Building a Wireless Mesh Network Temperature Sensor
- 1. Building a Wireless Mesh Networked Thermometer Michael Pigg June 3, 2010 This work is licensed under the Creative Commons Attribution- Noncommercial-Share Alike 3.0 United States License.
- 2. Chariot Solutions Practical, smartsoftware development powered by Java, open source and emerging technologies
- 3. An engineer* walks into a room ... *Software guy with old, dusty electrical technology degree, really
- 4. and notices it’stoo cold.
- 5. He walks intoanother and notices it’s too warm.
- 6. Hire someone tofix it?
- 7.
- 8. Build a systemto monitor temperature in multiple rooms.
- 9. Must have... Stories! •The system should be able to collect temperature data from at least 12 locations • The system should record collected temperatures in a database for later analysis • The system shall not require ripping into walls to run wires • Sensors shall not require ugly power bricks • The system should be able to control external devices
- 10. Temp Temp Temp Output Module Module Module Control Module Temp Module Ether Control System
- 11. Sensor Output Voltage Analog to Temp Digital Module Convertor Digital Value of Voltage Wireless Transmitter
- 12. Sensor Requirements • Lowcurrent draw • Can operate from 2 AA batteries • Output a nice linear voltage with a positive correlation to temperature • Come in a through-hole (not surface mount) package
- 13. MCP9700 • 6 uAcurrent draw (sweet!) • Output ranges from 0V to 2V • Comes in TO-92 package (3-pin through- hole)
- 14. Voltage to Temperature Tc = (V - 0.5) / 0.01 Output (V) Temp (deg C) 0 -50 0.5 0 0.75 25 0.9 40 1.2 70
- 15. Establishing a Reference •ADCs need a reference voltage • MCP9700 outputs 0-2V • As a practical matter, 1.2V = 70 deg C (158 F) is much warmer than I hope to measure • So a 1.2 V voltage reference should do
- 16. LM285LP • 1.235 Vnominal shunt reference • requires only10µA to provide consistent voltage
- 17. Digi XBee • Wireless2.4GHz module based on 802.15.4 spec • 100 ft indoor range • Operates on 2.8 to 3.4 V • 50mA operational • 50uA standby • Built-in Analog-to-Digital converter (ADC)
- 19. Major Temp Module Parts • XBee • MCP9700 • LM285 (1.2 V Reference) • 2 AA batteries and holder • Case - Hammond 1593P series • SchmartBoard 2mm proto board
- 21. n PA i ned ig Des Top-secret Prototype
- 22. Wireless Module Vref Temp Sensor (under board) Text Super Soldering Job* Professional Wiring* *Not so much
- 23. Temp Temp Temp Module Module Module Temp Ether Module Control System
- 24. XBee, meet Computer • Droids makes a nice XBee to USB board • This will allow software to communicate with XBee network • Driver for USB chip is built into Linux, can be installed for Mac or Windows
- 25.
- 26. Speaking XBee • XBeesupports two modes • AT - Acts like a modem with AT commands (hello, 1995) • API - Uses a byte protocol documented in the XBee product manual
- 27. XBee Interface Protocol • XBee operating in API mode • Basic frame format Start Length API-specific Checksum Delimiter 2 bytes, MSB data 1 byte 0x7E first n bytes
- 28. Module Address Command • Command ID = MY • This command uses the ‘AT’ command API, which has an ID of 0x08 Start Length API-specific data Checksum Delimiter 2 bytes, MSB n bytes 1 byte 0x7E first Frame AT Parameter API ID ID Command Value
- 29. Request Address Start Length API Fr. ID Command Checksum 0x7E 0x00 0x04 0x08 0x01 0x4D (M) 0x59 (Y) 0x50 Correlation 0xFF - Sum ID of data bytes
- 30. Response Start Length API Fr. ID Command 0x7E 0x00 0x04 0x08 0x01 0x4D (M) 0x59 (Y) Same as request Address Checksum 0x0001 0x4F
- 31. This is lookingugly
- 32. Java: Who needs unsignednumbers?
- 33. Apache Mina • Javalibrary for asynchronous I/O • Helps with • Implementing custom protocol coders and decoders • Dealing with partial packets • Provides a serial port transport so that we don’t have to deal with those details
- 34. XBeeLib • Implementation ofXBee API protocol • Written in Java • Based on Apache Mina • Open source, BSD license • http://kenai.com/projects/xbeelib
- 35. XBeeLib xb Shell xmon Shell Command Command XBeeService Mina Core Mina Serial Connector USB RXTX
- 36. XBeeLib xb Shell xmon Shell Command Command XBeeService Mina Core Command Encoder Mina Serial Connector USB RXTX
- 37. XBeeLib xb Shell xmon Shell Command Command XBeeService Mina Core Command Response Decoder Command Encoder IO Data Frame Decoder Mina Serial Connector USB RXTX
- 38. Control System OSGi contai ner XBeeLib XBee (transport handling)
- 39. OSGi • A runtimeframework for Java • Software is deployed as bundles • An application is composed of one or more bundles
- 40. OSGi = Services •The core idea is to encourage a modular approach to building applications • Only classes explicitly declared as shared can be seen by other bundles • Provides mechanism for bundles to provide services to other bundles
- 41. Apache Felix • Apacheimplementation of OSGi standard • Provides a run-time platform for the monitoring software
- 42. Felix Shell • Providesan interactive console for the OSGi runtime environment • Implementing a shell command • Create class that implements Command • Register an instance of the class with the OSGi service registry
- 43.
- 44. pHomeNet • Provides application-levelservices • Monitoring sensors • Acting on observations • Viewing collected observations • http://kenai.com/projects/phomenet
- 45. If an XBeetransmits but nobody is listening...
- 46. Listening to XBees •xbee-listener bundle listens for incoming samples from XBee modules • Attempts to find a handler for the sample • Handlers implement XbeeAnalogDataTransfomer • If sample can be transformed to observation, call ObservationRecorder to persist in database • Post an OSGi event about the observation
- 47. Control System OSGi Service Registry Xbee Listener Observation Recorder Derby EclipseLink JPA XBeeLib XBee USB (transport handling)
- 48. Making sense ofit all • temp-sensor bundle implements XbeeAnalogDataTransformer for temperature modules • Decodes samples to temperature observations • Provides ability to configure instances of temperature sensors
- 49. Control System OSGi Service Registry Temperature Module Services Xbee Listener Observation Recorder Derby EclipseLink JPA XBeeLib XBee USB (transport handling)
- 50. Demo temp-sensor bundle
- 51. Let’s be controlling •Switch bundle supports modules that turn outputs on/off • Listen for observation events posted by xbee-listener bundle • Provide ability to configure instances of switch modules
- 52. Control System OSGi Service Control Module Handler Registry Temperature Module Services Xbee Listener Observation Recorder Derby EclipseLink JPA XBeeLib XBee USB (transport handling)
- 53. Demo xbee-switch bundle
- 54. pHomeNet Status • Mostlya research project to date, despite it’s motivation • TODOs • Expand support for controllable devices • Expand sensor support (One Wire devices, external temperature probes)
- 55. Resources • XBee 802.15.4 OEM module • http://www.digi.com/products/wireless/point-multipoint/xbee-series1- module.jsp#overview • Droids XBee USB board • http://www.droids.it/990_002.html • MCP9700 Temperature Sensor • http://www.microchip.com/wwwproducts/Devices.aspx? dDocName=en022289
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- #25 Built our Sensor\n If an XBee transmits and nobody is listening, has it actually transmitted?\n Yes, but it’s not useful\n We need something to listen to the XBee network\n
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