Public street lights are an important part of urban public utilities. Most of the traditional street lamp control systems use timers or photoelectric control devices to realize the switch control of street lamps. It is difficult to make timely adjustments according to actual conditions and needs. Inspection and maintenance are generally done manually, which is time-consuming and labor-intensive. Therefore, in order to change this backward street lamp management method and improve the city's modernization level, a practical solution is proposed. One uses GSM short message to realize remote monitoring of street lamps.
A system that is relatively mature, perfect, and widely used in the system is the main method of public mobile communication, providing a full range of services such as voice, SMS, and data. The Short Message Service (SMS) is a value service for transmitting user group information through the control channel of the GSM network. The short message service center performs the storage and forwarding functions, and each short message has a maximum of 140 bytes.
The technical solutions introduced in this paper are based on the reliable and economical delivery of SMS. At the same time, because Siemens, Motorola and other companies in the United States produce GSM industrial communication modules, these communication modules have all the functions of GSM wireless communication and provide standards. The UART serial interface, which supports the AT command set defined by GSM 07.05, provides great convenience for developing a GSM-based data communication system.
2 system structure Now the remote control system communication scheme generally adopts two major categories: wired and wireless. Wired type generally adopts data line, such as CAN bus. Such schemes generally need to lay special lines, which have large engineering volume, relatively large investment, and are easily interfered by urban construction. At the same time, the system has poor scalability, and the line aging needs to be updated to cause duplication. investment. The wireless type generally uses a digital radio station and a GSM/CDMA communication network. When using digital radio stations, not only do you need to apply for frequency and set up outdoor antennas or towers, but also the price of digital radio stations is high. The network of digital radio stations also needs regular maintenance. Therefore, if digital radio stations are used, once the number of monitored stations is higher, For a long time, the system cost will be high; and the GSM short message scheme makes full use of the existing GSM network in China. The GSM network has large coverage, fast transmission and reception speed, good anti-interference, high reliability, low SMS cost, and is especially suitable for information. Not large, for data services that require less real-time transmission. Therefore, the GSM short message scheme is very suitable for real-time telemetry remote control of urban street lamps, and the system construction cost is low.
The remote streetlight monitoring system based on GSM short message consists of a central monitoring unit and multiple field monitoring subsystems (RTUs). The system framework is shown as shown. In order to ensure the continuous and reliable operation of the system, the central monitoring unit is mainly composed of multiple industrial computers with parallel redundant structure and GSM communication modules. Through the SMS interaction with the RTU, on the one hand, it receives the information uploaded by each site RTU and Data, and put them into the local database, regular data backup to the remote database. On the other hand, the completion of the monitoring center issues control commands to the various on-site monitoring subsystems to achieve remote monitoring and control of the street lights. The on-site monitoring subsystem collects various parameters of the street lamp trunk in real time, and uploads data by SMS through the GSM network. If an abnormal situation occurs, the SMS alarm information is immediately sent to the monitoring center, and the corresponding site protection action is completed.
GSM wireless communication control terminal hardware design The field monitoring subsystem wireless communication part is mainly composed of Megal6 single-chip microcomputer and BENQM20 module. Mega16 is a high-performance low-power RISC chip produced by Atmel, which integrates 1KB of RAM and 2512B. Data E2PROM, 16KB Flash program memory, 8-channel 10-bit ADC and one USART serial interface, 32 I/O ports. Thanks to the powerful MCU, a large number of peripheral devices are saved, which greatly simplifies the hardware structure and improves the reliability of the system. In addition, the chip has a JTAG interface, which is especially suitable for on-site debugging and upgrading of software.
Provide 30-pin SMD function interface and peripheral device connection, high integration, small size, conducive to stable and reliable operation of the system under complex conditions, suitable for vehicle GPS, remote monitoring, low-voltage meter reading, wireless Internet access, wireless POS logistics control .
