127: GPS Voice Output

Transcription

1 127: GPS Voice Output by Kurt Peterson, Neil Peterson For ECE 401 Dept. of Electrical and Computer Engineering North Dakota State University May 2001 This project was supported under NSF grant BES Abstract: This report addresses the problem of building a device that will output global positioning information through an audio device, a speaker. The device will used by the blind to help them navigate, so it will have to be easy for them to use. Our approach uses a OEM bare board GPS receiver, a microprocessor, and a speech synthesizer along with a keypad as its main components to build a device that can be operated with one hand and output a person's position in relation to a destination that they want to reach. The final cost of the device is not yet known, but the estimated building costs is under $1000.

2 Chapter 1- Introduction 1.1 Introduction This report presents the design of a GPS voice output device for NDSU Senior Design ECE Background A blind person's cane can only help them get around so much. It does not tell them the direction they are heading, where they are, or how far they are from where they want to be. The cane only tells them what is in front of them. A seeing-eye dog cannot give them this information either. This GPS voice output device will provide this information to the blind user. 1.3 Objective Ideally, once completed, the operator of this device will be able to hear a variety of information by pushing a button. 1) coordinates of their current position in degrees latitude and longitude 2) direction that they are travelling 3) distance to their destination 4) directions to their destination The user will also be able to save the coordinates of a position in the device's memory, name the saved positions, and use these saved positions as destinations later. So, they will be able to get directions back to a position that they have saved. The device will output warnings to tell the user if the battery power is low or if satellite transmission is weak or lost. To be as useful as possible to the operator, the device should be quite accurate. 1.4 Scope This report this organized as follows: * Chapter 1: introduction to the problem and a general description of the device that will come out of the design process. * Chapter 2: previous work on similar projects is presented. The specifications which this device must meet are given, and the project is split up into several tasks for the design team. * Chapter 3: each section of the project is described in further detail. The options that were considered section are presented. Also, the chapter lists the design option that was selected and the reason for this selection. * Chapter 4: contains the circuit diagrams and flow charts for each section of the project. * Chapter 5: concludes the report and suggests future directions for follow-up design projects.

3 Chapter 2: Previous Work and Design Approach 2.1 Introduction Although the Global Positioning System was originally intended for military purposes, the public has used it for many years as a navigation aid. This has helped many people find their way when lost or exploring unfamiliar ground. With the increase in speech synthesis technology, it has been used in recent years to expand this aid to those who could are in need of help in navigation, the visually impaired. In this chapter, some existing designs are discussed. The features of these products are evaluated along with their shortcomings. The general block diagram of our proposed design is given, including a time line and division of work. 2.2 Previous Work In doing research into this project, three different designs were found that have utilized GPS technology to provide a complete navigational aid for the blind. These systems allow them to download maps of their cities with all the streets and any points of interest desired. The software used is able to read the maps and give directions according to street names. Because of the use of this talking map software, these systems offer more options than our design will be able to accomplish. All of these aids seem to present a useful product to the visually impaired. Therefore, the requirements and features of these designs are helpful to the design of our project Patented Devices All three of the devices researched have similar features and designs. They all utilize software that allows a user to download any map and have it read to them as they are navigating or plotting a course. This software requires the use of a notebook or desktop computer, and therefore all of these products are quite expensive. The first of these devices to be produced is a project called MoBIC ( Mobility of Blind and Elderly Interacting with Computers). The objective of this design was to develop a wearable navigation system that would increase the mobility of the blind. The project team interviewed a number of visually impaired people to find out what information would be the most beneficial to them. The results of these interviews showed that the most important feature was the user s current location and directions to required destination. Other information desired were the names of streets, environment layout, and points of interest including useful buildings and landmarks. The design was able to accomplish most of this with its software. Information on the environment layout, including steps, underpasses, and change in street level, was unable to be relayed to the user. The MoBIC design has two different modes. The pre-journey planning mode allows the user to navigate through a map and plot an optimum course. The other mode, the outdoor system, is the actual navigation end of the project. In this mode, the GPS receiver transmits positional data to the PC. The central computer also takes input from an electronic compass. GPS receivers are only able to give

