Team Members Brian Klug Michael Tran Nabeel Kibria Garrett Skinner Justin Bell John Sergeant tt2@dustball.com (Sends E-mail to all members) ii. Table of Contents i. Title Page ii. Table of Contents 1. Executive Summary 2. Analysis 2.1 Design 2.2 Specifications 2.3 Constraints 3. Assembly 3.1 Bottom, Front, Sides, and Back Panels 3.2 Top and Display Panel 3.3 Internal Assembly 3.4 Buttons and LCD Screen 3.5 Program 4. Drawings 4.1 Concept Drawing 4.2 Assembly 4.2.1 Sub Assembly 4.3 Detail Drawings 4.4 Final Electrical Schematic 5. Conclusion 5.1 Parts List 5.2 Cost 5.3 Special Thanks 5.4 Conclusion 6. References 1. Executive Summary This report contains Tech Team Two's production and design summary. The report will note a brief description of the design, our target objectives, along with the costs of our design (both time and money) along with the final results of our design. Our goal as a team is was assemble an electronic scale with a digital display of weight. We have been given approximately three months to reach this ultimate goal. The three months will served as time in which we consulted within our group to come up with initial design proposals, final design proposals, initial and final design specifications and drawings and finally we assembled, tested and presented our final product. Our ultimate was achieved as all these subliminal goals are achieved one by one. Throughout the first month and a half the team consulted each other and various references in order to propose various designs that matched the specifications of our electronic scales. After searching various Internet sites and magazines the team finally decided on what we wanted our scale design to be. We settled on a simple yet effective design. The scale design we chose is that of a simple box with a slanted face and an LCD screen, which displays weight. The design also calls for an opening in one of the sides to allow us to place the actual electronics inside of the scale. The opening will also serve as a window for those who wish to examine the inner bowels of the scale. Once our design proposition was finalized, the team began to master Pro/Engineer, a computerized 3-D drawing and assembly board. Within two weeks the final designs, 3-D drawings, and 3-D assembly designs had been completed. Once these steps were completed the team began analyzing the mathematics behind building the actual processor and electronics of the scale. The team also began to analyze how the strain gauges for the scale. This is the point at which the team is positioned and working on to this date. Once spring break was completed, the team began to start to actually put together our final product. Over the break, our computer engineer, Brian Klug, had already formulated the specifications and mathematics for all the electronics that would be required in the scale. Once the actual production of the scale began, Brian took about two to three weeks to put together the functioning wheatstone bridge, the amplifier and the processor for the LCD screen. Though Brian had these parts functioning in two to three weeks, there was some fine tuning necessary which took him up to the final days of class to perfect the scale and have it fully functioning to perform the tasks it was required to do and meet the project specifications. While Brian was taking care of the electronic aspects of the scale, the rest of the team spent about nine class days building the shell of the scale. On total, the team used the entire four weeks after spring break to perfect the scale to our designs and the project specifications. Our scale will not have a target customer since it will be donated to schools ranging from kindergarten to grade 12. They will use the scale to better understand how scales work. The scale that our group made had several restrictions that had to be met. First, the scale had to weigh up to 2000g, with an accuracy of +/- .5g. Secondly, the scale has to fit in a size 15-shoe box. Finally, the cost of the scale has to be under $150. The scale will be an enclosed devise, with an aluminum pan to hold the weight of the sample. A thin aluminum bar, 1/4" in width and 1/8" in height, will support this pan by a vertical rod. Attached to this beam will be a 120-ohm strain gauge. This strain gauge will be mounted directly under the pan's support piece for maximum