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The Child Leash Unleashed

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

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The Child Leash Unleashed

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  1. The Child Leash Unleashed ECE 445 Senior Design December 2, 2004 Conway Mai . Sophia Kang

  2. 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.

  3. Pet or Child?

  4. Functional Block Diagram Transponder-A Transponder-B Reader

  5. 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

  6. Original DesignBlock Diagram (Reader)

  7. R E C E I V E R

  8. Original DesignBlock Diagram (Transponder)

  9. Transponder Flow Diagram

  10. Component Breakdown Transponder Reader • Microcontroller • PIC16F872 • Transmitter • TXM-900-HP-II • Contact Sensor • MTS102 (Temp Sense) • LM358N (Op-amp) • 8-bit ADC (in PIC) • Microcontroller • PIC16F872 • Receiver • RXM-900-HP-II • Channel Switch • COTO-8041 (Relay) • LM358N (Op-amp)

  11. Block Diagram (Transponder) PIC16F872 CHILD Temperature Sensor To Parent Device Transmitter

  12. Block Diagram (Receiver) Receiver Child Data Display Data to Parent PIC16F872

  13. Implementation

  14. 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]

  15. Contact (temperature) Sensing Performance Requirements: • Skin at room temperature (~24˚C-25˚C) • Arms & Legs: 31˚C* • Feet & Hands: 29˚C* • Head, Chest & Abdomen: 34˚C* • Typical Variation: 5˚C • Possible Variation: 30˚C Challenge: • Temperature Sensor Range: 10mV • Amplifier insensitivity to small change for ADC *Source: http://www.science.uwc.ac.za/physiology/temperature/temperature.htm

  16. Contact Sensing Solution *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

  17. Protocol Design • To eliminate data corruption and noise on crowded frequency channels. • Packetization • Encoded Data • Bits 0-6: ID of Transponder • Bit 7: 0=Transponder not on, 1=Transponder on END WAKE UP ENCODED DATA 8 Bit Packet 8 Bit Packet 8 Bit Packet

  18. Transponder Flow Diagram

  19. R E C E I V E R

  20. 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.”

  21. 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)

  22. Channel Switch Functional Test Receiver A B

  23. Range Testing

  24. Contact Circuit Functional Test > 2.840V < 2.840V

  25. 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

  26. Future Recommendations • Higher noise tolerant protocol • Detect multiple children to one parent • Location/Directional detection of child • Passive powered transmitter • Low power consumption • User-friendly interface

  27. Conclusion • Accomplished: • One Child Communication • Two Child Communication • Alert System • Tamper Proof System • Learned: • Teamwork and Project Management • RF Technology, PIC, C Coding • Design Procedures

  28. Acknowledgements • Mo Zhou, our TA • Marty and Chirantan • Professor Swenson • Professor Bernhardt • ECE Parts Shop

  29. Questions?

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