Wireless Elevator Remote Control - Senior Design Project Lab | ECE 445, Study Guides, Projects, Research of Electrical and Electronics Engineering

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WIRELESS ELEVATOR REMOTE CONTROL

By

Patrick Goh Hamed Asghari

ECE 445, SENIOR DESIGN PROJECT

Spring 2007

TA: Dwayne Hagerman

May 1, 2007

Project No. 16

ii

ABSTRACT

The Wireless Elevator Remote Control (WERC) is a device intended to help people in wheelchairs call an elevator with ease without having to use the buttons on the wall which are often out of their reach. The WERC will consist of a transmitter unit which will be mounted on a wheelchair and a receiver unit which will be connected to the elevator call system.

The transmitter module is ergonomically designed to ensure that it can be easily operated even by people with physical limitations. The simplicity of the controller assures a low learning curve which eliminates the need for lengthy manuals or technical support. The main purpose of the transmitter is to enable the user to send a signal to call the elevator to a particular floor.

The receiver module is engineered such that it can be connected to any existing elevator system without altering the present components and functions of the elevator. Its main purpose will be to receive signals sent from the transmitter and translate those signals into appropriate output that would control the elevator.

• 1. INTRODUCTION TABLE OF CONTENTS
  • 1.1 Purpose...............................................................................................................................
  • 1.2 Benefits and Features
  • 1.3 Specifications
  • 1.4 Subprojects.........................................................................................................................
    • 1.4.1 Transmitter System
      • 1.4.1.1 Power Supply
      • 1.4.1.2 Joystick Controller
      • 1.4.1.3 Seven-Segment Display
      • 1.4.1.4 Transmitter
      • 1.4.1.5 Microcontroller
    • 1.4.2 Receiver System.........................................................................................................
      • 1.4.2.1 Receiver
      • 1.4.2.2 Elevator Process Controller
• 2. DESIGN PROCEDURE
  • 2.1 Power Supply Design.........................................................................................................
  • 2.2 Data Transmitter and Receiver Design
  • 2.3 Joystick Design
  • 2.4 PCB Layout and Enclosure Design....................................................................................
• 3. DESIGN DETAILS
  • 3.1 Overall Circuit Functionality
  • 3.2 Components
    • 3.2.1 Transmitter
      • 3.2.1.1 PIC Microcontroller
      • 3.2.1.2 Transmitter
      • 3.2.1.3 Clock Oscillator
      • 3.2.1.4 Seven-Segment Display
      • 3.2.1.5 Power Supply
    • 3.2.2 Receiver
      • 3.2.2.1 PIC Microcontroller
      • 3.2.2.2 Clock Oscillator
      • 3.1.2.3 Receiver
      • 3.1.2.4 Relays...............................................................................................................
• 4. DESIGN VERIFICATION
  • 4.1 Testing..............................................................................................................................
    • 4.1.1 Power Supply
    • 4.1.2 Oscillator..................................................................................................................
    • 4.1.3 Joystick and 7-Segment Display
    • 4.1.4 Transmitter and Receiver
  • 4.2 Conclusions......................................................................................................................
• 5. COST
  • 5.1 Parts.................................................................................................................................. iv
  • 5.2 Labor
• 6. CONCLUSIONS....................................................................................................................
  • 6.1 Accomplishments.............................................................................................................
  • 6.2 Uncertainties
  • 6.3 Ethical Considerations
  • 6.4 Future Work/Alternatives
  • REFERENCES.......................................................................................................................
  • APPENDIX A – PICTURES A.
  • APPENDIX B – TRANSMITTER PIC CODE A.
  • APPENDIX C – RECEIVER PIC CODE............................................................................ A.

1. INTRODUCTION

1.1 Purpose

The goal of our project is to enable elevators to be controlled from a distance without using the elevator control panels. We hope to use this device as an aid for people in wheelchairs. One of the main components of the device will be a remote control which should be small enough to be mounted on wheelchairs. It will contain all the necessary functions to control an elevator. Jeff Miller, an Elevator Mechanic Foreman at the University of Illinois, suggested using small joystick controllers and limiting the functions to the bare necessities of people in wheelchairs to avoid overcrowding the controller. Thus, the controller would be designed to accommodate the three main elevator functions, namely the elevator call function, a floor selector and a door open function. A separate receiver module will be designed to receive signals sent from the transmitter and control the elevator as specified by the user.

1.2 Benefits and Features

The basic benefits and features of our device are outlined below:

Benefits:

• Making elevators more wheelchair-friendly.
• Ability to call the elevator from a distance.
• Easy installation on elevators. No alterations to the elevator system.

Features:

• User-friendly controllers.
• Small and compact controllers.
• Includes all the necessary functions to control an elevator.
• Clear and bright seven-segment display for floor selection.

1.3 Specifications

The project was divided into two main components: the transmitter and the receiver as shown in the block diagram below in Figure 1.1. For individual module specification, refer to section 1.

