Rajesh Patel

Table of Contents

I. Abstract ................................................................................... 1

II. Introduction ................................................................................... 2

III. Host Unit ................................................................................... 4

IV. Remote Unit ................................................................................... 5

V. Door Detection Unit................................................................................. 6

VI. Microcontroller ................................................................................... 7

VII. Wireless Communication.......................................................................... 8

VIII.User Interface Control.............................................................................. 12

IX. User Screen ................................................................................... 13

X. Circuit Descriptions and Operations.......................................................... 15

a) Infrared Transceiver Subsystems.................................................... 15

b) Host Unit Circuitry ........................................................................ 16

c) Remote Unit Circuitry.................................................................... 16

XI. Time Line ................................................................................... 18

XII. Goals and Objectives............................................................................. 19

XIII. Future Work ................................................................................... 22

XIV. Summary and Conclusions...................................................................... 24

XV. References ................................................................................... 25

Appendices:

A Circuit Diagrams

B Flow Charts

C Source Code

Abstract

When walking around campus one is sure to notice the handicap accessible doors on almost all of the university’s buildings. These doors are a great benefit for people who are confined to wheelchairs and do not have the ability to open a normal door by themselves. Most of these handicap accessible doors use a button or light sensor that must be pushed or covered by one’s hand in order to activate the door. Although these devices do make access a little easier there is still a lot of room for improvement. The purpose of the Automated Building Accessibility System (ABAS) is to help ease this burden by allowing remote access to doors and elevators for persons confined to wheelchairs.

Introduction

Many buildings have devices to aid persons with disabilities in entering a building, especially those confined to a wheelchair. However, they often find these devices very cumbersome to use. Companies, such as Infralink, have come up with similar remote devices but nothing designed specifically for wheelchair users. These systems do not have the flexibility of the Automated Building Accessibility System (ABAS).

The Infralink elevator system is based on an infrared system very similar to that used in consumer electronics. The two major drawbacks to this system are: it is limited to controlling only elevators and the control device is not designed to be used by persons with limited dexterity. The ABAS is based on the Motorola 68HC11 microcontroller and the HSDL-8000 infrared transceiver. Such a microcontroller is easily adaptable to almost any situation. The ABAS remote control unit does not need to know anything about the internal functions of the device it is controlling. When the remote unit approaches the device, it receives information it will need to control the device. This is a very flexible system and adaptable to almost any control situation.

Host Unit

The host unit consists of a Motorola 68HC11 microcontroller, HSDL-8000 infrared transceiver, external elevator control panel interface, and added onboard circuitry to generate needed signals for the infrared transceiver. The host unit is the device which is mounted inside an elevator or by the door leading into the elevator. The host unit begins a cycle by sending out data via the infrared transceiver. The data which is sent out identifies which specific type of device the host unit is controlling. For instance, the data could identify the host unit as an elevator with ten floors, or a door leading into an elevator. Once the data is sent, the host unit then waits for an external signal from a remote unit. If no data is received back within three seconds the host unit will time out and repeat the cycle. If the host unit receives a signal from a remote unit it will translate the data and perform the indicated action. The host unit will also send confirmation data back out to the remote unit indicating it received the signal. The host unit will now go back to its normal cycle of sending out data and waiting for input.

The operation of the host unit allows it to be very versatile and user friendly in many situations. For instance, if two persons, each in a wheelchair, were to arrive at the elevator at the same time, the host unit would have no trouble servicing both requests almost simultaneously. From the time the host unit receives a request, sends out the control signal, and sends back a confirmation is approximately 0.1 seconds. This short time period allows the host unit to act as though it were servicing multiple requests simultaneously and therefore appearing transparent to multiple users.

Remote Unit

The remote unit is mounted on the wheelchair. It has a port to allow the connection of a device, such as a joystick, that will allow the user to control the unit. The display device is a 20 x 4 line Electro-Luminescent LCD display. It uses the same infrared transceiver as the host device for two way communications.

The program on this unit allows the user easy control over any device. When the person moves the joystick, it sends out infrared signals which can be used to open a door or other similar device that has only one choice. On the other hand, if the host device has a choice to be made, it will send out a wake up signal to the remote unit. Upon receiving this signal, the remote unit will turn on the LCD display and show the choices for the host unit. The user can then make a choice which will be repeatedly send until a confirmation has been received. If the remote unit does not receive anything from the host unit for more than a quarter of a second, it will go to sleep. It will wake upon receiving information from a host.