4 heading information while the user is moving. The use of an electronic compass allows the user to know their heading at all times. The device is controlled by a wrist-worn keypad. The articles found on the MoBIC project did not describe the talking map software used. The two other designs, Strider and GPS-Talk, discussed the requirements of the software, but did not explain how it worked. The Strider device uses Atlas Speaks, a software package developed under a joint effort of Arkenstone and VisuAide. This software seems very similar to Atlas, the program that is used by GPS-Talk, developed by the Sendero Group. Both of them seem to have similar features that can give more information that a printed map. This includes being able to give the length of each block in meters or feet. It can also give the heading and distance to any way-point or destination. They both can store a variety of points of interest. The software also allows the user to plot a course that can give them every block and turn of the route Published Articles A number of articles on these designs and GPS research were found on the Internet. The websites used are included in the references section of the report Shortcomings of These Devices Each of these products has many features that make them extremely useful as a navigational aid. However, the overall size, power consumption, and cost make them somewhat impractical to the average user. All of these designs are very similar, and most of the specifications are in the notebook PC. The PC will determine a big portion of the cost and the size. The lowest price found for any of these devices was around $900. The use of a microprocessor instead of an entire computer will cut our costs and size. The PIC processor costs around six dollars and consumes significantly less power than any notebook computer. Most new notebook PCs cost over $1000 and can cost as much as $6000. They use a rechargeable lithium-ion battery that can save on battery cost, but the best ones only have an operating time of about three hours on a charge. Most notebook computers are similar in size and weight. They are about the size of a notebook, 12 in. x 9 in., and weigh about nine pounds. 2.3 Specifications As described in the next section of this chapter (2.4), the project is composed of five main components: a GPS receiver, a microprocessor, a speech synthesizer, power supply, and a keypad. GPS Receiver The GPS receiver is possible the most important part of the design. The receiver must be able to send serial data including information on the current position and heading. It must also be able to send information on the present satellite conditions in case the link is lost. The overall accuracy has not been determined. Most receivers have the ability to receive a differential correction signal. The differential correction allows receivers to

5 obtain an accuracy of within five meters. The purpose of our design requires the best accuracy possible. Therefore, differential GPS will be an issue for next semester in 403. Microprocessor The microprocessor must be able to receive serial data at 4800 or 9600 baud from the GPS receiver. It must also be durable so it can sustain certain shocks to its system. The microprocessor must also have at least 20 I/0 pins. The inputs it must receive are nine from the keypad, one possible from the electronic compass, and the GPS receiver. The only output is to the speech synthesizer, which could take a possible 8 pins to receive data. Speech Synthesizer The speech synthesizer is also a key portion of the design. The most significant feature of the synthesizer is the ability to understand the synthetic speech. Controls for volume, pitch, and speed rate will be needed. Because the design does not use headphones, the speaker must be able to output the messages loud enough for the user to hear and understand. This explains the need for volume control. A desired feature would be a variety of different male and female voices. The reason for this feature is the possibility that certain voices might be easier to understand than others. Power Supply The power supply will need to provide a constant +5VDC to all of the components. The receivers considered require a minimum of +3VDC and a maximum of +5VDC. The microprocessors considered require a minimum of +5VDC. The keypad will use the same 5V source to drive the signals to the microprocessor. This 5V will also be used for the speech synthesizer. The fact that all the components will require the same input voltage will make the power supply design fairly simple. Keypad The keypad design will require the following specifications. The keypad will use nine buttons to be input to the microprocessor. These buttons will control certain functions of the device such as saving positions, sorting through these positions to plot a course, and outputting messages. The keys on the pad will have a resistance to them so they will not be pushed accidentally. The keypad itself must be easy to use with one hand. This will enable the user to employ the use of a cane or seeing eye dog as well as the device. 2.4 Block Diagram Most of the work for this design will be in writing code for the microprocessor. Although we have not determined all the aspects of the code, it can be split up into three parts: code to handle all the inputs from the devices, code to output data to the speech synthesizer, and code that will take the information received by the components and manipulate it to the desired output. Kurt is going to write the code to handle the input

