Wireless sensor networks

Wouldn't you like to not have wires between your controller and your sensors/actuators?

Wouldn't you like to program your installations without a serial/USB cable?

• at the Tekniska Museet we had an installation in the ceiling, we needed a crane every time we get there, plus we can't be alone (we can't operate the crane)

Issues

Power consumption

• Since you want no communication wires, you usually don't want power wires either
• In wire-full installations you usually transmit often, here it is preferred to transmit as little as possible to conserve power
• Gathering more data before a transmission, maybe transmit just an average or another type of aggregation
• Therefore a wireless sensor ("sensor node" in WSN parlance) is typically not just a sensor + radio, it also has some processing
• Typically nodes are autonomous

Communication

• Simplex/Duplex
• Unicast/Broadcast

Routing, Networking

• Some wireless sensors only transmit to a base station
• Others are also capable to receive, and transmit further (relay)
• Routing: information might travel from point A to point B indirectly, over a route
• Networking: at this level, the route between A and B is invisible, the programmer just knows that there will be a A-B connection and the system takes care of the rest
  • cluster, cluster head
• So even more processing power is needed on the nodes
• Sink= the final recipient of a message (the end of the route)

Reconfigurability

• the sensor node is a complex beast, so you need to rearrange its capabilities
• OTAP= over the air programming

The SunSPOT

• Can be regarded as a high-level implementation of WSN
• Follows the Java Micro Edition standard (CLDC and MIDP)
• "Java on the metal"
• Besides forming a wireless sensor network with OTAP, they are also multithreaded like any Java program

Installation

• follow the very nice booklet that comes in the kit. Look also at the safety info!
• a SPOT will only work with the API version installed on it because the SPOT firmware depends on the API!
• Installing from the net will give you recent API versions, which may mean that you need to upgrade the SPOTs.
• NB: mark the version of the installed API on the SPOT kit!
• The installer is a Java app, so you have to make sure Java is correctly installed (JAVA_HOME, PATH)
• Installing the SPOT SDK also offers you to install NetBeans
• After, the ant build tool is installed. Ant is crucial to operate the SPOTs (ANT_HOME, PATH)
• being a USB device, the SPOT needs a USB driver
• other arrangements need to be made sometimes to ensure good serial communication over the USB (rx-tx)
• on Mac OSX Leopard and up to 10.7, these precautions were needed. They may be needed still.
  • instead of sudo niutil... (as mentioned in the installation booklet) you have to run
    • sudo dscl . -append /Groups/uucp GroupMembership username
  • you might also need to download a fixed spotfinder , put it in the Sunspot installation home, in sdk/bin

The documentation in sdk/doc/*.pdf (links below are to the Orange = 2.0 version) or online

• owner's manual: nice quick overview of hardware and software
• theory of operation: detailed documentation,
  • electric limitations (currents, battery life)
  • states: run, idle, deep sleep
    • deep sleep entered automatically when all threads are sleeping, lots of power can be saved!
  • overall architecture
• developer guide (see below)
• if you installed NetBeans, a tab "SunSPOTs info" opens at startup, with useful links to Demos and other interesting possibilities
• emulator use (from 3.0 up)

Architecture

• The main board has an ARM processor
• The eDemo board has at Atmega88 microcontroller

Now connect to the SPOT

• Demos directory contains a number of applications, change dir to one of them in a command terminal
  • e.g. Demos/BounceDemo/BounceDemo-OnSPOT
  • the example actually comes pre-programmed on SPOTs
• ant info should connect to the SPOT and tell you its current parameters
  • notably the device IEEE MAC address which looks like 0014.4F01.0000.XXXX. The last 4 hexadecimal digits are written on the back of each SPOT
  • you need the address every time you want to connect (from a program) to the SPOT or program it over the air (OTAP)
• ant deploy will compile the program from the curent folder and send it to the SPOT connected on the USB
• Sometimes the deployment is not successful and that makes the spot behave strangely, reset itself continously, etc
• to fix that, execute ant resetlibrary
• ant run will run the current program on the SPOT
• the two commands above are also available in NetBeans in the project context-sensitive menu
• in ant you can combine more commands (ant deploy run)
• ant upgrade updates the firmware or the little operating system on the SPOT
• to program Over The Air (or do any operation over the air) :
  • make sure the remote (known as "free range") SPOT
    • has the OTA command server started (i.e. is listening to OTA programming commands). You can see that with ant info, if it is not enabled, run ant enableota
    • is well charged.
  • connect a "base station" to the USB
    • you can turn any SPOT into a basestation using ant selectbasestation disableota, then reset it
  • ant -DremoteId=0014.4F01.0000.XXXX deploy run will connect to the designated SPOT and peform the operation (in this case deploy, then run)
• USB programming typically needs reset, OTA typically does not, which is great

