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?