Specifications

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here. All modules depicted in fig. 3.1 directly tie to the controller and were specifically
selected to satisfy the requirements listed in section 3.1. Specifics on the elaboration of the
requirement on a module-to-module basis will be show n in sections 3.2.1 - 3.2.1.
3.2.1 Power Supply Module
The purpose of the Power Supply Module is to interface w ith external power and
reliably provide power to the rest of the platform’s subsystems. It must satisfy requirement
1, 2, 3, and 8. To do this, the module must accept a 3.0-6.0VDC at 600mA battery input,
an auxiliary power input required to tolerate up to 15VDC at 600mA, and a 3.3VDC backup
battery input. The output requirements consist of: controller logic power with 3.3-3.6VDC
at 300mA, SDI-12 communications power with 5.0VDC at 20mA, and 6.0, 9.0, 12.0, and
15.0VDC at 500mA sensor power. This module must supp ort unbroken power to a real-
time clock (RTC) for at least five years. The module must switch between its th ree inputs
seamlessly and be able to detect power failures. The entire power supply must consume less
than 20µA when in sleep mode and 0µA in backup power mode.
3.2.2 Controller Module
The Controller Module is the most complex of all the hardware m odules in the device.
For large embedded systems, this module could consist of 10,000 processors. However, to
balance the cost vs. performance r equ irements for the DataManager, the size and scope of
the controller subsystem must be limited to a single microcontroller unit (MCU) solution.
An MCU contains a processor core or CPU and a wide variety of peripherals like battery
supervisory circuits, timers, RAM and ROM m emory, and I/O ports.
After some considerable analysis, the designers concluded with the following subset of
the general requirements. This module must support:
1. A RTC that uses less than 5µA. Th is feature must interface directly with the power
module’s backup battery. 5µA will sustain the RTC for longer then five years without
power.