(Project Report)

ABSTRACT

Using the "Design process", a novel timing device was designed, constructed and tested. It had to meet the needs, wants, desire, and biases of the customer as per a preset list of criteria. As engineers, we had to understand what the customers’ needs were in order to meet their demands for a new or improved product. During this work, we examined the product description in order to identify with the system requirements. Size, weight, accuracy, operational life, and cost were some of the measurable quantities that were used to define the system, in which we surpassed the goal.

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ACKNOWLEDGEMENTS

The author would like to extend his sincere gratitude to Prof. Raney for his supervision of this work. This work would not have been completed without his advice and direction. The author would also like to thank Debbie Scott for her affectionate concern for the author’s well being.

The various discussion with Dr. Shrestha and Dr. Cunningham provided insights into the project for which the author extends his sincere appreciation. He also wishes to acknowledge his gratitude to Mr. Raul, Mr. Paulsen, and Mr. Chilukuri for their kind encouragement and moral support.

The work started with the blessing of the author’s family and was supported by the inspiration of his friends. He wishes to express his gratitude to his parents, Bijaya and Puja for their extraordinary moral support for which he could never thank them enough. The author also wishes to thank his brothers and sisters, John, Anjana, Tina, Srijana, Samjhana, Tunta, and Tony for being the delight that they are.

Last but not least, the author is extremely grateful to his mentor and buddy Mr. Ray Mutchler. Ray, I can never forget your kind scolds.

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TABLE OF CONTENTS

ABSTRACT …………………………………………………………………….. 1

ACKNOWLEDGEMENTS …………………………………………………….. 2

LIST OF ILLUSTRATIONS …………………………………………………… 4

LIST OF TABLES ……………………………………………………………… 5

SECTION

1. INTRODUCTION ……………………………………………… 6

1. DESCRIPTION OF THE PROBLEM ……………………… 6
2. REVIEW OF LITERATURE ……………………………….. 7
3. SIGNIFICANCE OF THE PRESENT WORK ……………… 8

1. DEVELOPMENT OF THE TIMER …………………………….. 9

1. POSSIBLE APPROACHES …………………………………. 9
2. DESIGN SELECTION ………………………………………. 10
3. TEST OF THE PROTOTYPE ……………………………….. 14

1. CONCLUSIONS …………………………………………………. 19

1. EXPENDITURE ……………………………………………… 20
2. PEER EVALUATION ……………………………………….. 21

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LIST OF ILLUSTRATIONS

1. Op-Amp Relaxation Oscillator ………………………………………… 12
2. Relaxation Oscillator IC Chip …………………………………………. . 13
3. Circuit Diagram of the Timer …………………………………………. . 15

4. The Master Timer ……………………………………………………….. 18

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LIST OF TABLES

1. System Requirements for the Timer …………………….…………. 7
2. Possible Approaches towards Designing of the Timer…...…………. 9
3. Components of the Timer …………………………………………… 16

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I. INTRODUCTION

The Basic Engineering Department at the University of Missouri-Rolla has a client who wishes to commission the development of a novel timing device. It must be a timing device that can be marketed in novelty stores or through mail-order novelty catalogues. Most importantly, it should be unique and attractive and should be one which would not be normally expected to be found in a houseware department or department store. It should have a finished appearance and should attractively fit for most any décor. It should not be bulky and heavy.

The client will market the timer for $ 125 with a profit of at least $ 50 per unit. The novel timing device must be built so as to meet the requirements as summarized in Table. I.

The design of the timer is to be judged on the basis of figure-of-merit (FOM) defined as following;

where,

Q - Performance factor assigned by judges evaluating the prototype demonstration,

A – Measure of the aesthetic quality

I – Measure of quality and completeness of instructions for operation

N – Measure of novelty and ingenuity of the design

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C – Cost rounded to nearest dollar, and

W – Weight rounded up to nearest higher pound.

