GPS (Global Positioning System) is the abbreviation for Global Satellite Positioning System. The GPS system is mainly divided into three parts: satellites, which provide positioning information in the sky; Control system to maintain the normal operation of satellites on the ground and ensure their health status; Receiver, a part commonly used by users. The positioning principle is to divide the Earth into 12 horizontal sections, each with two positioning satellites at a 180 degree angle. Therefore, standing at any point on the Earth, there are always twelve positioning satellites above your head. The distance, coordinates, and angles between satellites are known, and the distance between satellites and humans is measurable. According to geometric principles, the receiver usually only needs to receive information from three satellites to determine your two-dimensional coordinates, namely longitude and latitude. After receiving information from four satellites, the altitude can be further determined.

GPRS is the abbreviation for General Packet Radio System, and TC-205-02-8M5 is a technology between the second and third generations, commonly referred to as 2.5G, currently implemented through upgrading the GSM network. It is more appropriate to call it 2.5G because it is a hybrid that uses TDMA to transmit voice and grouping to transmit data.

GIS (Geographic Information System) originated in the early 1960s. It is a computer technology system based on geospatial databases and uses geographic model analysis methods to provide various spatial and dynamic geographic information, serving geographic research and decision-making.

The design of the vehicle monitoring system integrates GPS satellite navigation global positioning technology, GIS geographic information technology, computer network technology, and GPRS/GSM mobile communication technology. The vehicle monitoring system mainly consists of three parts: vehicle positioning, information dissemination, and communication. The vehicle positioning part is a terminal device installed on the controlled vehicle, which can determine the precise position of the user at a precise time on a global scale 24/7 and in real time through the global satellite positioning system GPS; Information release section: Geographic Information System (GIS) is a computer-aided decision-making information system established to obtain, store, retrieve, analyze, and display spatial positioning data; Communication part: GPRS general packet wireless service is a new carrier service developed on the existing GSM system, aiming to provide GSM users with packet data services.

Design of Vehicle Monitoring System

1.1 Overall design

The overall structure of the vehicle monitoring system is shown in Figure 1, which mainly includes a monitoring center and an onboard terminal. The two communicate with each other through GPRS wireless network and Internet interconnection network.

 

Vehicle monitoring system workflow: The onboard terminal collects GPS data and related information, TC-205-02-8M5 sends data to the monitoring center through GPRS, and the monitoring center processes the received GPS data and related information. Customers query vehicle information through the website; The monitoring center can issue corresponding control commands for each vehicle according to user requirements.

1.2 Design of Vehicle Monitoring System GPS

1.2.1 Module selection

Using M12 positioning module, M12 is a navigation device produced by Motorola, with extremely low power consumption, supporting RTCM (Radio Technical Commission for Maritime) format differential function, and the ability to reverse differential. It is output in NAEA0183 format.

M12 receivers are widely used in automotive positioning and scheduling systems.

1.2.2 Software Design

The M12 module can only transmit 54 bytes of data, which includes the latitude and longitude, speed, height, etc. of the target vehicle. Considering transmission costs and actual needs, only 8 bytes of latitude and longitude information can be taken.

Of course, in the microcomputer terminal of the control center, necessary processing must be performed on the received latitude and longitude in order to display it in the output device.

When receiving GPS data, in order to distinguish between GPRS data, relevant flag bits are set to prevent the reception of GPRS data. For the data collected by GPS, it is received first and then judged whether it is legal. This is different from GPRS (GPRS judges first and then receives different), which greatly increases the utilization rate of the PIC16F877 microcontroller through time-sharing operation.

Because the system uses the PIC16F877 microcontroller, due to its own reasons, we used assembly language to convert AT instructions into corresponding programs and write them into it. The main advantage is that it overcomes the small capacity of the PIC16F877 microcontroller and also leverages its characteristics of simple, convenient system instructions and high usage efficiency. Due to the length of the program, some codes are listed as follows:

 

1.3 Design of Vehicle Monitoring System GPRS

1.3.1 Module selection and design

Adopting the G20 module, G20 is a GPRS/GSM wireless communication module launched by Motorola, with built-in TCP/IP protocol stack, small size, fast communication speed, and equipped with comprehensive AT instructions. It is worth noting that in voltage conversion, it is necessary to convert the voltage received by PIC from 0-5V to a voltage that can be received by 0-3.6VG20.

1.3.2 Software design

Due to the fact that the G20 module comes with most AT instructions, it can facilitate the design of the software part. In the AT instructions, the latest AT+MIPCONF instructions provided by the G20 module are utilized to control the information sent back within a specified time, making it convenient to determine the online status of the network. The specific AT instruction process is shown in Figure 2.