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Figure 4-6: The Sheevaplug is shown connected to the microcontroller system using USB interface for receiving the
data and transmitting it over the Internet, using Ethernet connection. Sheevaplug also performs the analysis of incoming
data and notifies the caregiver after detecting the fall.
4.2.1
Ground connection provision to Sheevaplug computer
The connection from the final microcontroller to the Sheevaplug begins with a
wire with an RS-232 connection (grounded) then a USB connection (ungrounded) to the
Sheevaplug. That is the Sheevaplug is not grounded to the microcontroller system and
produces invalid characters as a data (see Figure 4-9, Figure 4-10). While it was clear this
was a grounding problem, its resolution was not easily forthcoming.
Discussions with the manufacturer were helpful but not conclusive. We ended up
analyzing the Sheevaplug circuit and circuit board to find a suitable ground pin. Figure
4-7 shows the Sheevaplug circuit board with its identified ground pin and connected this
pin to the AC supply ground as shown in Figure 4-8.
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