Zürich University Of Applied Sciences Institute of Embedded Systems InES Using FRAM in battery-less 802.15.4/zigBee applications (Presented at the 6 th European ZigBee Developers Conference Munich, 28 th June 2012) Prof. Dr. Marcel Meli Dipl. Ing. Marcel da Silva Contact: Marcel.meli@zhaw.ch 6 th European ZigBee Developers Conference, Munich 28 th June 2012. da Silva/Meli. Using FRAM in battery-less 802.15.4/ZigBee applications. 1
Outline A short presentation of our activities in low power wireless Introduction and motivation Challenges when implementing battery-less for 802.15.4 networks Wireless switch as example Tests and results Conclusions Questions 6 th European ZigBee Developers Conference, Munich 28 th June 2012. da Silva/Meli. Using FRAM in battery-less 802.15.4/ZigBee applications. 2
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, 1588...) Wireless: WPAN, RFID, UWB, Energy harvesting, very Low power applications Examples of Low power developments: Passive, Intelligent RFID Tag (RF harvesting) 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 6 th European ZigBee Developers Conference, Munich 28 th June 2012. da Silva/Meli. Using FRAM in battery-less 802.15.4/ZigBee applications. 3
Our activities 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 6 th European ZigBee Developers Conference, Munich 28 th June 2012. da Silva/Meli. Using FRAM in battery-less 802.15.4/ZigBee applications. 4
Our activities 6LoWPAN-Ethernet Bridge (Based on Cortex M3) Mobile node with cortex M0 also available. Running on EH CAN, JTAG Cortex M3 with 1588 PTP support USB 802.15.4 module PoE HW Ethernet 100 Mb/S 6LoWPAN-Ethernet Bridge 6 th European ZigBee Developers Conference, Munich 28 th June 2012. da Silva/Meli. Using FRAM in battery-less 802.15.4/ZigBee applications. 5
Our activities Wireless automation with different energy harvesting sources The receiver controls a lamp The sender can use different power sources Works with 802.15.4/Zigbee and other wireless protocols Electro-dynamic Seebeck Solar 6 th European ZigBee Developers Conference, Munich 28 th June 2012. da Silva/Meli. Using FRAM in battery-less 802.15.4/ZigBee applications. 6
Introduction and motivation Battery-free wireless sensor nodes are very convenient in many applications. (Measurement, building automation, ) Eliminate the costs associated with installing batteries. Reduce maintenance (and logistics) headaches. Can have a positive ecological impact (if well designed and well integrated in the system) For these reasons (and many more), they are gaining in popularity. There are limitations to the kind of application and wireless protocol that can successfully be implemented. Costs: EH systems are expensive (compared to battery powered) The actual justification is related to low installation and maintenance costs Amount of energy delivered Can the application work with the small amount of energy delivered by EH? The interest in 802.15.4-based wireless systems such as ZigBee has also led to its consideration for battery-less nodes. But, High overhead required in ZigBee more energy needed drives costs 6 th European ZigBee Developers Conference, Munich 28 th June 2012. da Silva/Meli. Using FRAM in battery-less 802.15.4/ZigBee applications. 7
Introduction and motivation This work shows that some of the new NV (non volatile) memories can: Help improve the quality of the design Improve the energy performance of EH (Energy Harvesting) powered nodes Reduce costs In this presentation we will: Review the parts needed in a wireless battery-less sensor Briefly talk about the complexity of the parts, and associated costs Present the challenges for 802.15.4/ZigBee in applications where little energy is available. Show how FRAM can be used to solve some of the challenges. Points illustrated by showing some energy measurements using FRAM Based on a wireless switch application, using different processors Our proposition is: By using FRAM, the quality and performance of EH powered 802.15.4/ZigBee wireless nodes is improved. This is also helpful in reducing the costs of nodes working on EH. 6 th European ZigBee Developers Conference, Munich 28 th June 2012. da Silva/Meli. Using FRAM in battery-less 802.15.4/ZigBee applications. 8
