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					Winland Electronics, Inc.


  Wireless Sensor Networks
“A Survey of Design Options”


       June 23, 2011
    Winland Electronics Overview
• Winland is a full service EMS (Electronic
  Manufacturing Services) provider
• Design and manufacture for customers in
  consumer, industrial and medical markets
•   $35M in sales
•   140 employees
•   Mankato, MN
•   58,000 sq ft.
•   Public – AMEX
•   Symbol (WEX)




                                              Slide 2 of 29
                  Winland at a glance
Wide range of customers
 •   Consumer products
 •   Medical electronics
 •   Computer hardware
 •   Industrial / Utility Equipment
 •   Wireless devices
 •   Sensors and security
     products
Why Deploy Wireless Networks
•   Installation labor costs reduced
•   Attractive appearance
•   Increased number of sensors
•   Some applications are impossible to hard wire




                                               Slide 4 of 32
  Network Solutions Available

• Drop-in Solutions
   All electronics complete


• Module Solutions
   RF section complete


• Discrete RF IC Solutions
   Full custom




                               Slide 5 of 32
   Wireless Frequency Bands

• Common sensor network license free bands
     418 MHz (Canada and U.S.)
     433 MHz (Europe)
     868 MHz (Europe)
     902 – 928 MHz (Canada and U.S.)
     2400 – 2483 MHz


• 2.4 GHz advantage
   World wide



                                        Slide 6 of 32
                Drop-in Solutions
Example manufacturers include Digi® and SensiCast®


                               Gateway devices:
                               used to convert wireless signals
                               to a PC or local display
                               Size: 7.7” x 4.1”




Wireless sensors:
used to convert sensor data
(temp, water detection, etc)
to a wireless signal
Size: 3.9” x 1.8”



                                                                  Slide 7 of 32
             Module Solutions
Example manufacturers include MeshNetics® and Digi®

                                 Meshnetics® ZigBit™ Module:
                                 FCC cerrtified, high and low
                                 power versions available
                                 Silicon: Atmel®
                                 Size: 0.9” x 0.5”




  Digi Xbee® Series 2 Module:
  FCC certified, high and low
  power versions available
  Silicon: Freescale® & Ember®
  Size: 1.0” x 1.1”


                                                            Slide 8 of 32
     Discrete RF IC Solutions
Example manufacturers include Atmel® and Freescale®

                                    Atmel® – AT86RF230:
                                    Radio transceiver targeted for
                                    IEEE 802.15.4 & Zigbee apps
                                    Size: 0.2” x 0.2”




   Freescale® - MC13193:
   Radio transceiver targeted for
   IEEE 802.15.4 & Zigbee apps
   Size: 0.2” x 0.2”




                                                               Slide 9 of 32
         Available Products Overview
Manufacture – Solution Type                            Line Of Sight               Battery Life
Part Number                                               Range
        Digi® –                    Drop-in                   300 feet             5.6 yrs w/ 3xN alk
     XA-B14-CS1R                                                                  (0.1% duty cycle)
     SensiCast® –                  Drop-in                   700 feet           2 yrs w/ 3.6V lithium
      TEHU-1121                                                                  (2min sleep cycle)
        Digi® –              Lo Power Module                 400 feet                 4.2 years**
     XB24-BUIT-004
     MeshNetics® –           Lo Power Module                760 feet*                 5.4 years**
     ZDM-A1281-A2
       Atmel® –                Discrete RF IC               760 feet*                5.7 years**
      AT86RF230                                                                  w/ ATMEGA micro
     Freescale® –              Discrete RF IC               510 feet*               3.9 years**
     MC13193FC                                                                  w/ MC9S08GT micro

*    Estimated line of sight range based on specified link budget using Frii’s range equation with
     transmitter and receiver gain set to -4dBm.

**   Battery life based on 0.1% duty cycle with 2 AA alkaline batteries fed into a 85% efficient regulator
     during active mode. Iq of regulator set to 10uA. Life listed is approximate only. Other external
     circuitry not included in calculations.
                                                                                            Slide 10 of 32
    Drop In, Module or Discrete?
     Application and EAU will drive your decision

•   Drop-in solutions
       Quick time to market
       Lowest product development costs
       Certifications complete (country specific)
       Limited application

•   Module solutions
       Middle of the road
       Certifications complete (country specific)

•   Discrete RF IC solutions
       Lowest per unit cost ($13 - $28 cheaper then module)
       Diverse application ready
       Form factor
       Design control


                                                               Slide 11 of 32
Wireless Challenges To Overcome

1.   Embed application with wireless protocol
2.   Network deployment ease
3.   RF Tuning / Layout Considerations
4.   Form Factor
5.   Power Consumption
6.   Bit Error Rate Testing
7.   Certification Testing

                        And many more!



