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Capstone Design Project

Silent Alarm System

Students: Su Huang & Fenghua Chen

Advisor: Professor James Hedrick

March 03, 2007

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Current Safety Alert System

Emergency phone booths

Surveillance cameras Wired together

(underground) Connect to Campus

Safety

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Disadvantages of Current System

Slow notification of incident Surveillance cameras have blind spots Fixed in numbers and locations

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What is a Silent Alarm System?

A personal safety alert system Mobile device Wireless transmission Easy, silent activation Instant alert to Campus Safety Better location tracking

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Keychain (student)

Central Station(Campus Safety)

Signal

Signal Signal

Schematic Diagram

Sub.

Substation

Key Chain (Student,

faculty, etc)

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The Big Picture

www.google.com

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The Project

Idea by Nelson Rosario Originally based on Parallax Education Board Migration to C8051 MCU platform Develop a communication platform for software

engineers Develop basic communication protocol Built a standalone prototype on a PCB board

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Design Specifications

Transmit Frequency: 433.92 MHz Transmit Range: 500ft Transmitter Output Power: -4 ~ 8 (dBm) Receiver Output Power: -4 ~ 4 (dBm) Baud Rate: 9600 bps Receiver Sensitivity: -106 ~ -118 (dBm) Meet all FCC and Public Safety regulations

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Hardware Components Microcontroller (C8051) Parallax RF Transceiver Parallax Education Board Keychain

Key Chain 433MHz Transceiver by All Spectrum Electronics

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Block Diagram

Transmitter Station Receiver Station

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Communication Protocol

Transmitter• Check for button

press

• Synchronization Start character

• Message

• End character

• Back to checking

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Communication Protocol (cont)

Receiver• Wait for start

character

• Getting message

• Wait for stop character

• Send alarm

• Back to wait

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Communication Protocol (cont)

Start signal: character “!” Message: can take up to as much as 25

ASCII characters Test message: string “IRE” End signal: character “@”

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Results

Spectrum Analyzer Antenna noise Receiver Sensitivity:

-106 ~ -118 dBm

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Results

Oscilloscope Message Data (no

transmission) Noise only

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State Diagram (Receiver#2)

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LR Receiver and LS Decoder

Linx Technologies®

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Progress Report

A prototype is built Signal/noise measurements using

Spectrum Analyzer Improving protocol to be more flexible

and noise resistant Building filter circuit

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Results

Oscilloscope Message Received !,I,R,E,@

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Results

Xmtrwide With Noise

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Disadvantages

Wireless signal strength problem False Alarms

• Solutions are: fine, lock, save ID on keychain

Device Failure Inaccurate position detection

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Future Thoughts

Open Shortest Path First More accurate position detection (i.e.

GPS) Vibration (feedback to user) Individual ID for each transmitter

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Acknowledgements

Advisor: Professor Hedrick Nelson Rosario

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Questions?