efficiency. The gauge will be connected within a wheatstone bridge, which will deliver its output to an amplifier. The voltage of the amplifier's output (0 to +5V) would be directed into a 12Bit A/D converter. This data will be sent via digital I/O lines to Parallax's Stamp II microprocessor. This information will be converted to a weight in grams, and a formula will be made to calculate the correct postage and display this on a backlit LCD screen. This screen will be mounted on an angle towards the user for maximum readability. This robust design should have no problems due to its simplicity, yet the power of the embedded system will provide the user with a state-of-the-art full-featured scale. After pushing the zero button, the scale will zero itself. There is an on/off button that is used to turn the scale on and off. On test day our scale came through with flying colors. It not only amazed our peers, but also fullfilled its task of weighing measures precisely. The scale hardly had any errors. We also met the cost specifications. Even though most of out technology had been donated to us, we calculated that our scale would have been ten dollars below the $150 maximum, even if we had bought all our own supplies. Due to our scales excellence in our class we were chosen to represent our class in the overall engineering school scale competition. In the overall competition our scale came in second place total, one tenth of a point behind the first place winner. Our scale won first place for aesthetics. I regret to add that the toughest obstacle the team reached, by far, was the conflict of finding anyone with the proper knowledge to help us. We never did find out why the amplifier refused to amplify beyond 1.38 volts (when supplied +5V), nor did we find an answer to as to why switching from breadboard to PC board would make the AD input oscillate. This absolutely, without a doubt, caused us to come in second place. I can only hope, the reason we did not have access to adequate university staff, was that because we are in a low-level course. 2. Analysis 2.1 Design Our scale will not have a target customer since it will be donated to schools ranging from kindergarten to grade 12. They will use the scale to better understand how scales work. The scale that our group made had several restrictions that had to be met. First, the scale had to weigh up to 2000g, with an accuracy of +/- .5g. Secondly, the scale has to fit in a size 15-shoe box. Finally, the cost of the scale has to be under $150. The scale will be an enclosed devise, with an aluminum pan to hold the weight of the sample. A thin aluminum bar, 1/4" in width and 1/8" in height, will support this pan by a vertical rod. Attached to this beam will be a 120 strain gauge. This strain gauge will be mounted directly under the pan's support piece for maximum efficiency. The gauge will be connected within a wheatstone bridge, which will deliver its output to an amplifier. The voltage of the amplifier's output (0 to +5V) would be directed into a 12Bit A/D converter. This data will be sent via digital I/O lines to Parallax's Stamp II microprocessor. This information will be converted to a weight in grams, and a formula will be made to calculate the correct postage and display this on a back-lit LCD screen. This screen will be mounted on an angle towards the user for maximum readability. This robust design should have no problems due to its simplicity, yet the power of the embedded system will provide the user with a state-of-the-art full-featured scale. After pushing the zero button, the scale will zero itself. There is an on/off button that is used to turn the scale on and off. 2.2 Specifications * Max weight: 1600g * Temperature range: 0º to +50º C * Operating Relative humidity: 90% max non-condensing * Power: Unregulated 9 Volts DC dry-cell * Power Consumption: 108mA * Power Capacity: 2000mAh * LCD Color: Yellow green (Easy to read, large display) * "Hi Tech" scale appeals to young students. * Back panel hinged for students to learn from inside component arrangement. 2.3 Constraints * The LCD's backlight consumes 90mA, accounting for most of the power consumed by the unit. * The fluid in the LCD display is the limiting component for the operative temperature range and operating relative humidity. * The maximum weight was limited by the amplification of the amplifer. 