1.4.1 Transmitter System

The transmitter system will consist of a power supply, a joystick controller, a 7-segment display and a transmitter. It will be small enough such that it can be mounted on a wheelchair and will be responsible for obtaining inputs from the user and transmitting the signals to the receiver system.

1.4.1.1 Power Supply

The power supply will drive all the components in the transmitter system, namely the 7-segment display, the microcontroller and the transmitter. The power supply will consist of a 9V battery, dropped down to 5V through a voltage regulator and an ON/OFF switch.

1.4.1.2 Joystick Controller

The joystick controller will be the main form of obtaining inputs from the user. The different directions of the joystick will serve different purposes as follows: the up and down directions will scroll through the available floors, the right direction will call the elevator to the current selected floor and the left direction will be dedicated to opening the elevator car door for safety reasons.

1.4.1.3 7-Segment Display

The 7-segment display will obtain the input from the joystick controller through the microcontroller and display the current selected floor to the user.

1.4.1.4 Transmitter

The transmitter will obtain the input from the joystick controller through the microcontroller and send packets of signals through an antenna. It will be designed to utilize the 903.37 MHz band.

1.4.1.5 Microcontroller

The microcontroller will receive its input signal from the joystick controller and after processing, it outputs the appropriate signal to the 7 segment display and the transmitter.

1.4.2 Receiver System

The receiver system will consist of a receiver and the elevator process controller. It will be responsible for detecting signals from the transmitter system and processing these signals. It will then communicate with the elevator and produce the appropriate results as desired by the user.

1.4.2.1 Receiver

The receiver circuit will detect packets of signals from the transmitter and filter out all other unwanted noise. It will then relay this signal to the elevator process controller for processing. The receiver will be powered by a 5V wall adapter.

1.4.2.2 Elevator Process Controller

The elevator process controller will process the signals received by the transmitter. It will consist of a microcontroller and several relays that will be wired parallel to the elevator control system. When the

appropriate signal is received, the corresponding relay will be closed, producing the same results as if a button is pressed on the elevator controller. The elevator process controller will be powered by a 5V wall adapter.

Figure 2.2 Flowchart of Joystick Debouncing

From Figure 2.2, we see that the microcontroller only processes a “high” signal from the joystick once for every time the joystick is pushed into the “high” position. After that, the debouncing algorithm goes into a loop state until the joystick is released back into the “low” position.

2.4 PCB Layout and Enclosure Design

The printed circuit board (PCB) was designed using the available Eagle software in the lab. The process of designing the PCB involved first drawing out the schematic of the circuit and then placing all the parts on the board and making the connections. We used the auto-route function in Eagle to generate the most efficient connections. The final designs of our PCBs are shown in Figure 2.3 below. For pictures of the completed PCB, refer to Figure A.1 in Appendix A.

Figure 2.3 PCB Layouts – On the Left is the Transmitter, on the Right is the Receiver

The enclosures consisted of plastic cases purchased from the ECE Parts Shop and RadioShack. We then made a layout of the components that would be placed in the cases along with the positions of the parts that needed to be cut out in order to fit the components in them. The enclosures were then sent to the ECE Machine Shop to be drilled and after it was completed, the PCBs and joysticks were installed in them. For pictures of the completed enclosures, refer to Figure A.2 in Appendix A.

The transmitter goes through four initializing states every time it is powered up. It supplies power to all the components, initializes the floor selection to “b” (basement), updates the seven-segment display and then enters a loop awaiting user input. Once it receives an input, it determines what input was received and processes it as described in section 1.4.1.2 above. For the case of the up and down input, the microcontroller always performs a check to ensure that the state never goes below “b” (basement) or above 3 (third floor).

Figure 3.2 shows the flowchart of the receiver side.

Figure 3.2 Flow Chart of Receiver

The receiver goes through four states every time it receives a signal. The microcontroller processes the signal and determines what was sent. If the signal is that of the door open button, the microcontroller closes the relay that would open the elevator door. If the signal is that of a floor selection, the microcontroller closes the appropriate relay to call the elevator to that particular floor.

3.2 Components

This section outlines all the components used in our design.

3.2.1 Transmitter

The overall schematic of the transmitter is shown in Figure 3.3. The current drawn by the transmitter is measured to be 52.35mA in an idle state and 65.70mA in an active state. Comparing these numbers to IMAX = 53.57 as derived in Equation 1.1, we see that our device is operating at a level that would ensure a battery life of approximately three months. The power drawn by the transmitter in the idle state is calculated as:

P W [ ] = I [ A ] ⋅ V V [ ] = 52.35 mA ⋅ 9 V = 0.4712 W (3.1)

While the power drawn during the active state is calculated as:

P W [ ] = I [ A ] ⋅ V V [ ] = 65.70 mA ⋅ 9 V = 0.5913 W (3.2)

Each component is explained in further detail below.

