a brief historyread.pudn.com/downloads192/doc/902617/4up-sensornethw.pdf · cpu type @[mhz] 32bit...

Wireless Sensor Network (WSN)Platforms

Christian Decker

Universität Karlsruhe

Institut für TelematikTelecooperation Officewww.teco.uni-karlsruhe.de

TecO 2Wireless Sensor Network Platforms

A Brief History

! 1978 DARPA-sponsored Distributed Sensor Nets Workshop (CMU), tracking for military applications

! 1993 WINS (UCLA): system design, networking, sensing, signal processing

! mid-1990s DARPA low power wireless integrated microsensors (LWIM)

! 1998 SensIT: distributed military sensor systems (29 research projects, 25 institutions)

! 1998 first spin-off Sensoria from WINS

! 1998 Smart Dust, MEMS based motes

! 1999 PicoRadio (UCB): ad hoc wireless network for low-cost, low energy sensor and monitoring nodes

! 2000 !AMPSFocus on sensor network comm. Protocols, LEACH

! 2001 Terminodes, MANET: low-power routing under mobilityand TCP/IP usage

! 2003 EU IST FP7 work program on Ambient Intelligence (AmI)

! 2007 EU Framework 7, „Cooperating Objects“


Early Platforms (1)

ISSS (1990-1994)

! 250 sensors (temperature, pressure, flow)

! 45 control points (valves, power)

! 22 distributed processing nodes

Implementation

! Mock-up (nuclear) power plant

! Boiler, heat exchangers, pumps, by-pass circuits

! Primary water coolant


Early Platforms (2)

SKIDS (1986-1991)

! EU FP1 project

! Distributed Tracking of people

! Cameras with embedded processing

! optical barriers, acoustic sensors

WSN like communication issues

! Non-fully connected networks

! Time varying and ad-hoc networks

! Communications management

! Distributed processing and data fusion


WSN Platform overview I just picked some....

Germany

! Some companies started, mostly university‘s spin-offs

! Lots of research platforms

World wide

! Several dozens commercial platforms from Start-ups, Spin-offs and other organisations

! Huge diversity of research platforms


Platform Diversity ... and it‘s growing


Drawing a lot of Comparisons

15.4 (BT/802.11)300-900MHz802.15.4802.15.4BTRadio

250 (720/11,000)15250250720Bandwidth [kb/s]

TinyOSTinyOSTinyOSTinyOSTinyOSOS support

YNAES-128AES-1284LFSR-128Security HW

1-100196271-250Power sleep [uA]

40/20/188 / 10 / 271 / 20 / 188 / 20 / 1815 / 24 / 24Power C/R/T [mA]

32,000128 + 51248 KB / 1024 KB128 + 512512FLASH [kB]

256/32,000410464SRAM [kB]

32b XS@13(104)8bit Atmel @816bit TI @88bit Atmel @832bit ARM @12CPU type @[MHz]

Imote 2Mica2TelosMicazImoteFeature


How to proceed?

Goal

! Learn a systematic way to the design and evaluation of wireless sensor network platforms

Method

! Decompose sensor network platforms

! Find design criteria

! Identify design choices

! Explain trade-offs


Lecture Outline

!Platform Design

!Radio Communication

!Sensors

!Energy


Design Criteria (1)

! Application computational requirements

" RAM, ROM, MIPS

! Ability to use host resources

" Host integration, e.g. PDAs, cell phones, controller,takes over some functionality

! Market flexibility

" Energy scavenging, radio frequency support (315 MHz, 433 MHz, 868 MHz, 2.4 GHz)

! Physical size

" Size of battery, antenna, integration with other systems

! Time to market

" Level of use of standard components vs. Integrated approach


Design Criteria (2)

! Networking capabilities

" Single vs. Multi-hop, multi-tier network architecture

" FFD vs. RFD in IEEE 802.15.4

! Chip-to-Chip Connectivity

" Noise, higher capacitance, higher power consumption

! Power source diversity

" power conditioning for energy scavenging techniques,rechargeable batteries, low power operations

! Packaging

" Material costs, design amortization

And there a certainly more...


Separation of Concerns

! Concept of breaking a computer program in distinct functionalities

! Probably coined by Edsger W. Dijkstra in "On the role of scientific thought" (1974)

" “..."the separation of concerns", which, even if not perfectly possible, is yet the only available technique for effective ordering of one's thoughts, that I know of.”

