Mechatronic Design of an Autonomous Search Vehicle

Utilizing Chemical Sensing

Tristan Boscardin and Jens Göhre

Advisor: Dr. Robert Gao

Electromechanical Systems Laboratory

Department of Mechanical and Industrial Engineering

University of Massachusetts at Amherst

12/23/2003

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I. Abstract

The use of chemical sensing for the purpose of mobile identification is a powerful

medium. Recent advances in chemical sensor arrays and “Lab-On-A-Chip” have

improve the ability to distinguish between different chemical compounds in a mobile

environment. The simplified problem of tracking a known chemical and identifying the

location of an alcohol marked vehicle was addressed in this project. In the context of this

problem three major concepts were implemented: energy efficiency, wireless sensor

network communication and mechatronic design. The autonomous search vehicle was

given a limited amount of resources approach this goal. The relationship between logic

analysis and memory usage was examined. These factors are linked directly to the

systems memory and sensing capabilities. In this case the memory was the limiting

factor.

II. Introduction

a. Project Description

Recent advances in chemical detection have been made, allowing for a

“Laboratory-On-A-Chip”, portable chemical identification, to be implemented.( Sandia

National Laboratories) Other technological developments have employed sensing array

to create an electronic nose, capable of distinguishing between different chemicals.(

Nagle, Guitierrez-Osuna, and Schiffman ) These innovations inspired the concept of

using chemical sensing capable to locate a chemical marked target, as opposed to more

conventional methods to identify and track an entity. Chemical idenitification is unique

in the aspect that it may not be visible or tangible as many other methods that are largely

been confined to the physical spectrum. Also chemically marked vehicles may leave a

trail, which does not require the tracker to follow in visible or audible range.

Another topic integrated into this project is the communication between sensing

systems. This is addressed though the communication of the vehicles. The

communication of sensor systems allows for the improved allocation of sensor resources,

to more efficiently achieve a task. The communication medium for this project was radio

transceivers, one for each vehicle and one for the base station. The concept of

communicating efficiently and securely was also investigated. With increased use of

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wireless communication between devices, this provides the ability to increase the

efficiency of a search, along with the ability to verify the search results.

The mechatronic design philosophy weighs the needs and metrics of

multidisciplinary requirement of system to achieve an optimal design. This mechatronic

design philosophy was integrated into the design of an autonomous search vehicle

utilizing chemical sensing to detect a target vehicle marked with an alcohol source. The

vehicle had several requirements: autonomous search capability, robust physical

characteristics, a collision avoidance method, wireless communication abilities, and

efficient use of computational resources. The vehicle was to work in conjunction with a

partner vehicle to identify the location of the alcohol source and both vehicles should

verify the source was found. Additionally the vehicle was required to communicate with

a base station, to notify it that the target was found or verified.

b. Background

Chemical sensors have been a standard tool in a few sectors of industry and the

scientific community. Recent advancements, made in the capability of chemical sensors,

have opened up new possibilities for technical applications and development. Many

industries also have a demand for chemical sensing capabilities and have been

implementing smart processing methods. The growing demand for homeland security

has also contributed to these developments, increasing the research for portable chemical

sensing devices, such as electronic noses and “Lab-On-A-Chip”.

Current research efforts are attempting to refine the physical capabilities of the

chemical sensors and the methodology of the chemical sensing process. Reducing the

physical size of a chemical sensor has run into several barriers, since many times set

surface areas are required to detect chemicals at a given sensitivity and the molecule

being measured sets a finite limit upon the sensors size. Chemical properties of different

materials are also being investigated along with the chemical properties of reactive

coatings and selectively permeable filters. The power usage of chemical sensors is also

being considered to enable more efficient devices with increased portability. The use of

chemical sensors arrays to detect the different properties of a chemical compound and be

able to identify a chemical by its finger print is also being investigated. Methods to

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reduce the response time of a chemical sensor are also a concern, as growing real-time

information demands are established.