                                            Slide 12 of 32
    Wireless Challenge #1 of 7
Embed application with wireless protocol




    Drop-in
      – N/A

    Module
      – Generally your application will send serial commands to the
        module (module dependent)

    Discrete
      – Interface directly with protocol
      – Protocol learning curve – commands to call functions
      – Availability of protocol support (3rd party vs. manufacturer)
                                                              Slide 13 of 32
           Wireless Protocols
• Zigbee
    Mesh network
    Self healing
    Interoperable



• IEEE 802.15.4
    Star network



• Proprietary
    Custom network topologies
    faster data rates (not limited to 250K bits/s)
                                                      Slide 14 of 32
      Wireless Challenge #2 of 7

Network deployment ease (depends on application)

  Drop-in, Module and Discrete
    – Design user interface to add and remove sensors
        » Ensures foreign sensors don’t attach to your gateway
        » Ensures your sensors don’t attach to foreign gateways


    – Design user interface to accommodate sensor diagnostics
        » Examples: Link quality, Received power, Bit Error Rate, etc.


    – Quick start guide




                                                             Slide 15 of 32
           Wireless Challenge #3 of 7
RF Tuning / Layout Considerations


  Drop-in
    – N/A

  Module
    – Ideally place module near corner of PCB
    – Follow guidelines per the module datasheet

  Discrete
    –    Impedance matching
    –    Transmission lines
    –    Antenna design (multipath considerations)
    –    Current return paths
                                                             (Discrete RF IC Layout)



        Improper RF tuning and layout results in degraded wireless range
                                                                              Slide 16 of 32
                   Wireless Range


Range Variations from:
    RF Design / Layout
    Environment
    Protocol (star network vs mesh network)
       – Repeaters can increase coverage

Range (without repeaters):
    Low power (105dB link budget maximum)
       – 35 to 100 feet indoors
       – 500 to 1000 feet outdoors (line of sight)

    High power (110 dB link budget minimum)
       – 100 to 200 feet indoors
       – 1 to 2.5 miles outdoors (line of sight)


                                                     Slide 17 of 32
      Estimating Wireless Range
Frii’s range equation (dB form):

          Pr = Pt + Gt + Gr – 10log(4π/λ)2 – 10log(R)n

Where:
Pr = Receive power – sensitivity (dBm)
Pt = Transmission power (dBm)
Gr = Receive gain – amplification, antennas, component loss (dB)
Gt = Transmission gain – amplification, antennas, component loss (dB)
λ = Wavelength – speed of light / frequency (meters)
R = Range (meters)
n = Propagation constant – accounts for obstructions, reflections, etc
      n = 2 (outdoors - line of sight at 2.4GHz)
      n = 5 (average indoors at 2.4 GHz)
      n = 7 (Indoors with 3+ walls at 2.4GHz)




                                                                Slide 18 of 32
      Estimating Wireless Range
Example:
Calculate the average indoor range of the Atmel AT86RF230. Assume the
antennas have no gain and are 50% efficient. 2dB of loss exists between
the transceiver and the antenna due to component loss.

Answer:
• From the Atmel AT86RF230 data sheet:
      Pr = -101dBm
      Pt = +3dBm
      Frequency = 2.4 GHz

•   λ = speed of light / frequency = 3x10^8 / 2.4x10^9 = 0.125 meters
•   n = 5 (average indoor propagation constant at 2.4GHz)
•   Gt = -3dB (50% efficient antenna) + -2dB (component loss) = -5dB
•   Gr = Receive gain is the same as above transmission gain = -5dB
•   Pr = Pt + Gt + Gr – 10log(4π/λ)2 – 10log(R)n

                     R = 25 meters or 82 feet
                                                                Slide 19 of 32
   Wireless Challenge #4 of 7

Form Factor

   Drop-in
     – Limited choices


   Module
     – Module size (length x width) may cause issues
     – Many modules require headers that increase height


   Discrete
     – Full control


                                                  Slide 20 of 32
   Wireless Challenge #5 of 7

Power Consumption

   Drop-in
     – Limited choices

   Module and Discrete
     – Generally very good
     – Total power consumption will increase from:
        »   External MCU
        »   Watch dog reset circuits
        »   Brown out detection circuits
        »   Quiescent current from all IC’s on the board
        »   Etc

                                                           Slide 21 of 32
Power Consumption / Battery Life
Battery life varies from:
    Sleep mode power consumption - most critical
       – regulator current consumption
       – Watchdog reset & brownout detection circuitry

    Active mode power consumption
       – RF: TX/RX consumption & antenna switches
       – MCU & application specific circuitry

    Duty cycle = active time / (active + sleep time)
       – Typical active time: 3 – 100ms
       – Typical sleep time: 1s – 1h

    Battery capacity
       – Remember to supply a given power requirement:
         Battery current  as battery voltage 

                                                     Slide 22 of 32
           Estimating Battery Life




Where:
D = duty cycle (%)                                    L = battery life (years)
Ia = active current (mA)                              Is = sleep current (uA)
Ta = active time (ms)                                 Ts = sleep time (s)
C = battery current capacity (mAh)                    8760 = hrs per year

