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Bus Alert System

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Bus Alert System – PowerPoint PPT presentation

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Title: Bus Alert System


1
Bus Alert System
  • Group 11
  • Scott Wettstein
  • ECE 445 Senior Design Lab
  • Summer 2005
  • TA Timothy OConnell

2
Introduction
  • The Bus Alert System makes riding the bus easier
    and more reliable
  • Hopeful passengers push a button that alerts the
    next bus to arrive that someone wants to load
    using wireless RF technology

3
Benefits
  • Bus driver doesnt have to take his/her eyes off
    the road to see if someone wants to load at the
    next stop
  • Passengers wishing to load dont have to worry
    about getting passed by

4
Features
  • Push button to signal next bus to stop at that
    station
  • Bus driver has push button to reset the signal
  • LED on bus to alert driver
  • LED at station to show that button has been pushed

5
Objective
  • Design, build, and test a feasible product
  • Gain experience through doing

6
Additions to Original Design
  • Added hex displays for demo purposes
  • Added LED to station to show that button has been
    pushed
  • Added batteries to replace bench power supplies
  • Added crystal oscillator to drive PIC

7
Block Diagram
8
Main Hardware
  • PIC16F877A Microcontroller
  • LINX Transmitter TXM-900-HP3-PPS
  • LINX Receiver RXM-900-HP3-PPS
  • LINX Antenna ANT-916-PW-QW
  • SPST NC Pushbutton
  • Yellow LED

9
More Hardware
  • 10MHz Crystal Oscillator Clock
  • Hex Display Bus only
  • AA Batteries 4.5V

10
Bus Circuit
11
Station Circuit
12
PIC
  • RS232 serial communication with Transmitter and
    Receiver
  • Takes input from Pushbutton
  • Outputs single LED
  • Outputs to Hex Displays Bus only

13
LINX Transmitter
  • Operates on parallel channel must be same as
    receiving Receiver
  • Transmits digital data serially
  • Needs appropriate antenna with 50? coaxial cable
  • Will not transmit until CTS Clear to Send line
    is high

14
LINX Receiver
  • Operates on parallel channel must be same as
    receiving Transmitter
  • Receives digital data serially
  • Needs appropriate antenna with 50? coaxial cable

15
LINX Antenna
  • Omni-directional
  • Whip style
  • One for each Transmitter and Receiver
  • Mounted on aluminum mount

16
Pushbutton
  • Single-Pull-Single-Throw
  • Normally Closed
  • Logic low when closed logic high when momentary
    open due to
  • 1k? pull-up resistor
  • Mounted on aluminum
  • mount

17
Yellow LED
  • Driven by current
  • initiated by different
  • voltage levels across
  • 330? resistor

18
Software
  • Code on PIC microcontrollers uses C language
  • Different code for bus and station

19
Bus PIC Flow Chart
20
Station PIC Flow Chart
21
Data Packets
  • Start Byte Station to Bus 0xF0 Bus to
    Station 0xE8
  • BusID Byte
  • StationID byte
  • Allows up to 254 buses and 254 stations per bus
    not including start bytes to eliminate
    confusion

22
Testing LINX Transmitter/Receiver
  • Transmitted square wave from function generator
    and viewed results from receiver
  • Tested all 4 chips at the same time on 2
    different parallel channels

23
Bus Waveform
Channel 1 Function Generator Output 10kHz, 5V
P-P Channel 2 Receiver Input from station
24
Station Waveform
Channel 1 Function Generator Output 5kHz, 5V
P-P Channel 2 Receiver Input from bus
25
Battery Lifetime Measurements
  • According to Energizer, AA batteries have a
    capacity of 2850mAh
  • Actual Station and Bus circuits identical so
    current approximately the same 48.5mA
  • Battery lifetime 58.8 hours

26
Successes
  • LINX Transmitter/Receiver testing
  • Simple PIC communication through TX/RX before Hex
    Displays
  • Final PIC communication including Hex Displays

27
Challenges
  • Button batteries couldnt supply appropriate
    power
  • Bypass capacitor short
  • PIC C code kbhit() and getc()

28
Hardware Recommendations
  • Different batteries D cell with 20500mAh
  • Better quality test board
  • Antenna interference considerations stations in
    residential neighborhoods with 900MHz portable
    phones

29
Software Recommendations
  • Need more info on kbhit() and getc()
  • Check PIC memory directly for RCIF bit flag set
    when reception is complete
  • Have bus send acknowledge signal station only
    sending once then waiting
  • Reset bus code if another bus gets to station
    first multiple buses on same route

30
Thank You
  • Special Thanks Tim OConnell
  • Any Questions?
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