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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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

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

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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.