Figure 1: Sensor Diagram

Sensors are quickly becoming a pervasive element of human life; many people

often forget that they are even in use. “A Sensor is a device, which responds to an input

quantity by generating a functionally related output usually in the form of an electrical or

optical signal.” (http://www.dcu.ie/~best/st.htm) Figure 1: Sensor Diagram. In the case

of a generic chemical sensor, a chemical signal is sensed, typically modified into an

electrical signal, and an output. “The fundamental purpose of sensors is to assist in

process control by providing data to a process control system.”

(http://islnotes.cps.msu.edu/trp/adv/sen_pur.html) Figure 2: Control System. The

process control system is used to increase the quality and the efficiency with which the

plant is produced.

Figure 2: Control System

Chemical Sensing Offers a Unique Problem. “Unlike imaging (visual sensing)

technologies where only one type of light (e.g., infrared or visible range) is detected and

sound (auditory sensing) technologies where only one type of pressure wave is detected,

chemical sensors must transduce a variety of input stimuli using a variety of transduction

mechanisms or reactions.“ (Wilson, Hoyt, Janata, Booksh, and Obando) Figure 3:

Sensor Modifier Output transduc

Chemical signal Electrical signal Magnetical signal Mechanical signal Radiant signal Thermal signal

Chemical signal electrical signal Magnetical signal Mechanical signal Radiant signal Thermal signal

Reference Generator

Sensor

Control Function Plant Σ

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Chemical Sensor. The varieties of stimuli require the implementation of an array of

sensors, or selective sensor coatings are used to identify a chemical. Frequently

applications can assume a closed system, where all the gases are known. This requires

fewer sensors, since the different characteristic properties of the gases are known. Often

times, though, this is not the case, and a large array of chemical sensors must be used.

Another difficulty with chemical sensing is that different sensors sense different

chemicals.

Figure 3: Chemical Sensor

III. Project Design

a. Approach/Philosophy

ElectricalSystem

Sensor System

ComputationalSystem

MechanicalSystem

Communications System

NavigationalSystem

Figure 4: System Design

Signal processing,

display or PC

Transducer

Analyte

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The mechatronic design philosophy accounted for the needs and metrics of the

system to achieve the optimal results. Initially, the mechatronic analysis for the

autonomous search vehicle was made on a large scale. The resources, constraints, and

basic needs of the system were identified, Table 1: Initial Analysis. The identification

of the initial analysis and allowed for the basic system structure to be developed, Figure

4: System Design. The system is composed of sub-systems or sections that interface

together. While each system is flexible, some of the systems predetermined due to

provided components or requirements. The computational system was a Motorola

M68HC11E9 microcontroller supplied with an evaluation board developing tool,

Appendix A: Motorola M68HC11E9. The communication system consisted of a RFM

DR3001 wireless communication module with serial interface. The mechanical system

(mobile platform) was a radio controlled car. There was extensive freedom in the design

of the sensor, navigational and electrical systems.

Table 1: Initial Analysis

b. Design Metrics

The design was then analyzed using more detailed design metrics, Table 2:

Design Metrics. The needs of the design to accomplish the goal were identified. The

physical requirements to the needs, metrics, were then shown to illustrate what constraint

each design decision produces for the system. These inherent design constraints were

coupled with given mobile platform, microcontroller, fiscal, and temporal constraints;

influencing the design decisions.

There were several stagnant or difficult to control metrics. The size of the vehicle

could not be radically altered given the temporal and budgetary constraints. The given

Initial Analysis

Resource Constraints Need Computational System Memory, Processing Autonomy

Navigational System Sensors, Computational System Obstacle Avoidance, Localization

Sensors Cost Chemical, Navigational

Electrical System Battery Powered Interface Systems

Mobile Platform 3 Point Steering, 2WD Controllable

Communication Distance, Energy Requirements Communicate with Other Entities

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microcontroller gave a finite restriction on the processing speed and total memory

available. The response time of the system was largely tied to the individual needs of

components and the processing speed of the microcontroller, and could not easily be

altered. These limitations were considered constants in the design. When possible, the

influence that each constraint brought to the design was reduced through design

decisions.

