EE43/100 Fall 2005 R. M. White1EE 43/100 Smart Dust Lab: Theory1. ObjectivesThe purpose of this experiment is to introduce you to a new sophisticated wireless sensorsystem that can be used to make a wide variety of measurements. Along the way, you’llalso experiment with individual sensors of temperature and illumination like those on thewireless “motes” -- so-called because they are only about an inch across now and canultimately be made much smaller. The wireless sensor system that we’ll explore, whichcommunicates via high-frequency radio waves, was named Smart Dust by its inventor,Kris Pister, a Berkeley EECS prof.2. Introducing Smart DustA Smart Dust mote is an electronic package composed of: an integrated-circuit radiotransmitter and receiver (the combination is called a “transceiver”); a microcontroller thatcontrols the operation of the mote; a random-access memory (RAM) like the one(s) inyour computer; a “flash” memory like the one that stores pictures in a digital camera;some standard sensors – a resistive temperature sensor and a semiconductor illumination(light) sensor that produces a current when it is illuminated; an analog-to-digitalconverter (ADC) that converts the analog temperature and illumination sensor outputs todigital form for transmission elsewhere; a power source for the mote (typically a battery);and an antenna used both for transmitting and receiving signals.The motes we’ll use – called “Mica2dot” motes (don’t ask) – also have three light-emitting diodes (LEDs) on them. The red LED indicates when the mote is turned on; theyellow and green LEDs flash when mote-to-mote communication is occurring. TheExperiment Guide describes this more fully.A computer software operating system – TinyOS – was developed in Berkeley’sComputer Science Division to control mote operation. When wireless motes are firstdispersed in an area – a room, a hallway, a building, or in a meadow – they autonomouslyattempt to set up a network along which they can send information from one mote toanother. Somewhere, one mote is plugged into a special printed circuit board (PCB) thatis connected to the serial port of a computer, such as a laptop. This board is known as a“base station”; its function is to collect the data provided to it by the assembly of motes.The topology of a typical Smart Dust mote network is shown in Fig. 1 below.Fig. 2 shows a magnified view of one of the Smart Dust wireless sensor motes. Severalof its components are identified; beneath the printed circuit board that you see is anintegrated circuit like those used in portable telephones to drive an antenna connected tothe mote for transmitting the mote identification and measured sensor data to the basestation. These motes are made commercially by the Xbow Company (“cross-bow”),which you can reach at www.xbow.com .EE43/100 Fall 2005 R. M. White2Fig. 1. Topology of a typical Smart Dust mote network.EE43/100 Fall 2005 R. M. White3Fig. 2. Magnified view of the Smart Dust mote. The wireless telephone chip is beneaththis printed circuit board. The mote connects to a short antenna for transmitting andreceiving radio waves.MICA2DOTWireless MoteDigital TemperatureSensorDigital LightSensor3.6 Volt LithiumBatteryON-OFF SwitchGeneral PurposeLEDsProgrammingConnectorEE43/100 Fall 2005 R. M. White4Each mote in the network has a unique identifier that it uses to preface each of itstransmissions. Every mote transmits any sensor data that it has taken, along withinformation from other motes sent to it for passing along to the base station. If the propersoftware has been installed in the base station’s computer, the network topology can bedisplayed on the base station’s monitor. One should thus be able to observe when motesare added to the network, or when they leave it. The sensor data taken by each motecould also be displayed, processed and stored by that computer.3. UsesThe possible uses are limited only by the available sensors and by the range that thesemotes can achieve – tens to hundreds of meters with radio communication, up to miles incertain circumstances when the motes are outfitted for optical communication usinglasers.The long list of sensed quantities that have been demonstrated includes: temperature,illumination, relative humidity, toxic gases, magnetic field, sound, acceleration, androtation rate. As examples of some of their uses, motes bearing on-board accelerometersare being installed on the Golden Gate bridge to measure the accelerations produced bywind and traffic, and burrowing birds on an Eastern seaboard island are being monitoredunobtrusively in their nests by motes that measure temperature and illumination, whichare surrogate indications of burrow occupancy and activity.A key feature of the motes is their low cost. The motes that you will use costapproximately $100 each in a quantity order of a few hundreds, and it is predicted thatwithin a year or so the price might be as low as a few dollars. An important practicalrequirement is that the power required by any mote be kept low to prolong battery life;this means that the mote radios must be efficient, and that any sensors used must requirevery little power. Present motes require 10-20 mW for radio transmission and reception,and a number of sensors are available that are either passive (require no power source, anexample being a photodiode for measuring illumination) or have low powerrequirements.3. ReferencesHere are two web sites you can check out: robotics.eecs.berkeley.edu/~pister/SmartDust/ http://webs.cs.Berkeley.edu/tos/EE43/100 Fall 2005 R. M. White5EE 43 Smart Dust Lab: Experiment GuideSmart Dust MotesThe motes that you’ll use are contained in translucent plastic boxes that measure 1.5 x 2.5x 0.6 cubic inches. There is an insulated antenna (inside the plastic tubing – a sodastraw) attached to the box. You can turn on a mote by moving the black slide switch(visible through a hole in the box) with a small key or a pencil point; move the switchhandle in the direction of the attachment point of the antenna to turn it on. Be sure toturn the motes off when you’re finished with them to prevent battery drain.Each pair of students will have available two motes in which stored TinyOS programsenable them to transmit and receive signals from similar motes, but be immune totransmissions from other motes. The boxes are marked S (send) or R (receive) to
View Full Document
Unlocking...