TABLE I. System Requirements for the Timer

B. REVIEW OF LITERATURE

The art and science of making clock or timepiece or watch as they are variously called depending on their size, feature, and use, is some 400 years old. This craft has

gone through countless revisions starting from the rope and bell of the tower or staple

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clock to an assembly of swinging pendulum, wheels and springs of the grandfather clock to the battery-powered quartz watch with liquid crystal display. The advancement in various fields of science and technology touched each and every aspect of this great craft.

There are plenty of books and articles on this fascinating subject. Just to name a couple, COGGINS’¹ "Clocks, Construction, Maintenance, and Repair" and SMITH’s⁷ "How to Repair Clocks" come to mind. COGGINS has presented a very informative summary on the various kinds of clocks, their construction, maintenance, and repair while SMITH has focussed on primarily the art of repairing clocks of various builds.

C. SIGNIFICANCE OF THE PRESENT WORK

The present work is primarily, meant to educate us in understanding how an engineering design process is undertaken and then, to implement the knowledge thus acquired to develop a design product. The various phases of the engineering design process could be considered to have the following steps:

• Identification of system requirements,
• Exploration of various approaches,
• Conduction of feasibility analysis and selection process,
• Development of a detailed design, and
• Implementation and test of the prototype.

Thus, this project provides us with a real knowledge of an engineering design process and teaches us by way of real experience, how to excel as an engineer.

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II. DEVELOPMENT OF THE TIMER

During our "brain storming" session, we thought about and analyzed various different approaches to design a timer that meets the specifications summarized in Table I. Some were realistic while others were too far fetched. These ideas, and especially, the problems with them are summarized in Table II.

TABLE II. Possible Approaches towards Designing of the Timer

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B. DESIGN SELECTION

After several weeks of research, it became clear that designing an electrical timer was the best approach to meet the system requirements most effectively. Using electrical components, we could minimize the weight and size of the timer. Furthermore, using an electrical approach we could make the product more unique and at the same time increase the figure of merit of the product.

Electric clocks fall into certain fairly well-defined categories⁷. There is the motor driven clock direct from the mains or, in portable form, by a tuning fork kept in vibration by a transistor and magnet. There is the mechanical movement with spring or weight which is regularly rewound by a magnet or motor. There are the direct contact magnetic impulse types, and the gravity impulse type in which a falling arm gives the impulse but is electro-magnetically reinstated. Then, there is the magnetic balance and, of course, the more purely electronic quartz movement which has become quite popular. Some of the older types involving direct electrical contact between metal points have also been updated so that this switching is performed by the effect of a magnet as it approaches contacts in a "reed switch", or by the relay effects of a transistor which detects the current induced in a coil by a magnetic balance. The majority of electric clocks follow a plan opposite to that of ordinary clockwork in that they use a fast oscillator actually to drive a reducing gear train which ends with the hands or other indicators. Some employ light emitting diodes (LED) or liquid crystal displays to give a digital read-out.

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Our timer is based on the idea of electrical relaxation oscillator. A source of regular oscillation leads to a generation of regularly spaced pulses. These pulses could be used to produce a periodic output and function as a timer.

The relaxation oscillator can be made by charging a capacitor through a resistor, then discharging it rapidly when the voltage reaches some threshold, beginning the cycle anew. Figure 1 shows a classic RC relaxation oscillator. When the power is first applied, the op-amp output goes to positive saturation. The capacitor begins charging up toward V₊, with time constant RC. When it reaches one-half the supply voltage, the op-amp switches into negative saturation, and the capacitor begins discharging toward V_- with the same time constant. The cycle repeats indefinitely with period 2.2RC³.

In our timer, we have used an integrated circuit (IC) chip that operates as a relaxation oscillator like the operational amplifier discussed above. This IC chip consists of two sets of units each of which has 23 transistors, 2 diodes and 16 resistors on a silicon chip. Figure 2 shows the circuit diagram of such a unit (IC) chip. When the power is applied, the capacitor is discharged so the IC chip is triggered, causing the output to go HIGH, the discharge transistor to turn off, and the capacitor to begin charging to V_cc. When it has reached 2/3 V_cc, the THRESHOLD input is triggered, causing the output to go LOW and the discharge transistor to turn on, discharging the capacitor. Operation is now cyclic, with the capacitor’s voltage going between 1/3 V_cc and 2/3 V_cc.

