ECE 477 Final Presentation Group 8  Fall 2004

Outline Project overviewProject overview Block diagramBlock diagram Professional componentsProfessional components Design componentsDesign components Success criteria demonstrationsSuccess criteria demonstrations Individual contributionsIndividual contributions Project summaryProject summary Questions / discussionQuestions / discussion

Project Overview Objective: To design and build a shopping cart capable of following a shopper around a storeObjective: To design and build a shopping cart capable of following a shopper around a store –Shopper carries an ultrasonic beacon –Cart follows beacon by maintaining fixed signal strength (within a small range) –Infrared sensors mounted on cart enable it to avoid obstacles

Block Diagram Atmel ATMega32L Motor 1 Sharp GP2D15 Sharp GP2D15 Ultrasonic Receiver 1 Ultrasonic Receiver 2 Motor 2 PWM IRQ A/D

Professional Components Constraint analysis and component selection rationaleConstraint analysis and component selection rationale Patent liability analysisPatent liability analysis Reliability and safety analysisReliability and safety analysis Ethical and environmental impact analysisEthical and environmental impact analysis

Constraint Analysis Microcontroller Constraints:Microcontroller Constraints: –Moderate clocking speed (1 – 4 MHz) –Modest space constraints –Peripheral requirements A/D ConverterA/D Converter RTI/Timer module and PWMRTI/Timer module and PWM External InterruptsExternal Interrupts –Power and cost efficient

Constraint Analysis Microcontroller Candidates:Microcontroller Candidates: –Rabbit / PIC: Did not offer required combination of peripherals –HC05 / HC11: One-time programmable memory –MC9S08GT32 / ATMega32L: Identical feature set – Atmel chip was chosen due to ready availability of development tools

Constraint Analysis Infrared Proximity SensorInfrared Proximity Sensor –Prime candidates were Sharp GP2D12 and Sharp GP2D15 (analog vs digital) –Chose GP2D15 – digital output was more convenient and did not tie up A/D DC MotorDC Motor –Fast enough to keep up with a person –Sufficient torque to power 6lb. cart –Jameco 10:1, 600RPM,12V DC geared motor

Patent Liability Analysis Using Sensors to track / locate objectsUsing Sensors to track / locate objects – US Pat # 5,165,064 Uses array of ultrasonic transducers to locate a beaconUses array of ultrasonic transducers to locate a beacon – US Pat # 5,491,670 Uses multiple ultrasonic beacons to triangulate positionUses multiple ultrasonic beacons to triangulate position –US Pat # 6,567,044 Uses sensors to determine locationUses sensors to determine location All cause problems under doctrine of equivalents. First is also literalAll cause problems under doctrine of equivalents. First is also literal

Patent Liability Analysis Other Patent Liability issuesOther Patent Liability issues –US Pat # 4,751,658 Uses sensors to avoid obstaclesUses sensors to avoid obstacles –US Pat # 5,911,767 Has a central control that uses sensor data to determine future actionHas a central control that uses sensor data to determine future action –US Pat # 4,710,020 Uses sensors to determine distance of a transmitterUses sensors to determine distance of a transmitter The first is a literal infringement rest are infringements under the doctrine of equivalentsThe first is a literal infringement rest are infringements under the doctrine of equivalents

Reliability/Safety Analysis Reliability Drivers:Reliability Drivers: –Heat : Increased heat increases unreliability –Component Derating: Prevents wear out Product Specific Drivers:Product Specific Drivers: –Low power microcontroller, good ventilation, lowers unreliability caused by heat –High current through motors and IR leads to non-derated power chips power chips

Reliability/Safety Analysis Components have failure rates of the order of 10E-6 or betterComponents have failure rates of the order of 10E-6 or better Acceptable for a non-critical applicationAcceptable for a non-critical application Components analyzed for failure:Components analyzed for failure: –ATMega32L – 4.29E-6 fails –Max663 – 3.336E-6 fails –IRL530N – 4.795E-6 fails

Reliability/Safety Analysis FMECA-FMECA- –5 major blocks: U/S transmitter, U/S receivers, IR sensors, Motor drive circuitry, Power circuitry –Critical reliability problem - potential collision with user: Motors stuck onMotors stuck on Defective IR sensorsDefective IR sensors –Both components well derated, and should not fail, leading to high overall safety of cart. overall safety of cart.

Ethical/Environmental Analysis Environmental Impact Manufacture of semiconductorsManufacture of semiconductors –Environmentally unfriendly Soldering on PCBsSoldering on PCBs –Exposure to lead Plastic casingPlastic casing –Recyclable

Ethical/Environmental Analysis Environmental Impact ElectricityElectricity –Precious resource used Battery DisposalBattery Disposal –Careful and correct disposal needed

Ethical/Environmental Analysis Ethical Impact SafetySafety –Warning labels –Documentation –Safety mechanisms ReliabilityReliability –Perform as stated in user manual

Design Components Packaging design considerationsPackaging design considerations Schematic design considerationsSchematic design considerations PCB layout design considerationsPCB layout design considerations Software design considerationsSoftware design considerations

Packaging Design Board mounted on bottom trayBoard mounted on bottom tray Board dimensions - 4” x 6 ”Board dimensions - 4” x 6 ” Motors with wheels attached mounted at bottom – front wheel driveMotors with wheels attached mounted at bottom – front wheel drive Two ultrasonic sensors mounted at front endTwo ultrasonic sensors mounted at front end Two infrared sensors mounted atTwo infrared sensors mounted at front corners