Figure 3.3 Transmitter Schematic

3.2.1.1 PIC Microcontroller (IC2)

We used a PIC16F877A-I/P microcontroller to process all the inputs from the user and control the seven-segment display and the transmitter. The joystick is connected to pins RA2-RA5 in the following order: left, right, up and down. Pins RD0-RD7 are used to control the seven-segment display as shown in the schematic. The PIC generates the data to be transmitted using its built-in Manchester encoding scheme and outputs this data on pin RC6 to the transmitter. The PIC also generates a logic output on pin RC0 to turn the transmitter off when not transmitting data in order to save power. The code of the microcontroller for the transmitter can be found in Appendix B.

Each component is explained in further detail below.

Figure 3.4 Receiver Schematic

3.2.2.1 PIC Microcontroller (IC1)

The PIC (PIC16F877A-I/P) receives the data from the receiver from pin RC7 and processes it to determine what was sent. The PIC then generates the appropriate control signals through pins RC0-RC to close the corresponding relays (K1-K4) to produce the desired outcome by the user. The code of the microcontroller for the receiver can be found in Appendix C.

3.2.2.2 Clock Oscillator (QG1)

Refer to section 3.2.1.3 above.

3.2.2.3 Receiver (U$1)

The receiver used is the Linx RXM-900-HP3-PPS chip. Input is obtained from a Linx ANT-916-CW- QW (X9) through pin 1 and the data is sent to the PIC via the data pin. Pins CS0-CS2 are connected to

dip switches (SWS003) through 900Ω pull down resistors (R1-R3) for channel selection. This is again only implemented in the testing procedure and not in the final product for reasons explained in section 3.2.1.2 above.

3.2.2.4 Relays The relays used (K1-K6) are the T77S1D10-05 from Tyco Electronics Corp. They are rated at 10A at 120VAC. Input signals are obtained from the PIC which go through 5kΩ resistors (R4-R9) to drop the current down to 6mA before connecting into the base of 2N3904 transistors (Q1-Q6). The transistors are used as switches to provide the necessary voltage and current to control the relays. The current through the relays was measured to be at 54mA. 1N4001 diodes (D1-D6) were connected in parallel to the coils of the relays to protect the circuit from spikes in the current when the transistors switch on and off. From the schematic, we see that when the transistors are on, current will flow through the relays and the transistors. When the transistors are turned off by the PIC, the current trapped in the coils of the relays would be forced to either go back into the source or into the PIC which could damage the components. By adding the diode however, the current trapped in the coils of the relay when the transistors turn off can now go through the relay, around a closed loop, until it is dissipated. Thus we would not have a spike of current through the device.

4.1.3 Joystick and 7-Segment Display

The testing procedure for these 2 components was also very simple. We moved the joystick in all four directions and wired the outputs to all the inputs of the 7-Segment Display. We observed that all the correct LEDs on the 7-Segment Display lit up in response to the joystick commands.

4.1.4 Transmitter and Receiver

This is by far the most important test of our device that ensures proper functionality of the circuit as a whole. In our design review, we had specified that we would like to transmit from a distance of 100 ft. Initially, when we tested the range with the circuit still wired on the breadboard, we weren’t able to achieve a range greater than 20 ft behind closed doors. Therefore, before we started taking quantitative measurements, we needed to improve the range. We made the following modifications to improve the range to over 160 ft behind closed doors:

• Decreasing the baud rate from 9600 to 300 by trial and error in the PIC code
• Mounting the circuit on the PCBs resulted in less loss in wires

As the transmitted signal traverses the atmosphere its power level decreases at a rate inversely proportional to the distance traveled and proportional to the wavelength of the signal. Equation 4. accounts for only the diminishing voltage without accounting for absorption or dispersion by the atmosphere.

Path Loss = 10 { }

20 log d dB

×  

The Friis Equation (4.2) gives a more complete accounting for all the factors from the transmitter to the receiver: 2

16 2 2

Tx Rx Rx Tx

G G

P P

d L

λ π

where GTx = Transmitter Antenna Gain, GRx = Receiver Antenna Gain, λ = wavelength, d = separation distance and L = system loss factor (≥1)

Using a very useful and convenient applet from http://www.rfcafe.com, we tabulated what the theoretic attenuation would be for our system. The result is summarized in Table 4.1 below and accompanied by the corresponding plot in Figure 4.1.

Distance (ft) 1 2 3 5 10 15 20 25 30 35 50 60 Atten. (dB) 21.2 27.3 30.8 35.2 41.2 44.8 47.3 49.2 50.8 52.1 55.2 56.

Table 4.1 Attenuation vs. Distance data

Figure 4.1 Theoretical plot of Attenuation vs. Distance

After we confirmed the improvement in our range qualitatively, we started taking quantitative measurements. The most convenient and readily available test was the Received Signal Strength Indicator (RSSI). Pin 14 of the receiver module outputs an analog voltage that is proportional to the strength of the received signal. Using an oscilloscope, we gathered the data in Table 4.2 and made the corresponding plot in Figure 4.2.

Distance (ft) 1 2 3 5 10 15 20 25 30 35 50 60 RSSI (Volts) 2.3 2.27 2.13 2.16 1.98 1.91 1.85 1.7 1.68 1.65 1.62 1.

Table 4.2 RSSI vs. Distance data

Figure 4.2 Plot of RSSI vs. Distance