The system uses a built in LCD interface to control the LCD, the connections are

detailed in appendix A. The NMIT-20 board also has a built in keypad interface, this is used to connect the external control devices. In this implementation of the system, the connections are detailed in appendix A. To help better understand the operations of the host and remote units please refer to the flow charts in appendix B.

Door Detection Unit

The door detection unit has two main designs. The first design, modeled by the prototype, is a straight infrared detection designed to trip a relay when an infrared signal is detected. The second design incorporates security measures to allow entry to specific users.

The first design is implemented using an infrared transceiver and a simple circuit to trip a relay when a signal is received. This unit has an effective range 1 inch to approximately 10 feet. The effective angle of approach is 20° ±5°. A simple detection circuit was determined to be sufficient for most main entrance doors. When approaching a door the user does not want a choice, he/she just wants the door to open. The second design will be developed for buildings where access needs to limited to specific personnel. The security design will incorporate a basic stamp microcontroller and an infrared transceiver. This design will use a two step security procedure which will be entirely transparent to the end user. The building unit will send out a random number which will be processed by the remote unit and then sent back to the building unit for the appropriate response. The second step of the security involves sending a user specific code along with the generated response. The microcontroller will compare the user code with a list of approved users and allow or deny access to the building.

Microcontroller

The following criterion were considered in choosing a microprocessor for this system:

· Low cost.

· Ability to interface with a LCD, Joystick, and infrared I/O

· Programmable in C

· Good development environment

· Memory upgradable to 32k of RAM

Two different microcontrollers were considered: the Basic Stamp II by Parallax and the 68HC11 by Motorola. The Basic Stamp II has some features that the 68HC11 did not, such as the ability to generate X-10 signals (used in home automation) and a very small size. However, it is only programmable in Basic and has insufficient RAM. Also, it does not have the expandability that the 68HC11 does. The 68HC11 uses a memory mapped I/O system which will allow interfacing of multiple devices and it is upgradable to 32k of RAM.

For these reasons, we decided to use two 68HC11 development kits from New Micros Inc. (NMIT). The NMIT board can be programmed in any of the following languages: Assembly, Forth, Basic, and small C. The two programming languages used in the ABAS are: Assembly and small C. Small C allowed the design team to begin writing the code with a minimal amount of delay. The design team used inline Assembly with the small C to keep the code small and efficient.

With the NMIT development board, interfacing with the 68HC11 was fairly easy. The board has built in interfaces for an LCD display and a keypad port which we used to interface a joystick controller. The infrared transceiver from Hewlett Packard was designed to interface with a serial port, with a few modifications (illustrated appendix A) the design team was able to implement this system.

Wireless Communication

When choosing a communication device for ABAS, many parameters had to be taken into account. These parameters included distance between remote and host unit, price, and interfacing with the 68HC11 microprocessor. All the parameters were closely examined before choosing the components used for communication. There are two types of technologies which could have been used for communication on the ABAS, RF(radio frequency), and IR(infrared). Both technologies have their advantages and disadvantages. The technology which was decided to be the most suitable for the application is IR.

One of the main concerns when choosing the communication technology was the ease of operation for the wheelchair user. Depending on whether the IR communication device is using line-of-sight(LOS) or a diffuse signal, the wheelchair user might have to worry about aligning the receiving and sending units. Using an LOS IR device could be potentially frustrating for a person in a wheelchair when trying to align the IR transceivers. Using a diffuse IR device would alleviate most problems associated with aligning IR transceivers but not all. RF communication would be the obvious solution to eliminating need for alignment between the remote and host units but it suffers from other drawbacks.

An RF device has communication properties that the design team deemed unacceptable. The ABAS uses a two-way communication system. A sensing device mounted near an automatic door or elevator also has a transmitting device. The host unit is continuously sending out a signal and then looking for a remote unit. When the host unit detects the remote unit's signal it automatically sends a signal back to confirm that it has received the remote unit’s signal. Imagine the confusion if there are five or ten host units in the RF operating range of the remote unit. Decoding techniques could be employed to conquer this obstacle, but this could also complicate the project.

When a wheelchair user approaches an elevator he/she would like to select an "up" or "down" button to fetch the elevator. The host unit controlling the elevator must somehow know which floor the wheelchair user is on. With an RF communication device, it would be difficult to differentiate between which floor the wheelchair user is currently on.

