Advertising position with battery-less Bluetooth Low Energy

Transcription

1 Zürich University Of Applied Sciences Institute of Embedded Systems InES Advertising position with battery-less Bluetooth Low Energy (Presented at Embedded World Conference Nuremberg, 1 st March 2012) Dipl. Ing. Michael Würth Prof. Dr. Marcel Meli Contact: Marcel.meli@zhaw.ch Embedded World Conference, Nuremberg 1 st March Meli/Würth. Advertising position with battery-less Ble. 1

2 Outline A short presentation of our activities in low power wireless Introduction and issues Hardware and software Tests and results Conclusions Questions Ble compatible T&RH sensor nodes. Display on smart phone Designed and developped by Sensirion and InES Embedded World Conference, Nuremberg 1 st March Meli/Würth. Advertising position with battery-less Ble. 2

3 Our activities Institute of Embedded Systems, Winterthur, Switzerland Part of Zurich University of Applied Sciences Involved in teaching, applied research projects Wired: Industrial Real Time Communication (Ethernet, ) Wireless: WPAN, RFID, UWB, Energy harvesting, very Low power applications Examples of Low power developments: Passive, Intelligent RFID Tag Battery-less: powered only by the RFID reader Uses a 32-Bit microcontroller to emulate protocols Successful emulation of LF, UHF, Gen2 Identification, sensor, security,... (RFID sensor network) Range of several meters Embedded World Conference, Nuremberg 1 st March Meli/Würth. Advertising position with battery-less Ble. 3

4 Our activities (New) Dynapic Wireless (Battery-less, wireless switch >10 million cycles) Battery-less, wireless piezo-switch (patent filed) > 10 million cycles Silent (no unwanted clicks), thin, flat, fits on many surfaces Embedded World Conference, Nuremberg 1 st March Meli/Würth. Advertising position with battery-less Ble. 4

5 Introduction and motivation Indoors navigation is an important theme where affordable solutions are still been sought. There are several places where the GPS signal is not available Railway stations, underground shopping centres, There is a need to be able to find one s way in those places too There have been (are) several attempts to solve the problem. One approach has been to have tags that regularly beam out their coordinates. The position information can be captured and used for direction, under the control of appropriate software. Tags and an appropriate navigation tool are required Advantageous to use same tool as for outdoors (GPS) navigation smart phones Ble is destined to be found on many telephones. Thus it is worth investigating how ble tags can be used as position tags. In this presentation, we are especially interested in the energy and maintenance aspects of tags. Thus the question: Can energy harvesting be used for Ble tags to improve indoors navigation? Embedded World Conference, Nuremberg 1 st March Meli/Würth. Advertising position with battery-less Ble. 5

6 Introduction and motivation As pointed earlier, several works have been done in the area of indoors navigation RF tags have been used in museum to help visitors Nokia has shown that RF tags and DoD methods (Direction of departure) can be used for indoors navigation (claims 30 cm accuracy) Navigation is recognised as important by the Bluetooth SIG. Some work in this direction is in progress. etc. There are several important aspects linked to the theme of navigation. Method, costs, accuracy, There are interesting references in the paper version of this presentation We are primarily concerned here with a method that is low cost No special tool, no new hardware for the user Easy integration with available navigation instruments (the smart phone) Easy to install and to maintain (tags that are not expensive and that can be installed nearly everywhere) Embedded World Conference, Nuremberg 1 st March Meli/Würth. Advertising position with battery-less Ble. 6

7 The method Tags with position information are mounted at different places The tags can broadcast their position (if needed with different power strengths) Coordinates or some other information useful for people Room E43 here., Journal shop here, Tags should be autonomous in order to go anywhere Batteries, energy harvesting. The data that is broadcast can be received with a normal mobile device Mobile phone, ipad, tablet, Appropriate software on the mobile device processes the received information and present it in a suitable form The amount of tags needed, depends on the area that should be covered and the required accuracy There will be many tags Installation costs are important Maintenance costs are important (replace batteries?) Embedded World Conference, Nuremberg 1 st March Meli/Würth. Advertising position with battery-less Ble. 7