" “focusing one's attention upon some aspect“

! Seems to be a recurrent design pattern also for WSN

Examples

! Processor – transceiver

! Communication protocol – transceiver

! Sensor board – communication board

! Power source – power consumer


Lecture Outline

!Platform Design" Components & Partitions

" Microprocessors


!Sensors

!Energy


Platform Components

Source:Callaway, Wireless Sensor Networks


Separation Decisions (1)

! All-in-one, SoC

RF TranceiverProtocol Handler

App. Processor

Data


App. Processor

Data

! Separates transceiver from the rest of the node

Example: Jennic, JN5139

Example: TecO Particle


Separation Decisions (2)

! Separate comm. protocol and application

RF Tranceiver Protocol HandlerDataApp.

Processor


App. Processor

Data

! Separate power conditioning from

Power

Conditioning

Example: BTNode rev3


Separation Decisions (3)Integration with Host

! Use regular sensor node

! Connector to embedded or PC system

! Serial line or USB interface dominant

Node

Components

DataHost

Interface

(serial, usb)

Network


Application ProcessorDesign Choices

Application-Specific Integrated Circuit (ASIC)

! Fast, low power

! Hardwired functionality, single purpose, high development costs

Field-Programmable Gate Array (FPGA)

! Transistor overhead # waste power!

! Used for prototyping

! But: Gets better, becomes more important

Microprocessors, -controller

! Slower (software), performance/watt low

! Flexibility compensates: control power consumption (powersaving modes), software is energy aware

! Multi-purpose device: same hardware runs multiple applications

! Fast and low-cost development, i.e. upgrades, patches, and reuseing, simplifies design of families of products


Application ProcessorMicroprocessors

Taxonomy

! Embedded processors

" RISC orr RISC-“like“ microcontrollers (MCU), 5-10 MIPS

" Integrated RAM, Program-ROM, A/D, I/O, WDT, ...

! Dedicated processors

" Digital signal processors (DSP), >30 MIPS

" basieren inzwischen oft auf eingebetteten Prozessoren

! System-on-Chip, SOC

" Wireless microcontroller, MCU + RF transceiver

" Often two cores in one housing

Processor architecture

! von Neumann

! Harvard


Harvard vs. Von Neuman

Von Neuman

! Volatile, energy consuming RAM (SRAM 1MB ca. 15mA) for program + data

! flexible

Harvard

! Data volatile, Progr. fix (ROM, Flash, EEPROM)

! Fast boot

! Data do not corruptprogram

! Keine Energie für Speichern Programme

! typ. energy consumption <10mA

! Faster, 2 Busses

Memory

CPUAddr.

Data Program Counter

Data

Memory CPUAddr.

Data

Program CounterPrg.

Memory

Addr.

Instructions


Popular Processors

Embedded Processors

! Arizona Microchip PIC Reihe (8-bit, 16-bit, Harvard)

" Huge number of derivates (several hundreds), contain busses and networks (CAN, RF,...)

" 1k-128k Flash Program memory, 32byte-8k RAM, bis 33 MIPS

" Low energy consumption (<8mA @5 MIPS), compatibility (similarcore) between derivates

! ATMEL AVR (8bit, Harvard)

" Market leader, several dozen derivates

" 1k-128k Flash, 32byte-4k RAM, max 20 MIPS

" Low energy consumption (<10mA @ 5MIPS)

! TI MSP430 (16 bit, von Neumann)

" several dozen derivates

" Bis 64 k Flash, 10 k RAM

" 5 Power Modi, extremly low energy consumption (few mA bis uA)

! 8051 verwandte Architekturen (Kern inzwischen frei!)


PIC 16F876

! Harvard architecture, RISC (35 Instruktionen), up to 20 MHz, 5 MIPS, power supply 2-5.5V

! ROM: 8K, RAM: 68 bytes

! Low Cost (2 Euro), Low Power

" < 0.6 mA typical @ 3V, 4 MHz

" 20 !A typical @ 3V, 32 kHz

" < 1 !A typical standby current

! Compact core, many I/O interfaces

! E.g. A/D, SPI, serial, I2C,...

