Design of vehicle navigation terminal based on microprocessor LPC2214 and GPS receiver

GPS has been developed in China for more than ten years, but it has always made major breakthroughs in the civilian field. In recent years, the prospect of GPS for civilian use has become increasingly clear, and user demand is rising. There are currently two applications that are promising: one is civilian navigation terminals, especially vehicle-mounted systems; the other is mobile positioning services based on mobile phones.

Navigation is the main way that LBS (Location Based Services) is applied to cars. At present, there are practical applications of car navigation in our country. One mode is "GPS receiver + simplified version of GIS engine + map data". Positioning information is obtained through the GPS receiver, and then the map stored in the machine is called to map the positioning information. To realize the navigation function on the electronic map. Although this mode is more convenient and fast, it also has its own limitations, such as higher cost, the inability to share map resources, and the inability to dynamically update the map. There is also a mode of "GPS receiver + GSM module + SMS service", which obtains positioning information through the GPS receiver, sends the positioning information to the control center in the form of SMS, and then dials the center phone number through the GSM module to obtain the positioning information by voice. Navigation information. This mode has lower cost and accurate information, but text messages generally have delays; experiments show that when the network delay is small, a 140-byte text message is transmitted in one direction, and the cumulative probability of a transmission delay of 6 seconds is 92.86 %, and calling to obtain navigation information is too slow and inconvenient. These problems can be better solved by combining with the operator's existing general packet radio service GPRS. GPRS allows users to send and receive data in end-to-end packet transfer mode without using network resources in circuit-switched mode, thus providing an efficient and low-cost wireless packet data service, especially suitable for intermittent and bursty situations. It is suitable for sexual and frequent, small-volume data transmission, and is also suitable for individual large-volume data transmission. Therefore, the vehicle-mounted terminal uses a high-performance processor and communicates with the information center through GPRS, which can fully realize remote map downloading and autonomous navigation.

This article introduces a low-cost vehicle navigation terminal based on ARM processor, supports GPRS, and gives a detailed description of the hardware design involved.

1 Introduction to LBS system model and vehicle navigation service terminal

1.1 LBS system model

The LBS system mainly consists of the global positioning system, mobile terminals, wireless communication networks and information service centers, as shown in Figure 1. In the picture, the GPS satellite provides positioning information, which is the key to the realization of the entire LBS system; the mobile terminal is mainly used to obtain location information, issue location service applications and interpret navigation information; the G3SM communication network is used to realize communication between the mobile terminal and the information service center; The information service center is the core of the positioning service system. It is responsible for information interaction with mobile terminals and network interconnection of various sub-centers. It completes the classification, recording and forwarding of various information and the flow of business information between sub-centers, and monitors the entire network. Monitor.

1.2 Terminal functions

This terminal is powered by vehicle power supply. After the power is turned on, each module starts automatically. The terminal has the following functions: GPS positioning function; real-time download of remote electronic maps; real-time display of positioning information and ground data; the main control chip can enter power-down mode to reduce power consumption, and pressing the corresponding function key can immediately wake up the main control chip.

1.3 Main modules of terminal

The GPS module uses TIM-LH from Swiss u-blox company. This GPS receiver can provide accurate navigation under dynamic conditions in areas with limited sky view, with a positioning accuracy radius of up to 2.5m; it has 2 full-duplex serial ports and supports NMEA, RBX and RTCM serial port protocols. The integration level is very high, the size is 25.4 mm×25.4mm, and the height is only 3mm.

The GPRS module uses Q2406A launched by French Wavecom company. The module supports two frequency bands: 900/1800MHz. The power of the frequency band is 2W (900MHz) and 1W (1800MHz) respectively. It supports WAP (Wireless Application Protocol), IrDA 1.2A protocol and GPRS; it has an AT data set interface and supports data, For voice, SMS, fax services, etc., the data download rate can reach 53.6 khps and the upload rate can reach 26.8 kbps.