Packaging Design Cart only moves forwardCart only moves forward –IR sensors only needed at front two corners –Ultrasonic sensors placed strategically to allow determination of beacon bearing Back wheels are freely rotating caster wheelsBack wheels are freely rotating caster wheels –Provides for smaller turning radius

Packaging Design Beacon carried by shopperBeacon carried by shopper –Small and light Circuit may be damaged/tampered withCircuit may be damaged/tampered with –All circuitry hidden Storage space must be maximizedStorage space must be maximized –No components placed in cart Batteries must be accessibleBatteries must be accessible –Batteries not hidden

Schematic Design Main SchematicMain Schematic –Headers for all sensors –Motor control MOSFETs –IR input inverted

Schematic Design Cart Power SupplyCart Power Supply –Power: 9.6V –6V rail –-6V rail –3.3V rail

Schematic Design TransmitterTransmitter –Max 663 –12 V battery –555 timer

Schematic Design ReceiverReceiver –LF353 op amps –Gain of 90 –Filter for noise

PCB Layout Design 5 PCBs – 1 U/S Transmitter, 3 U/S Receivers, 1 Main Board.5 PCBs – 1 U/S Transmitter, 3 U/S Receivers, 1 Main Board. Need modular layout to enable cutting of single board.Need modular layout to enable cutting of single board. Noise immunity:Noise immunity: –Bypass capacitors close to microcontroller and noise suppression capacitors between power and ground at intervals –Need wide, short traces to reduce inductance, thereby reducing current inductance, thereby reducing current spikes and noise. spikes and noise.

PCB Layout Design Noise Immunity:Noise Immunity: –No 90 o angles minimize wave reflections which lead to noise and radiation –Reduce interference between sub-circuits, by placing individual power and ground in parallel –High current motors need to be isolated from rest of circuit, powered directly from battery directly from battery –Copper pour

PCB Layout Design ReceiversTransmitterMain board

Software Design 32Kb flash, 2Kb SRAM – EEPROM not used32Kb flash, 2Kb SRAM – EEPROM not used Application code is organized in a command- driven fashionApplication code is organized in a command- driven fashion –Ultrasonic receivers are polled periodically –Infrared sensors generate interrupt requests –Main loop reads voltage samples and adjusts motor speeds

Software Design Main loop Flowchart Start Initialize on-board peripherals Enable global interrupts Read the last sampled front left, and front right voltages Is left or right voltage non- zero? Motor speed duty cycles = (255 – Voltage) * 1.5 Y Turn off both motors N

Software Design Periodic External Interrupt Interrupt Service Service Routine Routine Start Clear the interrupt flag Read left receiver Read right receiver Store voltage samples in global data structure Return Start Clear the interrupt flag Turn off opposite motor Adjust motor on same side Disable ultrasonic receiver polling Return

Success Criteria Demonstrations 1.Ability to generate a beacon signal - demo demo 2.Ability to identify the bearing of the beacon - demo demo 3.Ability to approximate the distance to the beacon using relative signal strength - demo demo 4.Ability to follow the beacon - demo demo 5.Ability to avoid obstacles in the path of motion - demo demo

Individual Contributions Team Leader – Aliasgar PoonawalaTeam Leader – Aliasgar Poonawala Team Member 2 – Raghuram RamanujanTeam Member 2 – Raghuram Ramanujan Team Member 3 – Clive LopezTeam Member 3 – Clive Lopez Team Member 4 – Mohan RokkamTeam Member 4 – Mohan Rokkam

Team Leader – Aliasgar Poonawala Packaging designPackaging design Ethical and environmental impact analysisEthical and environmental impact analysis Software debuggingSoftware debugging Component selectionComponent selection

Member 2 – Raghuram Ramanujan Design constraint analysis and component selectionDesign constraint analysis and component selection Software designSoftware design –Wrote diagnostic routines –Devised control algorithm and wrote core software modules Hardware designHardware design –Microcontroller interfacing –Infrared sensor interfacing Hardware debuggingHardware debugging

Member 3 – Clive Lopez PCB layout designPCB layout design Hardware designHardware design –Designed (and redesigned) ultrasonic circuits –Microcontroller interfacing Hardware debuggingHardware debugging Soldering and population of boardSoldering and population of board Reliability and safety analysisReliability and safety analysis Component selectionComponent selection PackagingPackaging

Member 4 – Mohan Rokkam Hardware designHardware design –Ultrasonic circuitry –Microcontroller interfacing Created and maintained webpageCreated and maintained webpage Hardware debuggingHardware debugging Soldering and population of boardSoldering and population of board Schematic designSchematic design Patent liability analysisPatent liability analysis Component selectionComponent selection PackagingPackaging

Project Summary Important lessons learnedImportant lessons learned –Fuses! –Use bypass capacitors –Effective time management –Trust team mates Important skills learnedImportant skills learned –OrCAD Capture and Layout –Soldering techniques –Power supply design –Ability to interpret datasheets

Project Summary Second iteration enhancementsSecond iteration enhancements –Better control algorithm –Better noise immunity for sensors –Ability to send different instructions via beacon –Support for multiple carts –Better beacon range –Additional sensors

Questions / Discussion