Patent ID: 6337620
Filing Date: 2002-01-08
Classification: B60R

Abstract:
A cipher type anti-theft system for cars using an in-car wiring to transmit a cipher comprising:an encoder/transmitter for generating a cipher and converting said cipher from digits into analog signals for loading onto said in-car wiring; and at least one decoder cut-off relay that can be installed at any point on any power supply circuit needed to start a car in a normal way, and said decoder cut-off relay, when receiving signals sent by said encoder and transmitter and representing a correct cipher, being capable of decoding said cipher and making said power supply circuit onto which said decoder cut-off relay is installed; whereby said cipher type anti-theft system can be conveniently installed in the car at a hidden position on the in-car wiring without producing any additional wiring that would otherwise form a trace for a thief to easily locate said anti-theft system wherein said encoder/transmitter comprises a 5V regulator that converts a 12V power source of said in-car wiring into a stabilized 5V voltage for use by said encoder/transmitter, a CPU circuit that generates a particular, square-wave cipher signal, a voltage drop sensing circuit that detects said 5V voltage for its stabilization in order to provide a RESET signal to said CPU circuit to restart a CPU included in a said CPU circuit, a MOS-FET driver circuit that amplifiers current and voltage of said signals sent by said encoder/transmitter, and a RLC oscillation circuit that modulates said received signals to high-frequency signals and said modulated high-frequency signals being coupled via a transformer to a 12V power cord included in said in-car wiring; and wherein said at least one decoder cut-off relay comprises a 5V regulator that converts said 12V power source of said in-car wiring into a stabilized 5V voltage for use by said at least one decoder cut-off relay, a reference voltage circuit that generates a reference voltage of 2.5V for using by a compare circuit as a reference in comparison, a RLC oscillation circuit that extracts said high-frequency signals from said 12V power supply and said extracted high-frequency signals being filtered, shaped and amplified for extraction of signals of particular frequencies, a compare circuit that shapes and amplifies said filtered signals into square-wave signals, a CPU circuit that reads in said square-wave signals and determines whether said signals representing a correct cipher in order to instruct said at least decoder cut-off relay to either make or break said power supply circuit to which said decoder cut-off relay is connected, and an EEPROM that memorizes said cipher set for the car and stores data needed by said CPU to determine whether said received signals representing a correct cipher.