6 data. Neil will write the code to output data to the speech synthesizer. We will both write the code to convert the data received to the preferred format. The other blocks of this project include the power supply, GPS receiver, speech synthesizer, and keypad. The project will be divided up as shown here. The electronic compass feature has not been confirmed as part of our design. This will be determined next semester in 403. Power Supply Kurt Peterson GPS Receiver Microprocessor Speech Synthesizer Kurt Peterson Kurt Peterson Neil Peterson Neil Peterson Electronic Compass Keypad??? Neil Peterson Block Diagram and Division of Work for GPS Voice Output The GPS receiver will receive data from the GPS satellites and possibly a differential correction signal. It will send this data to the microprocessor which will do all the calculations to get the desired units for the directions to be given. The user will choose what information is needed from the keypad, and the microprocessor will take these inputs and output the desired message to the speech synthesizer. The microprocessor may also take in an additional input from an electronic compass. This will allow the user to receive a heading reading even when not moving. It has not been determined if this will be used in our design, as research into electronic compasses has not given much results. 2.5 Time Line The following is the proposed time line for the design process next semester in 403. These deadlines may be subject to change, depending on when the components needed are received.

7 Date Proposed Work Done 1/9/00 * Speech synthesizer received 1/16/00 * C Compiler for PIC microprocessor installed on computer 1/23/00 * Code for speech synthesizer written for testing and debugging 1/30/00 * GPS receiver obtained for testing 2/15/00 * Keypad built for testing 2/22/00 * Code for receiving inputs from keypad written for debugging 3/15/00 * Code for receiving GPS data written for testing and debugging 3/22/00 * Code for manipulating GPS data to give desired outputs written 4/7/00 * Testing of all code and building a case for the complete device 5/7/00 * Final report and user s manual written 2.5 Conclusions This chapter has discussed the background of this project. It discussed the previously built designs of MoBIC, Strider, and GPS-Talk. This chapter also addressed the need for the proposed design. The factors that will try to be minimized in this design are cost, size, and power consumption. The tasks to be completed have been divided and a proposed time line was included. The next chapter will discuss these tasks in greater detail.

8 Chapter 3 Detailed Design 3.1 Introduction In this chapter, each section of the project is described in detail using block diagrams, options that were considered and those selected are presented in this chapter. 3.2 Keypad Detailed Block Diagram: The block diagram for the keypad is shown in Figure 3.1 below. Each button on the keypad corresponds to a function of the device. Table 3.1 lists the functionality of each button. In addition to their function, buttons four, six, two, and eight will allow the user to scroll through a list of letters when naming positions and courses. 1 Outputs: direction traveling.(heading) 2 Outputs: coordinates of current position. 3 Allows the operator to save the coordinates of the current position in the devices memory and name the position. 4 Outputs: direction to destination in degrees from North (Bearing). (N = 0, E = 90, S = 180, W = 270 ) 5 Outputs: distance (North or South) and distance (East or West) of destination in meters. 6 Outputs: distance to destination. 7 Allows the operator to plot a course using the positions that are saved in memory. 8 Allows the user to save the course that is currently plotted and name the course. 9 Allows the user to select a course from a list of saved courses Table 3.1 microprocessor input port Options Considered: Two options were considered in the decision of how to implement the keypad design. 1) Buying a keypad to meet our requirements was considered. This option required an extensive search on the Internet for a keypad that has 9 keys, can be connected to a microprocessor s port pins, and would be easy for a blind user to operate.

