This design mainly implements the two key technical links of the intelligent terminal of the electronic patrol system (Figure 1): GPS information acquisition and wireless interactive transmission of space position information and command of the main station.
system design
In the past, security inspections did not have much equipment. Each person had a walkie-talkie and a baton. With the advent of GPS, it becomes possible for the base station, the central station, to grasp the geographic location information of each security guard. That is, each security guard is equipped with a set of GPS positioning equipment, and a set of wireless transceiver equipment that sends its position information to the main station. Because it is costly to re-equip each security guard with a set of equipment, and it is not realistic to eliminate the existing intercom, so using the intercom as an existing channel carrier will do two things. It is convenient and practical to build an unprecedented security system.
Figure 1 Application of electronic inspection system
The combination of the motherboard and various functional modules constitutes a mobile intelligent terminal. It includes MCU namely single chip AT89S52, GPS receiving module, analog modulation and demodulation chip MSM6882, liquid crystal display module LCD1602, speech synthesis chip XF1M01, see Figure 2.
The mobile intelligent terminal completes the forward GPS data collection, processing and transmission, and reversely receives, recognizes and executes the command of the main station.
The GPS module outputs GPS information once per second, and the MCU collects it, and displays its own latitude, longitude, time and date on the display module. Then load the data to the intercom through the modem chip and then wirelessly transmit it to the main station to complete the forward task.
Figure 2 Smart terminal structure
Then there will be about half a second of time waiting for the command of the main station. If the command of the main station is received, the command type is judged according to the data frame, the corresponding data is extracted, and the corresponding display operation and voice prompt operation are performed after the MCU processing to complete the reverse To task.
When the terminal receives the target command information and executes the processing, the preamble is changed when it is retransmitted back to the main station to indicate that the command is received successfully, so that the main station makes corresponding processing. For example, the preamble can be changed from "start" to "start1".
Compared with the previous portable devices with single functions and lack of user-friendly interface, this GPS data collection, processing, and transmission integrated intelligent terminal has expanded functions. First of all, each security guard can see his latitude, longitude, time and date on the LCD screen, giving the security guard an intuitive and clear sense of geographic location. In addition, you can receive the command information from the main station in real time, and after processing by the MCU, compare the latitude and longitude of the place where the main station dispatches to the LCD screen and compare it with your own position to realize the transparency of the information. Another improvement is the intelligent voice prompt and the calculation of the angle offset. By receiving the latitude and longitude of the target dispatch location sent by the main station and comparing it with its own position, it clearly and clearly indicates how far the security guard should go. The system terminal adopts 51 series single chip microcomputer as MCU. Use the modem chip to load the signal to the intercom to achieve wireless transmission instead of an independent wireless communication module. The LCD screen selects the simple and easy-to-use LCD1602. The solution greatly reduces costs and is stable and reliable.
The system must formulate a reasonable flow (Figure 3) in order to give full play to the MCU's functions of data acquisition, processing and transmission.
In order to make the system work as stable as possible, as many functions as possible (both upstream and downstream have their own processing execution time), and data update as fast as possible (GPS data one frame per second, the system processing is not enough can be changed to two seconds Frame), the system must formulate a reasonable timing in order to allocate time uniformly.
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