A remote data acquisition system was developed to address the challenges of data transmission in remote naval areas. This system integrates GPS (Global Positioning System) and GIS (Geographic Information System) technologies, enabling intelligent and standardized data management. By leveraging these advanced tools, the system ensures accurate location tracking and efficient data handling, even in regions with limited connectivity.
The system is composed of two main components: data collection and transmission, as well as a centralized management system. The data acquisition unit includes key elements such as a watchdog circuit, data storage module, interface, and Modem (as illustrated in Figure 1).
Figure 1: Remote data acquisition system structure
Power-down protection plays a crucial role in ensuring system stability. In the event of an unexpected power loss or voltage drop, the system may become unstable, and even after power is restored, it might fail to operate correctly. To mitigate this risk, a power-down protection system is essential. This system typically consists of a low-power CMOS-RAM, a power supply circuit, and a control circuit. When the main power fails, the backup battery takes over, ensuring that the RAM remains powered and data integrity is maintained.
However, if the power supply cuts off before the RAM is properly protected, the microprocessor may attempt to read or write to the RAM while it's in a protected state, leading to potential system failure. To resolve this issue, a microprocessor monitoring circuit is used to synchronize the system reset with the power-down protection mechanism. This ensures that the memory is safeguarded during resets and can be accessed normally when the system is running. The MAX791 microprocessor monitor is employed for this purpose.
The MAX791 is a high-performance microprocessor power monitoring IC available in a 16-pin DIP package. It offers multiple functions, including microprocessor reset, battery backup, watchdog functionality, CMOS-RAM write protection, and power alarms. Its logic block diagram is shown in Figure 2. Key pins include VCC (power input), Vout (output), Vbatt (battery input), LOWLINE (low power output), SWT, WDI, WDO, and WDP (watchdog settings and outputs), as well as PFI and PFO (power failure input and output). When the power drops below 1.25V, PFO goes low, triggering an alarm signal.
Figure 2: MAX791 logic block diagram
Figure 3: Power-down protection circuit diagram
The power-down protection circuit implemented using the MAX791 ensures high reliability. The RST signal from the MAX791 is connected to the memory CE pin. When Vcc falls below the normal operating voltage, the RST output remains low, preventing the system from malfunctioning. A diode (IN4148) is used to switch between Vcc and the battery. Under normal conditions, Vcc charges the battery and powers the system. However, when Vcc is lost, the battery supplies power to the memory through the MAX791.
Additionally, the MAX791’s power alarm feature allows the system to capture critical data just before a power failure. As shown in Figure 2, when Vcc drops to 4.65V ± 150mV, the LOWLINE pin triggers a negative transition, sending an interrupt to the microcontroller. This short period (a few milliseconds) provides enough time to save breakpoints and real-time data in the interrupt service routine. After power is restored, the system can resume execution from the saved point.
In conclusion, compared to other circuits used for implementing watchdog functionality, the single-chip power-down protection system based on the MAX791 microprocessor monitor offers superior stability and speed. It significantly enhances the reliability of embedded systems and has demonstrated excellent performance in practical applications.
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