9 2) Building the keypad. This option required designing a keypad using push-button switches and logic circuits Options Selected: The second option (building our own keypad) was the one that we chose. One reason this option was chosen was to eliminate the time that would be spent searching for the item. Our initial searching did not produce any results. Also, this option allowed the keypad to be designed in exact accordance with the specifications. Designing our own keypad also allowed for the minimization of the number of pins required for the microprocessor to interface with the keypad. The blind user will be kept in mind while designing the keypad. Braille will be used to label each of the keys to distinguish one button from another. Also, a voice output will tell the user which key was pressed. 3.3 GPS Receiver Detailed Block Diagram: The block diagram for the GPS interface with the microprocessor is shown below. The GPS receiver sends NMEA-1083 output to the microprocessor. NMEA-0183 is a standard that defines an electrical interface and data protocol for communications between marine instrumentation. NMEA stands for the National Marine Electronics Association; the association developed the standard in NMEA-0183 data is sent at 4800 baud, and all the characters are printable ASCII text (plus carriage return and line feed). The standard calls for data to be transmitted in sentences. NMEA-0183 sentences begin with a $. The next two ASCII characters are the talker ID; GP is the talker ID for a GPS receiver. Some other talker ID s are LC (Loran-C receiver) and OM (Omega Navigation). The talker ID is followed by a three-letter sentence ID. After the sentence ID, the data is transmitted, and the data fields are separated by commas. Some sentences are terminated by a checksum; all sentences end in a carriage return line feed. A sentence may contain up to 82 ASCII characters including the $ and CR/LF. The data fields contain information such as position latitude and longitude, active satellites, and dilution of precision. The dilution of precision is a measure of the arrangement of the satellites in the sky. Low DOP numbers are good; the satellites are spread out. High DOP numbers are bad; the satellites may be arranged in a line, circle, or bunched together. In addition to the NMEA standard output, many of the GPS board manufacturers have developed their own standard to output GPS messages. For example, the Oncore M12 manufactured by Motorola outputs Motorola Binary Format messages as well as the NMEA-0183 standard messages. Also, the Jupiter GPS boards manufactured by Conexant output both Conexant Binary and NMEA-0183 messages. To receive these serial messages, the microprocessor's serial interface will be connected to the GPS's serial port as shown in figure 3.2.

10 To increase the accuracy of the GPS receiver, measurements can be made relative to a reference station at a known location. This is known as differential GPS. There are many forms of DGPS. They include Radiobeacon DGPS, FM subcarriers, and Cellular Digital Packet Data transmission. In the United States, the US Coast Guard and Army Corps of Engineers have constructed a network of Beacon stations that serve most of the eastern US, both coastlines, and the Great Lakes. Further plans exist to provide dual redundant coverage throughout the continental US. There are many advantages in the use of Radiobeacon DGPS. For one, they provide access to free differential corrections; other services are provided by private organizations that change annual fees. Also, the Beacon DGPS network broadcasts a long range signal which penetrates into valleys, and travels around obstacles; FM signals do not do this well. Furthermore, the radiobeacon network provides quality differential corrections which are continuously monitored for integrity. The differential corrections broadcast by the DGPS radiobeacon throughout the world are in RTCM SC-104 version 2 format. They generally employ 64 messages related to GPS. However, both Type 1 and Type 9 messages contain most of the required differential data. Figure 3.2 shows the connection of the radiobeacon receiver to the GPS unit. A decision about whether to use differential corrections in this device has not yet been made. However, if differential corrections are to be used, they will be the type broadcast by radiobeacon network because of their many advantages. power supply regulated 5V source GPS receiver power Radiobeacon receiver power NMEA Output RTCM SC104 input NMEA Input ground Microprocessor power data input RTCM SC-104 output ground TX Data RX Data ground figure 3.2

11 3.3.2 Options Considered: Many options were considered in selecting which GPS receiver to use in this device. All of these options fall into two main catagories: 1) The first option that was considered was using a typical hand-held GPS receiver with a LCD display. Most of these GPS receivers are able to sent NMEA-0183 output to a computer through a PC cable, so this type of receiver could be used in the design of this device. However, there are many disadvantages to using these hand-held GPS receivers. For instance, the LCD used to display the GPS output visually would be of no use to the operator of this device. Also, most of these receivers have menu-driven controls that would be very difficult for a blind operator to use. Another reason for not choosing this option was the physical size of the hand-held GPS receivers. 2) The second options that was considered was using a OEM bare board GPS receiver which outputs information such as position and velocity. A list of these receivers was found at: The web page is entitled "Overview of low-cost GPS receivers which output raw data". This is because the receivers output 'raw' GPS data, such as pseudorange, integrated carrier phase, Doppler shift, satellite ephemeris, as well as 'processed' data such as position and velocity. Table 3.3 below is a shorter version of the table that is shown on the web page. Some of the information in table 3.3 is taken directly web page's list. The rest was compiled from manufacturer's product briefs. All of the receivers listed in table 3.3 output NMEA-0183 information. Also, all of them take in RTCM differential correction information. Manufacturer Garmin Conexant Motorola Trimble Ashtech CMC CMC Type 25LP Jupiter Oncore Lassen G8 Allstar Superstar M2 Sk8 Accuracy 15m 6m CEP 25m SEP 25m 4.7m 16m 16m CEP RMS CEP CEP CEP DGPS 5m RMS 1m CEP 1-5m 2m CEP 3.0M 1m 1m CEP accuracy RMS CEP CEP # of channels Power W W W with no antenna 0.60 W with antenna 0.70 W board only 1.2 W 1.4W Size 1.83" x 2.75" x 0.45" 1.8" x 2.6" x 0.5" 1.57" x 2.36" x 0.39" 3.25" x 1.25" x 0.40 " 1.58" x 2.41" x 0.52" 1.8" x 2.8" x 0.51" 2.65" x 4.00" x 0.55" Price $125 $140 $200 $250 $140 $325 $120 Table 3.3