! (almost) no further components required

! Programming: C,Assembler

Example: Arizona Microchip PIC

ProgramMemory

RAM

Processor

Port A (A/D)

Port B (INT)

Port C (I/O, SPI, I2C, Ser)

Timer

Power-Up

WDT

Brown Out


Jennic, MCU+Zigbee (SOC)

Jennic JN5139, wireless microcontroller

! 32-bit RISC, 32MIPs, low power

! 192kB ROM for system code, protocol stack

! Up to 96kB RAM for data and bootloader

! 48-byte OTP eFuse: MAC ID, AES based code encryption

! On-chip power regulation for 2.2V to 3.6V

Communication

! 802.15.4 MAC and Zigbee protocol stack, 250 Kbit/s

! supporting co-ordinator, routerand end device

! Power consumption

! RX / TX: 34mA

! Deep Sleep: 0,2 uA

Interfaces

! 12-bit ADC, 11-bit DACs,

! 2 UARTs, 1 SPI, 2-wire serialinterface, up to 21 GPIO

Source:jennic.com


Lecture Outline

!Platform Design

!Radio Communication" Components and Design Choices

" Antenna

" Power Consumption

!Sensors

!Energy


Radio Subsystem

Components

! Transceiver

" (De-)Modulation, filtering, frequency generation, RSSI provision, gain control, frame synchronization data(de-)encoding, optional CRC

! Protocol

" Data format, payload packet structure

! Antenna

" Forms, material, characteristics

RF Tranceiver Protocol HandlerData

Antenna


Popular Radio Transceivers

Source:http://www.btnode.ethz.ch/Projects/RadioSystems


Radio Choices

! Too early to commit to a single radio for WSN

! Lots of RF chips available

" Providing carrier and modulation scheme, e.g. RFM TR1001

" RF modem solutions: wire replacements, e.g. radiometrix

" Standardized solutions: Phy, Mac, Network, Data format, e.g. Bluetooth, Zigbee

! Different applications might need different radios

" 802.15.4 (Zigbee Mac):medium data rate, low power

" Bluetooth: ubiquitous

" Wifi 802.11: installed infrastructure available

# Separation of Concerns

! Other requirements: antenna, bandwidth, range, power consumption


Example: BTNode

Dual radio approach

! High performance inter-node comm. (Back-bone)

" Bluetooth subsystem: Zeevo ZV4002, supporting AFH/SFH

" Scatternets with max. 4 Piconets/7 Slaves, BT v1.2compatible

! Low bandwidth inter-node comm.

" Low-power radio: Chipcon CC1000 operating in ISM band 433-915 MHz

" Compatible with Mica2

Zeevo ZV4002

CC1000

Source: BTNodes Hardware Reference


Example: Intel Imote!

! Imote" has an onboard ChipCon CC2420 (802.15.4)

! Other radio options via SDIO cards and UART/USB! SDIO connector too big (30x30 mm) and costly ($1.74) ! Only pins exposed through basic connector! SDIO connector board on your own

802.11b

Bluetooth

36

mm

48 mm

Advanced I/O

connector

Advanced I/O

connector

Crystal

Antenna

Optional SMA

connector

Mini USB

Connector

CC2420

Source:Lama Nachman, Intel Corporation Research


Antenna

Printed antenna

! Inexpensive

! Depends on dielectric and thickness of the board

! Inductor for tuning

SMD (chip) antenna

! SMD, Compact, cost-effective

! 868MHz,915MHz,2.45GHz

! Omnidirectional (horizontal)

! Separate from layout

Whip antenna

! Very simple, just a wire

! Omnidirectional (horizontal)

! Requires a large ground plate

Source: antennafactor.com Source: ETH

BTNode rev.3

Layout!

Particle 1/81

Source: RFM.com


Monopole Antenna (Whip)Radiation Pattern

Side View Top View

Communication

range

Symmetric Region Antenna orientation

independent regions

Communication

range

Source: Andreas Savvides"Sensor Network Hardware Platform Design"


Effects of Antenna Orientation

! RSSI: Receiver signal strength indicator

! Provided by radio hardware

! Foundation for location estimation


Eqn: Log-normal location model

Best angleWorst angle

No Comm.