We look at some demos

• The famous Bounce
  • plus the Desktop version
  • to run a Desktop version use ant host-run with a base-station connected to USB
• The telemetry demo (accelerometer)
  • start on a SPOT first, then run the desktop version, with a base-station connected to USB

To make our own project

• start from a copy of an existing one
• modify resources/META-INF/manifest.mf
  • change project name
  • change main class name
• If you work with NetBeans, change also nbproject/project.xml
• Here is an example project, working with the Red API

Debugging

• System.out.print just like in usual Java
  • It will show up in the output of ant run
• standard java debugging also available, through OTA
  • any java debugger can connect, then do breakpoints, etc
  • see owner's manual

The source for our examples is here. Put it in src/se/kth/csc/Lecture.java

EDemoBoard (the link to the official API is for the 2.0= Orange version)

• example program illustrates all aspects below, mostly one per thread
• simply un-comment threads (in the run() method) to see how they work
• Tricolor led control
  • ITriColorLED leds[] = EDemoBoard.getInstance().getLEDs()
  • leds[0].setOn() also leds[0].setColor(LEDColor.BLUE)
  • in general you can use directly EDemoBoard methods, or retrieve I* objects (like ILed) and use their methods in turn
  • dimming the tricolor LEDs :
    • EDemoBoard.getInstance().setLEDColorIntensity(EDemoBoard.LED1, ITriColorLEDController.BLUE, 64);
    • value goes from 0 to 255 so 64 is "quarter-on"
• reading on-board sensors
  • ILightSensor lightSensor = EDemoBoard.getInstance().getLightSensor(); lightSensor.getValue()
  • ITemperatureInput tempSensor = EDemoBoard.getInstance().getADCTemperature(); tempSensor.getCelsius()
  • ISwitch sw1 = EDemoBoard.getInstance().getSwitches()[0]; sw1.isOpen()
• reading accelerometer
  • IAccelerometer3D accel = EDemoBoard.getInstance().getAccelerometer();
  • accel.getAccelX()
• I/O connector (top corresponds to the left of the SunSPOT), see theory of operation, search for "I/O connector"
• 
  • GND
  • VDD: stable 3V for low-current digital work
  • V+5V stable 5V
  • SW1, SW2: buttons
  • D0-D4: General Purpose Input/Output (GPIO)
  • H0-H3: high-voltage, high-current output
    • VH must be connected, conveniently placed near V+5V for simple applications but really intended for a separate source
  • A0-A3: Analog-Digital converters
• digital out
  • EDemoBoard.getInstance().setPinValue(EDemoBoard.H0, true);
• digital in
  • EDemoBoard.getInstance().getPinValue(EDemoBoard.D0)
• analog in
  • EDemoBoard.getInstance().getScalarValue(EDemoBoard.A0)
• analog out (PWM)
  • EDemoBoard.getInstance().setPWM(EDemoBoard.H0, 255);
• PWM input as well!
• interrupt instead of polling
  • issues with deep sleep
  • EDemoBoard.getInstance().enablePinChangeInterrupt(EDemoBoard.D0, true, true);
  • PinDescriptor[ ]pdr= EDemoBoard.getInstance().waitForPinChange();
  • since the device is muti-threaded, you can wait for different changes at the same time
• servo driving
• event-based programming
  • a more advanced approach than polling and interrrupts
  • available only since the Purple SDK version
  • each sensor has can attach many listeners, for example ILightSensor defines addILightSensorThresholdListener(ILightSensorThresholdListener who)
    • when the sensor value changes over or under a certain threshold, a method of the listener object is called
  • similar for digital inputs, see IInputPin , addIInputPinListener(IInputPinListener who)
    • when the digital input changes to high or to low, a listener method is called

Coming up next: communication

• wireless communication between SPOTs
• communication between SPOT and Internet via base station (including http)
• serial communication between SPOT and other device via pins D1 (send) and D0 (receive)

More in the developer guide

• ant commands (e.g. traceroute)
• mode detailed device class list (I* classes)
• accessing system properties
• accessing SPOT flash memory
• communication over USB, serial, radio

SpotManager application

• java -jar SPOTManager.jar (or SPOTManager Java Web Start application)
• manages SPOTs and software versions
• there you can e.g. upgrade from current SDK version to higher versions