12 3.3.3 Options Selected The decision not to use a hand-held GPS receiver was made almost immediately. There were just too many disadvantages in using this type of GPS receiver. After looking through product briefs for the GPS board receivers in table 3.3, a first and second choice was made. The first choice for the receiver was the Jupiter receiver made by Conexant. After researching the product, it was found that Rockwell Collins was involved in the manufacturing of this receiver. The Jupiter was chosen for its high accuracy (with and without differential support), its low price, and Rockwell's reputation in the GPS industry. The second choice for the receiver was the Oncore M12 manufactured by Motorola. This receiver was chosen for its low power consumption, its small physical size, and because of Motorola's reputation as a leader in electronics. After making the choice of which GPS receiver to use, an attempt was made to locate distributors of the receiver. Some distributors of the Jupiter receiver were found on the internet and contacted by phone. Unfortunately, they could not give any information on availability or price. So, the second choice, the Oncore M12, was investigated further. After visiting Motorola's web page, a list of Oncore M12 distributors was found. Synergy was listed as the distributor closest to NDSU, so they were contacted through . Synergy replied with the information requested. The unit is available to order through them at a price of $96. Also, they gave the necessary instructions to obtain a copy of the user's manual. The advisor for this project, Floyd Patterson, is currently seeking information on the Jupiter GPS receiver. A final decision on which receiver to use has not yet been made. However, if the advisor's search does not provide any information about Jupiter's availability, the Motorola receiver will be chosen. 3.4 Speech Synthesizer Speech synthesis technology has been expanding in the past twenty years. Early speech synthesizer chip sets were limited in their ability to produce speech. As this technology has increased these limits have been broken. Speech synthesizers today are able to work with phonemes, the basic building blocks of words, allowing them to pronounce any word Detailed Block Diagram The desired speech synthesizer should follow the block diagram below. This diagram shows in detail the text-to-speech system required for our design. On the left, eight bits of ASCII data are taken into the data register. The controller then takes this data and uses its text-to-speech algorithms to develop a digital signal of the synthetic speech. This signal is passed to a digital-to-analog converter (DAC) which transforms the signal to an analog audio signal. The volume is controlled by a potentiometer between the DAC and low pass filter.

13 Figure Detailed Block Diagram 8 bit ASCII data Data Register RAM Input Buffer Andio Buffer DAC ROM Phoneme Tables Volume Control Controller Low Pass Filter SP+ SP Options Considered There were many options considered in deciding which synthesizer to use. Research into the current technology found many synthesizers that meet the requirements of our design and many that did not meet our requirements because of certain limitations. The three synthesizers that the most information was found were the HCS-II Voice Synthesizer, the V8600A module, and the DT1050 Digitalker. The following table compares their features. Synthesizer Table Options Considered HCS-II Voice Synthesizer V8600A Module DT1050 Digitalker Text-to-speech? Y Y N Volume Control? Y Y Possible external Speed Control of Speech? Variety of Voices? Power Consumption Y Y N N Y N 1.5W 110mW 0.54 W

