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Sebastian Bicelli, University of Brescia EUROSENSORS XIX - Barcelona - 13/09/2005 1
IMPLEMENTATION OF AN ENERGY EFFICIENT WIRELESS SMART SENSOR
University of Brescia, Dept. of Electronics for Automation and INFMVia Branze 38 - 25123 Brescia (Italy), Tel: +39-030-3715897 Fax: +39-030-380014
E-mail: [email protected], Web: http://www.ing.unibs.it/~wsnlab/
S. Bicelli, A. Flammini, D. Marioli, E. Sisinni, A. Taroni
OUTLINE
• Block diagram of a battery-powered wireless sensor• Sensor life estimation method• Experimental characterization of several prototypes
Sebastian Bicelli, University of Brescia EUROSENSORS XIX - Barcelona - 13/09/2005 2
IMPLEMENTATION OF AN ENERGY EFFICIENT WIRELESS SMART SENSOR
Low Power Wireless Sensor
Sensor ADC
Storage
Tx/Rx
Power Unit
Battery/Batteries
DESIGN GUIDELINES• How to design an efficient power supply?• How to estimate sensor life?• Which sensor to estimate a physical quantity?• It exists the “best microcontroller”?
Processor
SW
Sebastian Bicelli, University of Brescia EUROSENSORS XIX - Barcelona - 13/09/2005 3
IMPLEMENTATION OF AN ENERGY EFFICIENT WIRELESS SMART SENSOR
Batteries
34mm 26mm (14,5mm ) (10.5mm ) (26.2 x 17.5 mm)
61m
m
50 m
m
50 m
m
45 m
m
44.5
mm
‘D’ ‘C’ ‘AA’ ‘AAA’ ‘9V’
Zinc Carbon
Alkaline LithiumNickel -
CadmiumNickel Metal
Hydride (NiMH)Lithium Ion
Nominal Voltage [V] 1,5 1,5 3 1,2 1,2 3,6
Internal resistance Medium Low Low Very low Very low Very low
Capacity (AA) [mAh] 60-1800 2200 2100 600-1100 1300-2300 800-1000
Rechargeable? No (No) No Yes Yes Yes
Natural discharge Slow Slow Very slow Quick Quick
(30%/month)Quick
(20%/month)
Cost (AA, $) 1 1 3 2 2 3
Note Old Diffuse Toxic Old Diffuse Light, toxic
Sebastian Bicelli, University of Brescia EUROSENSORS XIX - Barcelona - 13/09/2005 4
IMPLEMENTATION OF AN ENERGY EFFICIENT WIRELESS SMART SENSOR
Power supply systems
LDO: Low Drop Out - Voltage regulators
Few components (only bypass capacitors)
High ouput current, low noise
Low cost
Low efficiency
Vin > Vout
Charge pump
Few components (inductorless)
Medium efficiency, Medium cost
Vin > Vout or Vout < Vin
Medium/high noise
Vout multiple of Vin
Low output current
Step up / Step down converter (Buck boost)
High efficiency, high cost
Medium/high output current
Vin > Vout or Vout < Vin
Inductor
Layout ad-hoc
High noise
Systems to increase battery usage
Important parameters: quiescent current, efficiency, transient response
Sebastian Bicelli, University of Brescia EUROSENSORS XIX - Barcelona - 13/09/2005 5
IMPLEMENTATION OF AN ENERGY EFFICIENT WIRELESS SMART SENSOR
Battery life L (Time to reach the cutoff voltage, ~ 70% Vbat)
meanccv IK
CL
,
T
TTTITITII RFasleepRFRFaa
meancc
,
• C (Ah): battery capacity• η: power supply efficiency• Kv: power supply output voltage gain • Icc,mean (A): mean current consumption of the wireless sensor
RF
sleepRF
a
sleepa I
ITT
I
ITT
IsleepTsleep
IaTa
IRFTRF
T>1s
Low data rate (T>1s)
Sebastian Bicelli, University of Brescia EUROSENSORS XIX - Barcelona - 13/09/2005 6
IMPLEMENTATION OF AN ENERGY EFFICIENT WIRELESS SMART SENSOR
Sensor conditioning• Low bias current • Ultra low power rail to rail• Shutdown pin
Processing UnitPeripheralsprescaler
UART
Timers
ADC
CPUprescaler
CPUMain clock
Sleep
Active
TimeC
urr
ent
Secondary clock
Sensor• low power • fast transient response
• SLEEP mode and WAKE UP mechanisms• Mixed signal microcontroller• Typical consumptions
Sleep: 1uA Run: 1mA High performance: 10mA
Sebastian Bicelli, University of Brescia EUROSENSORS XIX - Barcelona - 13/09/2005 7
IMPLEMENTATION OF AN ENERGY EFFICIENT WIRELESS SMART SENSOR
Radio subsystem
• Impact of the noise
• Ease of communication with other devices
• Consumption (10 - 100mA)
• Start-up time and available bandwidth
TRANSCEIVER
ANTENNA
• Chip antenna
• PCB antenna
• External antenna
Sebastian Bicelli, University of Brescia EUROSENSORS XIX - Barcelona - 13/09/2005 8