Table 2: Design Metrics

The major issues that resulted from the design metric analysis were the memory

usage, weight and energy consumption. The microcontroller influenced the memory

usage, given the technical size restrictions. Since there was a finite amount of memory

DESIGN METRICS Metric

Need

Size

Weight

Energy

Consum

ption

Processing Speed

Mem

ory Usage

Response Tim

e

Accurate Positioning x x x x

Great Sensitivity to Target x x x

Simple Communication

Over a Wide Distance x x x

Robust, Low-Power,

Accurate, Precise Sensor x x

Smart and Reliable Search

Algorithm x x x x

Small, Low-Power, Low-

Cost Electronics x x x

Smart and Reliable

Obstacle Avoidance

Algorithm x x x x

Secure Communication x x x

Simple and Accurate Motor

Control x x x x x

Robust Physical Structure x x x

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available, this requires for efficient and simple algorithms. The weight of the vehicle

could be controlled by selecting not using excessively heavy components. Energy

consumption was an essential consideration, since this is a mobile platform, thus practical

power sources are limited to batteries or fuel cells, with in our budgetary constraints. If

too much current is required more batteries are required. The design should be able to

operate for long periods of time.

IV. Navigational System Design

a. Design Analysis

The navigational system selection was dictated by two needs. The vehicle must

have a smart efficient search algorithm capable of avoiding obstacles, and the vehicle

must be capable of locating the partner group once they find the vehicle or having the

partner group locate the vehicle once the target vehicle is found. This infers the need for

a two tier navigational system. This was divided into two different spectrums, local and

global navigation. The local navigation is used for obstacle avoidance, to determine

where the vehicle should immediately move next. The global navigation was to establish

which direction the vehicle should be heading or to communicate were the vehicle

currently resides. While the question of how to achieve local navigation proved to be

simple, global navigation and the ability to communicate your position to another vehicle

brought forth a variety of different methodologies. Several different designs were

considered. The navigational system proved to be the largest design dilemma.

b. Local Navigational Design

The local navigational design selected uses infrared distance sensors to detect

obstacles in the vehicles path. Ultrasonic and laser range finders were also considered.

Ultrasonic distance sensing requires a considerably more current than the infrared

sensors, and both the ultrasonic and laser sensors were more expensive. The vehicle

required several infrared sensors, because each sensor was only reactive to objects in the

15 degrees cone of infrared emitted. Two types of infrared distance sensors were used

for the local navigation, digital and analog sensors. The digital sensors had set threshold,

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24 cm, and were used to sense obstacles approaching at an angle. The analog sensors had

a greater range, and were chosen because they offered a variable threshold that could be

set in the navigational algorithm to react to obstacles.

c. Global Navigational Design Alternatives

The restrictions that existed in this decision include the vehicle’s playing field is

inside a building. This prevents the use of GPS, since we are indoors, and magnetic

compasses, due to the large pieces of metal (beams) in the building. The decision not to

use encoders was made because of error propagation. A variety of triangulation methods

were investigated, but these proved to require additional hardware that was in excess of

our budgetary constraints. All of these methods also require significant amounts of

computation, taking up excessive amounts of memory.

d. Selected Global Navigational Design

The navigational scheme chosen involved a relative approach towards finding the

other group. When the target vehicle is found, the event is communicated using the

wireless communication module. The base station is notified first, and then the partner

group is notified. Upon the acknowledgement from the partner group, an infrared beacon

is transmitted, guiding the partner group, to the target vehicles location. The vehicles

were guided by sensing the infrared beacon using directionally placed infrared transistors.

This method was chosen because it meets our design need and provides a suitable metric

providing a simple algorithm with inexpensive hardware.

e. Design Ramifications

The design of the navigational system affects the layout of the electronic system,

most notably through sensor placement. This indicates that the basic navigational

concept must be chosen prior to the fabrication of electronic components. The use of

infrared sensors requires more sensors, thus taking up more pins, and requiring more

code. Consequently, more sensors also correlate with more information that will be

obtained about the obstacle that is detected. This potentially allows for a more powerful

navigational algorithm maybe implemented. The tradeoff, between information available

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and memory used, plays an integral role in this project. Memory usage efficiency has

been determined to be a key factor.

