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Weather in a Box Autonomous self-powered energy harvesting interface and power
management system for sensor applications and wireless data transmission
Fritz Huettinger Chair of Microelectronics, University of Freiburg
Maximilian Marx
Daniel Schillinger
Florian Kromer
European Analog Design Contest 2011
Content
Motivation
Fundamentals and idea
System design
Measurement and simulation results
Summary and outlook
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22.11.2011 Maximilian Marx, Daniel Schillinger, Florian Kromer - 3 -
Motivation
Distributed wireless sensor nodes
Send measurement data to server
For instance: in- and outdoor weather
monitoring
Energy harvesting generators
Solar cell or vibration driven
No wiring or batteries needed
Low fluctuant output power
Smart power management necessary
Server
Client
(WSN)
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Fundamentals and idea
Generator
Output power depends on load
Matching with internal resistance
Rg
+
-
Vg,oc
generator
+
-
VRLVg
RL
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Fundamentals and idea
Generator
Output power depends on load
Matching with internal resistance
Maximum power point
Voltage on capacitor is controlled
VMPP = kratio Vg,oc
kratio depends on generator type
Vibration-driven generator
kratio = 0.5
Solar cell kratio ≈ 0.7
Rg
+
-
Vg,oc
generator
Cin
+
-
VC,inVg
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System Design
Open circuit voltage sampling
unit (VSU)
Samples Vg,oc
Periodically connected to the
generator
Fast sampling
Low energy loss
Interface circuit is decoupled
during the sampling
Sampling capacitor and voltage
divider to set kratio
Provides reference voltage:
VMPP = kratio Vg,oc
Ambient
Energy
(Sun,
Wind,
Vibrations)
Open-
Circuit
Voltage
Sampling
Unit
(VSU)
Energy
Harvesting
Generator
Vg,oc
LS:
TI SN74AUP1T97
MOSFET:
CSD25401Q3
CSD16301Q2
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System Design
Boost converter
Controlled by load
matching unit
(LMU)
Compares VMPP
with Vcin
Single-step
approach
Input buffer Cin is
charged/discharged
between
upper/lower limit
Storage buffer Cstg
is charged
Vg,oc
Time
Voltage
VCin
VCstg
Ambient
Energy
(Sun,
Wind,
Vibrations)
Open-
Circuit
Voltage
Sampling
Unit
(VSU)
Boost
Converter
(L = 220 µH)
Load
Matching
Unit
(LMU)
Storage
Buffer
(Cstg =
10mF)
Energy
Harvesting
Generator
Input
Buffer
(Cin =
1µF)
Vc,inVg,oc
VMPP
upper limit
lower limit
Comp.: TI TLV3491
AND GATE: TI
SN74AUR2G80
VMPP
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System Design
Buck Converter
VCstg is not regulated
VCstg converted to regulated VCapp
Schmitt-Trigger is used to realize
PFM control
Time
Voltage
VCin
VCstg
VCapp
Comparator: TI TLV3491
LS: TI SN74AUP1T97
VREF: TI REF3312
Ambient
Energy
(Sun,
Wind,
Vibrations)
Open-
Circuit
Voltage
Sampling
Unit
(VSU)
Boost
Converter
(L = 220 µH)
Load
Matching
Unit
(LMU)
Storage
Buffer
(Cstg =
10mF)
Energy
Harvesting
Generator
Input
Buffer
(Cin =
1µF)
Vc,inVg,oc
VMPP
Buck
Converter
(L=560 µH)
Application
Buffer
(Capp =
22mF)
Vc,stg Vc,app
upper limit
lower limit
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System Design
Complete System
MSP430 controls VSU
and buck converter
I²C interface to sensors
Wireless transmission of
sensor data
Voltage supervisor
