ES1050 – Introductory Engineering
Design and Innovation Studio
ECE Case Study
Accelerometers in Interface
Design
Prof. Jayshri Sabarinathan
TEB 259 jsabarinathan@eng.uwo.ca
2009 11 25
1
Electrical/Computer
Engineering
Design Case Study
Wii:
2
Problem Definition

Design a controller that can allow natural
interactions with the game vs joy stick or
computer buttons
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Electrical/Software Control Systems
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Control Systems
Need for a automatic control?

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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
Combination
/ Software
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Control Systems
What do you need to consider in the design of
a control system?

Type of Control :
 Open
Loop
 Feedback



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Input / Output devices
Controller program/hardware
Hardware Control Interface
Software Control Interface
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Simple Control Block Diagram
Input Variables
Controller
Feedback
Output
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Control Systems Examples
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Garage Door Opener
Aircraft controllers
ABS braking systems
Air conditioning
Thermostats
Mars Rover Satellites
Human Brain
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Input Devices

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Joystick
Keyboard
Mouse
Touch screen
Sensors
Human eyes
TV remote
WII Remote
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Output Actuator devices
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Stepper Motors
Actuators
Pumps
Car Brakes
Robotic devices
Roomba
vacuum cleaner
Human Limbs
Television
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Electrical/Computer
Engineering
Design Case Study
Output device –
Television screen
Wii:
Input controller
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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
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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
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Outline – Motion sensing
Concept generation
 Design selection
 Accelerometer mathematics
 Accelerometer mechanics
 Accelerometer electrical theory

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Generate Concepts

Pendulum proposal
d

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Generated Concepts

Mercury Switch
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Generated Concepts

Motion capture
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Generated Concepts
Accelerometer


“Something to measure acceleration”
Untethered, inertial sensor
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Clicker question

Which concept would you go with for
motion sensing - portable?
Pendulum
B. Mercury Switch
C. Optical motion capture
D. Accelerometers
A.
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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?)
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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
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Decision Making
Evaluating our choices:
Option
Problems
Pendulum
Infrastructure, range
Mercury Sw
Range, resolution
Motion
Infrastructure
Capture
Accelerometer Maybe none, IF we
get the right one
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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
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Accelerometer Mathematics

We measure V=f(a), then:
a f
1
V 
v   a dt  v0 
p   v dt  p0 
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Accelerometer Mathematics
Not completely accurate – simplified model
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Accelerometer Mechanics
So how do we transduce acceleration?
Stationary
Can we instead transduce
this bending?
Acceleration
One dimensional model
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Accelerometer Theory
New problem: measure bending
L

1.
2.
A
R
L
A
L
R
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.
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Accelerometer Theory
Proposed circuit:
+
R1 (Fixed)
R2 (Variable)
Vin
+
-
Vout
-
R2
Vout 
Vin
R1  R 2
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Accelerometer Theory
Now, some math:
V1 
L

A
L
R1  
A
Vin
Stationary
L  L
A
V2 
Vout
L  L
R1  
A

Accelerating
L
A Vin
V 
L
R1  
A

Assuming L  L
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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
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Accelerometer Theory
Accelerometer for into plane acceleration or
pitch
Strain gauge
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Wii First Proposal
We can build something like this:
Computer monitors
and integrates
acceleration data
Acc 1
Acc 3
Acc 2
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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.
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Recap

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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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