Based on the use of RS485 and RS232, this article proposes an intelligent community control and management system structure based on the CAN or Communication Technology Research Institute of the Corte Institute of Measurement and Control Technology. Factors such as transmission rate and scalability have successfully solved the problem of building data communications.
First, system structure and working principle
This system is mainly composed of three main parts: user host, corridor machine and community management center:
(1) RS485: The user host acts as a terminal and uses a communication card to connect to the corridor machine. 1 RS485, up to 256 nodes can be connected to the communication card. RS485 communication card is used as the communication channel between the floors. The system cost is minimized and the reliability of data communication is guaranteed through software design at 50 kHz. Transmission speed, RS485 transmission distance up to 1200m, to meet the application between floors.
(2) CAN communication card: The corridor machine of each building communicates with the community management center through the CAN communication card. The CAN node of the community management center is the master node on the CAN communication card and is responsible for the inspection and control of the corridor machines. The CAN node of each corridor machine can be used as a slave node to access the CAN communication card at any time. As long as the central controller software is slightly adjusted, the hardware and other software can be used without modification, which has good scalability and is very suitable for Application in the community.
(3) RS232: The CAN communication card communicates with the upper computer of the cell management center through RS232. The information on the CAN communication card is received by the CAN transceiver to the central control unit, and the central control unit is then connected by the MAX232 level conversion chip to the central host computer. The PC software of the center is written in VC and provides a friendly operation interface for the management personnel.
2. System working principle
This system includes security analysis, automatic meter reading, and home appliance control. When the status of security in the home is not abnormal, the user host periodically reads the three table data and stores it in the external memory. When the management center wants to read the meter, the central PC sends a meter reading command to the CAN communication card of each communication unit sent by the central control unit to the system. After the corresponding number of the corridor machine receives the meter reading command from the CAN communication card, A meter reading command will be sent to the user host of the corresponding unit of the building to request the host to send back three tables of data, and the corridor machine will send the data of the three tables back to the center through the CAN communication card and be processed by the management staff. Once the security part is abnormal, the user host will ring the siren, dial the pre-stored phone and other alarm procedures, and notify the management center of the alarm information through the CAN communication card.
Second, the realization of CAN communication card communication
The CAN communication card works with two-wire serial communication. It has a powerful error detection function and can be used in high-noise interference environments. It shows its communication advantages in the cell control system:
â— The highest communication rate up to 1Mbps, the maximum communication distance up to 10km;
â—Using CRC check and unique data signal representation, with error recognition and automatic retransmission;
â— With priority and arbitration functions, software design allows up to 110 single-chip micro-CAN nodes to communicate, including SJA1000 initialization, CAN message transmission, and CAN message reception.
â— Scalability: The CAN node can access the communication card at any time. As long as the central controller software is slightly adjusted, hardware and other software can be used without modification.
1. CAN node design
Each CAN node in the system consists of a microcontroller, a CAN controller, a high-speed opto-isolator, and a CAN transceiver. SCM is mainly used for I / O control and information processing functions; CAN controller is mainly used for system communication, control of CAN information reception and transmission, we use an independent use of independent CAN controller SJA1000; CAN transceiver is mainly used To enhance the system's drive capability, we use the TJA1050; in order to avoid all kinds of interference on the communication card to affect the communication circuit, we added a high-speed optocoupler chip 6N137 with isolation function between the CAN controller and the CAN transceiver.
It should be noted that the CAN transceiver buffers use integrated components, so the RX1 pin should be connected to ground and the CBP bit in the CDR register should be set to 1; the communication card must have a 120 ohm resistor at each end, which plays a role in matching the impedance of the communication card. A very important role, otherwise the interference and reliability of data communications will be greatly reduced, and even unable to communicate.
2. CAN node communication software design, including SJA1000 initialization, CAN information transmission, CAN information reception.
The initialization includes the setting of the working mode, the setting of the receiving filter mode, the setting of the reception mask register AMR and the reception code register ACR, the setting of the baud rate parameter, and the setting of the interrupt enable register IER. SJA1000 initialization can only be performed in reset mode. After completing the SJA1000 initialization setup, the SJA1000 can return to work and perform normal communication tasks. The initialized program flow chart is shown in Figure 1.