Setup:

TX Power -15dBm


Effects in 3D

! Radio operates best in 2D plane

! Antenna effects become dominant at different heights

Conclusion

! In 2D

! good models for radio propagation (log-normal shadowing model)

! Most models applicable in symmetric propagation region

! In 3D:

! strong antenna effects (orientation, height)

! Increase rate of asymmetric links Source: Andreas Savvides

"Sensor Network Hardware Platform Design"

Setup:

TX Power -15dBm


Power Consumption

! Example: Chipcon CC2420 (IEEE 811.15.4) Radio Power Levels

-25

-15

-10

-7

-5

-3

-1

0

TX Power(dBm)

15.3

17.82

20.16

22.5

25.02

27.36

29.7

31.32

PowerConsumed(mW)

8

7

6

5

4

3

2

1

Level

)mW(1mW

P(mW)20logP(dBm) =

Avg. MCU consumption24mW



Lecture Outline

!Platform Design


!Sensors" Sensor boards

" Analog and digital sensors

" Sensor interfaces

!Energy


Design criteria

! Flexibility: separate communication from sensors (separation of concerns)

" Easy integration of new (specialized) sensors

" Complex: connector, mechanical robustness, housing

" Example: Motes, Particles

! Price: all on one board

" Compact design, small

" low flexibility

" Example: ESB, uPart

Sensor Boards

ESB, Source: SchilleruPart

Mote and sensorboard, Source:Xbow.com


Case study: Particle Sensors

Example: Generic Sensor board (Particle)

! Low power design

! Separate Co-processor for sensor processing (separation of concerns

! Sensors:

" Microphone, light, temperature, force, acceleration, movement

! Serial, I2C, SPI, A/D, PWM interfaces


Case study: uPart

! Idea: all-in-one, tiny, inexpensive

Technology

! MCU: 12F675 @ 4 MHz

! Memory: Program-Flash 1.4 kByte, RAM 64 Byte, EEPROM 128 Byte

! Communication: transmitter only

" 869 Mhz / 315 Mhz

" 2-FSK, ALOHA protocol

" 15m indoor, up to 30m outdoor

! Sensors

" Light, temperature, movement,voltage

! Power supply

" CR1632 coin cell

" Several months (~35s duty cycle)

uPart 1/40


Analog & Digital Sensors

Analog sensors

! Sensor output voltage encodes the sensor value

! ADC translates in digital value

Digital sensors

! Sensor value encoded as “1“ and “0”

! Example: Pulse-width modulation (PWM)

Internal Sensors

! MCU contains sensor, e.g. temperature

! Read out via memory mapped register, or specific ADC channel, e.g. MSP430

MCUSensor

GND

Vdd

Source: ADXL Datasheet


Analog-Digital Converter (ADC)

! From Analog to Digital

V(t)

The Digital Signal: 0010 0100 0100 0001…

ADC

Properties

! Sampling rate

! frequency of ADC usage

! limited by conversion time

! few us up to 10s of us

! Resolution

! vendor specific, e.g. 10bit (PIC18F), 12bit (MSP430)

Implementations

! Flash, Successive-Approximation, Sigma-Delta, Ramp-Compare, Pipeline

Source: http://entertainment.howstuffworks.com/analog-digital3.htm

MCUADC

SMD Mic

Example:Microphone


ExampleRamp-Compare ADC

Function

! Counter resets to 0 and counts up

! Comparator compares measured value andDACed counter

! V_measure == V_counter # stop counting, conversion done

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MSP430Internal Temperature Sensor

Features

! Low power

! Good accuracy, 12bit A/D conversion

! A bit noisy # 0.5°C accuracy (empirical value)

! Needs device specific calibration: V_SENSOR(0°C) = 986+/-5% mV # +/- 14°C

Calculation

! T [°C] = (V_SENSOR(T) – V_SENSOR(0°C)) / TC_SENSOR

Source: MSP430 Datasheet


Digital Sensors:Movement Sensor

Features

! Binary sensor, ballswitch (on/off state)

! Motion detection, orientation dependent

! No current, really low power sensor!

Encapsulated ball,

Shake it, you hear it!

