Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
ECE 477 Final Presentation Group 8 Fall 2004 Outline • • • • • • • • Project overview Block diagram Professional components Design components Success criteria demonstrations Individual contributions Project summary Questions / discussion Project Overview • Objective: 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 Sharp GP2D15 IRQ PWM Motor 1 PWM Motor 2 Atmel ATMega32L Sharp GP2D15 IRQ A/D Ultrasonic Receiver 1 A/D Ultrasonic Receiver 2 Professional Components • Constraint analysis and component selection rationale • Patent liability analysis • Reliability and safety analysis • Ethical and environmental impact analysis Constraint Analysis • Microcontroller Constraints: – Moderate clocking speed (1 – 4 MHz) – Modest space constraints – Peripheral requirements • A/D Converter • RTI/Timer module and PWM • External Interrupts – Power and cost efficient Constraint Analysis • 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 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 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 objects – US Pat # 5,165,064 • Uses array of ultrasonic transducers to locate a beacon – US Pat # 5,491,670 • Uses multiple ultrasonic beacons to triangulate position – US Pat # 6,567,044 • Uses sensors to determine location • All cause problems under doctrine of equivalents. First is also literal Patent Liability Analysis • Other Patent Liability issues – US Pat # 4,751,658 • Uses sensors to avoid obstacles – US Pat # 5,911,767 • Has a central control that uses sensor data to determine future action – US Pat # 4,710,020 • Uses sensors to determine distance of a transmitter • The first is a literal infringement rest are infringements under the doctrine of equivalents Reliability/Safety Analysis • Reliability Drivers: – Heat : Increased heat increases unreliability – Component Derating: Prevents wear out • 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 Reliability/Safety Analysis • Components have failure rates of the order of 10E-6 or better • Acceptable for a non-critical application • Components analyzed for failure: – ATMega32L – 4.29E-6 fails – Max663 – 3.336E-6 fails – IRL530N – 4.795E-6 fails Reliability/Safety Analysis • 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 on • Defective IR sensors – Both components well derated, and should not fail, leading to high overall safety of cart. Ethical/Environmental Analysis Environmental Impact • Manufacture of semiconductors – Environmentally unfriendly • Soldering on PCBs – Exposure to lead • Plastic casing – Recyclable Ethical/Environmental Analysis Environmental Impact • Electricity – Precious resource used • Battery Disposal – Careful and correct disposal needed Ethical/Environmental Analysis Ethical Impact • Safety – Warning labels – Documentation – Safety mechanisms • Reliability – Perform as stated in user manual Design Components • • • • Packaging design considerations Schematic design considerations PCB layout design considerations Software design considerations Packaging Design • Board mounted on bottom tray • Board dimensions - 4” x 6” • Motors with wheels attached mounted at bottom – front wheel drive • Two ultrasonic sensors mounted at front end • Two infrared sensors mounted at front corners Packaging Design • Cart 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 wheels – Provides for smaller turning radius Packaging Design • Beacon carried by shopper – Small and light • Circuit may be damaged/tampered with – All circuitry hidden • Storage space must be maximized – No components placed in cart • Batteries must be accessible – Batteries not hidden Schematic Design • Main Schematic – Headers for all sensors – Motor control MOSFETs – IR input inverted Schematic Design • Cart Power Supply – Power: 9.6V – 6V rail – -6V rail – 3.3V rail Schematic Design • Transmitter – Max 663 – 12 V battery – 555 timer Schematic Design • Receiver – 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. • Need modular layout to enable cutting of single board. • 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 spikes and noise. PCB Layout Design • Noise Immunity: o – No 90 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 – Copper pour PCB Layout Design Receivers Transmitter Main board Software Design • 32Kb flash, 2Kb SRAM – EEPROM not used • Application code is organized in a commanddriven fashion – Ultrasonic receivers are polled periodically – Infrared sensors generate interrupt requests – Main loop reads voltage samples and adjusts motor speeds Software Design Start Main loop Flowchart Initialize on-board peripherals Enable global interrupts Read the last sampled front left, and front right voltages Is left or right voltage nonzero? Y Motor speed duty cycles = (255 – Voltage) * 1.5 Turn off both motors N Software Design Periodic Interrupt Service Routine Start Start Clear the interrupt flag Clear the interrupt flag Read left receiver Turn off opposite motor Read right receiver Adjust motor on same side Store voltage samples in global data structure Disable ultrasonic receiver polling Return Return External Interrupt Service Routine Success Criteria Demonstrations 1. Ability to generate a beacon signal - demo 2. Ability to identify the bearing of the beacon - demo 3. Ability to approximate the distance to the beacon using relative signal strength demo 4. Ability to follow the beacon - demo 5. Ability to avoid obstacles in the path of motion - demo Individual Contributions • • • • Team Leader – Aliasgar Poonawala Team Member 2 – Raghuram Ramanujan Team Member 3 – Clive Lopez Team Member 4 – Mohan Rokkam Team Leader – Aliasgar Poonawala • • • • Packaging design Ethical and environmental impact analysis Software debugging Component selection Member 2 – Raghuram Ramanujan • Design constraint analysis and component selection • Software design – Wrote diagnostic routines – Devised control algorithm and wrote core software modules • Hardware design – Microcontroller interfacing – Infrared sensor interfacing • Hardware debugging Member 3 – Clive Lopez • PCB layout design • Hardware design – Designed (and redesigned) ultrasonic circuits – Microcontroller interfacing • Hardware debugging • Soldering and population of board • Reliability and safety analysis • Component selection • Packaging Member 4 – Mohan Rokkam • Hardware design – Ultrasonic circuitry – Microcontroller interfacing • Created and maintained webpage • Hardware debugging • Soldering and population of board • Schematic design • Patent liability analysis • Component selection • Packaging Project Summary • Important lessons learned – Fuses! – Use bypass capacitors – Effective time management – Trust team mates • Important skills learned – OrCAD Capture and Layout – Soldering techniques – Power supply design – Ability to interpret datasheets Project Summary • Second 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