V. Electronic Design

a. Design Methodology

The design of the electronic circuitry was created to provide hardware controls for

various functions and a meaningful human-vehicle interface so the system could easily be

interpreted and debugged. Primarily, the focus of the electronic design was on

efficiency; this was applied to efficiency of the computational system, as well as energy

consumption. The board layout was designed in an organized manner, such that the

components could easily be installed and verified for functionality. The board was tested

step by step to verify all the components worked and were correctly attached.

b. Electronic System to Evaluation Board Interface

The first component attached to the board was the 60 pin connector. This allows

all the other components to be interfaced to the microcontroller and tested. This also

provides a common ground between all the electronic components for functionality. The

60 pin connector also creates modularity of the design so it can potentially be reused in

other systems or with slight modification to other microcontrollers that can adhere to a

standard pin-out.

c. Control of a Mobile Platform

The control of the mobile platform was done by exploiting the existing controls of

the mobile platform. The mobile platform, which was once a radio control car, contained

all the transistors and H-bridges required for connecting the electronic system to the

motors. Through observation of the original control chips interaction with the pre-

existing circuitry when sending the vehicle signals to go left, right, forward or backward,

the correct pins to control the car were identified, Appendix B: Pre-Existing Pin

Identification. The original chip was extracted, and replaced with a socket.

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d. Pulse Width Modulation

Circuitry to improve the resolution of the pulse width modulation signal was also

included. This was done in hardware to save program memory, so no interrupt would

have to be generated. The use of an AND gate and a hex inverter doubled the rate of the

signal that could be supplied to the forward and reverse pins, Appendix C: PWM.

e. Human Interface

Two tools were built into the electronic circuitry to provide a meaningful interface

between the search vehicle and the human observer. This interface consisted of 4 light

emitting diodes (LEDs) and 4 7-segment displays, Appendix D: 7-Segment/LED. Each

7-segment display had a binary coded decimal (BCD) decoder, to reduce the number of

output lines required to select each 7-segment display. The human interfaces were used

for debugging and as developmental tools. The LEDs were used to communicate the

state of the vehicle, and the 7-segment displays were used to display sensor readings.

f. A to D Conversion

The analog to digital conversion hardware consisted of connection to the

chemical, infrared phototransistors, analog distance sensors, and a connection to the

voltage reference. The phototransistors and the chemical sensors were placed in sockets

in their respective locations. The analog distance sensors were connected to the board

using male and female three pin headers. The voltage reference for the A to D

conversion was created using a variable voltage regulator set to three volts.

g. Infrared Sensor

Several different infrared sensors were used in this design. The infrared sensors

were divided into two classes, the first for local navigation and the second for global

navigation. The local navigational sensors consisted of three types of distance sensors,

with sensitivities and outputs. The global navigational sensors were comprised of an

array of sensors pointed in different directions. The distance sensors were attached to

the male headers on circuit board using female headers, so the circuit board could be

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completely removed from the vehicle. The infrared emitters and detectors were attached

to the circuit board on sockets so they could be readily replaced.

The local navigational distance sensors exploited their different characteristics

through a layered configuration, Appendix F: Infrared Distance Sensor

Configuration. The 10 to 80cm analog sensors, Sharp GP2D12, were used to detect the

presence of a potential obstacle. The 4 to 30 cm analog sensor, Sharp GP2D120, is used

to get close to an obstacle to take a chemical measurement. The 24 cm digital sensors,

Sharp GP2D15, are used to prevent the car from colliding with walls or obstacles

approached at extreme angles.

The global navigational system used infrared phototransistors and emitters to

locate the partner car. The 3 phototransistors, Radioshack 276-145, were pointed in

unique directions to guide the vehicle towards the partner vehicle once a communication

signal was received that the partner vehicle had found the opposing car. The vehicle was

also outfitted with several infrared emitters, Radioshack 276-143, to act as a beacon for

the partner vehicle once the target vehicle was found.

h. Chemical Sensors

The semi-conducting oxide chemical sensors, FIS SB-30-00, used were installed

into sockets on the circuit board. The heaters required for chemical detection operated

off a 1volt power supply generated with a voltage divider, while the circuit for the chip

required a 5 volt power source.

i. Communication Module

The communication circuit provided was a RFM DR3001 868.35 MHz

transceiver module. This allowed for use of the serial interface with the Motorola

M68HC11E9 to be used to transmit and receive data, using only one additional output pin

for a select line. The module was mounted on the board using a socket and powered

using a variable voltage regulator with 3 volts.

j. Design Problems Encountered

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There were three major design problems encountered within the implementation

of the electrical system. The first problem was that the board required much more current

then planned. This result was primarily an oversight of how much power was required to

drive all of the LEDs, since the 4 7-segment displays were not counted as 28 LEDs, or

the infrared LEDs that required 100 ma of current each. With this information, our

current calculation makes sense, Appendix G: Current Allocation.