8 Introduction and motivation We have shown at several occasions that energy harvesting is possible with many wireless protocols that are found on the market today. Ble sensor nodes can be powered with EH (Wireless Congress 2011) ZigBee: We have shown examples of wireless switches and examples of sensor powered by a small solar cell ZigBee compatible frames are sent with sensor data or switch information (Demo in 2008 and 2010 at the European ZigBee Developer s Conference) No Batteries, No maintenance Embedded World Conference, Nuremberg 1 st March Meli/Würth. Advertising position with battery-less Ble. 8

9 Introduction and motivation (what is Ble?) Some interesting aspects of Ble A low power addition to the already well established Bluetooth Very good base, thanks to Bluetooth BT classic is present in millions of devices (PC, phones, ) It is expected that the new variation (including support for Ble) will rapidly spread in phones and PCs, etc Several manufacturers of silicon. Comparable to Competition cheap better devices (also lower in power consumption) Interesting technical aspects. 2.4 GHz ISM band. 40 channels (communicating parties can make a rendezvous on a given channel. 3 channels dedicated for advertising Helps in getting the message through also in presence of interference Embedded World Conference, Nuremberg 1 st March Meli/Würth. Advertising position with battery-less Ble. 9

10 Design For advertising position, a very simple architecture can be used. There are tags powered by EH (small solar cells). It is assumed that light is always available. A star configuration can easily be built, with battery-free tags acting as slaves. Data is simply broadcasted. The host can be any device capable of scanning the channels and receiving data from the position tags. In this application, data can be lost without big consequences. Data is frequently repeated Nodes should be cheap and deliver useful data Embedded World Conference, Nuremberg 1 st March Meli/Würth. Advertising position with battery-less Ble. 10

11 Design The main elements of the system should allow low power operation. They are shown below. Solar cell (as small as possible) delivering as little as 300 mv DC/DC converter to get the low voltage high enough for the electronics EM9301 Ble radio capable of running down to 0.8 volt EM6819 microcontroller capable of running down to 0.9 volt A small capacitor is used to store the energy for sending the position information As host, we used a sniffer Most of the phones available with Ble still have limited features. Embedded World Conference, Nuremberg 1 st March Meli/Würth. Advertising position with battery-less Ble. 11

12 Design The main elements of the system. EM9301 Ble controller capable of running down to 0.8 volt Direct connection to PCB antenna Optimised for low power dBm The power can be easily changed to reduce interference and improve range or accuracy EM6819 Low power microcontroller Sub volt operation possible from flash 1 MIPS, 3volts Embedded World Conference, Nuremberg 1 st March Meli/Würth. Advertising position with battery-less Ble. 12

13 Design The main elements of the system. DC/DC converter Capable of starting at 0.3 volts with small current A dual ported NV memory Can be read/written over a wired (SPI, ) or wireless (RFID) interface Such a element helps to program position information in the tag A phone equipped with NFC (or another RFID protocol) can be used to quickly program the tags Indy2050 Solar cell Graetzel Cell (cheap to manufacture) Good in office environment 35mm x 50mm Efficiency is getting better Smaller cells (IXYS Single Cell) were also tried Embedded World Conference, Nuremberg 1 st March Meli/Würth. Advertising position with battery-less Ble. 13

14 Frame format and contents Communication can occur In connected mode more energy needed More data exchange for agreement between parties In advertisement mode less energy, data in Adv frame. Format of the frame used to send data Needed fields are as shown below. lsb LL packet format Access address Preamble (1 octet) Access address (4 octets) PDU (2 to 39 octets) b (0x8E89BED6) (this is the access address of all adv. Packets) msb CRC (3 octets) Adv. PDU format Header (16-Bit) Pload (length in header) Header of ADV PDU PDU type (4 bits) RFU (2 bits) TxAdd (1 bit) RxAdd (1 bit) Length (6 bits) RFU (2 bits) PDU type ADV_ NONCONN_IND 0100 (b0 b3) Payload ADV_ NONCONN_IND ADVA (6 octets) ADV Data (0-31 octets) Embedded World Conference, Nuremberg 1 st March Meli/Würth. Advertising position with battery-less Ble. 14

