Component State Current (in mA)
Processor active 8
sleep 0.01
Radio active 8
transmit 16
sleep 0.001
PIR active 0.292
sleep 0.001
Acoustic active 0.575
sleep 0.001
Magnetometer active 6.48
sleep 0.001
One LED active 2.2
sleep 0.001
Flash Read 6.2
Write 18.4
Sleep 0.002
Buzzer active 15
sleep 0.001
4. One-Time Control Operations: There were several one-time activities
performed in the ExScal application. The major ones among them were
wireless reprogramming and localization. These operations required the
sensor nodes to be active for a long duration (on the order of tens of
minutes), send a large number of messages (in reprogramming), and perform
actuation activities (e.g., sounding buzzers). All of these consume
significant energy.
5. Frequency of Events: Every event requires the sensors near the event
to not only stay awake for a few seconds to detect the event but also to
transmit messages in a multi-hop sensor network, and potentially route
other XSM??™s messages. Staying awake with the processor and all the sensors
active consumes significant energy and the total energy consumed
this way depends on the frequency of the events.
Each of the above factors dictate which fine-grained power management
schemes can be used in ExScal and which ones are not usable. For example,
LPL can be used in ExScal but the periodic sleeping time of the radio should
be low enough (less than 400 ms) to satisfy the two second event notification
latency.
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