Asynchronous wake-up scheme for wireless light curtains

Transcription

1 Institute of Embedded Systems InES Asynchronous wake-up scheme for wireless light curtains (Presented at Wireless Congress, Munich November 2008) Prof. Dr. Marcel Meli Prof. Hans Käser Dipl. Ing. FH. Martin Würms Daniel Almer, David Benoît Contact: 1 1

2 Outline Who we are Introduction The problem The solution The modules Tests and results Conclusions (Acknowledgement: Wireless curtains example pictures in this document taken from CEDES, Landquart, CH) 2 2

3 Who we are: InES, design examples Activities of the Wireless Systems Group Microcontrollers (Atmel, CoolRisc, Microchip, Propeller, PSoC/PRoC, Freescale,...) Wireless PAN systems (BT, , ZigBee) WirelessUSB, ANTS, Nanotron, UWB RFID (125 KHz UHF), RFID radar, pairing Activities in Low Power, use of Energy Harvesting, positioning 32x16 mm, 32-bit micro+radio / ZigBee compatible Portable RFID reader with Wireless PAN link Single chip (PRoC) 3 3

4 Who we are: InES, design examples No Batteries Wireless Battery-less switch Very Low Power microcontroller + Radio, Use of EH module Compatible with / ZigBee Multichannel sniffer to monitor based protocols All channels can be monitored (1 microsecond accuracy) Ethernet to Gateway, with PoE Install And Forget 4 4

5 Introduction What are wireless curtains? Sensors with IR emitters / receivers used to detect the presence of an object Both elements on one side (reflection) or on opposite sides possible Several pairs to cover a larger area (with different sequencing) Use of wireless curtains Protection of areas where there is movement Detection of presence Safety for automatic doors...etc 5 5

6 Cables The problem Not so aesthetic Not flexible enough, maintenance costs 6 6

7 The problem Replace data cables to sensors with wireless link Batteries as power source, but should not be replaced every week At the best, once a year (or never!! ) 7 7

8 The problem Power consumption Receiver on all the time will lead to a waste of energy Obvious wireless solution will involve a synchronous timer to generate an acceptable duty cycle But there are limits to acceptable duty cycle Fast reaction is needed to avoid accidents Events leading to opening/closing of door are asynchronous Thus, most wake-up sequences will be in vain The best will be to wake up microcontrollers and communicate only when it is needed 8 8

9 The solution Design a communication on-demand system Receiver normally off Communication only starts when main controller requests it Request of communication achieved by using a circuitry that consumes on average less than the timer wake-up sequence (wake-up + communication to find out if opening/closing activity requested) RFID wake-up device is used: 125 KHz About 5 m range (enough in this application) Wake-up pattern recognition possible (multiple doors in same area) 9 9

10 The solution Atmel Microcontroller: ATmega324 Transceiver: AT86RF230 Austriamicrosystems Wake-up: AS3931 Em Marin RFID reader: EM4095 Premo 3D Antenna: From Premo = 10 10

11 Solution Atmel Microcontroller: ATmega324 Transceiver: AT86RF230 Austriamicrosystems Wake-up: AS3931 Em Marin RFID reader: EM4095 Premo 3D Antenna: From Premo 11 11

12 Synchronous solution Periodic wake-up timer on IR sender, IR receiver Wake-up after timer expires TX/RX active Check if open/close door activity required No go back to sleep (milliseconds wasted) Yes Communicate with main controller to deliver sensing information for safety (several seconds) Go back to sleep when opening/closing activity terminated 12 12

13 Asynchronous solution IR sender, IR receiver in power down mode If request to open/close door Main controller sends an RFID wake-up sequence IR sender and IR receiver woken up communication with main controller to deliver sensing information for safety (needs many seconds) Go back to sleep when opening/closing activity terminated 13 13

14 Results (simulation conditions) Time needed to close the door 2 sec Energy available in battery 2400 mah Polling interval for synchronous variation 3 sec Radio transmit time sec CPU running time sec Radio transmit current 20 ma CPU alone active 5 ma Only wake-up circuit is active ma The measured values are: TX power set for maximal power. Micro in power down; Wake-up device on; radio off 28 ua Micro running; Wake-up device on; radio in RX mode ma Micro running; wake-up device on; radio sending every 15 ms ma Micro running; wake-up device on; radio off 5.38 ma 14 14

15 Results 15 hours service per day 15 15

16 Results Simulation with more possibilities 16 16

17 Conclusions The asynchronous mode leads to energy savings Range reduced to about 5m because of RFID sender (this is enough in this application) Better results if: TX power reduced for the small range Newest low power 8-bit micros and transceivers used 17 17

18 Future work and thanks Use of new low power microprocessors and transceivers Consideration of the RUBEE standard Thanks Thanks to Anatec for providing devices Thanks to CEDES for discussion of the theme 18 18

19 More information? Prof. Dr. Marcel Meli, Head of Wireless Systems Group Zurich University of Applied Sciences (ZHAW) Institute of Embedded Systems (InES) Technikumstr. 9 CH-8401 Winterthur Phone:

20 Questions???? 20 20