The second problem, which partially was related to the massive current

requirements, was that the microcontroller board was resetting itself. This was happening

due to the noise that was coming from the batteries. This was increasingly destabilized

with the addition of a secondary battery pack. The current was smoothed out with a large

capacitor, 470 µF, solving the resetting problem, by slowing the change in supplied

voltage.

The third problem arose from the chemical sensors. The chemical sensors

response sensitivity to the chemical agent, ethanol, was not optimal in the chemical range

that we were measuring, Figure 5: Chemical Sensor Response. The change in

resistance was very small, thus no noticeable change in the signal existed.

Figure 5: Chemical Sensor Response

VI. Software Development

a. Design Philosophy

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The software was developed in separate modules to guarantee their individual

functionality, and allow for parallel development of different aspects of the search,

detection, navigation, and communication algorithms. These modules after passing

individual inspection were then merged into the complete code. In order to prevent

contention for hardware resources, and allow for development of the electronic system

concurrently with the software, several of the I/O pins were reserved for known sensors,

Appendix H: Pin Assignments. The final step in the software design was the

optimization of code.

b. I/O pins

The first module written was the code to control the input and output pins used to

control the motor. This module allowed the testing of the car controls. The module was

also modified for turning LEDs on and off, and the output of data to the 7-segment

displays.

c. Timers and PWM

The logical next step in vehicle control is the implementation of timers. The

initial timer consisted of a delay function that rested in a computational loop, for a

number of cycles. This was quickly improved upon by using a comparator and a timer

built into the chip. This created accurate delays, essential for measuring with the

chemical sensors. The PWM was implemented in a similar fashion, using a comparator

with the timer to toggle a line, allowing for speed control of the vehicle. The duty cycle

of this function was change by changing the value in the comparator. The PWM was also

used in the braking algorithm, to slow the vehicle when obstacles are detected.

d. A to D Conversion, Obstacle Avoidance, and Chemical Detection

Analog to digital conversion was required by the distance sensors and the

chemical sensors. Multiple Channels were sampled at the same time to obtain either the

chemical or infrared distance sensors, or both channels needed to be sampled to obtain

the phototransistor values. The chemical sensor and the infrared distance sensor values

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were displayed on the 7-segment displays for the purpose of debugging and providing a

meaningful human interface.

e. Search Algorithm

The A to D conversion along with the I/O pin control and PWM allowed for the

implementation of the search algorithm. The global navigational system was ignored if

the vehicle was not contacted by the partner vehicle to verify the presence of the target

vehicle. If the partner vehicle communicates the chemical presence then the vehicle uses

the readings of the infrared transistors to guide the vehicle to the partner vehicle. For

example if the right transceiver detected the infrared signal the vehicle would turn right,

if the left detect the signal it would turn left, or if the front detected the signal it would go

straight. If no signal was detected then the vehicle would default to the local search

algorithm.

The local navigational methodology was made simple due to the limited amount

of memory available, yet it tried to yield and effective search algorithm. The algorithm

was designed to produce a sweeping pattern across the playing field, stopping if an

obstacle was detected the checking if was a chemical source, Appendix I: Navigation

Diagrams. If it was not the chemical source, the chemical measurement did not meet the

threshold, the vehicle would make a 180 degree turn. These turns would alternate left

and right when obstacles are detected. If the chemical threshold is detected, then the

vehicle will stop, transmit to the base station that the target is found, transmit to the

partner vehicle that the target is found and emit an infrared beacon for the partner vehicle

to follow.

f. Communication

The communication utilized the serial communication lines available on the

Motorola M68HC11E9 and one output line, functioning as a select pin. The data was

simply broad cast within the protocol, waiting for acknowledges from the receiver of the

data after the transmission is complete. When data is received from the transceiver over

the serial line, an interrupt is generated. This function was enabled to avoid polling the

serial status register for new data. The protocol created, Appendix J: Communication

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Protocol, was followed in the receive using a state machine, checking for the correct start

symbol, to-address, packet numbers, size, and message. The data was acknowledged

when all of these conditions were met.

g. Optimization

The main problem with the software design was the memory usage and allocation.

