OSHUG #26 Low Power Wireless Sensors


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Short talk given at #OSHUG (Open Source Hardware Users Group) event #26 in London 16th May 2013. Quick overview of the OpenEnergyMonitor project and how we use wireless sensors to collect data. Practical examples of home temperature monitoring cross referenced with SAP calculator building fabric modelling, heat pump monitoring and bee hive temperature monitoring!

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OSHUG #26 Low Power Wireless Sensors

  1. 1. Low Power Wireless SensorsGlyn Hudson @openenergymon OSHUG #26 16/05/13...and their role in helping us build a sustainable future
  2. 2. 2Open-source sustainable technologiesTechnology that empowers us to participate in creating a futurewhere we live within ecological limits.openenergymonitor.org
  3. 3. 3Sustainable EnergyTools to help us work towardssustainable energy in a way thatadds up.Energy Stacks based on DavidMacKays book: withouthotair.comTrystans Stack 2012Only 17% Sustainable Energy2030Target*2012 UKAverage2012Trystan*CAT zerocarbonbritain.com/
  4. 4. 4OpenEnergyMonitor.orgOpen-source energy monitoring
  5. 5. 5The OpenEnergyMonitor System
  6. 6. 6http://openenergymonitor.org/emon/emontx
  7. 7. 8Raspberry Pihttp://openenergymonitor.org/emon/emonbase/raspberrypi
  8. 8. 9An open-source web-app forprocessing, logging andvisualising energy, temperatureand other environmental data●Open-source, downloadableand installable on your ownserver (e.g RaspberryPi)●Specifically designed withprocessing and visualisingenergy data in mind.● Written in php, mysql,javascript and jquery● Follows MVC architectureemoncms.orgopenenergymonitor.org/emon/emoncmsgithub.com/emoncms
  9. 9. Visual Dashboard EditorDrop & drop, customisable graphs, re-sizeable widgets, buttons and live feeds
  10. 10. 11ContentsTechnology of a wireless node- Wireless considerations- Wireless Module Hardware- Mircrocontrollers- Low power optimisation- Battery Life EstimationPractical Examples- Home Temperature and Energy Monitoring- Home energy modelling & simulation- Heat Pump Monitoring- Bee Hive Temperature MonitoringThe Future- Current Hardware PrototypesLive Demo?
  11. 11. 12Wireless Considerations – ISMbands● Industrial Scientific and Medical● Licence exempt● 433Mhz, 915Mhz, 868Mhz and2.4GHz● Commonly used for low power, lowrange wireless transmission● Applications need to be interferencetolerant● 433/868/912MHz - Restricted dutycycle <10%● Lower frequencys have less freespace attenuation and betterpropagation – better range2.4GHz 433MHz / 868Mhz / 915MhzWifi DoorbellsBluetooth Security SystemsZigbee Cordless telephonesWeather Stations
  12. 12. 13Low Power Wireless ModulesRFM12B(HopeRF)SRF (Ciseco)TI - CC1110XBEE (Digi) NRF24L01+(Nordic Semi)Interface SPI Serial / SPI Serial SPIFreq 868 Mhz 868 Mhz 2.4GHz 2.4 GhzAESEncryptionNO YES YES NOPower Supply 2.2V - 3.8V 2.0V - 3.6V 2.1V – 3.6V 1.9 – 3.6 VRx / TX Power 14 / 23mA 20 / 36.2mA 35/ 38mA 11.3/13.5maSleep mode 1 132.2ua @2.6v26uASleep mode 2 0.3uA 0.2uA @2.6v <1uA <1uA (900nA)Price (inc VAT)x1 May 2013£4.79 £11.52made in UK!£17 £4RegulatoryApprovalFCC/ETSINo In Progress Yes Nohttp://blog.homelabs.org.uk/wireless-connectivity/
  13. 13. 14Microcontrollers● Ciseco RFu – ATmega328 MCU plus SRF /RFM12B radio in XBEE form factor●Designed & made in UKATmega328 with Arduino Unobootloader+ commonly used+ easy to develop for using Arduino IDE+ easy to upload code and debug+ active community- not the most low power option, but nottoo bad:6.8mA running @ 16Mhz 3.3V4.6uA while sleeping
