of two components, a receiver and a transmitter. The receiver is installed in the car which sends a signal to the central locking system to unlock or lock the doors on receiving an encrypted signal from the transmitter.

Bluetooth-based systems use a mobile phone’s Bluetooth connectivity instead of the conventional 315/434 MHz RF waves for this operation, eliminating the need for a separate key fob. The receiver system constantly searches for the mobile device on basis of the mobile’s MAC number which is programmed into the system. Once the mobile device comes into range of the system and gets successfully identified, the central locking system is activated. Upon pressing the button on the door handle, the doors are unlocked. When the mobile device goes out of range and the system becomes disconnected from the mobile phone, the doors are locked again.

Construction

In a sample implementation, the Hardware required to build the system is as follows:

• Microcontroller
• Bluetooth module
• Motor driver/ Relay
• +5v Voltage regulator (7805)

The TXD and RXD of Bluetooth module to RXD and TXD of the microcontroller, they operate at Transistor-Transistor Logic (TTL) level. The interfacing is done using UART (Universal Asynchronous Receiver Transmitter).

The motor driver/relay is used in order to operate the Actuators in the central locking system which operate in 12 volts compared to microcontroller that operates in 5 volts.

Working

The microcontroller is programmed to initiate the Bluetooth module to search for a mobile device having same Bluetooth MAC address that is already in the microcontroller’s memory. The microcontroller sends instructions to the Bluetooth module according to a specific AT-command set that is defined by the Bluetooth module manufacturer. When the mobile device is in range the Bluetooth module pairs with the mobile and after successful completion of pairing the Bluetooth module informs the microcontroller. The microcontroller then sends an input to a relay or a motor driver which drives the actuator that locks ore unlocks the doors. The system remains connected to the mobile till it is in range and disconnects when the mobile goes out of range which locks the doors automatically.

Sensors

Bluetooth module

Actuators

Door lock actuators

For More Information

[1] Microcontroller UART protocol, Soceityofrobots.com

[2] Automotive keyless entry systems, Wikipedia.

[3] Blueconnect AT-Command set (example), Blueconnect Bluetooth module.

[4] Bluetooth and Microcontroller Interfacing, vshamu.wordpress, March 20, 2011.