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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 INFM Via 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
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Page 1: IMPLEMENTATION OF AN ENERGY EFFICIENT WIRELESS SMART SENSOR Sebastian Bicelli, University of BresciaEUROSENSORS XIX - Barcelona - 13/09/2005 1 University.

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

Page 2: IMPLEMENTATION OF AN ENERGY EFFICIENT WIRELESS SMART SENSOR Sebastian Bicelli, University of BresciaEUROSENSORS XIX - Barcelona - 13/09/2005 1 University.

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

Page 3: IMPLEMENTATION OF AN ENERGY EFFICIENT WIRELESS SMART SENSOR Sebastian Bicelli, University of BresciaEUROSENSORS XIX - Barcelona - 13/09/2005 1 University.

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

Page 4: IMPLEMENTATION OF AN ENERGY EFFICIENT WIRELESS SMART SENSOR Sebastian Bicelli, University of BresciaEUROSENSORS XIX - Barcelona - 13/09/2005 1 University.

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

Page 5: IMPLEMENTATION OF AN ENERGY EFFICIENT WIRELESS SMART SENSOR Sebastian Bicelli, University of BresciaEUROSENSORS XIX - Barcelona - 13/09/2005 1 University.

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)

Page 6: IMPLEMENTATION OF AN ENERGY EFFICIENT WIRELESS SMART SENSOR Sebastian Bicelli, University of BresciaEUROSENSORS XIX - Barcelona - 13/09/2005 1 University.

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

Page 7: IMPLEMENTATION OF AN ENERGY EFFICIENT WIRELESS SMART SENSOR Sebastian Bicelli, University of BresciaEUROSENSORS XIX - Barcelona - 13/09/2005 1 University.

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

Page 8: IMPLEMENTATION OF AN ENERGY EFFICIENT WIRELESS SMART SENSOR Sebastian Bicelli, University of BresciaEUROSENSORS XIX - Barcelona - 13/09/2005 1 University.

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

Page 9: IMPLEMENTATION OF AN ENERGY EFFICIENT WIRELESS SMART SENSOR Sebastian Bicelli, University of BresciaEUROSENSORS XIX - Barcelona - 13/09/2005 1 University.

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

Page 10: IMPLEMENTATION OF AN ENERGY EFFICIENT WIRELESS SMART SENSOR Sebastian Bicelli, University of BresciaEUROSENSORS XIX - Barcelona - 13/09/2005 1 University.

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

Page 11: IMPLEMENTATION OF AN ENERGY EFFICIENT WIRELESS SMART SENSOR Sebastian Bicelli, University of BresciaEUROSENSORS XIX - Barcelona - 13/09/2005 1 University.

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

Page 12: IMPLEMENTATION OF AN ENERGY EFFICIENT WIRELESS SMART SENSOR Sebastian Bicelli, University of BresciaEUROSENSORS XIX - Barcelona - 13/09/2005 1 University.

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

Page 13: IMPLEMENTATION OF AN ENERGY EFFICIENT WIRELESS SMART SENSOR Sebastian Bicelli, University of BresciaEUROSENSORS XIX - Barcelona - 13/09/2005 1 University.

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


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