Typical sensor node Block diagram of a wireless sensor node powered with EH Energy Harvester Energy conditioning DC/DC Up/down converter Microcontroller 802.15.4 Transceiver 2.4 GHz Antenna Storage Sensor/ Actuator Costs are related to 2 major factors (the factors are also linked) Harvester cost: depends on the harvesting method and needed energy E.g. Small or large solar cell The energy available is often small and variable in quantity over time Conditioning, power management and storage should match the application Energy conditioning + DC/DC add to the costs Storage can vary from a simple capacitor to expensive rechargeable element Microcontroller + transceiver are normally low cost devices. 6 th European ZigBee Developers Conference, Munich 28 th June 2012. da Silva/Meli. Using FRAM in battery-less 802.15.4/ZigBee applications. 9
Typical sensor node Battery with the proper voltage will replace many parts in EH system Battery Microcontroller 802.15.4 Transceiver 2.4 GHz Antenna Sensor/ Actuator It is therefore important to find ways of reducing the costs of energy management system in EH wireless nodes. Keep the harvester as cheap as possible ( reduce energy needs) Keep the storage small and easy (simple capacitors when possible) Certain rechargeable elements introduce much complexity and also weakens the system limited number of recharges, gradual loss of storage over the years, As much as possible, use the energy as it is produced Accumulate energy only for tasks that cannot wait or be suspended 6 th European ZigBee Developers Conference, Munich 28 th June 2012. da Silva/Meli. Using FRAM in battery-less 802.15.4/ZigBee applications. 10
Typical sensor node Energy Harvester Energy conditioning DC/DC Up/down converter Microcontroller 802.15.4 Transceiver 2.4 GHz Antenna Battery Storage FRAM Components such as microcontroller and radio are getting better they need less energy. So their energy need has been(and is) going down. This is an advantage with standard wireless systems Some of the problems associated with energy will become easier to solve Several manufacturers competition quality and price improve Competition for market shares Better radios, better microcontrollers (reduced prices and energy needs) 6 th European ZigBee Developers Conference, Munich 28 th June 2012. da Silva/Meli. Using FRAM in battery-less 802.15.4/ZigBee applications. 11
Typical sensor node NV memory can help lower the complexity Energy Harvester Energy conditioning DC/DC Up/down converter Microcontroller 802.15.4 Transceiver 2.4 GHz Antenna Storage FRAM Sensor/ Actuator Save states between runs, without fear of losing important data if there is not enough power The system can safely be switched off if needed The processor can be made to work with the available energy, reducing some of the complexity of accumulation/storage process But it is important to use NV memory That does not consume much energy That can be read/written fast (tens to hundreds of ns) That can be used for the lifetime of the product (millions of read/write cycles) 6 th European ZigBee Developers Conference, Munich 28 th June 2012. da Silva/Meli. Using FRAM in battery-less 802.15.4/ZigBee applications. 12