15 Frame format and contents Format of the frame used to send data When enough energy is accumulated, the system will start up. Position data will be read, processed, then transmitted. Broadcasted data can be read by host, provided it is monitoring that channel at the time the data is sent. We made trials with several packets size as pload With a 16 bytes pload, the frame is 32 octets long. Format of frame used to send data Preamble Access adr. Header ADVA ADV data CRC 1 octet 4 octets (0x8E89BED6) 2 octets 6 octets Coordinates (e.g 16 bytes) 3 octets Software was written to be energy efficient The system waits for enough energy to be accumulated After start, radio initialised Position data is read from NV memory and processed as needed Data is sent on 1 or more ADV channels If the storage is large enough, the micro can be made to go in sleep mode and wait for a timer to wake it up. Embedded World Conference, Nuremberg 1 st March Meli/Würth. Advertising position with battery-less Ble. 15

16 Tests and results Several tests were carried out to evaluate various aspects of the system The current profile of a the system while processing and sending a typical frame was recorded an analysed. The effect of the luminosity on the time interval between measurements was observed. Different solar cells were tried Tags work also with very small cells Tests were made using only 1 ADV channel, or using the 3 ADV channels. For different luminosity, the time between ADV frames was measured. In an untimed system, the more energy (the higher the luminosity is), the faster the frames are sent. This is also a way of estimating luminosity. Embedded World Conference, Nuremberg 1 st March Meli/Würth. Advertising position with battery-less Ble. 16

17 Previous measurements: Made for a system that needed 130uJ) Light mostly from Neon tubes Cell type Quantiy Architecture Luminosity (Lux) Time between 2 frames (secs) IXYS Triple Cell 4 Parallel IXYS Single Cell 4 Series IXYS Single Cell G24i Indy Light mostly from the sun Cell type Quantity architecture Luminosity (Lux) Time between 2 successive frames (S) IXYS Triple Cell 4 Parallel IXYS Single Cell 4 Series IXYS Single Cell G24i Indy Mesurements during 169 Mins (2.8h), 1 frame sent every 11.3s. Adv on 1 channel Frames received by Sniffer on correct channel 900 Frames received by scanner (scanning 3 Adv channels) % received frames 69.11% lost frames Embedded World Conference, Nuremberg 1 st March Meli/Würth. Advertising position with battery-less Ble. 17

18 Tests and results The dynamic profile of the current shows how energy is used Constant power supply of 2.5 volts and RF output power of 0dBm. For the ADV packets used, overhead = 16 bytes, total bytes sent = 16 bytes + pload (per channel) Data sent on 1 ADV channel with stable power supply. Pload = 8 bytes.total energy from power on until data is sent is ~ 25mJ Up: VDD (1V/div) Down: IDD of system (5mA/div) Startup micro and transceiver Initialise, load data to send Send 1 ADV message Embedded World Conference, Nuremberg 1 st March Meli/Würth. Advertising position with battery-less Ble. 18

19 Tests and results The dynamic profile of the current shows how energy is used Constant power supply of 2.5 volts and RF output power of 0dBm. For the ADV packets used, overhead = 16 bytes, total bytes sent = 16 bytes + pload (per channel) Pload = 16 bytes, Data sent on all 3 ADV channels, one after the other. Total energy needed is ~54 mj. Up: VDD (1V/div) Down: IDD of system (5mA/div) Startup micro and transceiver Initialise, load data to send Send 3 ADV messages Embedded World Conference, Nuremberg 1 st March Meli/Würth. Advertising position with battery-less Ble. 19