3. Assembly 3.1 Bottom, Front, Sides, and Back Panels o Apply glue to all four edges of the bottom panel o Place front, sides, and back panel against the corresponding sides of the back panel(refer to 3D drawing) o Clamp all opposite sides in order to secure the glue o Drill 1/8" holes through the side panels into the bottom, front, and back panels. Also drill holes along top edge for the top panel that will be placed later. Note: Holes are represented in picture o Fasten panels together with 3/4" brass screws using screwdriver. 3.2 Top and Display Panel o Place Angled sides of the top and display panels adjacent to one another o Apply the two hinges over the two panels 1/4" from the edges parallel with the gap between them o Fasten the hinges to the panels with the 1/4" brass screws supplied with the hinges o This assembly is now ready to be joined with the other part o Apply glue to sides of the top panel and assemble into the place where the top panel is to go. o Fasten together the top and side panels with 3/4" screws 3.3 Internal Assembly o Along the inside of the front panel, place the two small blocks against the front panels in the corners with glue o The round AL bar comes down from the pan to a horizontal bar. o On this bar is a strain gauge, which is connected to the processor board. o A speaker mounted on the right is also connected to this board. o The LCD and power/zero buttons are also connected. o A Micro switch & light bulb combo provide Refrigerator door technology. 3.4 Buttons and LCD Screen o Slide button boxes into slots Note: No glue is needed o Apply button covers to the boxes o Apply LCD screen into slot from the back side of the display panel o Fasten four corners of the screen to the display panel with the supplied screws 3.5 Program Below is the source code to the BS2-IC. 'PREPARE VARIABLES butt var byte ' Variable for Zero button zero var word ' Offset for zeroing weight var word ' Holds weight (after zeroing) misc var word ' Hold misc calculations (weight/postage..) AD var word ' Variable to hold 12-bit AD result. ' INITIALIZE DISPLAY, AD, SOFTWARE butt=0 pause 450 serout 3,16416,[$FE] serout 3,16416,["C"] serout 3,16416,[$FE] serout 3,16416,["C"] serout 3,16416,[$FE] serout 3,16416,["F"] serout 3,16416,[$FE] serout 3,16416,["X"] serout 3,16416,[$FE] serout 3,16416,["B1"] high 0 high 2 'SHOW LOGO 'gosub logo 'ZERO SCALE :zer misc=0 serout 3,16416,[$FE] serout 3,16416,["X"] serout 3,16416,[$FE] serout 3,16416,["G"] serout 3,16416,[$04] serout 3,16416,[$02] serout 3,16416,["Z e r o i n g" ] FREQOUT 4,50,200:pause 50:gosub inzero:zero= misc:pause 50 FREQOUT 4,50,200:pause 50:gosub inzero:zero=zero+misc:pause 50 FREQOUT 4,50,200:pause 50:gosub inzero:zero=zero+misc:pause 50 FREQOUT 4,50,200:pause 50:gosub inzero:zero=zero+misc:pause 50 zero=zero/4 'MAIN LOOP again: pause 5 button 5,1,255,255,butt,1,zer 'GET INPUT low 0 shiftout 2,1,lsbfirst,[%1101\4] shiftin 2,1,msbpost,[AD\12] high 0 if AD>1050 then oops weight=(AD-Zero) if weight>4096 then lw if weight<0 then lw :lwb if weight>1024 then hw :hwb :backc serout 3,16416,[$FE]:serout 3,16416,["G"]:serout 3,16416,[$09]:serout 3,16416,[$03] serout 3,16416,["debug "] serout 3,16416,[DEC AD] serout 3,16416,[" "] 'SHOW WEIGHT serout 3,16416,[$FE]:serout 3,16416,["G"]:serout 3,16416,[$01]:serout 3,16416,[$01] serout 3,16416,[DEC Weight * 20 / 13] serout 3,16416,["g / "] serout 3,16416,[DEC Weight * ((20 / 13) * 3) / 85] serout 3,16416,["."] serout 3,16416,[DEC Weight * ((20 / 13) * 3) // 85 * 10 / 85] serout 3,16416,[ "oz "] 'FREQOUT 4,8,AD*4,AD*3 ' BAR GRAPH serout 3,16416,[$FE]: serout 3,16416,["h"]: serout 3,16416,[$FE]: serout 3,16416,[$7C]: serout 3,16416,[$01]: serout 3,16416,[$04]: serout 3,16416,[$00]: serout 3,16416,[weight / 10]: serout 3,16416,[$FE]:serout 3,16416,["G"]:serout 3,16416,[$01]:serout 3,16416,[$03] serout 3,16416,[$FE]:serout 3,16416,["G"]:serout 3,16416,[$01]:serout 3,16416,[$03] misc=Weight * 20 / 13 if misc > 10 and misc < 35 then g1 if misc > 80 and misc < 120 then g2 if misc > 180 and misc < 220 then g3 if misc > 370 and misc < 430 then g4 if misc > 470 and misc < 530 then g5 if misc > 960 and misc < 1040 then g6 backguess serout 3,16416,[" "] 'SHOW POSTAGE serout 3,16416,[$FE]:serout 3,16416,["G"]:serout 3,16416,[$01]:serout 3,16416,[$02] if (Weight * ((20 / 13) * 