Note:
To predict Ia & Is (currents sourced from batteries) you will need to know:
• Battery voltage vs. service life at specified active current (battery data sheet)
• Regulator output voltage (regulator data sheet)
• Regulator efficiency vs. input voltage (regulator data sheet)

                                                                            Slide 23 of 32
              Estimating Battery Life
Example:
Using 2 AA alkaline batteries in series specified at 2530mAh, how long will the
batteries last if a wireless sensor consumes 35mA at 3.3V while active and 75uA
at 3.3V while asleep. The sensor sleeps for 30 seconds between active durations
of 25ms. (2 batteries in series double voltage while capacity remains constant)

Answer:
• Batteries must source more then 35mA (voltage conversion & efficiency)
         Assume 90% efficiency from regulator & average battery voltage of 2.7V
                  » 3.3V * 35mA = 2.7V * i * 90% -> i = 48mA

•   During very low current draw regulators become less efficient
         Assume 68% efficiency from regulator using similar math to above -> i =125uA

•   Plug the values into the equations:




                                                                                    Slide 24 of 32
      Wireless Challenge #6 of 7

Bit Error Rate (BER) Testing


    Drop-in
      – No control

    Module and Discrete
      – Testing required as external circuitry will add
        noise to the board causing reduced sensitivity
          » This noise will likely be channel specific and is caused
            by resonant frequencies from crystals, MCU core
            speed, bus speed, etc.



                                                                Slide 25 of 32
           Bit Error Rate Testing
Why perform Bit Error Rate Testing:
•   Noise on your PCB from other components will cause the sensitivity
    to degrade from what is published on the data sheet
•   Sensitivity may vary across the different channels


How to perform Bit Error Rate Testing:
•   Measure the output of a transmitter and attenuate the signal to the
    sensitivity value that you hope to obtain (include all cable losses).
•   Connect your device under test
    (DUT) as shown below:




•   If signals reach the DUT with less then 1% (typical) BER, increase
    the attenuation; if it is more then 1% BER, decrease the attenuation.


                                                                   Slide 26 of 32
          Duration of BER Testing
BER accuracy is increased with duration of the test


Confidence Level - Std Deviation              Confidence Level - Std Deviation
    80.00%            1.2816                       68.27%             1
    90.00%            1.6449                       95.45%             2
    95.00%            1.9600                       99.73%             3
    99.00%            2.5758                       99.994%            4
    99.90%            3.2905                      99.9999%            5

Example:
How many bit errors would you need to obtain before you can stop the test
assuming your BER is accurate to within 5% with a confidence level of 99%? How
much time would this take at 5 samples / second and an expected BER of 1%?

Answer:




                                                                     Slide 27 of 32
      Wireless Challenge #7 of 7

Certification Testing (U.S., Canada & Europe)

    Drop-in
      – Complete (country specific)

    Module
      – Intentional radiator testing complete (country specific)
      – The following testing may still be required on your product
          » Product Safety
          » Unintentional emissions
          » Immunity

    Discrete
      – Certification testing required


                                                          Slide 28 of 32
     Typical Certification Costs

United States only: FCC certification costs:
     Intentional Radiator test costs - $2,500*
     FCC submittal costs - $2,600*



Europe, U.S. & Canada: Total certification costs:
     Intentional Radiator test costs - $4,500*
     Total submittal costs - $7,150*


*Assuming 2 unique models, NRTL cert mark, rates subject to change



                                                            Slide 29 of 32
   Drop-in vs. Module vs. Discrete
                                           Drop-in              Module               Discrete
Development Schedule                                                               
Cost / System* (quantity 100)                $995                $1870                $2310

Cost / System* (quantity 500)                $660                 $605                 $640

Cost / System* (quantity 1K)                 $605                 $440                 $420

Cost / System* (quantity 10K)                $550                 $295                 $230

Form Factor                                                                       
Diverse Application Ready                                                         
Design Control                                                                    
               = good                      = better                   = best


All costs listed include BOM, development labor, certification and production costs. All costs are
approximate only and do not reflect any specific Drop-in, Module or Discrete solution.
*System defined as 1 gateway and 4 wireless temperature sensors.

                                                                                         Slide 30 of 32
Winland Wireless Design Example
                   EA800 Design Project




             (EA800)                                   (EA800 close up)

 Network solution: Discrete RF IC

 Protocol: 802.15.4

 Temperature Sensor BOM cost: $16.45
 • Includes plastics, PCB, antenna, electronics, etc
 • EAU 1K


                                                       (Temperature Sensor)
                                                                              Slide 31 of 32
           Wireless Sensor Networks

                            Questions?
                                  Contact Information

        David Liverseed                                        Greg Burneske
      Electrical Engineer                                     VP of Engineering
 E: dgliverseed@winland.com                              E: gwburneske@winland.com
       www.winland.com                                        www.winland.com




All registered and unregistered trademarks used herein are the property of their respective owners.
Winland Electronics is not affiliated with, or endorsed by, any of the owners of these marks.



                                                                                        Slide 32 of 32

				
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