Challenges while implementing EH nodes for ZigBee There are several challenges when using EH and 802.15.4/ZigBee We will not go into much details, more information in presentations given at the European ZigBee Developer s Conferences in the previous years. 2008 First battery-less switch using the ZigBee protocoll 2009 Pairing issues discussed 2010 Using tiny solar cells for ZigBee A short review of some challenges: The energy problems associated with the large overhead in communication Large overhead more data to transmit/receive more energy required Updating the counters (APS) Needs to be done in NV memory. Often! Flash and EEPROM limited in write cycles Channel changes How does a non-powered node learn about a channel change? Problems associated with joining the network and binding end points There might not be enough energy to start a joining procedure that needs several data packets (energy problems). Add-on to Zigbee might address some issues (Green power) 6 th European ZigBee Developers Conference, Munich 28 th June 2012. da Silva/Meli. Using FRAM in battery-less 802.15.4/ZigBee applications. 13
Challenge1: overhead of ZB is too large more energy Switch example: The overhead is important Octets 2 1 0/2 0/2/8 0/2 0/2/8 0/5/6/10/14 Variable 2 Fields MAC Frame control Sequenc e number Dest. PAN Dest. Addr. Source PAN Source Addr. Security Header Payload FC S Example 2 1 2 2 0 2 0 Variable 2 Octets 2 2 2 1 1 0/8 0/8 0/1 var var Fields Frame Dest. Source Radius Seq. Dest. Source Multicast NWK control Addr. Addr. Nber Addr. Addr. cntr. Src. Route subfr. Frame payload Octets 1 0/1 0/2 0/2 0/2 0/1 1 Variable Fields APS Frame control Dest. endpoint Group Addr. Cluster Id. Profile Id. Source endpoint. APS counter Payload The red is actually the information you want to work on Lots of other bytes going with (+ 6 bytes at PHY level) 6 th European ZigBee Developers Conference, Munich 28 th June 2012. da Silva/Meli. Using FRAM in battery-less 802.15.4/ZigBee applications. 14
Challenge1: overhead of ZB is too large more energy To be able to send switch commands for ZigBee, the following is needed: Clear channel assessment (switch on the receiver to verify channel activity) Transmit ~ 30 + 2 + 6 = 38 bytes. (30 bytes of data + 2 bytes (FCS) on MAC layer, 6 Bytes for PHY overhead) All these layers will also mean more time/energy is required Receive ACK and react. Resent if data was not received Or do nothing ( you can also ignore the ACK) The overhead is important you waste most of the energy This is not really wasted because many extra bytes contribute to the flexibility of 802.15.4/ZigBee As energy needs are reduced in other areas, this flexibility could keep you going. Protocols that were designed too just have little room for growth or have to use cumbersome ways to deal with new needs. 6 th European ZigBee Developers Conference, Munich 28 th June 2012. da Silva/Meli. Using FRAM in battery-less 802.15.4/ZigBee applications. 15
Challenge2: Joining, binding more energy We will just say pairing. With pairing we refer to all what is needed to set up the communication so that 2 end devices can properly and securely exchange information Proper frequency channel, joining a network, binding end points, security parameters, Pairing involves the exchange of many parameters (channel number, src/dest/pan addr, endpoint ID... ) 6 th European ZigBee Developers Conference, Munich 28 th June 2012. da Silva/Meli. Using FRAM in battery-less 802.15.4/ZigBee applications. 16
Wireless switch (popular example) Prototypes were built (with and without FRAM) using the elements below ECO100 Energy Harvester Energy conditioning LDO Microcontroller 802.15.4 Transceiver 2.4 GHz Antenna Stable power supply For tests Small capacitor FRAM Measurements made for: System without FRAM (EEPROM used as NV memory) System with FRAM (instead of EEPROM) Different microcontrollers (from: Texas, Atmel, NXP) The point here is not the comparison of microcontrollers. We simply show different ways of using the FRAM and the impact on energy EH as power, stable supply as power 6 th European ZigBee Developers Conference, Munich 28 th June 2012. da Silva/Meli. Using FRAM in battery-less 802.15.4/ZigBee applications. 17
