Wireless Elevator Control for the Disabled

1
Wireless Elevator Control for the Disabled

• By
• Hita Padia, Young Ki Kim, Khine Han Group 17
• ECE 445
• April 26, 2007

2
Introduction

• To help disabled people who have difficulties in
  reaching the elevator control buttons to call or
  select floors.
• Uses RF communications instead of IR detection

3
Features

• Calling elevator within a range of 20ft.
• LCD screen to display floor selections.
• Door Open, Send buttons and joystick on the
  control box for desired floor selections.
• Detachable control box on wheelchair.
• Expandable design (currently 4-floor prototype)

4
System overview

• Hardware
• -LINX HP3 Series Transmitter and Receiver
• -916 MHz Whip and Microchip antennas
• -2 x 8 character LCD
• -Joystick and Push Buttons
• -PIC microcontrollers (16F877A)
• - Power Supplies 9V batteries and AC to DC
  Adapter
• - Reed Relays
• Software
• - Programming PICs in C

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Completed Project Picture
6
Design Overview
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Hardware overview- TX module

• - PIC16F877A Microcontroller
• - Transmitter (Linx TXM-900-HP3-PPS)
• - Chip Antenna (ANT-916-SP)
• - 2X8 LCD for displaying floor numbers or
  characters
• - Joystick for selecting floors
• - Two push buttons for door-open and
  select/send operations
• - 9V batteries

8
TXM Circuit Microcontroller

• PIC16F877A (SMD type)
• - Receive signals from joystick and push
  buttons
• - Determine and send corresponding data bits to
  the LCD screen
• - Also determine when and which bytes should be
  sent to the receiver
• - Sleep mode unless interrupt signals are
  received from the inputs

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TXM Circuit Transmitter

• Transmitter (Linx TXM-900-HP3-PPS)
• - 915.37 MHz operation selected by DIP-switch
  on board (CS2, CS1, CS0 1,0,1)
• - Send the data received from PIC to the RXM

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TXM Circuit Chip Antenna

• Chip Antenna
• - Send signals at 916MHz
• - resistant to proximity effects with good
  isotropic radiation patterns

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TXM Circuit User Interface

• 2X8 LCD Screen
• - Interfaced with PIC
• - Displays starting floor in first row and
  destination floor in second row
• - Displays Door Open if the door open button
  is pressed

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TXM Circuit Joystick

• Joystick (4-way Microswitch)
• - Scroll through the LCD screen
• - Select both the starting and destination
  floors
• - Movements interfaced with PIC to control
  the floor numbers display on the LCD screen
• - Association with screen scrolling
• Left-Right movement destination
  floor
• 
  selection
• Up-Down movement starting floor
  selection

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TXM Circuit Push Buttons

• Push Buttons (SPDT momentary switches)
• - Send signals to PIC for transmission
• - Two push buttons for Send (blue button) and
  Door-Open (white button)
• - Need to press Send button twice
• 1st Press signals PIC to send selected floor s
• 2nd Press signals elevator has arrived at
  starting floor
• - Pressing Door-Open button signals PIC to
  send corresponding data byte (0xff) to RXM

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TXM Circuit Schematic
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Hardware overview- RX module

• Components
• - PIC 16F877A
• - Receiver (RXM-900-HP3-PPS)
• - Darlington Transistors
• - 5V DC Reed Relay Switches
• - Protection Diodes

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RXM Circuit Microcontroller

• Polls the receiver for data
• Data received is determined and hamming corrected
  before data execution
• Supplies small current to the base of the
  darlingtons to turn them on according to data

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RXM Circuit Receiver

• Same 916MHz configuration as transmitter

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RXM Circuit Antennas
4th 3rd 2nd G

• Antennas placed every 2 floors using coaxial
  cables
• Hanged upside down in the elevators hoist-way
• Connected to the RXM through a splitter

Elevator Hoist-way
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RXM Circuit Darlington Transistors

• Amplifies the small current from PIC to turn on
  the reed relay switches
• High current gain
• Current adjustments are made by using different
  resistances at the emitter

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RXM Circuit Reed Relays (NO)

• Operates at 5V DC
• Connected in parallel to the relay switches
  inside the elevators control circuitry
• Closing time of reed relay is set to 500ms
  enough to charge up the elevators relays
• Low power consumption (20 mA each)

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RXM Circuit Protection Diodes

• Placed in parallel with the reed relays
• Prevents large back emf from the relays (when
  transistor switch is turned off) from damaging
  the transistors

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Receiving Module Schematic
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Software Programming Key Points

• Smd_tmodule.hex, Tmodule.hex
• Smd version is the complete program for PCB
• Hard to add any new connections
• Breadboard version uses DIP type PICs
• Both include an LED flashing for 10s after PIC
  has waken up
• Both interrupt driven turn off LCD and
  transmitter before going to sleep
• - Power up process initialize LCD