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Fig. 1 Op-Amp Relaxation Oscillator

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Fig. 2 Relaxation Oscillator IC Chip

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Figure 3 shows the complete circuit diagram for our timer. The IC chip has 14 pins as shown. Unit one of this composite chip generate pulses that oscillate at a frequency determined by R1 and C1. Unit two is a one-shot that drives a relay via diode D1. Unit one triggers unit two once per cycle. The output is led to drive a motor, produce a siren and turn on the light emitting diodes (LED). The motor is connected to a carousel planted on the box that houses the entire circuit including the motor. The motor spins every minute, thus, rotating the carousel every minute. The LED turns on and the speaker buzz at the same time. The various components of the timer are listed in Table III and their price is listed in Appendix A.

C. TEST OF THE PROTOTYPE

The prototype of the timer was constructed based on the circuit diagram shown in Figure 3. It was then tested against the system requirements as summarized in Table I. Our timer met each and every criteria.

The requirement demands that the designed timer operate for 3 minutes while our timer operates indefinitely. The requirement demands an audible and visual indicator at 1, 2, and 3 minutes from the start of the operation. Our timer produces audible (siren from the speaker), visual (LED turning on), and also an entertaining visual display (carousel rotating around bunch of circus clowns) every minute. The requirement demands that the indicator must be within +/- 10 seconds of the indicated elapsed time while our timer has an accuracy of less than +/- 1 second. The requirement prohibits the use of commercial

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Fig. 3 Circuit Diagram of the Timer

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Table III. Components of the Timer

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clock parts. Our timer does not have any commercial clock part. The requirement

demands that the volume be small than 6 cubic feet and not weigh more than 20 pounds. Our timer is a mere 6 inches wide, 8 inches long, and 3 inches tall box with a carousel stand of around 7 inches height. Its weight of 3 pounds is very light compared to 20 pounds, the maximum weight specified. The requirement demands the timer to be self-contained and capable of operating without outside interference. Our timer meets this criterion perfectly. Once the switch is flipped on, our timer keeps on operating until the switch is turned off or the battery runs out. If it does, the battery could be recharged. The cost involved for the production of the timer is around $ 30, much lower as compared to the price ceiling of $ 50 specified in the system requirements. If the timer as designed, is to be produced in a large scale, this cost could be expected to drop considerably. It will prove to be very rewarding financially.

Figure 4 shows our master timer. The carousel with the circus clowns are situated on the top of the box glued securely. The figure shows the switch which sets the timer on by a mere flip.

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Fig. 4 The Master Timer

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III. CONCLUSIONS

The master timer is constructed as per the requirements. It was tested and found to not only meet the preset system requirements but exceeded the goals a great deal in its overall appearance, operational quality and performance. This project proved to be a very valuable learning experience of an engineering design process.

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APPENDIX A. EXPENDITURE

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BIBLIOGRAPHY

1. Coggins, Frank W.,"Clocks Construction, Maintenance, and Repair", Tab Books Inc. PA, 1984
2. Gendler, Joel R., "Physics", D.C. Heath and Company, MA, 1992
3. Horowitz, Paul and Hill, Winfield, "The Art of Electronics", 2^nd ed., Cambridge University Press, MA, 1989
4. Krause, Paul C. and Wasynczuk, Oleg, "Electromechanical Motion Devices", McGraw-Hill Book Company, NY, 1989
5. McPherson, George, "An Introduction to Electrical Machines and Transformers", John Wiley and Sons, NY, 1981
6. Sarma, Mulukutla S., "Electric Machines- Steady State Theory and Dynamic Performance", 2^nd ed., West Publishing Company, NY, 1994
7. Smith, Eric, "How to Repair Clocks", Tab Books Inc., PA, 1979
8. Streetman, Ben G., "Solid State Electronic Devices", 4^th ed., Prentice Hall, NJ, 1995
9. Valkenburgh, Van, "Basic Synchros and Servomechanisms", vol. 1, Rider Publishers, Inc. NY, 1955

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