The Child Leash Unleashed by x5YKdrJ

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									The Child Leash Unleashed




             ECE 445
           Senior Design

          December 2, 2004
       Conway Mai . Sophia Kang
                                 Introduction

   The FBI estimates that 85-90% of missing
    persons are juveniles
   In approximately 725,000 cases (or 2,000
    per day) the disappearance of a child was
    reported
   "Juvenile“ Category - 651,209 cases


     Source: Federal Bureau of Investigation, National Crime Information Center (NCIC), Missing Person File.
Pet or Child?
Functional Block Diagram
  Transponder-A   Transponder-B




                  Reader
               Deliverables
   Reliable and accurate data transmission
   Predefine range and signal coverage
   Robust alert system
   Tamper-proof system
   Uniquely identify multiple children
   Portable / Easily concealable package
   Low-cost solution and implementation
   Original Design
Block Diagram (Reader)

   Transmitter




   PIC16F872     Receiver




     Display     PARENT
R        Tell Child A to
           Transmit
                                          Tell Child B to
                                            Transmit



E   No     Valid Child               No     Valid Child
           A's WAKE                         B 's WAKE
           UP Packe t?                      UP Packe t?


C                  Yes                              Yes


    No      Valid Child              No      Valid Child


E
            A's DATA                         B 's DATA
             Packe t?                         Packe t?


                    Yes                             Yes


I   No      Valid Child
             A's END
             Packe t?
                                     No      Valid Child
                                              B 's END
                                              Packe t?




V                   Yes                               Yes


         Encode DATA                      Encode DATA
            Packet                           Packet

E
R                          Display DATA
         Original Design
  Block Diagram (Transponder)

                      Transmitter




        Temperature
CHILD                 PIC16F872     Receiver
          Circuit
Transponder Flow Diagram
        IDLE STATE:
        Wait for signal




          READ
        Temperature




          ENCODE
            Data



       Transmit WAKE
       UP, DATA, END
           Packets
          Component Breakdown
     Transponder                      Reader

   Microcontroller              Microcontroller
       PIC16F872                    PIC16F872
   Transmitter                  Receiver
       TXM-900-HP-II                RXM-900-HP-II
   Contact Sensor               Channel Switch
       MTS102 (Temp Sense)          COTO-8041 (Relay)
       LM358N (Op-amp)              LM358N (Op-amp)
       8-bit ADC (in PIC)
Block Diagram (Transponder)

                                        PIC16F872


CHILD        Temperature Sensor



        To
        Parent
        Device
                          Transmitter
Block Diagram (Receiver)




   Child Data   Receiver




Display
Data to
                PIC16F872
Parent
Implementation
    Transmitter / Receiver Selection
   Key Capabilities:
       Transmitter
            Channel Selection (8 channels) [902-928Mhz]
            Clear To Send (CTS) Indicator
            Power Down Pin
            No internal power output attenuation!
       Receiver
            Channel Selection (8 channels) [902-928Mhz]
Contact (temperature) Sensing
Performance Requirements:
 Skin at room temperature (~24˚C-25˚C)

    Arms & Legs: 31˚C*                                                              Vbe vs. Temp

    Feet & Hands: 29˚C*
                                     700




                                                        Vbe Voltage (mV)
                                     650
    Head, Chest & Abdomen: 34˚C*    600
                                     550
 Typical Variation: 5˚C             500

 Possible Variation: 30˚C           450
                                                                           400
                                                                                 0      50     100
Challenge:                                      Temperature (C)

 Temperature Sensor Range: 10mV

 Amplifier insensitivity to small change for ADC


               *Source: http://www.science.uwc.ac.za/physiology/temperature/temperature.htm
Contact Sensing Solution
  R14
      V  V   1.6M (Vambient  Vbody )  258 V
  R13               6.2k
  *assumes R14=R5 and R13=R6




                                           Theoretical Gain = 258 V/V
                                           Tested Gain = 228 V/V
                                           Vsat = 3.759 V
                                           Example Calculation:
                                                12mV*258 = 3.096 V
                                                Saturation condition:
                                                      Difference > 15 mV
                       Protocol Design
   To eliminate data corruption and noise on
    crowded frequency channels.
   Packetization
     WAKE UP             ENCODED DATA       END
        8 Bit Packet       8 Bit Packet   8 Bit Packet

