Specifications

7.3. HARDWARE DESIGN
Simple The operator should be presented with a clear, simple interface with
the minimum number of buttons and displays.
Easily understood Status indication should be intuitive, for example: a
descriptive error message is more useful than a flashing general error
light.
Power efficient In order to maximise battery life, it is important that the
status display not c onsume exces sive power.
Viewable in sunlight The device will be operating outdoors. Many displays
(for example, LEDs) are often difficult to read in sunlight. Such displays
will not be useful in this application.
Bearing these considerations in mind, a reflective LCD module was chosen
as the primary display. These units are very power-efficient (3mA peak
consumption), are visible in direct sunlight (reflective, rather than transmissive
type) and operate at standard 5V logic levels[18].
The Powertip PC10602 unit does not feature a back-light and is thus only
visible when the ambient light level is sufficient. This was done to save on the
power consumption and device cost. It is not considered a problem as it is
unlikely that an operator will need to read the display in low-light conditions.
This module is intelligent, featuring the industry standard Hitachi HD44780
interface.
All device settings can be adjusted remotely via SMS. The logger checks
for SMS setting updates before sending each email. A single button was
added to the device which forces the unit to upload all gathered data and
check for any setup commands immediately.
7.3.4 Power Supply
The system’s power supply is global – the GSM logger module shares its
power rails with the RFID module and any other connected peripherals.
This power supply w ill be co-located with the uplink module and the battery
charging code will be executed on the same microprocessor as the uplink
logger. Details of the power supply design can be found in Section 8.
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