The initial design was ambitious for the limited 512 bytes of EEPROM and 512 bytes of

RAM. This required the simplification of complex modules and the use of efficient

programming techniques and insightful use of RAM and EEPROM.

VII. Conclusions

The current methods to identify and track an entity have largely been confined to

the physical spectrum. Through inspection of biological methods, it is observed that

many predators hunt using the discrimination of scent, a chemical method. This

approach is particularly useful since one retains the ability to follow a target, and also in

many instances remain out of the target’s visual, audible, and many times the target’s

olfactory ranges. This gives the predator the element of surprise, evading the natural

defense mechanisms of the prey.

The autonomous search vehicle given a minimal amount of resources attempted to

approach this goal. Clearly the performance of the vehicle was limited to the amount of

data it could sense and the power of the logic the system contains. These factors are

linked directly to the systems memory and sensing capabilities. In this case the memory

was the limiting factor. The autonomous search vehicle addressed a series of deeper

issues: energy efficiency, wireless communication, and mechatronic design. Energy

efficiency is a key issue when dealing with a mobile platform that does not generate its

own power, the system requires a minimum of the maximum amount of energy to

complete the task, even though this is often not optimal, and a minimal amount of energy

consumption is desired. The use of wireless communication between sensing system to

yield a common goal can create significant increase in process efficiency, and the

redundant checking offers a layer of data verification. This was addressed in our project,

but unfortunately stands unverified. Mechatronic design seemed to be the largest issue

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in this project, since the design factors were all interrelated. Through the consideration of

interdisciplinary factor in the original design, a superior design was achieved, Appendix

L: Final Result.

a. Future Research

The autonomous search vehicle offers a variety of paths for future research.

Primarily, improvements in better use of the sensor data and extending the research into

larger scale mobile sensor networks could be followed up. The distribution of

intelligence through out the system could offer one solution to the limited capabilities of

the microprocessor. Smart components could preprocess the data, creating a feature

based system, which allows for the reduction of code required to assess the data. Further,

greater navigational functionality could be implemented through the development of

positioning technique, so improved search algorithms could be executed.

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VIII. References

Aktan, Comfort, and Shanis. Managing Multi-Hazard Risk at Metropolitan USA.

Cernosek, Yelton, Colburn, Anderson, Staton, Osbourn, Bartholomew, Martinez, Ricco,

and Crooks. Detection of Volatile Organics Using a Surface Acoustic Wave

Array System.

www.fisinc.co.jp/S_SB30.htm , FIS Inc.

Hopkin and Lewis. Detection and Classification of Arrays of Carbon Black/Organic

Polymer Composite Chemiresistive Vapor Detectors for the Nerve Agent

Stimulants Dimethylmethylphosphonate and Diisopropylmethylphosphonate.

islnotes.cps.msu.edu/trp/adv/sen_pur.html, Purpose of Sensors.

Moseley, P.T. Solid State Gas Sensors.

Nagle, Guitierrez-Osuna, and Schiffman. The How and Why of the Electronic Nose.

Stetter, Penrose, and Yao. Sensors, Chemical Sensors, Electrochemical Sensors, and

ECS.

Wide, Winquist, Bergsten, and Petriu. The Human-Based Multisensor Fusion Method for

Artificial Nose and Tongue Sensor Data.

www.dcu.ie/~best/st.htm, What is Sensor Technology.

www.npi.gov.au/handbooks/pubs/voc.pdf, Total VOCs and the NPI.

www.sandia.gov, Sandia National Laboratories.