   Encoded Data
       Bits 0-6: ID of Transponder
       Bit 7: 0=Transponder not on, 1=Transponder on
                 7 6 5 4 3 2 1 0
Transponder Flow Diagram

       START:
  Initialize, Power   Encode DATA
        Down             Packet



                       Transmit All
 Power Transmitter       Packets
        Up            Continuously (1
                           Sec)



     Gather            Power Down
 Temperature Data      Transmitter
R                  One Child
                                            One/T wo
                                           Child Mode?
                                                                   Two Child




E           Select "A"
            Frequency                                             ALERT




C           Signal or Idle                 Increment "No
                                                                                               Increment "No
                                                                 Signal or Idle
            for too long?
                               No Signal   Signal" Counter       for too long?
                                                                                   No Signal   Signal" Counter


E                     Signal
                                                                          Signal


            Valid WAKE                     Increment "Bad


I
                                                                Valid END                      Increment "Bad
            UP Packet?         Not Valid   Signal" Counter
                                                                 Packet?           Not Valid   Signal" Counter

    ALERT           Valid



V           Signal or Idle
            for too long?
                               No Signal
                                           Increment "No
                                           Signal" Counter
                                                             DISPLAY/Indicate
                                                             if Transponder ON
                                                              or OFF the child.




E
                     Signal



            Valid DAT A                    Increment "Bad
              Packet?          Not Valid   Signal" Counter


R
               Alert System


   Alert system checks three functionalities:
     kbhit() returns false
     Data from rs232 does not match the packets
      sent by the transmitter
     In the encoded data, temperature is “bad.”
                 Timing Issues

   Three timing issues to consider:
       Receiver has to be on before the transponder
       Time between powering up the transmitter
        and when it sends valid data (1.2 ms)
       Frequency channel switching (8 – 10 ms)
Channel Switch Functional Test

            Receiver


              A


              B
                     Range Testing

                                                          40
            1
                                                          30
    8                 2
                                                          20




                              Distance(ft)
                                                          10

          Parent                                            0
7                         3
        (Receiver)                           -40   -20    -10 0          20   40

                                                          -20

    6                 4                                   -30

            5                                             -40
                                                         Distance (ft)
                     Contact Circuit Functional Test
                                       Voltage Difference vs. Output Voltage
                                                                                   y = 0.2287x + 0.4621
                                                                                        R2 = 0.9665
                                                  4.000
                             > 2.840V             3.500
Output Voltage (V)




                                                  3.000
                                                  2.500
                                                  2.000
                             < 2.840V             1.500
                                                  1.000
                                                  0.500
                                                  0.000
                     -15.0     -10.0       -5.0           0.0    5.0        10.0       15.0       20.0
                                                  Voltage Difference (mV)
              Successes & Challenges
   Data integrity:
       Challenges
            Timing issues (inconsistencies): Transmitter power down
            Noise (same frequency): Wireless protocol
   Two-Child Implementation:
       Challenges
            Range: Output Power Control
            Communication: Transmitter power down
   Contact Sensing:
       Challenges
            Sensitivity: Differential amplifier of ambient temperature vs. contact temp.
   Tools and Concepts:
       Challenges
            Understanding wireless communication and protocol
            Learning new development tools
       Future Recommendations

o   Higher noise tolerant protocol
o   Detect multiple children to one parent
o   Location/Directional detection of child
o   Passive powered transmitter
o   Low power consumption
o   User-friendly interface
                  Conclusion
o   Accomplished:
     One Child Communication
     Two Child Communication

     Alert System

     Tamper Proof System

o   Learned:
    o   Teamwork and Project Management
    o   RF Technology, PIC, C Coding
    o   Design Procedures
          Acknowledgements

o   Mo Zhou, our TA
o   Marty and Chirantan
o   Professor Swenson
o   Professor Bernhardt
o   ECE Parts Shop
Questions?

								
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