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Software Programming

• Smd_rmodule.hex, Rmodule.hex
• - Both include an LED test signal that lights up
  whenever data is received from receiver
• - Nothing happens if unexpected data is received
• -

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Software Hamming Code (7,4)

• Data from transmitter is encoded in Hamming and
  decoded by the receiver side PIC
• Last 7 bits sent by PIC is data encoded in
  Hamming, MSB is used to differentiate between
  door open and floor selections

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Hamming Code Limitations

• 1-bit error correction feature but data sent is
  limited to 4 bits (for 8 bit transmission)
• Suggested Solution
• - Encode an 8-bit data in 4-bit chunks and
  transmit twice

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TXM Power Supply Circuit

• Two 9V Lithium batteries in parallel.
• Use of MC33375 5V (SMD type) voltage regulator
  to step down voltage to 5V
• Damage protection by connecting 1N4004 diodes in
  series with each battery power line

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TXM Power Supply Schematic
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Verification Procedures

• MC33375 Voltage Regulator Test(1)
• - Connect 1uF and 0.1uF capacitors to both
  input and output of the regulator in parallel
• - Connect a load R100ohm to the output of
  regulator
• -Supply 12V to 2V with Agilent E6361A Power
  Supply
• - Measure and observe the voltage across the
  load and the current flowing through the load
  using mutimeter whether it steps down to 5Vdc and
  draw proper current or not

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Verification Procedures

• Test for MC33375-5.0R2G(2)
• - Oscilloscope measurement of voltage across a
  100 ohms load
• - somewhat stable but high ripple component

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Verification Procedures

• Test for MC33375-5.0R2G (3)
• - Add one more 1uF E.L to its output in
  parallel to reduce the ripple
• -Supply 9V with Agilent E6361A
• - Measure and observe the voltage across the
  load using oscilloscope
• - More stable, smaller ripples

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RX Circuit Power Supply

• Wall-Power (120Vac, 60Hz)
• AC/DC Adapter (5Vdc)

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RXM Power Supply Schematic
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Verification Procedures

• Test for AC to 5V DC Adapter
• - Connect output of adapter to 10uF E.L and
  0.1uF in parallel as the datasheet recommended
• - Measure and observe the voltage that
  adapter outputs using oscilloscope

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Verification Procedures

• Testing the LINX RX and TX range
• Input at the RX
  Output at TX at 22 feet
  

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Testing the LINX RX and TX range (Continued)

• Output at RX at 30 feet

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Testing Darlington Transistors
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Power Consumption

• Current Flowing Through the Circuits
• Power Consumption

State TXM RXM
Active 51.8mA 70mA
Idle 42.6mA 40mA
State TXM RXM
Active 0.4662 Watts 0.35 Watts
Idle 0.3834Watts 0.2 Watts
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Battery Life

• We use two 9V Lithium batteries in parallel to
  raise the current capacity of power supply for
  TXM.
• A 9V Lithium battery has a current capacity of
  1.2Ah
• The Equation for Battery Life
• Battery Life

State Irequired tlife
Active 51.8mA 46.33hr
Idle 42.6mA 56.34hr
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Testing ProcedureTransmitting and Receiving
Antenna

• Power Transmitted from the Transmitting Micro
  chip Antenna -20.647dBm

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Safety Considerations

• Lithium batteries can explode when shorted
  separation of power and ground pins and
  insulation
• FCC Compliance Verification still needed
• High voltage operation of relay switches in the
  elevator circuitry hooking up the RXM with an
  elevator requires a professional

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Problems Encountered

• PIC Microcontroller Problems
• - Programming SMD type PIC
• - Interfacing PIC with LCD display
• - Interrupt INT_RDA not working
• Image Source http//img.akizukidenshi.com/images/
  org/pic16f877-pt.jpg

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Problems Encountered (continued)

• Strength of Microstrip antenna not strong enough
  when enclosed in the circuit box
• Reed relays from ECE store room found to be
  unable to stand the 120V connection to the
  elevators relay switches
• Coaxial cable gain of new (RG-58C) vs gain of
  old (RG-174)

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Results!

• Correct and stable interface with LCD and inputs
• Successful control of elevator relays
• Range Problems
• - 36 ft antenna found to work well in vertical
  direction (w/o a lot of obstables)
• - Thick walls around elevator obstructing signal
  reception

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Recommendations

• Place antennas outside of the hoist-way
• Signal amplifiers connected to each reception
  antenna
• Use a weather resistant whip antenna for the
  transmission side and place antenna outside the
  box

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Idea Extensions

• Usage of transceivers on both modules - every
  building with receiver hooked up can then send
  of floors it has to transmitter once within
  range
• Similar concept for other purposes
• - Opening building entrances

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Credits

• Professor Gary Swenson
• Dwayne Hagerman
• Jeff Miller
• Professor Franke
• Mark and all the guys from Parts Shop
• Machine Shop guys
• Fellow 445 students

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Thank You

• Questions?
• Comments?