• count #states (on/off)

• continous state length

• on/off cycle

Signal (ideal) :Switch opened Vdd

Switch closed GND

GND Vdd

ADXL acceleration sensor

and ball switch


Digital SensorsAcceleration sensor

Example: ADXL202/210

! Micro-Electro-Mechanical Systems (MEMS)

! High accuracy

! Needs calibration

Sensor signal: Pulse-width modulation (PWM)

! g value encoded as ratio T1/T2 (=Duty cylce)

! 0 g = 50 % duty cycle

! Scale factor 4% per g

Source: ADXL Datasheet

Source: Microchip.com

Source: Grace Kim, itp.nyu.edu


Digital SensorsSensor Bus

Sensors

! Usually more complex: Sensor + interpretation electronic+ protocol + bus driver

! Typical bus interfaces: I2C, One-Wire

http://www.maxim-ic.com/appnotes.cfm/an_pk/4024


Popular Sensors

! Light (usually analog or PWM and some I2C) " Thermopile (mostly analog, some PWM) " Ultraviolet (analog or PWM) " IR (analog, PWM, and a few I2C) " Visible Light (analog, PWM, and a few I2C) " Color sensors (PWM)

! Magnetic (analog, I2C) ! Sound (analog)

" Ultrasound (analog, PWM) ! Accelerometers (SPI, I2C, analog and PWM) ! Temperature sensors (I2C, analog and PWM) ! Pressure sensors (analog, SPI) ! Humidity (custom I2C) ! Touch sensors (analog or PWM)


Problems with Sensors

! Systematic problems

" Sensors must be aligned to an application

! Orientation of sensors is crucial

" placement of movement sensor is an interesting research question!

! Sampling intervals too large

" Inaccurate results

" Missed events

" Idea: increase sampling rate (and therewith transmit rate)

Source: Albrecht Schmidt, Summer School 2005


Lecture Outline

!Platform Design


!Sensors" Sensor boards

" Analog and digital sensors

" Sensor interfaces

!Energy


Serial Line Communication

RS232

! Voltage level between -15V and +15V

! Alternative: 0-5V „TTL“ Level

! 2 lines: Transmit+Receive (TxD, RxD),

! Optional: 2 handshake lines (RTS/CTS)

http://www.maxim-ic.com/appnotes.cfm/appnote_number/83/

Bit 0

Bit 1


Example: RS232

! Regular transmission format: 8N1, i.e. 8 data bits, no parity, 1 stop bit

! Start bit is mandatory, baud rate must be known or is detected

! This example: 7e2

http://www.arcelect.com/rs232.htm


Sensor InterfaceInter-Integrated Circuit I2C, I!C

! A.K.A. 2-wire bus (due to Philips patent)

! Lots of devices – sensors, memory, actuators, e.g. Motherboardfor temperature measurement, battery control

! 2 Lines + GND for all devices:

" SDA (data line)

" SCL (clock line)

" Terminated: Open Collector with pull-up resistor

! Synchr. Master-Slave operation, Multi-master possible, MCU often provides HW driver

! Max. 112 slaves, address often fix in peripheral HW (7bit)

! 100kbit/s, 400kbit/s, 3.4 Mbit/s (brutto)


Sensor Interface I2C Protocol

http://www.maxim-ic.com/appnotes.cfm/an_pk/4024

Slave ack/nack master data

Slave can keep SCL low, if not ready (clock stretching)


Serial Peripheral Interface (SPI)

Serial Peripheral Interface, Microwire

! 1 master, 1 or more slaves

! Standardfall: Ein Master

! 3 lines+GND+Chip Select (CS):

" Serial Data In (SDI)

" Serial Data Out (SDO)

" Serial Data Clock (SCKL)

! High Speed (several MBit/s)

! Synchronous, duplex

! SD-Card, Memory-Chips (Flash, SRAM), RF chips (CC2430, TR1001)

http://www.mct.net/faq/spi.html


Advantages / Disadvantages

1. No bus, 1:1.

2. Slow (115kBit-1.2Mbit)

3. No clock (async)

1. Simple

2. No master

3. Handshake

4. Duplex

Serial

1. Speed: limited to 3.4MHz

2. Half-duplex operation

3. Open-drain bus lines require pullup resistors

4. Reduced noise immunity

1. Fewer bus lineconnections

2. Multiple devices share the same bus

3. Data is acknowledged

I2C

1. Larger number of bus lineconnections

2. Individual chip-select lines required to communicate with more than one slave at a time

3. No acknowledgment ofreceived data

1. Speed

2. No pullup resistors required

3. Full-duplex operation

4. Noise immunity

SPI

DisadvantagesAdvantagesInterface

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Lecture Outline

!Platform Design


!Sensors

!Energy" Batteries

" Power conditioning

" Energy management & scavenging


Batteries

Primary Cells / Alkaline

! Non-rechargeable, no capacity given

! 1.5V, long lifetime

Rechargable Cells

! NiMh, Lithium

! High current

! 1.2V, 2800 mAh capacity (AA)