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IX. Appendices

Appendix A: Motorola M68HC11E9 Microcontroller EVBU Development Tool

Appendix B: Pre-Existing Pins

Appendix C: PWM

Appendix D: 7 Segment/LED

Appendix E: Program Flow Chart

Appendix F: Infrared Distance Sensor Configuration

Appendix G: Current Allocation

Appendix H: Pin Assignment

Appendix I: Navigation Diagrams

Appendix J: Communication Protocol

Appendix K: Vehicle Schematic

Appendix L: Final Result

20

Appendix A: Motorola M68HC11E9 Microcontroller EVBU Development Tool

SEE ATTACHED: “M68HC11E.PDF”

21

Appendix B: Pre-Existing Pins

Figure 6: Pre-Existing Pins

22

Appendix C: PWM

PWM

OC4

OC3

OC2

0000 FFFFTCNT

USERVAL1 USERVAL28000

PA0PA1PA2PA3PA4PA5PA6PA7

PB0PB1PB2PB3PB4PB5PB6PB7

PWM

PWM Forward

PWM BackwardRIGHT

LEFT

PWM= OC2 OR ( OC3 AND OC4) = OC2 AND OC3 AND OC4

23

Appendix D: 7 Segment/LED

24

Appendix E: Program Flow Chart

Init

Go Forward

Check IR Sensors

Obstaclefound?

Stop

Measure

Chemicalfound?

Go Back

Stop

Communicate to BaseStation

Communicate to Team

Wait for Team to Arrive

Last Turn ==right?

turn left

Check IR sensors

Obstaclefound?

Stop

Go Back

Stop

turn left

Check IR sensors

Obstaclefound?

Stop

Go Back

Stop

no

yes

no

no no

yes

yes yes

25

Appendix F: Infrared Distance Sensor Configuration

30cm

Ana

log

IRS

eneo

r

80cm

Ana

log

IR S

enso

r80

cm A

nalo

g IR

Sen

sor

24cm Digital IR Sensor

24cm

Digi

tal IR

Senso

r

Figure 7: Infrared Distance Sensor Configuration

26

Appendix G: Current Allocation

Table 3: Current Allocation

Current Drain (estimated maximum= 1562 mA)

80

560 260

40012250

LEDs7 Segment DisplaysChemical SensorsIR LEDsTranciever ModuleIR Distance Sensors

27

Appendix H: Pin Assignment

Table 4: Pin Assignment

PIN PORT Direction Description 9 C 0 O 7 SEG CONTROL 1 10 1 O 7 SEG CONTROL 2 11 2 O 7 SEG CONTROL 3 12 3 O 7 SEG CONTROL 4 13 4 O 7 SEG DATA A 14 5 O 7 SEG DATA B 15 6 O 7 SEG DATA C 16 7 O 7 SEG DATA D 20 D 0 I RxD 21 1 O TxD 22 2 O R/T SELECT 23 3 O IR Transmitter 24 4 I IR Digital Distance Sensor 1 25 5 I IR Digital Distance Sensor 2 27 A 7 28 6 O PWM OC2 29 5 O PWM OC3 30 4 O PWM OC4 31 3 32 2 33 1 34 0 35 B 7 O LED 4 36 6 O LED 3 37 5 O LED 2 38 4 O LED 1 39 3 O LEFT 40 2 O RIGHT 41 1 O BACK 42 0 O FWD 43 E 0 I IR Analog Distance Sensor 1 44 4 I IR Transistor 1 45 1 I IR Analog Distance Sensor 2 46 5 I IR Transistor 2 47 2 I IR Analog Distance Sensor 3 48 6 I IR Transistor 3 49 3 I Chemical Sensor 1 50 7 I Chemical Sensor 2

28

Appendix I: Navigation Diagrams

Figure 8: Sweep 1

Figure 9: Sweep 2

29

Appendix J: Communication Protocol

Table 5: Communication Protocol

Protocol DataPreamble 0xFFStart Symbol 0x7ETo/From 0x67Packet Number 0x01Size/Status 0x01Message 0x01FCS 0x01

30

Appendix K: Vehicle Schematic

MC68HC11

1 3

Custom Board

RF �Monolithic

24 5

Evaluation Board

AND

NOT

1 2 3 4

LED

Chemical Sensor

1 2

IR-LED1 2 3 4

BCD-7SEG Decoder

Battery Pack

IR Distance Sensor

Figure 10: Vehicle Schematic

31

Appendix L: Final Result