Any type of RF device sold in the United States must first be FCC (Federal Communications Commission) approved to insure it complies with their standards. IR devices do not have to worry about interference from other IR devices nearby which operate at the same frequency like RF devices do. This is a great benefit for IR devices when one considers the amount of time required to have an equipment FCC certified. The above reasons are why an IR device was chosen for communication instead of an RF device.

Although an IR communication device is much more suited for the task at hand, it still has some drawbacks. Some of the major drawbacks to using IR are its limited operating range and directional orientation. If a LOS IR device is used for communication, aligning the remote and host unit transceivers could cause difficulties. The proper placement of the IR transceivers on the host and remote units is essential for the operation of an LOS IR device.

Diffuse IR communication is where there is not a direct path between the receiving and transmitting IR device. The IR signal is allowed to reflect off any surface in the proximity of the transmitting device before finally reaching the IR receiver. Most indoor surfaces will reflect between 40% and 90% of an IR signal with 80% being typical for plaster walls. A diffuse IR signal generally has to travel farther than a LOS IR signal which severely decreases the signal’s strength. An easy way to compensate for the signal loss due to reflection is to increase the intensity of the transmitted signal. Increasing signal strength on the remote device would lead to added battery consumption, therefore, decreasing battery life. Diffuse IR communication would also be unsuitable for outdoor operation when considering the larger distances between reflecting surfaces.

The design team decided on the following design for IR communication which will consist of LOS IR transceivers. The remote unit uses two sets of transceivers with one pointing vertical and the other pointing horizontal. The host unit will also have two sets of transceivers with one mounted on the ceiling and the other on the wall, for inside devices. Outdoor units will use one detector mounted next to the device. When a person in a wheelchair approaches a door or elevator head-on, communication will be done between the horizontal remote unit transceiver and the wall mounted host unit transceiver. If a wheelchair user approaches a door or elevator from a non forward angle then the communication will be done between the vertical remote unit transceiver and the ceiling mounted host unit transceiver. The optical cone(see figure 2) created by the IR transceivers is what determines the operating distance when communication is done between the ceiling unit and the remote vertical unit. The IR transceiver that is used for communication is the HSDL-1000 manufactured by Hewlett- Packard. The HSDL-1000 has an operating range of approximately 1 meter by itself. This distance is obviously to short for the design of ABAS. Increasing the range to 4.4 meters was accomplished by the addition of an LED(light emitting diode), provided with the HSDL-8000 transceiver kit. The HSDL-8000 is a board which includes the HSDL-1000 transceiver and a modulator/demodulator chip. Special signal processing techniques can be employed to increase the range even further with maximum errorless transmissions reaching 10 meters. The communication between the HSDL-8000 and the 68HC11 was accomplished with serial data transmissions.

There was one more communication issue that needed to be addressed and that was security. The ABAS can be designed to allow a wheelchair user to have security clearance for special doors if the need arises. Both the remote and host units could be programmed to allow for entering, updating, and deleting passwords. Typing in a password when one is required could be a major chore for many people who are confined to wheelchairs. If the host unit sends a signal saying that a password is required, the remote unit would automatically send the password when the open door option is selected. From the users point of view, everything will appear to operate as if no password was required. This method of using passwords helps to insure that the ABAS is as user friendly as possible which was an important design goal of the project.

User Interface Control

Several man hours went into the research and preliminary design of the user interface for the Automated Building Accessibility System (ABAS). Some of the original designs that were considered called for a large three button input device. One button would be for scrolling up, one for scrolling down and the third button would be an enter key. This input device was dropped in favor of the joystick.

The ABAS design team decided to use the joystick input device after speaking with Cathy Peer at the University Hospital - Assistive Technologies. It was found that the majority of persons confined to a wheelchair have limited dexterity. Most wheelchair users tend to have use of their shoulder muscles and elbow joints, but limited use of their wrist and fingers. Because of these physical limitations, the joystick was found to be the input device of choice. The users will be able move the joystick up and down to scroll through the selections on the screen. Moving the joystick left or right simulates an enter key function.

Another issue was the size of the joystick device. Since wheelchair users are confined to a fairly small area, it would be advantageous to keep the joystick small. The joystick on the final prototype will be about 2” high and mounted directly on the remote unit. The next problem was where and how to mount the remote controller. The most logical solution is to mount the controller on the outside of one of the arm rests. We also decided to make the controller removable, since the wheelchair sides need to fold down so that the user can be moved in and out of the chair.

