Fig 1. General hardware structure of the PLB system
The ultra-low-power standby circuit is used to control the system power up or down. When the system in the state of ultra-low power standby, once the system touches the water or launch button pressed, the system power up. When the system is in the state of working, once the cancel button pressed, the system returns to ultra-low power standby. The battery is used to power the system. The DC-DC converter is used to convert the battery voltage to the system’s operating voltage. The RDSS module and RDSS antenna are used to realize transmitting distress information to the Beidou satellite and receiving information from the rescue center. The COSPAS-SARSAT transmitter and 406MHz antenna are used to transmit rescue information to COSPAS-SARSAT rescue center. Vital signs monitoring sensors are temperature sensors that monitor the ear temperature of persons in distress. LEDs are used to show the status of the transmitter, when the red light is on indicates that the system is working, when the green light flashes indicates that it is transmitting distress information, when the green light is on for a long time indicates that the information from the rescue centre is received. SD card module is used to store the information of people in distress. The cancel button controls the system to cancel the transmit. The GNSS receiver and the GNSS receiver antenna are for positioning; The STM32 controller is used to control these modules.
Its logical sequence proposed is as flows. First, when the PLB is in standby mode, the battery only provides power to the ultra-low-power circuit. Second, when the person is in marine accident that falls into the sea or presses the manual start switch, the reset circuit will generate a reset signal. Then the switch circuit controlled by the reset signal, the switch circuit will be opened which result in the battery voltage is allowed to supply to the system. And then, the STM32F413 controller is powered on and control to output a high voltage to remain the switch circuit opens, and the battery continues to supply to the system. At this moment, the STM32F413 controller controls the GNSS receiver receive the location information, the SD card store the location information, the LEDs flash, the life detect sensor collect the human life information, the BeiDou transmitter and COSPAS-SARSAT transmitter transmit the SOS information to the BeiDou Rescue centre or the global search and rescue organization through the medium of electromagnetic waves. When the BeiDou Rescue centre or the global search and rescue organization received the SOS information , it feeds back the PLB a feedback information through the BeiDou receiver. When the BeiDou receiver of the PLB receives the feedback electromagnetic wave signal, it decodes it, converts it into feedback information, and transmits it to the STM32 controller through the serial port, then stop sending SOS message to rescue centre and the BeiDou receiver will still works. When the receiver receives the message for asking for location, it will send the location information to the related organizations. Last, when the cancel button is pressed, the STM32 controller controls the switch circuit disconnected and the system will powered off.
In our system, the power consumption mainly comes from the COSPAS transmitter, the BeiDou transmitter and Beidou receiver. We can let the receiver work to realize the interaction with the rescue center. When it is determined that the rescue centre received the distress signal to stop transmitting distress information to save power, thus extending the working time of the PLB.
The program flowchart for our PL is shown in Fig2.