Based on monolithic integrated circuit automobile security alarm system designAbstract: Decodes the automobile security system using them on litchis integrated circuit interior resources realization jump code, it each time uses the remote control password all is changing, both enhanced the system security, and greatly reduced the cost.Keyword: Monolithic integrated circuit, Automobile security system , Code/decodeIntroductionIs unceasingly progressive along with the social economy and the high tech rapid development, in the routine work and the life, the automobile has become the people ideal transportation vehicle. But the following motor vehicle the case which robbed gradually is also in creased has created the pilot economical property loss. In order tore duce the automobile to rob the event the formation rate, for has the automobile the user to provide the safety control, simply develops one kind to be reliable, the ease of operation, can send out in the discovery normal condition to the pilot reports to the police the reminder and the security warning safety system has the practical significance. This article based on to the existing automobile security alarm system generalized analysis, develops one kind of brand-new security alarm system. This system has mainly used the jump code code/decoding principle, causes the overall system to be safer, greatly reduces password explaining rate.1. System principle of workThe automobile security alarm system the remote control which carries by the driver and installs in the automobile the controller two parts composes. The remote control and the controller all use eight CMOS which American AT-MEL Corporation produces the AVR monolithic integrated circuit, this series monolithic integrated circuit based on new simplifies instruction R the ISC structure, includes the service life most to be few is 1,000 time writes/scratches the circulation the Flash program memory, as well as the service life at least is 100,000time writes/scratches the circulation E the EPROM data-carrier storage, some 2 only have when the entire piece cleaning can clean the programming encryption locks the localization.1.1 System designThe automobile security examination uses the ultrasonic sensor. The ultrasonic sensor is composed by the ultrasonic wave transmission circuit and the supersonic reception electric circuit, in the automobile cab appropriate position, installs the ultrasonic wave launch/receiver, as well as switch electric circuit T1. When the automobile parks the vehicle owner person must leave the automobile, with remote control closed switch T1, the automobile alarm system sat garrisons the condition, around the system use ultrasonic wave examination vehicle obstacle. Launches the partial electric circuits likes chart 1 to show. When its P1 mouth P1.1, P1.2 to the D trig , the P1.0 control ultrasonic wave launch, are 0, the photo electricity coupler outputs the TP1 end is 1, the permission ultrasonic wave launch, launches/the receive ultrasonic wave in turn, the circulation repeatedly carries on. Simultaneously the monolithic integrated circuit interior counter starts to count. The steam distance between vehicles obstacle distance is the time which sends out through the sound navigation and ranging reflects spends determines and carries on the computation. The reflection signal causes the D trigger to produce interrupt request signal INT1,simultaneously stops counting, reads takes counts the value, calculates the actual distance after the formula, then carries on the comparison with the datum distance, if examines when the actual distance is bigger than reference value 80cm, does not carry on the accustom-optics to report to the police; If some people approach the automobile to enter the cab, the examination actual distance is smaller than or was equal to when reference value 80cm, through monolithic integrated circuit P2.2 and the P2.3 port, actuates the indicating lamp display circuit and the sound alarm circuit, sends out three two flash. And triggers a high level, the actuation is wire less signal transmission circuit.Chart 1 Ultrasonic wave transmission circuit1.2 Code/decoding principleThe present automobile remote control security system are many is usesVD5026/27, PT2262/72, HT12E/D and so on the general code/decodes the electric circuit, its password decided by the component address, each set of security systems use a fixed invariable password. Along with the micro processing technology development, through the receiver emote control transmitting message, may intercept this fixed password, moreover general arranges the decoding address to lose the person to carry the component size limit, its quantity is impossible too much, can obtain not repeatedly codes very is also limited, also can very quickly explain the password with the automatic scanner. Therefore, this kind of password fixed invariable automobile security system has received the seri