User Screen

The type of display used for the Automated Building Accessibility System (ABAS) is a backlit liquid crystal display (LCD). The display has four lines with twenty characters per line. The reason for choosing this size display was that it must be large enough to display sufficient information and also be compact enough so it does not obstruct the user. Backlighting is necessary for the user to be able to easily read the display in an indoor environments with extremely low ambient light or outside at night.

Many manufacturers had LCD displays that met these requirements. One main concern was to find a display that readily interfaced with the 68HC11. Fortunately, companies such as Optrex, Hitachi, and Sanyo supply such devices. Another main concern was to find one with its own onboard processor that can accept American Standard Code for Information Interchange (ASCII) characters. The final display chosen for the ABAS was the Optrex DMC-20434.

Although the current design of the ABAS uses a LCD character display, it might be desirable to use a LCD graphics display for special users with poor vision. Character displays tend to have character sizes which are usually around 0.21 inches. This is much to small for anyone with limited vision. This obstacle could be overcome by using a graphics display and programming larger characters for the display. Of course, this would require a different LCD interface with the 68HC11 and also more programming to support the graphical display. To see a sample display of a menu on the ABAS, please refer to figure 3 (Note: The star on the figure refers to the cursor position of the joystick).

Circuit Descriptions and Operations

The host and remote units both use the same type of microcontroller, so the following circuit descriptions will only detail the parts of each system which are different. In order to see the actual circuit connections please refer to appendix A which contains detailed schematics.

A. Infrared Transceiver Subsystem

The 68HC11 uses Port D pins 0 and 1 for serial communication. Port D pin 5 is used to control an analog switch to prevent feedback from the infrared transceiver. Immediately before data is sent from PD1 on the 68HC11 to S_out, on the infrared transceiver, PD5 is set low as to disable the analog switch. When the analog switch is disabled no data can be read into PD0 on the 68HC11 from Rcv on the infrared transceiver. After data has been sent out through the infrared transceiver, PD5 is set high to enable the analog switch and allow data to be read into PD0 on the 68HC11. Without this disabling mechanism, the 68HC11 would receive feedback from the infrared transceiver and create confusion with the host or remote unit’s program.

The infrared transceiver requires an input signal which is 16 times (16X) faster than the baud rate of the transceiver. In order to generate the 16X signal used by the infrared transceiver, a TTL oscillator and a divide by twelve counter are used on both the host and remote unit. The 16X signal is used by the infrared transceiver for its 3/16 modulation/demodulation scheme. A crystal oscillator could not be found which was exactly 153.6 kHz which is the frequency of the 16X signal. The TTL oscillator used has a frequency of 1.8432 MHz which is exactly twelve times the needed frequency. The output from this TTL oscillator is fed into the divide by twelve counter and its most significant bit output pin is used as the 16X signal for the infrared transceiver.

B. Host Unit Circuitry

On the host unit Port A pins 4 - 7 on the 68HC11 are used as outputs to the elevator control circuit. These four pins are connected directly to a 4 x 16 decoder. In the prototype the outputs from the 4 x 16 decoder are connected to LED’s instead of relays. When a signal is sent to Port A these pins are held high for 0.5 seconds in order to allow visual confirmation of proper operation of the circuit. In the actual circuit this 0.5 second delay would not be necessary. The delay would only have to be long enough for the relay to make a good contact and simulate pushing the appropriate button.

C. Remote Unit Circuitry

The remote unit uses Port E for the input from the joystick. The joystick has four switches which are closed depending on which way it is pushed. 13 out of the 14 LCD pins connect directly to the LCD connector on the 68HC11 board. The remaining pin is connected to a potentiometer to control the contrast. A transistor and resistor are connected to Port A pin 6 which is used to control the power to the inverter. The inverter produces the AC signal which is used for the backlighting on the LCD. When Port A pin 6 is high the inverter is turned off, when pin 6 goes low, the inverter has power and the backlighting comes on.

Timeline

The ABAS design group had a few obstacles in the completion of the project.

The infrared communication did not work as expected and the programs took longer than expected to write.

As detailed in the report, there were problems interfacing the IR transceiver with the HC11. When transmitting, the design team had a problem with feedback. For example, a character sent out would also be received. This problem was solved by using an analog switch to disable the receive line of the IR transceiver. This solution was achieved after many failed attempts to solve this problem.

The programs also took longer than expected to write. There were two reasons for this. First, the infrared problems were partially solved using software control. This held back the development of the programs. Second, the design team did not have access to any type of debugger. As a result, the debugging process was much longer than expected.

