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University of Brescia, Dept. of Electronics for Automation and INFM Via Branze 38 - 25123 Brescia (Italy), Tel: +39-030-

IMPLEMENTATION OF AN ENERGY EFFICIENT WIRELESS SMART SENSOR. S. Bicelli , A. Flammini, D. Marioli, E. Sisinni, A. Taroni. University of Brescia, Dept. of Electronics for Automation and INFM Via Branze 38 - 25123 Brescia (Italy), Tel: +39-030-3715897 Fax: +39-030-380014

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University of Brescia, Dept. of Electronics for Automation and INFM Via Branze 38 - 25123 Brescia (Italy), Tel: +39-030-

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  1. IMPLEMENTATION OF AN ENERGY EFFICIENT WIRELESS SMART SENSOR S. Bicelli, A. Flammini, D. Marioli, E. Sisinni, A. Taroni 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: sebastian.bicelli@ing.unibs.it, Web: http://www.ing.unibs.it/~wsnlab/ • 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 1

  2. Low Power Wireless Sensor SW Processor Sensor ADC Tx/Rx Storage 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”? Sebastian Bicelli, University of Brescia EUROSENSORS XIX - Barcelona - 13/09/2005 2

  3. 61mm 50 mm 50 mm 44.5 mm 45 mm 34mm  26mm  (14,5mm ) (10.5mm ) (26.2 x 17.5 mm) ‘C’ ‘D’ ‘AA’ ‘AAA’ ‘9V’ Batteries Sebastian Bicelli, University of Brescia EUROSENSORS XIX - Barcelona - 13/09/2005 3

  4. Power supply systems Systems to increase battery usage Important parameters: quiescent current, efficiency, transient response Sebastian Bicelli, University of Brescia EUROSENSORS XIX - Barcelona - 13/09/2005 4

  5. Battery life L (Time to reach the cutoff voltage, ~ 70% Vbat) • C (Ah): battery capacity • η: power supply efficiency • Kv: power supply output voltage gain • Icc,mean(A): mean current consumption • of the wireless sensor Isleep Tsleep T>1s Ia Ta IRF TRF Low data rate (T>1s) Sebastian Bicelli, University of Brescia EUROSENSORS XIX - Barcelona - 13/09/2005 5

  6. Sensor • Sensor conditioning • Low bias current • Ultra low power rail to rail • Shutdown pin • low power • fast transient response Peripherals prescaler UART Timers Processing Unit Secondary clock ADC • SLEEP mode and WAKE UP mechanisms • Mixed signal microcontroller • Typical consumptions • Sleep: 1uA • Run: 1mA • High performance: 10mA CPU prescaler Main clock CPU Active Current Sleep Time Sebastian Bicelli, University of Brescia EUROSENSORS XIX - Barcelona - 13/09/2005 6

  7. Radio subsystem TRANSCEIVER • Impact of the noise • Ease of communication with other devices • Consumption (10 - 100mA) • Start-up time and available bandwidth ANTENNA • Chip antenna • PCB antenna • External antenna Sebastian Bicelli, University of Brescia EUROSENSORS XIX - Barcelona - 13/09/2005 7

  8. The realized prototypes Hardware PCB antenna RF Transceiver IEEE802.15.4 and Proprietary Low power microcontroller and PSOC LDO, Stepup, Charge pump AA Batteries alkaline and rechargeable Software Wireless USB (proprietary) Zigbee (IEEE802.15.4) • Star topology • Time division multiplexing OK Search coord. Tx: 14 bytes Wait ACK (11 bytes) Sleep Timeout x4 Timeout Wake up Sebastian Bicelli, University of Brescia EUROSENSORS XIX - Barcelona - 13/09/2005 8

  9. Experimental results: batteries characterization Temperature Different behaviour: Discharge mode Battery type 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 • 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) Sebastian Bicelli, University of Brescia EUROSENSORS XIX - Barcelona - 13/09/2005 9

  10. Batteries characterization: voltage discharge curves Sebastian Bicelli, University of Brescia EUROSENSORS XIX - Barcelona - 13/09/2005 10

  11. Power supply systems characterization I0=100mA, V0=3.3V Transient Response Sebastian Bicelli, University of Brescia EUROSENSORS XIX - Barcelona - 13/09/2005 11

  12. Transceiver characterization MC13192 Tx (30mA, 448s) Sleep [52 µA, 9989 ms] 0.052 mA Measure [10 mA, 10 ms] 0.010 mA Tx/Rx [30 mA, 1.1 ms] 0.003 mA Rx (30mA, ~650s) Sleep (2.3μA) Idle (500μA,7.2+0.5ms) Icc,mean 0.065 mA 1 AA alkaline battery (2.2Ah) + STEPUP 98% 1.38 years Tsleep=10s Sebastian Bicelli, University of Brescia EUROSENSORS XIX - Barcelona - 13/09/2005 12

  13. Conclusions Subject: how to design an efficient battery powered wireless sensor • 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 • 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. Sebastian Bicelli, University of Brescia EUROSENSORS XIX - Barcelona - 13/09/2005 13

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