Design and application of the central door lock co

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Design and application of central door lock control device of automobile

the door lock of automobile has two states: unlocking and locking. When locking, the door cannot be opened through the inner and outer handles. Central door lock control device: it is an electrical device that controls the state of door lock. It is a safety and comfort system in automotive electrical appliances. The general working principle can be illustrated in Figure 1: when the car key is rotated or the door lift is pulled, the locking mechanism will be driven to move, the status switches K and K2 will act, the capacitor C1 (or C2) will discharge, the relay J1 (or J2) will be pulled in, and the executive motor M1 (or m2) will be powered on to drive the locking mechanism to act. After the power is discharged, the relay is released, the motor stops, and the locking process is automatically completed. Connect the actuating motors of all car doors (including the trunk) together and act at the same time to realize the centralized control of door locks, which is very convenient to use. Figure 1 shows the principle circuit. There are many kinds of actual circuits and execution devices, but the principle is similar, and the purpose is to realize the centralized control of door lock. With the development of technology and the improvement of automobile comfort, practical functions such as automatic locking have appeared based on manual control circuit and single chip microcomputer control technology. After the introduction of wireless control technology, the system is more convenient to use. However, due to the characteristics of wireless control and the fact that cars are special commodities, they are easy to be invaded illegally. For example, the use of "air interception" and "scanning attempt" to obtain legal identity forces the gradual elimination of fixed codes. The application of new code hopping coding technology greatly reduces the possibility of illegal intrusion such as interception and scanning. In addition, even if there is forced intrusion (such as smashing windows and prying doors), the new built-in anti-theft alarm circuit will send an alarm to deter intruders, and even directly send help information. Even if the illegal operation succeeds, the system will immediately cut off the ignition and fuel system of the engine to prevent further human invasion

it can be seen that the central door lock is not only convenient to use, but also improves the safety performance. Many automobile factories have been used as factory standard equipment increasingly

1 the composition and signal flow of the central door lock system are shown in Figure 2. The system is mainly composed of the main controller, actuator, remote controller and connecting harness. The remote controller is composed of coding circuit, transmitting circuit and battery. It usually has a button. It is a small transmitting device and can be carried with you. The main controller is composed of wireless receiving module, power supply (DC-DC converter), main control chip (generally single chip microcomputer), input and output interface circuit (to complete the matching between circuits). It is an intelligent control unit, which is installed in a hidden position in the car. Actuators generally include door lock motor, alarm horn, power relay, alarm lamp, fuel shut-off valve, etc. The door lock motor is integrated with the door lock; The warning lamp is shared with the vehicle turn signal lamp; The power relay and fuel shut-off valve are installed in a concealed position. Next, the design and application of the system are analyzed from each unit circuit

2 coding circuit

coding technology includes fixed coding technology and skip coding technology. Its circuit is shown in Figure 3 and Figure 4 respectively. The coding structure diagram is shown in Figure 5 and Figure 6 respectively

2.1 fixed encoding circuit

the pin of encoding chip PT2262 (and decoding PT2272) is the address setting pin. There are three states (suspended, positive power supply, grounding) to choose from, which can constitute 38 kinds of encoding. The code is serially output by 17 pins (dout). The coding structure is shown in Figure 5. Each group consists of address code, data code and synchronization code to form a complete word code. When the circuit is fixed, the word code is fixed, and it is exactly the same every time, so it is called fixed coding. Each character code is separated by a synchronization code, and at least 4 groups of characters are generated each time. If the transmitter keeps pressing the key, the encoding chip will also output continuously

2.2 code hopping coding circuit

coding chip hcs200 integrates KEELOQ algorithm and other functions, with four key interfaces, which can generate various function codes. Built in electrically erasable memory is used to store serial number (SN), encryption key (EN key), synchronization code (sync), seed code (seed), etc. Serial number is used to identify different objects; The encryption key is used to encrypt the output data, which increases the difficulty of decoding. It does not output directly; The synchronization code is used to resist interception. Every time a key is pressed, the value of the synchronization counter is updated. After encryption and transformation, it is serially output by 694 (PWM)

3 wireless transmitting and receiving circuit

wireless transmitting circuit and wireless receiving circuit are shown in Figure 7 and figure 8 respectively

the wireless transmission circuit shown in Figure 7 is a single transistor oscillation circuit, and the input signal of the coding circuit acts as a bias voltage. When a key is pressed, the coding circuit is powered on and outputs serial signal voltage. The high-frequency transmitting circuit vibrates and generates equal amplitude high-frequency oscillation. The emission circuit stops oscillating after the key is released. It can be seen that the transmitting circuit is completely controlled by the digital signal output by the encoding circuit, so that the transmitting circuit completes amplitude keying (ASK modulation), which is equivalent to amplitude modulation with a modulation system of 100%. The oscillation signal generates electromagnetic wave through the inductance composed of printed circuit and sends it to the air

the wireless receiving circuit shown in Figure 8 is a regenerative detection circuit that works under intermittent oscillation. After being shaped and amplified by njm2904, the performance of plastic packaging materials can be improved to a voltage opposite to the transmitting end by using low-cost technology, which is directly transmitted to the oil supply code circuit of the experimental machine