Goals and Objectives

The objective of the ABAS project was to create a device which could successfully control an elevator and/or automatic door, through an infrared communication link. The exact criteria for determining the success or failure of the ABAS included operating distance, angle, and reliability between the host and remote units. The goal was to obtain a distance of at least 10 feet at an angle of 15°± 5°, off center, with 90% accuracy.

The design team did a series of tests at angles ranging from 0° to 35°, and distances of 1 to 11 feet. The following table shows success /failure at the specified requirements:

Distance in Feet:

Angle:

x indicates error free transmission

+ indicates delayed response in reception

- indicate failure to communicate

The above data was summarized into a graphical bar chart shown below.

Another goal of the ABAS was keep the cost down to an affordable level. The completed unit will cost approximately $250 per remote unit, $100 for a standard door detection unit, $200 for secure door detection unit, and $200 per host unit. The last goal of the ABAS was to make the system user friendly. This was obtained by making the remote unit menu driven. Host units send out the type of device they are controlling which tells the remote unit which menu to display for the user. The ABAS design team, supported by the above data, feels that the system has achieved and even surpassed the defined goals and objectives.

Future Work

There are several upgrade paths possible for the Automated Building Accessibility System (ABAS). Such possibilities could include allowing for vehicle entry control, X-10 signal generation, directions to bus stops for handicap accessible buses, and directory assistance in buildings are just a few. The following sections detail ideas on how to implement the above mentioned upgrades.

Vehicle entry can be a very cumbersome task for persons in wheelchairs. At the present time, most handicap equipped vehicles have some type of lift to help a person enter the vehicle which must be activated a control on the vehicle. This process can be automated through remote control systems, making the ABAS a perfect solution.

Another possibility is X-10 signal generation. X-10 signal generation is a method of sending control signals over existing home electrical wiring. Many current home automation systems designed to help persons with disabilities use X-10 signals. A device to be controlled is plugged into a special box, which plugs into an existing socket. This special box receives signals through the house wiring from a control box. This control box receives its instructions from a remote controller which is controlled by the user. The ABAS system could replace the existing remote controllers thereby allowing the users to conveniently control all devices from one remote controller.

Another improvement could be assisting persons confined to wheelchairs to find the routes of handicap accessible buses. Some city governments have expressed an interest in such a device. By adding a Global Positioning Satellite system (GPS), and local area maps to the ABAS system, persons confined to a wheelchair could have such knowledge. Finally, another system improvement would be to add directory assistance for buildings. When looking at a directory of stores in a mall, the directory is typically positioned at an upward angle. This makes viewing the directory very difficult and sometimes impossible for persons confined to a wheelchair. The ABAS could be designed to display such information, by allowing accepting signals input from unit positioned at the displayed directory.

There are several possibilities for additional improvements on the ABAS. This ABAS was designed in such away that any device that is currently under remote control could be controlled by the ABAS with simple modification to the current system.

Summary and Conclusions

The ABAS is an integrated solution for allowing persons confined to wheelchairs easy access to elevators and doors through the use of two way infrared communication. The ABAS prototype is comprised of a host unit, remote unit, and a door detector unit. All units communicate through infrared and then activate a specified device. The system was designed to be flexible and easily adaptable to various control situations.

Test data has shown that the ABAS is a feasible and a practical solution to a common problem. The ABAS could be implemented as a cost effective and trouble free system to help increase the mobility of persons confined to wheelchairs. The ABAS has the potential of revolutionizing the area of assistive technologies.

References

1- Kelley A. and I. Pohl, A Book on C, The Benjamin Cummings Publishing Company,1992.

2- MOTOROLA, M68HC11 Reference Manual, Rev. 3 1991.

3- Ali M. and J. Gillispie, Design and Interfacing of the IBM PC, PS and Compatibles, v.2. (1995).

4- Sedra A. and K. Smith, Microelectronics Circuits, Saunders College Publishing, 1991.

5- Wakerly J., Digital Design Principles and Practices, Prentice Hall, Englewood Cliffs, New Jersey, 1994.

6- OPTREX CORPORATION, Liquid Crystal Display Manual, 1995.

7- TEXAS INSTRUMENT, TTL Logic Data Book, 1988.

8- HEWLETT PACKARD, IrDA Data Link Design Guide, 1995.

9- Jones B. and G. Guntle, Teach Yourself Advanced C, SAMS Publishing,1994.