ES050 – Introductory Engineering Design and Innovation Studio 1 ECE Case Study Accelerometers in Interface Design Prof. Ken McIsaac

2 Outline Review of generated concepts Design selection Accelerometer mathematics Accelerometer mechanics Accelerometer electrical theory

3 Review of Generated Concepts Pendulum proposal  d

4 Review of Generated Concepts Mercury Switch

5 Review of Generated Concepts Motion capture

6 Review of Generated Concepts Accelerometer “Something to measure acceleration” Untethered, inertial sensor

7 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) Accuracy (How close to reality is the model?) Resolution (How fine motions can we detect?) Form factor (weight/size) Cost #1 #3 #4 #5 #6 Range of motion (What can the user do?)#2

8 Decision Making Evaluating our choices: OptionProblems PendulumInfrastructure, range Mercury SwRange, resolution Motion Capture Infrastructure AccelerometerMaybe none, IF we get the right one

9 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

10 Accelerometer Mathematics We measure V=f(a), then:

11 Accelerometer Mathematics As it happens, this is inaccurate, but who cares?

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

13 Accelerometer Theory New problem: measure bending A L  1. Resistance of a wire varies with length 2. Length of a bent strut changes So…the resistance of a wire bonded to the strut detects the bending.

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

15 Accelerometer Theory Now, some math: Stationary Accelerating Assuming

16 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

17 Accelerometer Theory Accelerometer for into plane acceleration or pitch Strain gauge

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

19 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.