OSHUG #26 Low Power Wireless Sensors
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Low Power Wireless Sensors
Glyn Hudson @openenergymon OSHUG #26 16/05/13
...and their role in helping us build a sustainable future
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Open-source sustainable technologies
Technology that empowers us to participate in creating a future where we live within ecological limits.
openenergymonitor.org
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Sustainable EnergyTools to help us work towards sustainable energy in a way that adds up.
Energy Stacks based on DavidMacKay's book: withouthotair.comTrystan's Stack 2012
Only 17% Sustainable Energy
2030Target*
2012 UK Average
2012 Trystan
*CAT zerocarbonbritain.com/
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OpenEnergyMonitor.orgOpen-source energy monitoring
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The OpenEnergyMonitor System
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6http://openenergymonitor.org/emon/emontx
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Raspberry Pi
http://openenergymonitor.org/emon/emonbase/raspberrypi
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An open-source web-app for processing, logging and visualising energy, temperature and other environmental data
●Open-source, downloadable and installable on your own server (e.g RaspberryPi)
●Specifically designed with processing and visualising energy data in mind.
● Written in php, mysql, javascript and jquery
● Follows MVC architecture
emoncms.orgopenenergymonitor.org/emon/emoncmsgithub.com/emoncms
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Visual Dashboard Editor
Drop & drop, customisable graphs, re-sizeable widgets, buttons and live feeds
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Contents
Technology of a wireless node- Wireless considerations - Wireless Module Hardware- Mircrocontrollers- Low power optimisation - Battery Life Estimation
Practical Examples - Home Temperature and Energy Monitoring- Home energy modelling & simulation - Heat Pump Monitoring- Bee Hive Temperature Monitoring
The Future - Current Hardware Prototypes
Live Demo?
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Wireless Considerations – ISM bands
● Industrial Scientific and Medical
● Licence exempt
● 433Mhz, 915Mhz, 868Mhz and 2.4GHz
● Commonly used for low power, low range wireless transmission
● Applications need to be interference tolerant
● 433/868/912MHz - Restricted duty cycle <10%
● Lower frequency's have less free space attenuation and better propagation – better range
2.4GHz 433MHz / 868Mhz / 915Mhz
Wifi Doorbells
Bluetooth Security Systems
Zigbee Cordless telephones
Weather Stations
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Low Power Wireless Modules
RFM12B (HopeRF)
SRF (Ciseco) TI - CC1110
XBEE (Digi) NRF24L01+ (Nordic Semi)
Interface SPI Serial / SPI Serial SPI
Freq 868 Mhz 868 Mhz 2.4GHz 2.4 Ghz
AES Encryption
NO YES YES NO
Power Supply 2.2V - 3.8V 2.0V - 3.6V 2.1V – 3.6V 1.9 – 3.6 V
Rx / TX Power 14 / 23mA 20 / 36.2mA 35/ 38mA 11.3/13.5ma
Sleep mode 1 132.2ua @ 2.6v
26uA
Sleep mode 2 0.3uA 0.2uA @2.6v <1uA <1uA (900nA)
Price (inc VAT) x1 May 2013
£4.79 £11.52made in UK!
£17 £4
Regulatory Approval FCC/ETSI
No In Progress Yes No
http://blog.homelabs.org.uk/wireless-connectivity/
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Microcontrollers
● Ciseco RFu – ATmega328 MCU plus SRF / RFM12B radio in XBEE form factor
● Designed & made in UK
ATmega328 with Arduino Uno bootloader
+ commonly used+ easy to develop for using Arduino IDE+ easy to upload code and debug+ active community- not the most low power option, but not too bad:
6.8mA running @ 16Mhz 3.3V 4.6uA while sleeping
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emonTx / emonTx Arduino
ShieldEnergy monitoring
node
emonTx Low Power Temp
Semi – populated emonTx with 2 x
AA and DS28B20 temperature
sensor
NanodeRFWeb-connected base station -
Arduino clone with ENC28J60
Ethernet and RFM12B wireless
onboard
RFM12PiRFM12B wireless
Raspberry Pi expansion board. Uses Pi's Serial
UART GPIO pins
OpenEnergyMonitor Modules – ATmega328 & RFM12B wireless
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http://nathan.chantrell.net/tinytx-wireless-sensor/
ATtiny84 Based Nodes
x
http://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 debug
Examples with DS18B20 temperate sensor and DHT22 Humidity Sensor
TinyTX – Nathan Chantrell
Funky Sensor – Martin Harizanov JeeNode Micro – JCW JeeLabs
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Low Power Ticks - software
● AVR sleep mode
– Disable all unneeded functions (e.g ADC) and put processor to sleep
– Reduce current consumption from 6.4mA to 4.6uA
● Requires internal watchdog timer or external interrupt to wakeup
● Radio should also be put to sleep
– if not needed for receiving packets
– 14mA (Rx) / 23mA (Tx) reduced to 0.3uA when 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.cpp
http://jeelabs.org/2011/06/26/current-measurements/
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Simple Low Power RFM12B example
● Simple sketch to send out an ever increasing integer once every minute
● Estimated battery life of 3 years on a single 1300mAhr 3.3V LiPo battery – ATmega328 @ 16Mhz, approx average current draw <57uA
http://jeelabs.org/2013/04/18/9-50-days-and-counting/
JeeLabs Real word test, 2.5 years and still going!
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Battery Life Estimator Tool
http://oregonembedded.com/batterycalc.htm
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Low Power Tricks - Hardware
● Turn off sensor in-between reads – e.g. DS18B20 VCC powered from MCU digital I/O
● Don't use a voltage regulator – Eliminate quiescent current draw: MCP1702 1.6 uA , LM7805 5-8mA!)
● DC-DC boost converter ● Disable ATmega BOD – Arduino default is 2.6V (Brown
Out Detection)
● Slow down – ATmega328 can work down to 1.8V with 4Mhz clock – default is 16Mhz
● Energy harvesting – Mini solar PV
– Battery less operation
– Super capacitor
– PFET to disable RFM12B at startup
Energy consumption of RFM12B packet transmission with ATtiny84. Duration 5.7ms,
average: 10mA, peak 25mA
http://jeelabs.org/2010/09/03/jeenode-goes-solar/
http://harizanov.com/2013/04/scope-screenshots/
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Practical Example – Home Temperature Monitoring
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Home Heating Energy Input & Temperature Monitoring
January 2011 - April 2013
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Real World Monitoring Data
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Heat Pump MonitoringJohn Cantor, heat pump consultant
● Remotely monitor heat pump performance
● Identify problems
● Optimise control by providing feedback
www.heatpumps.co.ukhttp://openenergymonitor.org/emon/applications/heatpump
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RF Link
Ambient Temp probe
Solar PV
Battery
Core temperature probe
Winter 2010
Bee Hive MonitoringClive Hudson, Meirionnydd Bee Keepers
http://openenergymonitor.org/emon/beehive/v2
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A 'normal' bee temperature week
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The Future - Hardware Prototypes
emonTHTEMPERATURE & HUMIDITY
open hardware
emonTxV3
energy monitoring node
openenergymonitor.orgopen hardware
● SMT design● Enclosures
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Thank you.