controls startup
Ambient
Energy
(Sun,
Wind,
Vibrations)
Open-
Circuit
Voltage
Sampling
Unit
(VSU)
Boost
Converter
(L = 220 µH)
Load
Matching
Unit
(LMU)
Storage
Buffer
(Cstg =
10 mF)
Buck
Converter
(L=560 µH)
Application
Buffer
(Capp =
22 mF)
Microcontroller
MSP430F2274
Pressure
sensor
Bosch
BMP085
Humidity
sensor
Sensirion
SHT21
RF trans-
ceiver
TI
CC2420
Voltage
Supervisor
(SVS)
Energy
Harvesting
Generator
Input
Buffer
(Cin =
1 µF)
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System Design
Complete System
MSP430 controls VSU
and buck converter
I²C interface to sensors
Wireless transmission of
sensor data
Voltage supervisor
controls startup
Simulation and Measurement results
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Spice Simulation
Verify functionality and dimensioning
Using TI Spice models
System Startup
Phase 1: All active devices turned off
Phase 2: Boost converter and LMU is
working to enable system to start with
low Vg,oc
Phase 3: MSP430 and VSU is working,
Vg,oc is sampled and input voltage is
adapted
(1)
(1)
(2)
(2) (3)
(3)
Simulation
Measurement
Measurement results
Load matching
Vg,oc is sampled every 200 ms
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(1) (2) (3)
Measurement results
Load matching
Vg,oc is sampled every 200 ms
VCin is adapted to 0.7 Vg,oc
Vg,oc = 2.65 V VCin = 1.85 V
Supply RF transceiver
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Summary and Outlook
WSN for weather monitoring powered by energy harvesting
generators
Efficient self-startup
Maximum power point tracking
Reliable power management for sensors and RF transceiver
Outlook
Measurements with different generator types
Integrating complete RF protocol
Long-term field test
Integrated circuit (ASIC)
Acknowledgment
We would like to thank:
Texas Instruments
Fritz Huettinger Chair of Microelectronics
Prof. Dr.Ing-Yiannos Manoli
Dominic Maurath
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Thank you for your attention!
VSU
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TI
CSD25401Q3
500 kΩ
Vvsu
DMSP2
5 MΩ
500 kΩ
Cref1
200 nF
Cref2
470 µF
TI
CSD25401Q3
TI
CSD16301Q2
VCstg
500 kΩ
VCapp
5 MΩ
ONSemiconductor
BAT54C
M1
M6
M7
D3
U4
U6
DMSP3
DMSP1
VCstg
Open circuit voltage
sampling unit (VSU)
Levelshifter (I)
TI
SN74AUP1T97
Levelshifter (NI)
TI
SN74AUP1T97
Energy harvesting
generatorInput Buffer
(Cin)
start-up
branch
RVSH1 RVSH2
LMU
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TI TLV3491
VCapp VCapp
DMSP1
1 MΩ
ST1
U2a
Open Circuit
Voltage
Sampling Unit
(VSU)
Boost Converter
Input Buffer
(Cin) VCapp
Voltage
supervisor
TI SN74AUP2G80
Load Matching Unit
U2bDboost,onVvsh
Vin
ST1
Weather in a Box - Circuit
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TI
CSD25401Q3
TI
SN74AUP1T9
7
500 kΩ
MSP1
SI1050x
1
MΩ
Uref 1
Uref 1
TI
TLV3491
MSP2
5 MΩ
500 kΩ
Cref1
470 nF
Cref2
470 µFTI
CSD25401Q
3
TI
CSD16301Q2
Cbuf2
Cbuf2
Cbuf1
1 uF
NSR1020MW2T1G
Cbuf2
10 mF
1 MΩ
NSR1020MW2T1GCbuf3
22 mFMSP430F2274
TI
SN74AUP1T9
7
Cbuf2
MSP4
Cbuf3
TI
TLV3491
Int1
MSP1
MSP2
MSP3
MSP4
500
kΩ
Cbuf3
1 MΩ
Levelshifter (NI)
TI
SN74AUP1T97
Cbuf2
MSP
3
1 MΩ
5 MΩ
ONSemiconduct
or
BAT54C
LS2_Out
ADC
M1
M2
M3
M4
M5
D2
D3
D4
L1 L2
U1
U4
U5
U6
U7
U8BSH20
5
Cbuf3
U2
Cbuf3
TI SN74AUP2G80
ADC
MSP1
Voltage
supervisor
TPS3106E16
Cbuf3
Out 1 Out 2
M6
U9
Voltage
reference
REF3312
1,25 V
U10
+
INPUT
-