14 Cost $ $ $29.00 National Semiconductor s DT1050 Digitalker was originally considered because of its low cost. After examining the features of this chip set, the limitations of its speech conversion were found to be well below the requirements of our design. According to the data sheet which was included with the chip set, the vocabulary consisted of a list of about eighty set words, the letters of the alphabet, and a limited set of numbers. These words and numbers all have a specific address in the Speech ROM. To have the desired word read, a microcontroller would have to send its specific address to the speech controller. The speech controller would then retrieve the word from the Speech ROM, and output it through an amplifier to a speaker. The chip set required additional operational amplifiers to control the volume of the speech output. There was no control over the rate or pitch of the speech. These limitations were the reason that the Digitalker was not chosen. The other synthesizer not chosen was the HCS-II Voice Synthesizer built by Creative Control Concepts. Unlike the Digitalker, it does not have a limited vocabulary. The HCS-II is a complete text-to-speech voice synthesizer. It has the ability to work with phonemes and create an exception dictionary for any words that are not pronounced correctly. Control of speech rate, pitch, volume, and tone are all possible with this synthesizer. The HCS-II was a highly functional option that would have easily suited our design Option Selected and Why The synthesizer that was chosen for this design was the V8600A Module manufactured by RC Systems, Inc. This speech synthesizer is able to convert English ASCII text into speech automatically. The only additional requirements for operation are a 5V power supply and a speaker. The information on the V8600A was obtained from its user s manual which was downloaded from RC website, This ease of operation was a big factor in the selection of this device. The V8600A has three built in interfaces, including a microprocessor interface. Since our design is using a microprocessor to drive the speech to the synthesizer, the V8600A seemed to be the ideal choice. The synthesizer also had all of the features that were required of it. This included a choice of five voices and control of speech rate, pitch, and volume. The cost of the V8600A was the determining characteristic between it and the HCS-II Voice Synthesizer. While the V8600A costs about $145, the HCS-II costs about twice that much, $ Microprocessor The microprocessor in our design will handle a number of inputs from the GPS receiver and keypad. It will also generate the output that will drive the speech synthesizer. Since it is the central control of the system, it is essential that of its requirements are met.

15 3.5.1 Detailed Block Diagram The block diagram below shows the flow of data into and out of the microprocessor. The rate of the serial data coming in from the GPS receiver can be determined by the receiver. The most common rates found for these receivers is either 4800 or 9600 baud. The information is sent in sentences according to the NMEA-0183 format. This format was discussed in section 3.3. The other input is from the keypad. The format will be that which was discussed in section 3.2. The output from the microprocessor to the speech synthesizer will required 10 pins, 8 for data and 2 for handshaking. Figure Detailed Block Diagram GPS Data from Receiver Serial Comm. Port Microprocessor General I/O Port 8 Bit ASCII Text for Speech Synthesizer 4 Inputs from Keypad General I/O Port Options Considered There are a variety of microprocessors that could be used in this design. The three considered were the PIC16F876 manufactured by Microchip, and Motorola s and the 68HC11. The experience with the and 68HC11 were the main reason they were considered. All of them meet the requirements of input and output pins. The 68HC11 has 26 pins for input/output. It also has a Serial Communications Interface (SCI). This is also true for the and PIC16F876. The current use of the PIC at NDSU made it the best choice Option Selected The PIC16F876 was the final choice for our microcontroller. It meets all of the requirements easily. It also uses flash memory which speeds up development time. It has a simple design which results in a small chip with very low power consumption. It has a SCI and 22 input/output lines. The chip is rather inexpensive, costing only six dollars. Also, the PIC16F876 is currently the main microcontroller in use by NDSU. Consulting Jake Glower, an evaluation board was obtained. The evaluation board has a liquid crystal display (LCD) that allows the developer to display information. Light emitting diodes (LED) are also tied to each port pin for seeing its status visually. The use of the PIC by NDSU in previous projects was the main reason that it was chosen. The documentation of

