Low Power Wireless Sensors can provide concise environmental monitoring through small, low-power nodes. The document discusses wireless considerations for such nodes using standards like 868MHz. It then describes the hardware and software used in open-source monitoring nodes, including microcontrollers, wireless modules, and power optimization techniques. Practical applications discussed include home energy and temperature monitoring, heat pump oversight, and bee hive observation.

1. 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 Energy
Tools to help us work towards
sustainable energy in a way that
adds up.
Energy Stacks based on David
MacKay's book: withouthotair.comTrystan's Stack 2012
Only 17% Sustainable Energy
2030
Target*
2012 UK
Average
2012
Trystan
*CAT zerocarbonbritain.com/

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OpenEnergyMonitor.org
Open-source energy monitoring

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The OpenEnergyMonitor System

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http://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.org
openenergymonitor.org/emon/emoncms
github.com/emoncms

10. 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 £11.52
made 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
Shield
Energy monitoring
node
emonTx Low
Power Temp
Semi – populated
emonTx with 2 x
AA and DS28B20
temperature
sensor
NanodeRF
Web-connected
base station -
Arduino clone with
ENC28J60
Ethernet and
RFM12B wireless
onboard
RFM12Pi
RFM12B 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 Monitoring
John 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 Monitoring
Clive 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
emonTH
TEMPERATURE & HUMIDITY
open hardware
emonTxV3
energy monitoring node
openenergymonitor.org
open hardware
● SMT design
● Enclosures

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Thank you.