This terminal uses an ARM microprocessor as the main control chip and combines it with GPRS to achieve real-time map downloading and rapid processing. LPC2214 is a 16/32-bit microprocessor based on the ARM7TIDMI (Thumb) core launched by Philips. The 128-bit memory interface and unique acceleration structure enable 32-bit codes to run at the maximum rate clock; its high-speed computing capabilities are map data Fast processing is guaranteed, and the cost performance is much higher than that of ordinary microcontrollers. LPC2214 has an 8/16/32-bit external memory interface, which can configure 4 external memories, each memory can reach 16 MB, providing conditions for large amounts of data storage and downloading of embedded operating systems; and the chip has power The control module can make the terminal enter power-down mode when navigation is not needed temporarily, which greatly reduces power consumption. In addition, the Jun chip has two serial ports, an embedded on-chip programmable phase-locked loop PLL, and the maximum operating frequency of the CPU can reach 60MHz.

2 Design and analysis of key hardware of vehicle navigation service terminal

The hardware structure of the vehicle navigation service terminal is shown in Figure 2. The serial port O of the LPC2214 is connected to the GSM/GPRS module, and the serial port l is connected to the GPS module. The liquid crystal display (LCD) is connected to the ARM chip in parallel and uses 8-bit data transmission; the keyboard uses matrix scanning and is controlled by 8 GPIO port lines.

After the terminal is powered on, log in to GPRS through software settings; after receiving the GPS data, the GPS module automatically sends it to the main control chip through serial port 1; after receiving the GPS data, the main control chip selects the required information and displays the positioning information on the LCD. When you need surrounding map information, press the corresponding function key, the main control chip scans the keyboard signal, transfers the positioning information to the GSM/GPRS module through serial port 0, and sends it to the information service center in the form of SMS, and downloads the surrounding map through GPRS. Data, the main control chip reads the map data through serial port 0, and displays it on the LCD after processing to achieve autonomous navigation.

2.1 Design and analysis of power circuit

The terminal system requires the power module to provide 3 voltages: 3.3V, 1.8V and 5V. Among them: the core power supply voltage of LPC2214 is 1.8V; the I/O port power supply voltage of LPC2214, the power supply voltage of TIM-LH and Q2406A is 3.3V; the power supply voltage of the LCD is 5V. This terminal is powered by a vehicle power supply, and the voltage is generally 12V or 14V. National's LM2576 series power supply chips are selected to obtain 5V and 3.3V voltages. The specific plan is: select LM2576-5. O obtains a voltage of 5V, LM2576-3.3 obtains a voltage of 3.3V, and then the voltage of 3.3V is the input voltage and a voltage of 1.8V is obtained through the power chip LMllll7-l.8.

2.2 GPS module peripheral circuit

After the GPS module TIM-LH is powered on, it sends GPS data to the outside through the serial port. The data formats include RMC (Recommended Minirnum SpecificGNSS Data), GGA (Global Positioning System Fix Data), etc. The data in the corresponding format can be programmed as needed. The default baud rate of serial port 1 of the TIM-LH chip is 9 600 bps, and the default baud rate of serial port 2 is 57 600 bps, which can be changed through software; if a certain serial port is not used, the corresponding serial port input terminal should be connected to a pull-up resistance.

The peripheral circuit schematic diagram of TIM-LH is shown in Figure 4. The external reset port REXET_N is active at low level and is very sensitive. If not used, leave it blank. Cannot connect to high level. The TIM-LH module automatically resets after powering on. Usually the reset signal is used when the module is not working properly. In the design, it is enough to use the control power supply to reset, so that the control will be more flexible and reliable; and the module There are very few crashes. If you want to restart, you can also use commands to control it through the program. When designing the PCB, copper should be applied around the GPS chip to shield it from external interference.

2.3 GSM/GPRS module and processor interface design and SIM card interface circuit

The GSM module communicates with the ARM chip through a standard serial port, and the maximum baud rate can reach 115 200 bps. The serial port output level of the processor LPC2214 is 3.3V, and level conversion needs to be performed in the middle. The MAX3232 of MAXIM Company is selected to achieve this. The serial communication between LPC2124 and GSM module adopts the simplest three-wire connection method, that is, the three ports of ground, sending data and receiving data are connected, and the receiving data and sending data ports should cross each other.