4 decoding circuit and control circuit composed of single chip microcomputer

for the status of fixed coder quality, it will last for a long time code, which can be decoded by special chip PT2272 hardware (Fig. 9) or single chip microcomputer software (FIG. 10). Decoding idea: when the hardware decoding circuit PT2272 detects that the address code is the same and the data code is consistent for two consecutive times, it drives the "1" in the data code to drive the corresponding data output end to high level (VT end is synchronized to high level)

when decoding with single-chip microcomputer software, the program recognizes the pulse width of the following word code after judging the synchronization code. For example, start timing from the first falling edge, and constantly detect the level change. As soon as there is a level change, immediately record the level width. Continue to count until the second falling edge appears (because the input is the inverse code). Record the interval between the two falling edges and repeat the above steps. Judge the interval. If it is within the respective allowable error range, translate this code point, otherwise it will be considered as error code and discarded. After 12 code points are detected continuously and correctly, the address code and data code are compared, and the result is the same, and the data code is output. Because of the characteristics of wireless transmission, the first group of word codes are very vulnerable to low-level interference and often generate error codes, so the program can be discarded

for skip code coding, it can also be decoded by hardware with a special decoding chip (such as hcs5xx), or by software with a single chip microcomputer with built-in KEELOQ decoding software. The code skipping software and hardware decoding follow the KEELOQ algorithm: that is, after confirming the serial number matching, the received data is decrypted by KEELOQ, and then check whether the synchronization counter matches. After confirming its matching, the received key signal instructions are processed (KEELOQ algorithm can be found in relevant literature)

KEELOQ encryption and decryption technology is a multi change, anti interception, safe and reliable encryption and decryption technology. At present, this technology is only in the hands of a few foreign companies. They use the advantages of integrated circuit design to package this technology in chips

KEELOQ technology is a complex protocol with the following characteristics. ① The security is very good: after the same command is encoded by kkeeloq, the word code is different every time (in a very long cycle), and this change is irregular. ② Only after obtaining (through learning) the encryption key of the encoder in advance can the received data be effectively decoded. ③ Specific objects can only be used after learning the information of a coder. ④ The stored learning information can be cleared at any time to invalidate the original code, which can effectively avoid illegal use by third parties. ⑤ Code hopping technology can prevent the harm caused by being intercepted and then forwarded

it is these characteristics that make KEELOQ technology suitable for wireless control of central door lock

Figure 9 is the schematic diagram of the central door lock system with fixed coding, which realizes wireless remote control through hardware decoding, and does not have sound and light prompt and anti-theft alarm functions. The structure is relatively simple, the coding is fixed, and the anti-theft effect is poor. At present, it is less used in cars. Figure 10 is the schematic diagram of the hopping code controller, which is based on wireless transmission, KEELOQ encryption and decryption technology, plus the advantages of single chip microcomputer in control. It not only ensures the security requirements, but also flexibly realizes practical functions such as audible and visual prompt and automatic locking

the circuit shown in Figure 10 mainly realizes the following functions. ① Basic functions: manual and remote unlocking and locking. ② Sound and light prompt function: when the remote control receives the effective signal, it will send out a certain sound and flash the alarm light at the same time of locking. ③ Automatic locking function: the third braking locking of driving, and automatic unlocking after flameout and parking. ④ Anti theft alarm function: when the owner locks the door and leaves the vehicle (the door lamp switch, ignition switch are disconnected, and the door lock is in the locked state) for 5S, enter the warning state. The system detects the vibration sensor signal (Figure 11), and carries out alarm control according to the preset vibration level (adjust VR1)

the system is a comprehensive application of microprogrammed control of single chip microcomputer and wireless encryption technology. During the design, insulating parts, chemical instruments, optical instruments and other parts can realize a variety of practical functions by appropriately adding hardware circuits and introducing necessary electrical signals, which can be coordinated by single-chip microcomputer software. Through the understanding of the electrical structure of the whole vehicle and the analysis of customer needs, we can develop a central door lock control device with novel functions, high safety and a certain level of intelligence. Facts have proved that this kind of intelligent central door lock control device (also known as anti-theft device) is widely used and recognized by the majority of car owners. In practical application, how to strengthen the reliability and improve the service life of the system is a must for software and hardware design. Various measures should be taken, such as adding watchdog, voltage detection reset circuit (U3 in Figure 10), using software traps, improving the quality of components, etc. (end)

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