  14. 14. 15emonTx /emonTx ArduinoShieldEnergy monitoringnodeemonTx LowPower TempSemi – populatedemonTx with 2 xAA and DS28B20temperaturesensorNanodeRFWeb-connectedbase station -Arduino clone withENC28J60Ethernet andRFM12B wirelessonboardRFM12PiRFM12B wirelessRaspberry Piexpansion board.Uses Pis SerialUART GPIO pinsOpenEnergyMonitor Modules –ATmega328 & RFM12B wireless
  15. 15. 16http://nathan.chantrell.net/tinytx-wireless-sensor/ATtiny84 Based Nodesxhttp://harizanov.com/wiki/wiki-home/funky/http://jeelabs.net/projects/hardware/wiki/JeeNode_Micro+ Cheaper and smaller than ATmega328+ easily run off internal 8Mhz oscillator+ Can use Arduino IDE (with some tweaks)- Does not support hardware serial- Requires ISP programmer to upload code- Harder to debugExamples with DS18B20 temperate sensorand DHT22 Humidity SensorTinyTX – Nathan ChantrellFunky Sensor – Martin Harizanov JeeNodeMicro –JCWJeeLabs
  16. 16. 17Low Power Ticks - software●AVR sleep mode– Disable all unneeded functions (e.gADC) and put processor to sleep– Reduce current consumption from 6.4mAto 4.6uA●Requires internal watchdog timer orexternal interrupt to wakeup●Radio should also be put to sleep– if not needed for receiving packets– 14mA (Rx) / 23mA (Tx) reduced to 0.3uAwhen sleeping for RFM12B* Running @ 16Mhz 3.3V - 6.4mA* SLEEP_MODE_IDLE -the least power savings (2.8mA* SLEEP_MODE_ADC* SLEEP_MODE_PWR_SAVE* SLEEP_MODE_STANDBY* SLEEP_MODE_PWR_DOWN -the most power savings (4.6uA)https://github.com/jcw/jeelib/blob/master/Ports.cpphttp://jeelabs.org/2011/06/26/current-measurements/
  17. 17. 18Simple Low Power RFM12B example● Simple sketch to sendout an ever increasinginteger once everyminute●Estimated battery life of3 years on a single1300mAhr 3.3V LiPobattery – ATmega328 @ 16Mhz,approx average current draw <57uAhttp://jeelabs.org/2013/04/18/9-50-days-and-counting/JeeLabs Real word test, 2.5 years and still going!
  18. 18. 19Battery Life Estimator Toolhttp://oregonembedded.com/batterycalc.htm
  19. 19. 20Low Power Tricks - Hardware● Turn off sensor in-between reads – e.g. DS18B20VCC powered from MCU digital I/O●Dont use a voltage regulator – Eliminate quiescentcurrent draw: MCP1702 1.6 uA , LM7805 5-8mA!)●DC-DC boost converter●Disable ATmega BOD – Arduino default is 2.6V (BrownOut Detection)●Slow down – ATmega328 can work down to 1.8Vwith 4Mhz clock – default is 16Mhz● Energy harvesting– Mini solar PV– Battery less operation– Super capacitor– PFET to disable RFM12B at startupEnergy consumption of RFM12B packettransmission with ATtiny84. Duration 5.7ms,average: 10mA, peak 25mAhttp://jeelabs.org/2010/09/03/jeenode-goes-solar/http://harizanov.com/2013/04/scope-screenshots/
  20. 20. 21Practical Example – HomeTemperature Monitoring
  21. 21. 22Home Heating Energy Input &Temperature MonitoringJanuary 2011 -April 2013
  22. 22. 23
  23. 23. 24
  24. 24. 25
  25. 25. 26
  26. 26. 27Real World Monitoring Data
  27. 27. 28Heat Pump MonitoringJohn Cantor, heat pump consultant● Remotely monitor heat pumpperformance● Identify problems● Optimise control by providingfeedbackwww.heatpumps.co.ukhttp://openenergymonitor.org/emon/applications/heatpump
  28. 28. 29
  29. 29. 30RFLinkAmbientTempprobeSolarPVBatteryCore temperature probeWinter 2010Bee Hive MonitoringClive Hudson, Meirionnydd Bee Keepershttp://openenergymonitor.org/emon/beehive/v2
  30. 30. 31A normal bee temperature week
  31. 31. 32The Future - Hardware PrototypesemonTHTEMPERATURE & HUMIDITYopen hardwareemonTxV3energy monitoring nodeopenenergymonitor.orgopen hardware● SMT design● Enclosures
  32. 32. 33Thank you.