Circuit Design of Anti-lost Personal Positioning System Based on GPS/GSM Technology

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Development of anti-lost personal positioning system using GPS/GSM technology. The system is used to search for and protect lost children or elderly people with intellectual disabilities. The system uses GPS positioning technology to obtain the position of the protected person, determine whether it is out of the safe area, and send its location information to the user through the GSM network. The user can set the working status of the system through the GSM network. The internal control of the system is completed by the single-chip microcomputer, which receives GPS data and commands from the user, and gives corresponding processing after analysis. The positioning accuracy of the system is within 10 meters, and the user can be notified of the position of the protected person in time.

Personal positioning system hardware

The personal positioning system is mainly composed of four parts, namely GSM module, GPS receiver module, single chip control circuit and power supply circuit. The GPS module is responsible for receiving the positioning data; the GSM module sends and receives short messages under the control of the single chip microcomputer; the single chip control circuit analyzes the GPS positioning data and makes corresponding processing according to the user's settings. The power circuit is generated by the 7805 and LM294lCS as +5V and +4.2v DC voltages, respectively. The +5V DC voltage is used as the working power supply of the single-chip microcomputer and the GPS module, and the +4.2V DC voltage is supplied to the GSM module.

Single chip control circuit

The system uses the widely used AT89C52 microcontroller as the MCU. It has 8k bytes of Flash program memory and 1256 bytes of RAM inside. There is only one universal asynchronous serial port inside the microcontroller. In order to be able to communicate with GPS and GSM modules at the same time, the MCU needs two serial ports. Therefore, the system uses the serial port expansion chip GM8123 to simultaneously transmit and receive GPS data and GSM data. The interface circuit between the MCU and the GM8123 module is shown in Figure 2.

When the serial port expansion chip GM8123 is operating in multi-channel operation mode, the mode control pin MS=0. Multi-channel mode allows 3 sub-ports to work simultaneously at full duplex. In this working mode, the address lines STADD1 ～O of the chip are input ports, and the MCU controls the sub-serial port that wants to send data, and the address lines SRADD1 ～0 are output ports for returning the sub-serial port address of the received data to the MCU. Through the control of the chip, the single chip microcomputer can simultaneously communicate with the GPS module and the GSM module in full duplex.