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ECE Case Study

ECE Case Study. Accelerometers in Interface Design Prof. Jayshri Sabarinathan TEB 259 jsabarinathan@eng.uwo.ca 2009 11 25. Electrical/Computer Engineering Design Case Study. Wii:. Problem Definition.

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ECE Case Study

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  1. ECE Case Study Accelerometers in Interface Design Prof. Jayshri Sabarinathan TEB 259 jsabarinathan@eng.uwo.ca 2009 11 25

  2. Electrical/Computer EngineeringDesign Case Study Wii:

  3. Problem Definition • Design a controller that can allow natural interactions with the game vs joy stick or computer buttons

  4. Electrical/Software Control Systems

  5. Interactive – respond to user inputs Automation - Continuous functioning at location with minimal manual intervention Interdisciplinary engineering solutions Remote access Control mechanism Mechanical / Civil Chemical Electrical / Software Control Systems Need for a automatic control? Combination

  6. Type of Control : Open Loop Feedback Input / Output devices Controller program/hardware Hardware Control Interface Software Control Interface Control Systems What do you need to consider in the design of a control system?

  7. Simple Control Block Diagram Input Variables Controller Feedback Output

  8. Garage Door Opener Aircraft controllers ABS braking systems Air conditioning Thermostats Mars Rover Satellites Human Brain Control Systems Examples

  9. Joystick Keyboard Mouse Touch screen Sensors Human eyes TV remote WII Remote Input Devices

  10. Stepper Motors Actuators Pumps Car Brakes Robotic devices Roomba vacuum cleaner Human Limbs Television Output Actuator devices

  11. Electrical/Computer EngineeringDesign Case Study Wii: Output device – Television screen Input controller

  12. Functionality Okay, we now know what we would like a controller to do. How do we do it? Functionality we would like - Portable handheld controller device - Motion sensing when controller is moved - Wireless/Remote to not be tethered to a spot

  13. Objectives & Constraints - Portable handheld controller device There are enough remote hand held electronics that we know what is a good size needed - Motion sensing when controller is moved This is trickier – need device in a small portable device to provide acceleration information - Wireless/Remote to not be tethered to a spot Again infrared wireless technology already in use. No need wire to connect and relay information a few feet away. Infrared detectors in controller can triangulate based on light source at screen

  14. Outline – Motion sensing • Concept generation • Design selection • Accelerometer mathematics • Accelerometer mechanics • Accelerometer electrical theory

  15. Generate Concepts • Pendulum proposal d 

  16. Generated Concepts • Mercury Switch

  17. Generated Concepts • Motion capture

  18. Generated Concepts Accelerometer • “Something to measure acceleration” • Untethered, inertial sensor

  19. Clicker question • Which concept would you go with for motion sensing - portable? • Pendulum • Mercury Switch • Optical motion capture • Accelerometers

  20. Decision Making Now, we have a set of concepts. What criteria would we use to choose between them? Clicker Question #2: Which one would be most important to you? 1. Infrastructure (ease of installation) 2. Accuracy (How close to reality is the model?) 3. Resolution (How fine motions can we detect?) 4. Form factor (weight/size) 5. Cost 6. Range of motion (What can the user do?)

  21. Decision Making Now, we have a set of concepts. What criteria would we use to choose between them? Some thoughts I had: • Infrastructure (ease of installation) #1 • Accuracy (How close to reality is the model?) #6 • Resolution (How fine motions can we detect?) #3 • Form factor (weight/size) #4 • Cost #5 • Range of motion (What can the user do?) #2

  22. Decision Making Evaluating our choices:

  23. Accelerometer Mathematics • A transducer is a device that measures a physical quantity and turns it into an electrical signal • An accelerometer is a transducer that turns acceleration into voltage

  24. Accelerometer Mathematics • We measure V=f(a), then:

  25. Accelerometer Mathematics Not completely accurate – simplified model

  26. Accelerometer Mechanics So how do we transduce acceleration? Stationary Can we instead transduce this bending? Acceleration One dimensional model

  27. Accelerometer Theory New problem: measure bending L  A Resistance of a wire varies with length Length of a bent strut changes So…the resistance of a wire bonded to the strut detects the bending.

  28. Accelerometer Theory Proposed circuit: + R1 (Fixed) Vout R2 (Variable) + Vin - -

  29. Accelerometer Theory Now, some math: Stationary Accelerating Assuming

  30. Accelerometer Theory This will work, but it is hard to measure, so… Strain gauges are thin wires folded and printed onto flexible foils. They magnify the deformation effect on resistance

  31. Accelerometer Theory Accelerometer for into plane acceleration or pitch Strain gauge

  32. Wii First Proposal We can build something like this: Computer monitors and integrates acceleration data Acc 1 Acc 3 Acc 2

  33. Design Evaluation Our design will work, but: • It is too big • It is difficult (= costly) to manufacture We need a design iteration to resolve these problems.

  34. Recap • Problem definition • Functionality -> existing technology to solve some features • Objectives Constraints • Concepts – decision making -> accelerometers • Analysis/ Calculations • Simplify • Next step : Iteration- need something smaller

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