20 Tests and results Power profile of the system powered using the solar cell and DC/DC converter. It can be clearly seen how the system voltage goes down as the storage is emptied. Care should be taken for the voltage to be high enough for all the packets. Up: VDD (1V/div) Down: IDD of system (5mA/div) Embedded World Conference, Nuremberg 1 st March Meli/Würth. Advertising position with battery-less Ble. 20

21 Tests and results Data was sent to a Ble receiver (captured here in sniffer mode) Position information can be can be seen in AdvData Field (here 16 bytes) Embedded World Conference, Nuremberg 1 st March Meli/Würth. Advertising position with battery-less Ble. 21

22 Tests and results Office luminosity is 1600 Lux, message sent on all 3 ADV channels Data is sent all 3 ADV channels. Office luminosity is ~1600 Lux. Solar cell (G24i) used to power the radio and micro. Pload = 8 bytes, RF power = 0dBm. About 2 seconds needed between messages with 1600 lux (compare with what happens before and after less light) Cstor = 33mF, Von = 2.4 Volts, Voff = 1.6 Volt 10sec/div, 0.5V/div ~1600 Lux Embedded World Conference, Nuremberg 1 st March Meli/Würth. Advertising position with battery-less Ble. 22

23 Tests and results Office luminosity at 400 Lux, message sent on all 3 ADV channels Data is sent all 3 ADV channels. Office luminosity is ~400 Lux. Solar cell(g24i) is used to power the radio and micro. Pload = 8 bytes, RF power = 0dBm. About 7.95 seconds needed between messages Cstor = 33mF, Von = 2.4 Volts, Voff = 1.6 Volt 5sec/div, 0.5V/div Embedded World Conference, Nuremberg 1 st March Meli/Würth. Advertising position with battery-less Ble. 23

24 Conclusions It is possible to power Ble (Bluetooth Low Energy) nodes with energy harvested using small and cheap solar cells A low-cost beacon node has been build with little components The node can be powered with a small solar cell designed for office environment. Less than 58 mj are needed to advertise on all channels in an environment of 400 Lux, sending data every 8 seconds. That should be enough for someone walking in a building Advertisement mode was used in order to limit the energy requirements Working on different channels helps to improve the quality (reduce interference problems) Advertising on 1 channel allows messages to be sent more frequently Data received by a mobile phone can be used for positioning Format of data and other mechanisms should be described and agreed upon by the BT SIG (otherwise, proprietary) For accuracy, references given in the paper should be consulted. Future work: Host implementation part + tests in building Embedded World Conference, Nuremberg 1 st March Meli/Würth. Advertising position with battery-less Ble. 24

25 Thanks, more information Thanks to the following firms for their help and support. EM Microelectronics SA in Marin, Switzerland G24i in Wales For more information: Michael Würth, Bsc in Computing Prof. Dr. Marcel Meli, Head of Wireless Systems Groupce Zurich University of Applied Sciences (ZHAW) Institute of Embedded Systems (InES) Technikumstr. 9 CH-8401 Winterthur Phone: Embedded World Conference, Nuremberg 1 st March Meli/Würth. Advertising position with battery-less Ble. 25

26 Question time????? Embedded World Conference, Nuremberg 1 st March Meli/Würth. Advertising position with battery-less Ble. 26

27 Our activities Wireless automation with different energy harvesting sources The receiver controls a lamp The sender can use different power sources Works with /Zigbee and other wireless protocols Electro-dynamic Seebeck Solar Embedded World Conference, Nuremberg 1 st March Meli/Würth. Advertising position with battery-less Ble. 27

28 Our activities 6WLoPAN-Ethernet Bridge CAN, JTAG Cortex M3 with 1588 PTP support USB module PoE HW Ethernet 100 Mb/S 6WLoPAN-Ethernet Bridge Embedded World Conference, Nuremberg 1 st March Meli/Würth. Advertising position with battery-less Ble. 28