Coin Cells

! ~200 mAh

! Often not rechargable

! Low continuous current (max. 200 uA)

! Higher current burns out the cell

Source: greenbatteries.com

Source: wikipedia


Battery Behavior (1)

Rate-Capacity effect

! High discharge / current

! Useable overall capacity decreases

Recovery effect

! After discharge, cell voltage recovers

Source: T. L. Martin. Balancing Batteries, Power, and Performance:System Issues in CPU Speed-Setting for Mobile Computing.


Battery Behavior (2)

Discharge curves

! Voltage decreases

! Sensor node has lower supply limit (cut-off voltage)

! # not all capacity is useable

Other effects

! Self discharge, age

! Temperature while under load, during storing, while loading


Power Conditioning

Motivation

! Multiple components: processor, radio, sensors, ...

! Multiple power sources: battery, coin cell, solar cells, ...

# Requires Separation of Concerns

! power conditioning by voltage regulation

Features

! 1. Provide operating voltage

! 2. Maintain operating voltage

! 3. Guarantee load performance (watt)


Power Converter

Linear regulator

! Down converter, Vin > Vout

! Low noise # preferable for noise sens. RF circuits

! Voltage difference (drop out) 20-50mV (power waste!)

! Minimize drop out in low power nodes

Switching regulator

! Step-up and/or step-down converter, 1.2V battery # 3V sensor node

! Inductor, diode and filter capacitor, switch (IC)

! Switching creates ripple

" # needs high quality capacitors, expensive

" # noise for RF and sensor circuits (additional filter caps)


Example: Inductive Boost Converter

Source:Callaway, Wireless Sensor Networks


Energy Saving Potential

Technology

! Low power components

" Minimal chip size

" Low voltage, low current, low frequency

! Radio modules down to 0.9V (Source: Abidi, Low-power radio

frequency ICs for portable communication)

Node Architecture

! High loss through busses, driver, multiplexer

! Reduce components and interconnections

! Power-off I/O

! No external memory


Energy ManagementMulti-Cell Operation

Multi-cell

! Use several (heterogeneous) battery cells

! Switch between cells

! Exploit discharge and recovery effects

Sequential discharge

! Discharge one battery after an other

Uniform switching discharge

! Switch uniformly between cells

Proportional switching discharge

! Switch according to load and remaining capacity

! # all cells are equally drained

Node

V1

V2

Switch

V1

Source: Benini et al. Discharge Current Steering for Battery Lifetime Optimization


Energy Scavenging (1)

MEMS Power generator through vibration

Thermal scavenging (Seiko)

Movement


Energy Scavenging (2)

Source: Paradiso, Starner


Conclusion

Summary

! WSN occupy a vast design space

! Some dimensions

" Processors, radio, sensors, energy

Lessons learned

! Various design choices and criteria

! There is always a trade-off.

! # Separation of Concerns seems to be a recurrent design principle

Outlook

! More standards will emerge (IEEE 802.15.4 was the beginning, upcoming: WirelessHART)

! More spin-offs will drive quasi-standard platforms (the next Mote), but for specific application area # standards of diversity


Next cool things in WSN...

Nanotube Radio

! Radio and receiver using carbon nano tubes (CNT)

Source: K. Jensen, J. Weldon, H. Garcia, and A. Zettl, "Nanotube Radio"

Source: Chris Rutherglen and Peter Burke"Carbon Nanotube Radio"


Credits

! Edgar H. Callaway, Jr. „Wireless Sensor Networks –Architectures and Protocols“

! Michael Beigl, TU Braunschweig: Bus systems

! H.F. Durrant-Whyte, ARC Sidney: SKIDS and ISSS

! Andreas Savvides „Sensor Network Hardware PlatformDesign“: Antenna, RSSI investigations

a brief historyread.pudn.com/downloads192/doc/902617/4up-sensornethw.pdf · cpu type @[mhz] 32bit...

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