Since the M20 uses a logic signal level of 276V and the interface level of the Mega16 is 5V, level conversion is required between the two. The interface level conversion circuit designed in this paper is as shown. The M20's 6 pin is the M20 power enable pin (active low). The 14 pin is the M20RS232TXD pin and the 13 pin is the M20RS232RXD pin. Considering that the frequent reading and writing of the SIM card affects the life of the SIM card, the AT command is used to make the M20 receive the short message and directly output the data from the M20 serial port to the MCU, instead of saving it in the SIM card, so the M20 of the M16 is controlled by the PA0 of the Mega16. Foot (RS232CTS) When Mega16 is processing SMS, PA0 outputs a high level. During this period, even if M20 receives a new SMS, it will be temporarily stored in the cache. After waiting for Mega16 to process the previous SMS, PA0 outputs low level. Re-set the M20's 18 feet to ensure that the SMS data will not be lost.
The software design of the 4GSM wireless communication control terminal part of Shenshi uses the AT command to communicate between Megal6 and M20, and completes the sending and receiving of short messages. The communication protocol between M20 and Mega16 uses the default setting of M20: 9600b/s1 bit start bit, 8 data bits, no parity bit, 1 stop bit. Due to the large number of AT commands, Table 1 lists only the common commands related to the SMS function in the design.
For the control of short messages, there are three modes: Block mode, PDU mode based on AT command and TEXT mode. In the current application, the PDU mode has gradually replaced the Block mode. All domestic telecommunication offices support PDU mode short messages, so the PDU mode has wide applicability, while the TEXT mode can only send ASC code information, and cannot send hexadecimal data. Information, so PDU mode SMS is used for data transmission.
Table 1 Instruction Function Description Setting SMS Center Number Read Short Message Send Short Message Display New Received Short Message In general, the M20 received SMS message is saved in the SIM card. The MCU uses AT+CMGR and AT+CMGL two commands. Complete the function of the MCU to accept SMS data. Since the number of reading and writing of the SIM card is limited, the M20 receives the short message directly from the serial port, and does not save it in the SIM card, and does not need to use the above two instructions. The software initialization process between Mega16 and M20 is as shown.
The following example shows how to send the collected data packet 457A) and the on-site temperature (T=23*C) to the monitoring center in PDU mode. The operation process is as follows: Check if the M20 is working properly. Set the SMS format to be sent in PDU mode. PDU format SMS contains 28 bytes of PDU format. Note: 001100 SMS control bit (hexadecimal) indicates that the target number is 13 digits, 81 indicates the format of the target number, and the actual destination number before the encoding is 8613386804051, encoding method. : Every two digits are negated, odd digits complement F. (protocol identification) (indicating that the short message type is 8-bit encoding) A7: VP value (sms aging 24 hours) 0D: short message length (3 bytes) three-phase voltage, The six current values ​​and the temperature value (hexadecimal) voltage and current are processed in two bytes, and the temperature is one byte.
If the data of the valid content of the short message is hexadecimal, no encoding is needed, and it can be sent directly; if the letter is sent, it needs to be ASC encoded, and the 7-bit ASC code sequence is compressed into 8 bits. Because various types of monitoring information are encoded in the communication protocol, only the hexadecimal data type is used, which is relatively easy to handle. For the analysis of the received PDU format short message, it can be related to the content because it is not described in the space.
5 Test results We conducted a long-term on-site simulation test on the designed system. The system operation is stable and reliable, and fully meets the requirements of remote monitoring of street lamps. It is the three-phase voltage and current data of the main road of the street lamp displayed by the monitoring center computer.
6 Conclusion The combination of measurement and control and modern communication technology has changed the status quo of street lighting management.
Data acquisition, recording and fault alarms are automatically completed, which greatly improves the efficiency of street lamp management.
The field monitoring subsystem can be expanded as needed without being limited by number.
It is cheap and easy to expand and use on a large scale.
Line communication can be smoothly upgraded to GPRS by SMS for more economical and reliable service.
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