The goal of the Smart Dust project is to build a
self-contained, millimeter-scale sensing and communication platform for
a massively distributed sensor network. This device will be
around the size of a grain of sand and will contain sensors,
computational ability, bi-directional wireless communications, and a
power supply, while being inexpensive enough to deploy by the
hundreds. The science and engineering goal of the project is to
build a complete, complex system in a tiny volume using state-of-the
art technologies (as opposed to futuristic technologies), which will
require evolutionary and revolutionary advances in integration,
miniaturization, and energy management. We forsee many
applications for this technology:
Brief description of the
operation of the mote:
The Smart Dust mote is run by a microcontroller that not only
determines the tasks performed by the mote, but controls power to the
various components of the system to conserve energy. Periodically the
microcontroller gets a reading from one of the sensors, which measure
one of a number of physical or chemical stimuli such as temperature,
ambient light, vibration, acceleration, or air pressure, processes the
data, and stores it in memory. It also occasionally turns on the
optical receiver to see if anyone is trying to communicate with it.
This communication may include new programs or messages from other
motes. In response to a message or upon its own initiative the
microcontroller will use the corner cube retroreflector or laser to
transmit sensor data or a message to a base station or another mote.
Longer description of the
operation of the mote:
The primary constraint in the design of the Smart Dust motes is
volume, which in turn puts a severe constraint on energy since we do
not have much room for batteries or large solar cells. Thus, the motes
must operate efficiently and conserve energy whenever possible. Most of
the time, the majority of the mote is powered off with only a clock and
a few timers running. When a timer expires, it powers up a part of the
mote to carry out a job, then powers off. A few of the timers control
the sensors that measure one of a number of physical or chemical
stimuli such as temperature, ambient light, vibration, acceleration, or
air pressure. When one of these timers expires, it powers up the
corresponding sensor, takes a sample, and converts it to a digital
word. If the data is interesting, it may either be stored directly in
the SRAM or the microcontroller is powered up to perform more complex
operations with it. When this task is complete, everything is again
powered down and the timer begins counting again.
Another timer controls the receiver. When that timer expires, the
receiver powers up and looks for an incoming packet. If it doesn't see
one after a certain length of time, it is powered down again. The mote
can receive several types of packets, including ones that are new
program code that is stored in the program memory. This allows the user
to change the behavior of the mote remotely. Packets may also include
messages from the base station or other motes. When one of these is
received, the microcontroller is powered up and used to interpret the
contents of the message. The message may tell the mote to do something
in particular, or it may be a message that is just being passed from
one mote to another on its way to a particular destination. In response
to a message or to another timer expiring, the microcontroller will
assemble a packet containing sensor data or a message and transmit it
using either the corner cube retroreflector or the laser diode,
depending on which it has. The corner cube retroreflector transmits
information just by moving a mirror and thus changing the reflection of
a laser beam from the base station. This technique is substantially
more energy efficient than actually generating some radiation. With the
laser diode and a set of beam scanning mirrors, we can transmit data in
any direction desired, allowing the mote to communicate with other
Smart Dust motes.
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