16 other project explaining how they used the microcontroller should ease in programming. 3.6 Power Supply The power supply for the whole system must run on some type of battery. Depending on the GPS receiver selected, it may run on its own battery. The speech synthesizer, microcontroller, and keypad must all receive power from a +5VDC source. This voltage should be regulated so it can not exceed the maximum rated voltage for the parts. The power supply has not been completed, and it will be left for design in 403. The voltage should also be measured using the analog to digital converter on the microprocessor. The result of this measurement will determine the warning message generated when battery power is low Detailed Block Diagram +5VDC A/D V8600A PIC Keypad Chapter 4 Circuit Diagrams & Flow Charts 4.1 Introduction: This chapter presents the circuit diagrams and flow charts for each section of the design. 4.2 Keypad: The circuit diagram for the keypad is shown below, figure 4.1. The switches will be push-button switches; they will momentarily drive the appropriate input pins to 5 volts. For example, pushing button 1 will send 0001 to the microprocessor; pushing button 2 will send 0010, and so on. Pushing any button will result in a rising edge on the interrupt pin connected to the microprocessor. After the microprocessor detects a rising edge on this pin, it will read the four input pins to determine which button was pushed and take the appropriate action.

17 +5V MSB LSB interrupt Microprocessor input port Figure GPS Receiver: Figure 4.2 is a flow chart that shows how the information is sent from the GPS receiver to the memory of the microprocessor. The microprocessor will receive information from the GPS receiver every 1-5 seconds and update its memory if the information is valid. The baud rate at which the information is transmitted and received is adjustable, and whatever works best with the update rate chosen will be used. Send an input command to the GPS and satellite information continuously at a specified rate Receive information from the GPS Is the data valid? (taken from satellite info.)

18 4.4.1 Circuit Diagram for V8600A to Microprocessor Connection RD# CS# WR# RD# WR# d0--d7 d0-d7 Microprocessor V8600A This diagram shows the connections needed between the V8600A Microprocessor and the V8600A. The 8 bits of ASCII data are sent in parallel from the microprocessor to the V8600A speech synthesizer. The RD#, CS#, and WR# signals are for handshaking between the two components. The RD# and WR# of the V8600A are active low. When RD# is low data can be sent from the V8600A to the microprocessor. This data will contain the current status of the synthesizer. If the RD# signal is high, the data bus is held in a high impedance state. WR# controls the flow of data from the microprocessor to the V8600A. The contents of the data bus are written to the synthesizer on the rising edge of WR# Flow Chart for Writing Data to V8600A START Read Status Register RDY = 1? NO YES Write Byte to V8600A Read Status Register YES

19 This flowchart shows the steps needed to write data to the V8600A speech synthesizer. The microprocessor must read the status of the synthesizer until the RDY bit is set. This lets the microprocessor know that the synthesizer has finished processing the last byte written. The program must also wait for RDY to become zero. This makes sure that the next time the routine is called that the V8600A is indeed ready to accept another byte. The timeout is needed if an interrupt can occur during the writing of data to the V8600A. An interrupt can cause the missed reception of RDY going low. The timeout must be at least 15 us, the maximum amount of time it takes RDY to go low after writing a byte of data. 4.5 Basic Microprocessor Flow Chart START Receive GPS data Compute all Desired Outputs NO Has a Button Been Pushed? YES Output the Desired Information NO Is the Microprocessor Done Writing Data? YES This flow chart shows the basic flow of the complete program used by the microprocessor. It does not show the different outputs that can be chosen, but gives a general description of what the program should do. The basic program will receive data

20 from the GPS receiver and do the calculations needed to give the desired outputs. If no button is pressed, the microprocessor will update the information from the GPS receiver until one is. Once the microprocessor is outputting data to the V8600A speech synthesizer, it will remain their until the last byte is written. Then it will exit this mode and again update data from the receiver.

21 Chapter 5: Future Work & Conclusions: 5.1 Conclusions: The device has not been tested, so we don t know how it will perform overall. However, if all the specifications are met in testing, the device should be very useful to the blind operator. 5.2 Future Work: The decision of whether or not to use differential GPS open for ECE 403. If our design team does not implement DGPS, this may be done by another team in the future. Also, using a digital compass to give heading information was considered. This option has not been researched in detail. This leaves another possibility for future work on this device. References: 1) The NMEA FAQ written by Peter Bennet 2) Overview of low-cost GPS receivers which output raw data 3) Overview of GPS and DGPS