3) / 85) > 31 then pri2 if (Weight * ((20 / 13) * 3) / 85) > 14 then pri serout 3,16416,["First-Class $"] serout 3,16416,[$FE]:serout 3,16416,["G"]:serout 3,16416,[$11]:serout 3,16416,[$02] serout 3,16416,["0 "] serout 3,16416,[$FE]:serout 3,16416,["G"]:serout 3,16416,[$0E]:serout 3,16416,[$02] misc=33 + (22 * (Weight * ((20 / 13) * 3) / 85)) serout 3,16416,[DEC misc/100] serout 3,16416,["."] serout 3,16416,[DEC misc-(misc/100*100)] goto again pri: serout 3,16416,["Priority Mail $3.20"] goto again pri2: serout 3,16416,["Priority Mail $4.30"] goto again 'WARNING oops: weight=1050 serout 3,16416,[$FE]:serout 3,16416,["G"]:serout 3,16416,[$03]:serout 3,16416,[$04] serout 3,16416,["Too much weight!"] FREQOUT 4,100,600 FREQOUT 4,200,300 goto backc 'ERROR CHECKING ON INPUT lw: weight=0 goto lwb hw: weight=1024 goto hwb 'LOGO logo: serout 3,16416,[$FE]:serout 3,16416,["X"] ' Clear screen ' Large Digits serout 3,16416,[$FE] serout 3,16416,["n"] serout 3,16416,[$FE]:serout 3,16416,["G"]:serout 3,16416,[$06]:serout 3,16416,[$02] serout 3,16416,["Tech"] serout 3,16416,[$FE]:serout 3,16416,["G"]:serout 3,16416,[$08]:serout 3,16416,[$03] serout 3,16416,["Team"] serout 3,16416,[$FE]:serout 3,16416,[$23]:serout 3,16416,[$0D]:serout 3,16416,[$02] gosub beeps pause 2000 serout 3,16416,[$FE] serout 3,16416,["X"] serout 3,16416,["***Tech Team Two****"] serout 3,16416,[$FE]:serout 3,16416,["G"]:serout 3,16416,[$01]:serout 3,16416,[$03] serout 3,16416,[" Our Postal Scale "] serout 3,16416,[" Welcomes You :) "] gosub beeps pause 2000 serout 3,16416,[$FE]:serout 3,16416,["G"]:serout 3,16416,[$01]:serout 3,16416,[$02] serout 3,16416,[" Brian Klug "] serout 3,16416,[" John Sergeant "] serout 3,16416,[" Garret Skinner "] gosub beeps pause 2500 serout 3,16416,[$FE]:serout 3,16416,["G"]:serout 3,16416,[$01]:serout 3,16416,[$02] serout 3,16416,[" Mike Tran "] serout 3,16416,[" Justin Bell "] serout 3,16416,[" Nabeel Kibria "] gosub beeps pause 2500 serout 3,16416,[$FE]:serout 3,16416,["X"] ' Clear screen return 'AUDIO OUTPUT beeps: FREQOUT 4,300,1000 PAUSE 70 FREQOUT 4,200,2000 PAUSE 70 FREQOUT 4,100,7000 PAUSE 70 FREQOUT 4,40,2000 PAUSE 70 FREQOUT 4,40,2000 PAUSE 70 FREQOUT 4,40,1000 return inzero: low 0 shiftout 2,1,lsbfirst,[%1101\4] shiftin 2,1,msbpost,[misc\12] high 0 return 'Insti-Guess technology :g1 serout 3,16416,["20g"] goto backguess :g2 serout 3,16416,["100g"] goto backguess :g3 serout 3,16416,["200g"] goto backguess :g4 serout 3,16416,["300g"] goto backguess :g5 serout 3,16416,["500g"] goto backguess :g6 serout 3,16416,["1000g"] goto backguess 5. Conclusion 5.1 Parts List Part Description Price Battery 9 Volts DC $5 BS2-IC Basic Stamp Module 11Mhz Microprocessor $41 A/D Converter 12 Bit $26 LCD Module 20x4 Backlit $40 Quad Op Amp 1/4 used $1 Assorted Resistors See Circuit Diagram $1.95 Wire/Solder/Misc. $1 PC Board Standard Radioshack $5 Metal Pan 4x5" $3.48 Aluminum bar 5 1/2" $0.30 Strain Guage 120 Ohm $1 Paint Red and Silver $2 Silver Knob Round $1 SPST Switch Left $0.89 SPST Button Right $0.89 Hinge & Screws Brass $2 Pine Wood 3 piece 6" * 2 ft $12.60 Total ~$146 5.2 Cost The final cost of the scale was $146 (including donated parts). 5.3 Special Thanks * Thanks to Parallax Inc for their generous donation of the BS2-IC chip and related programming tools. * Thanks to Matrix Orbital for the generous donation of their top-of-the-line 20x4 Backlit LCD module with serial interface. 5.4 Conclusion We are very proud of our scale. I have never learned so much about electronics or engineering in my life. We enjoyed the challenge. I've never seen a scale like it before; we appreciate all the comments from the staff "This is the best design I have ever seen..", etc. Thanks 6. References "Postal Accounting Makes Money--Legally." Modern_Office Technology, 33(1), 24(1998). Page 24. "Interactive Guide To Strain Measurement Technology" http://www.measurementsgroup.com/guide/index.htm Online. Internet. Measurements Group, Inc. January 1999 Edition Burns, Robert W. "On-board truck scale--Digital Strain Gage Conditioner Philips" Microcontroller Electronic NewsLetter. ISSUE 34 - APRIL 1998 James W. Dally Introduction to Engineering Design Book 2 Knoxville TN: College House Enterprises, LLC. 1997 Pollock, John L. "Cognitive carpentry: a blue print for how to build a person" Cambridge, Mass: MIT Press, 1995. Page 377 1