Wireless switch example FRAM Microcontroller MSP430FR5739, Texas Instruments. Features an FRAM as NV memory. The use of this FRAM opens the doors to very interesting concepts. Partition of memory for code and data is flexible cost reduction There are not many microcontrollers with FRAM on the market. A couple of other firms are also preparing such devices Own (the one you know) microcontroller + external FRAM can also be used This option enables to use a micro that one wants, providing that it is a low power microcontroller. Low power FRAM FM25P16 from Ramtron (16Kb device) VDD range: 1.8 3.6 V Current =3.2mA @ 100 KHz Current =35mA @ 1 MHz SPI serial communication until 1 MHz Needs 1ms to power up 6 th European ZigBee Developers Conference, Munich 28 th June 2012. da Silva/Meli. Using FRAM in battery-less 802.15.4/ZigBee applications. 18
Wireless switch example Microcontroller from Atmel ATmega324PV 8-Bit micro with EEPROM as non-volatile memory. Works down to 1.8 V Microcontroller from NXP NXP LPC1114 32-Bit (cortex M0) Works down to 1.8 V Transceiver from Atmel AT86RF231 Used already in our first work (no longer the best in terms of energy, but widely available) >12 ma Tx/Rx current @ 0dBm 6 th European ZigBee Developers Conference, Munich 28 th June 2012. da Silva/Meli. Using FRAM in battery-less 802.15.4/ZigBee applications. 19
Tests Test set-up Wireless battery-less switch built by ZHAW-InES Lamp with ZigBee receiver from Adhoco Dynamic power measurement system from Agilent used to monitor energy 802.15.4 sniffer used to verify frames Transmitter set at 0dBm Harvester, diodes, storage, capacitors FRAM Micro Transceiver 6 th European ZigBee Developers Conference, Munich 28 th June 2012. da Silva/Meli. Using FRAM in battery-less 802.15.4/ZigBee applications. 20
Results: micro including FRAM (EH without LDO) Update of APS in NV. FRAM FRAM is used to update APS in non-volatile counter EH is used. Voltage still high enough after the whole operation is completed Less than 50mJ is enough (EH voltage high) (To give an idea: this is about 40 year on a CR2032 pressing the switch every minute limited by self discharge) 6 th European ZigBee Developers Conference, Munich 28 th June 2012. da Silva/Meli. Using FRAM in battery-less 802.15.4/ZigBee applications. 21
Results: Micro with on chip EEPROM (EH without LDO) Update of APS in NV. EEPROM EEPROM used to update APS in non-volatile counter EH is used. No LDO or comparator. Voltage high more energy Voltage gets dangerously low (program not optimised) 6 th European ZigBee Developers Conference, Munich 28 th June 2012. da Silva/Meli. Using FRAM in battery-less 802.15.4/ZigBee applications. 22
Results: Micro with EEPROM Update of APS in NV. EEPROM (in micro) EEPROM used to update APS in non-volatile counter EH is used with LDO and comparator to keep voltage low EEPROM is first read, incremented and written back (erase + write) 6 th European ZigBee Developers Conference, Munich 28 th June 2012. da Silva/Meli. Using FRAM in battery-less 802.15.4/ZigBee applications. 23
Results Micro with integrated FRAM FRAM is used to update APS in non-volatile counter Stable power supply, @ 2volts Less than 40mJ is enough to complete the task (compared to 70mJ with EEPROM) Start up of systems, initialize, send Looking only at the processing, sending, 30mJ will be enough 6 th European ZigBee Developers Conference, Munich 28 th June 2012. da Silva/Meli. Using FRAM in battery-less 802.15.4/ZigBee applications. 24
Results: 8-bit micro and serial FRAM FRAM is used to update APS in non-volatile counter Stable power supply, @ 2volts About 41mJ is enough to complete the task (compared to 70mJ with EEPROM) Start up of systems, initialize, send FRAM energy needs very small (mostly from SPI) 6 th European ZigBee Developers Conference, Munich 28 th June 2012. da Silva/Meli. Using FRAM in battery-less 802.15.4/ZigBee applications. 25
