Specifications

500mA at 6VDC and 200mA at 15VDC. P-channel open-drain outputs must be used on all

switches.

3.2.7 Serial Communications Module

The general requirements state that the device must be conﬁgurable by PC or by

long distance data radios. The Serial Communications Mo dule must therefore support this

function. The common RS-232C speciﬁcation [34] is widely used today. To support this

protocol, a translator IC must be included to generate RS-232 voltage levels. Such an IC can

use a lot of power, so any chip selected to perform this operation must be power-wise and

support a micro power mode when no cable is connected. When there is a cable connected

to the device, a cable detect signal must be sent to the MCU. The device must support

standard baud rates between 9.6k and 115.2k baud.

3.2.8 ZigBee Communications Module

The ZigBee Communications Module is present to satisfy the requirement for an em-

bedded ZigBee Mesh radio. For this design, due to the imposed time limit and development

costs, it was determined that the pur chase of an existing ZigBee platform was appropriate.

This reinforces wireless interface-ability by starting the design with a working radio. This

module must communicate through a UART or SPI port. The module must be FCC ap-

proved and able to communicate up to a mile. It also needs to be power conscious, using

less then 30mA when receiving data. Finally, the module must support ﬁ rmware changes

enabling the swap ping of n etwork personalities.

3.2.9 External Flash Module

The purpose of this ﬂash module is to provide space for non-volatile memory storage

for logs and other critical ﬁles. This module must be able to store at least 40,000 data

points. This will allow a device with six sensors measuring at one hour intervals to measure

up to nine months. It also must have at least 250 Kbytes for other data. The actually IC

selected must communicate usin g SPI.