GPS / GSM technology is used to develop an anti loss personal positioning system. The system is used to search and protect lost children or the mentally retarded elderly. The system uses GPS positioning technology to obtain the position of the protected person, judge whether he is out of the safe area, and send his position information to the user through GSM network. Users can set the working state of the system through GSM network. The internal control of the system is completed by single chip microcomputer. It receives GPS data and commands from users, and gives corresponding processing after analysis. The positioning accuracy of the system is within 10m, and the user can be informed 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 microcomputer control circuit and power supply circuit. GPS module is responsible for receiving positioning data; GSM module sends and receives short messages under the control of MCU; The single chip microcomputer control circuit analyzes the GPS positioning data and makes corresponding processing according to the user’s settings. The power supply circuit generates + 5V and + 4.2V DC voltage by 7805 and lm294lcs respectively+ 5V DC voltage is used as the working power supply of MCU and GPS module, and + 4.2V DC voltage is provided to GSM module.

  Single chip microcomputer control circuit

The widely used AT89C52 single chip microcomputer is selected as MCU. It has 8K bytes of flash program memory and 1256 bytes of ram. There is only one general asynchronous serial port in the MCU. In order to communicate with GPS and GSM modules at the same time, MCU needs two serial ports. Therefore, the system uses the serial port expansion chip gm8123 to transmit and receive GPS data and GSM data at the same time. The interface circuit between MCU and gm8123 module is shown in Figure 2.

  Circuit design of anti loss personal positioning system based on GPS / GSM Technology

When the serial port expansion chip gm8123 works in the multi-channel working mode, the mode control pin Ms = 0. The multi-channel mode allows three sub serial ports to work on both sites at the same time. In this working mode, the address line staddl ~ o of the chip is the input port, and the MCU controls and selects the sub serial port that wants to send data. The address line sraddl ~ 0 is the output port, which is used to return the sub serial port address of the received data to the MCU. By controlling the chip, the single chip microcomputer can communicate with GPS module and GSM module in full duplex at the same time.

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