Results: 32-Bit micro with serial FRAM FRAM is used to update APS in non-volatile counter Stable power supply, @ 2volts About 47mJ is enough to complete the task (41mJ without the sleep) Start up of systems, init, sending (compared to 70mJ with EEPROM) The FRAM energy need is very small (mostly from SPI) 6 th European ZigBee Developers Conference, Munich 28 th June 2012. da Silva/Meli. Using FRAM in battery-less 802.15.4/ZigBee applications. 26
Results: 8-bit micro with serial FRAM (EH + LDO) FRAM is used to update APS in non-volatile counter Energy from EH and external LDO About 40mJ is enough to complete the task Start up of systems, init, sending FRAM energy needs very small (mostly from SPI) 6 th European ZigBee Developers Conference, Munich 28 th June 2012. da Silva/Meli. Using FRAM in battery-less 802.15.4/ZigBee applications. 27
Results: 32-Bit micro with serial FRAM (EH +LDO) FRAM is used to update APS in non-volatile counter Energy from EH and external LDO About 43mJ is enough to complete the task (37mJ without the sleep) Start up of systems, init, sending FRAM energy needs very small (mostly from SPI) 6 th European ZigBee Developers Conference, Munich 28 th June 2012. da Silva/Meli. Using FRAM in battery-less 802.15.4/ZigBee applications. 28
Sniffer: 1 activation, 2 frames sent, FRAM micro used Packet index: 1 Length: 32 Raw data (hex): 41 88 01 32 00 01 00 6F 79 48 00 00 00 6F 79 0A 01 00 0A 06 00 04 01 10 07 11 53 02 46 C9 RSSI [dbm]: -52 Correlation value: 108 CRC OK: 1 Packet index: 2 Length: 32 Raw data (hex): 41 88 01 32 00 01 00 6F 79 48 00 00 00 6F 79 0A 01 00 0A 06 00 04 01 10 07 11 53 02 46 C9 RSSI [dbm]: -53 Correlation value: 108 CRC OK: 1 Packet index: 3 Length: 32 Raw data (hex): 41 88 01 32 00 01 00 6F 79 48 00 00 00 6F 79 0A 01 00 0A 06 00 04 01 10 08 11 53 02 46 C9 RSSI [dbm]: -55 Correlation value: 108 CRC OK: 1 Packet index: 4 Length: 32 Raw data (hex): 41 88 01 32 00 01 00 6F 79 48 00 00 00 6F 79 0A 01 00 0A 06 00 04 01 10 08 11 53 02 46 C9 RSSI [dbm]: -56 Correlation value: 108 CRC OK: 1 6 th European ZigBee Developers Conference, Munich 28 th June 2012. da Silva/Meli. Using FRAM in battery-less 802.15.4/ZigBee applications. 29
Conclusions Use of FRAM as NV memory in battery-less wireless sensors possible. Needs far less energy with FRAM compared to EEPROM. 40mJ - 50mJ compared to 70mJ with EEPROM More energy available for retransmit or other activities Can use micros with integrated FRAM There are not yet many of them on the market Can also use micros with serial low energy FRAM 8-Bit 32-Bit Results comparable Use of FRAM improves quality and life time (needed for EH) FRAM can be rewritten millions of time (lifetime of the product) Flash can be rewritten thousands of time EEPROM can be rewritten about hundred thousand times The properties of FRAM mean that It is possible to save processor status and when there is not enough power. One can use FRAM to save and restore processor status (fast, little energy) Use energy when available less costs for power management 6 th European ZigBee Developers Conference, Munich 28 th June 2012. da Silva/Meli. Using FRAM in battery-less 802.15.4/ZigBee applications. 30
Thanks, more information Thanks to NXP,TI and Ramtron for providing devices For more information: Marcel Da Silva, Bsc in Computer Scienceskizhakenath@zhaw.ch Prof. Dr. Marcel Meli, Head of Wireless Systems Groupcel.meli@zhaw.ch Zurich University of Applied Sciences (ZHAW) Institute of Embedded Systems (InES) Technikumstr. 9 CH-8401 Winterthur Phone: +41 58 934 75 25 6 th European ZigBee Developers Conference, Munich 28 th June 2012. da Silva/Meli. Using FRAM in battery-less 802.15.4/ZigBee applications. 31
Question time????? 6 th European ZigBee Developers Conference, Munich 28 th June 2012. da Silva/Meli. Using FRAM in battery-less 802.15.4/ZigBee applications. 32