Chart SEQ Charts** Initialization Flow for ARABIC 1 SJA1000
2. CAN node software design
â— Send data subroutine
The sending data subroutine is responsible for the sending of the node message. The sending of the CAN message is done automatically by the CAN controller. When sending, it only needs to combine the information to be sent into a frame message in a specific format, and send it to the SJA1000 send buffer area, and start the sending command. The sending method can choose to use the inquiry mode or the interruption mode. In the program, we use the interruption mode. For the interrupt mode, the sending subroutine is divided into two parts: one is sending the main program, which is mainly used to send control information; when the sending buffer is full, the information to be sent is temporarily stored in the temporary storage area; and the second is the interrupt service routine. Responsible for sending temporarily stored information in the temporary storage area. Sending data program flow chart shown in Figure 4
The receiving data subroutine is responsible for the receipt of the node message and processing of other conditions. The information is also automatically completed by the CAN controller from the CAN communication card to the CAN receiving buffer. The receiving program only needs to read the information to be received from the receiving buffer. The receiving program can also use the query method or interrupt method, both of which are quite similar to each other. In the program, we use the interrupt receiving method and have stronger real-time performance.
â— Receive data subroutine
The ST720 engine room environmental monitoring instrument sends out an alarm signal. After the alarm information is processed by the ST720, the relevant maintenance personnel are notified of the telephone alarm through voice and the alarm information is sent to the monitoring equipment room hard disk recorder. The computer room monitoring alarm software installed in the hard disk recorder is collected. After the alarm information, command the video surveillance software to start recording on the site
Like. The software-processed alarm information and video recording information are transmitted to the E1/10Base converter through the DVR network adapter, and the converted E1 data reaches the remaining 2M ports of the optical transceiver of the transmission switch data. The optical transceiver transmits the data to the center through the optical cable. Room; The data received by the corresponding 2M port of the optical transceiver on the center room side through the E1/10Base converter
After data conversion, the converted Ethernet data enters the monitoring host through the computer network card. The computer room environment monitoring software and video monitoring software accurately and intuitively display the alarm information and video data received on the monitor. The room maintenance personnel will Accurately locate the fault location so that you can quickly deal with the situation.
Third, summary
The intelligent community control and management system proposed in this paper comprehensively considers factors such as cost and reliability. Based on the mature RS485 and RS232 technologies, the intelligent communication of intelligent building systems is realized using CAN communication cards, and the system is improved. The internal communication rate and real-time performance reduce the error transmission rate. In addition, the CAN node can access the communication card at any time. As long as the central controller software is slightly adjusted, the hardware and other software can be used without modification, and the good scalability is particularly suitable for residential districts that are still being developed. This system has been made into a finished product that has proven to be highly reliable and easy to expand in actual use.
RF is any frequency within the electromagnetic spectrum associated with the propagation of radio waves. When RF current is supplied to the antenna, an electromagnetic field is created, which is then able to propagate or propagate through space. Many wireless technologies are based on radio frequency field propagation. These frequencies form part of the electromagnetic radiation spectrum.
RF coaxial cables are cables that transmit electromagnetic energy in the radio frequency range. Radio frequency cables are indispensable components in various radio communication systems and electronic equipment. They are widely used in wireless communication and broadcasting, television, radar, navigation, computers and instruments.
RF coaxial cable is the most commonly used construction type. Because the inner and outer conductors are in concentric positions, the electromagnetic energy is limited to propagate in the medium between the inner and outer conductors, so it has significant advantages such as small attenuation, high shielding performance, wide operating frequency bandwidth and stable performance. Typically used to transmit radio frequency energy from 500 kHz to 18 GHz. At present, there are two types of commonly used RF coaxial cables: 50Ω and 75Ω RF coaxial cables. The characteristic impedance of 75Ω RF coaxial cable is often used in CATV network, so it is called CATV cable, and the transmission bandwidth can reach 1GHz. At present, the transmission bandwidth of commonly used CATV cable is 750MHz.
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