IMPLEMENTATION OF AN ENERGY EFFICIENT WIRELESS SMART SENSOR
The realized prototypes
AA Batteries alkaline and rechargeable
LDO, Stepup, Charge pump
Low power microcontroller and PSOC
RF Transceiver IEEE802.15.4 and Proprietary
PCB antenna
Hardware
Software
Wireless USB(proprietary)
Zigbee(IEEE802.15.4)
• Star topology• Time division multiplexing
Search coord. Tx: 14 bytes Wait ACK (11 bytes)
Sleep
Wake up
OK
Timeout
Timeout x4
Sebastian Bicelli, University of Brescia EUROSENSORS XIX - Barcelona - 13/09/2005 9
IMPLEMENTATION OF AN ENERGY EFFICIENT WIRELESS SMART SENSOR
Experimental results: batteries characterization
Different behaviour:
Temperature
Discharge mode
Battery type
• Constant resistive load: constant resistive load (R = 40Ω)
• Pulsating load: 500ms with a constant resistive load (R = 20Ω), 500ms without load (period T = 1 s and duty cycle D = 50%)
• Constant current mode: load requires always the same current (50,25 mA)
Batteries tested
• Rechargeable 1.2V 2.3Ah NiMH battery NH15 by Energizer (BATR)
• Alkaline 1.5V 2.85Ah Zn/MnO2 E91 by Energizer (BAT1)
• Alkaline 1.5V 2.85Ah Zn/MnO2 MN1500 by Duracell (BAT2)
Discharge mode
Sebastian Bicelli, University of Brescia EUROSENSORS XIX - Barcelona - 13/09/2005 10
IMPLEMENTATION OF AN ENERGY EFFICIENT WIRELESS SMART SENSOR
Batteries characterization: voltage discharge curves
0 10 20 30 40 50 60 70 80 900
0.2
0.4
0.6
0.8
1
1.2
1.4
Hours [h]
Ene
rgiz
er r
icar
icab
ile -
Vou
t [V
]
0 20 40 60 80 100 1200.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
Hours [h]
Dur
acel
l - V
out
[V]
0 20 40 60 80 100 1200
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
Hours [h]E
nerg
izer
- V
out
[V]
Temp. = 23°C Duracell alk. Energizer alk. Energizer r.
Continuous disch., R=40Ω (Vcut-off=0.8V) 96.3 h 88.2 h 63.9 h
Pulsed discharge, R=20Ω (Vcut-off=0.8V) 93.2 h 90.3 h 66.6 h
Pulsed discharge, R=20Ω (Vcut-off=1.0V) 79.6 h 75.7 h 65.5 h
Continuous disch., I=25mA (Vcut-off=0.8V) 125.2 h 123.8 h 90.2 h
Continuous disch., I=50mA (Vcut-off=0.8V) 59.2 h 58.7 h 45.0 h
Sebastian Bicelli, University of Brescia EUROSENSORS XIX - Barcelona - 13/09/2005 11
IMPLEMENTATION OF AN ENERGY EFFICIENT WIRELESS SMART SENSOR
Power supply systems characterization
10000
II VI
VIEfficiency
LDOTPS76633
LDOTPS79433
STEP UPTPS61016
CHARGE P.MCP1252
VI [V] 3.6 3.6 1.4 3.0
Measured 90% 90% 98% 70%
Expected -- -- >90% >60%
Transient Response
TPS76633 TPS79433 TPS61016 MCP1252
40 µs 12 µs 1.2 µs 1.4 µs
I0=100mA, V0=3.3V
Sebastian Bicelli, University of Brescia EUROSENSORS XIX - Barcelona - 13/09/2005 12
IMPLEMENTATION OF AN ENERGY EFFICIENT WIRELESS SMART SENSOR
Transceiver characterizationCYWUSB6934 MC13192 CC2420
Sleep <10 µA <10 µA <20 µA
Idle 3.3 mA 880 µA 440 µA
Transmitting 67 mA 30 mA 18 mA
Receiving 60 mA 30 mA 19.2 mA
Tx (30mA, 448s)
Rx (30mA, ~650s)
Idle (500μA,7.2+0.5ms)
Sleep (2.3μA)
Tsleep=10s
MC13192
Sleep [52 µA, 9989 ms] 0.052 mAMeasure [10 mA, 10 ms] 0.010 mATx/Rx [30 mA, 1.1 ms] 0.003 mA Icc,mean 0.065 mA 1 AA alkaline battery (2.2Ah) + STEPUP 98%
1.38 years
Sebastian Bicelli, University of Brescia EUROSENSORS XIX - Barcelona - 13/09/2005 13
IMPLEMENTATION OF AN ENERGY EFFICIENT WIRELESS SMART SENSOR
Conclusions
Subject: how to design an efficient battery powered wireless sensor
Future evolutions:• Sensors: system on Chip (i.e. microcontroller with transceiver)• Power supply systems: low power real time clock and low quiescient current, high efficiency LDO, charge pump and step up.
Results: • Simple method to estimate sensor life• Sleep current is the most important factor in low data rate applications• Importance of battery selection and experimental characterization• Efficiency/Cost trade off determines the power supply architecture• New sensors, conditioning circuits and microcontroller must be
considered to limit power consumption