IAT 267 Introduction to Technological Systems
Spring 2021
Helmine Serban and Amal Vincent
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Lecture 2:
Technological systems – Principles
Input, Output and Transduction
Electricity Concepts – Serial and Parallel Circuits
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Updates on Canvas
• See ‘Announcements’ for posting from teaching staff
• Canvas is our main way of communication
• Course schedule has been posted under ‘Course
Information’
– This schedule might change during the term
• See also the other documents posted under Course Info
module.
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Announcement: Quiz 1
• Next week – in lecture time slot
• 15 minutes quiz
• Multiple choice, T/F, short-answer and longer
answer questions
• Covers Unit 1 and Unit 2 (lecture, workshop and
readings)
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Homework
• Mini-quiz – 5 minutes
• Study lecture 1 and 2 and then proceed to this
quiz
• Good practice for next week’s quiz
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For Workshops
• Workshops consists of hands-on exercises
– This week: Basic circuit + building serial and parallel
circuits
– We will still use the simulation package – Tinkercad
– Starting next week, you will need to have a kit – it is
expected that all students have a kit at this time
• For all workshops: come prepared – review lecture
notes from previous week, do your homework
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Review from Last Week
• Technological systems
– Many different categories
– Computer systems: focus of this course
• Embedded systems
• Components of an embedded systems
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In-Class Exercise
• Analyze an example of a technological system
that contains an embedded computer system
and briefly describe the roles of the three
components below:
– CPU
– Sensor(s)
– Actuator(s)
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Review From Last Week
• What are the key concepts of computer
systems?
– Universal computing device
– Transformations between layers
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Question
Two computers, A and B, are identical except for the fact that A
has a ‘Subtract’ instruction and B does not. Both have ‘Add’
instructions. Both have instructions that can take a value and
produce the negative of that value.
Which computer is able to solve more problems? Justify your
answer.
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Review From Last Week
• Basics of electricity
• Electric circuit
– Closed loop
– Producer of energy: source
– Consumer of energy: load
• Electronic components and their roles
• Schematics and symbols for components
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In-Class Exercise 2
• Match the item in column 1 with the
description in column 2:
Item
Description
1 Resistor
A Variable resistor.
2 LED
B Limits the current flow in a circuit
3 Potentiometer
C Permits the flow of electricity in one
direction and blocks it in the other
direction
D Must be connected correctly in the
circuit - longer pin to +, shorter pin to -.
5 Diode
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Review – What is a short-circuit?
• Circuit with no load
• Explain why a short-circuit should be avoided
– Your explanation should be based on Ohm’s Law
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Goals for Today
Technological systems – key concepts
Computer systems – how we interact with them
The elements of interaction
The tools
Electricity concepts – series and parallel circuits
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Technological Systems
Real-world
constraints
Trade-offs
Iterative
Design
Feedback
Key
Concepts
Complexity
managemen
t techniques
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1. Iterative Design
• Imagine something  Design it  Build it  Get it to
work
• Design cycle
• Even the process of choosing a project requires
several iterations
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2. Trade-offs
• Multiple interacting domains and subsystems in a project 
solving one problem can create others
– Space/time trade-off: By compressing an image you can
reduce transmission time/costs at the expense of CPU time
to perform the compression and decompression.
• Important aspect of trade-offs: they make it clear that there is
no single ‘right’ or ‘best’ solution; rather each solution comes
with its own benefits and drawbacks.
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3. Real-world Constraints
• Design of a system: in many cases involves multiple
interacting parts and domains, each with its own issues
– Example: comparison between the ‘bin-sorting’ problem in
computer science and the task of designing a device that would sort
marbles in different bins
Single Domain vs. Multiple Domains
• Bin-sorting problem (computer science perspective)
• Purely computational - developing an algorithm that solves the
problem, using the least amount of time and computer memory
• Also called Bucket‐Sorting: works by partitioning an array into a
number of buckets:
– Set up an array of initially empty "buckets.“
– Scatter: Go over the original array, putting each object in its bucket
– Sort each non-empty bucket
– Gather: Visit the buckets in order and put all elements back into the
original array
Physical sorting of marbles into bins: several
issues
• Sensor system that would differentiate the marbles, based on
certain parameters
• Marbles have mass and volume and need to be transported to
the correct bin
• Determine when the correct bin has been reached
– How to insert the marble into the bin
– Computation, but time and space requirements will not be
primary concerns
4. Feedback
• Common in natural systems, engineered devices
• State of the system – equilibrium state
• Examples:
– Negative feedback: ball on the bottom of a hill: if perturbed
from this position, it will roll back to the bottom (back to the
equilibrium state)
– Positive feedback: ball on the top of a hill: if perturbed from
this position, it will roll further away from the top of the hill
(away from the equilibrium state)
More examples of feedback
Positive feedback: The Tacoma
Narrows Bridge collapsed in 1940, due
to a design flaw that allowed positive
feedback to dominate.
Negative feedback: Thermostat
When the temperature in a heated room reaches a
certain upper limit the room heating is switched off so
that the temperature begins to fall. When the
temperature drops to a lower limit, the heating is
switched on again. Provided the limits are close to each
other, a steady room temperature is maintained.
Positive feedback: Alarm or panic can spread by positive feedback
among a herd of animals to cause a stampede
Source: Wikipedia
5. Controlling Complexity
• Abstraction: ‘black-box’ entities with simple interfaces
– Programmable devices (microcontrollers, field-programmable
logic devices) that can be used effectively without having to
completely understand the details of how they work.
• Modularity: composing systems of reusable, mix-and-match
parts
– E.g., small circuit design to perform a specific function:
microcontroller + temperature sensor + servomotor used to
control temperature – can be reused in several courses and
different projects
Summary of key concepts
Technological Systems:
•
•
•
•
•
Iterative design
Trade-offs
Managing complexity
Real-world constraints
Feedback
Computer Systems
• Universal computing device
• Transformations between layers
Interaction with the Computer System
• How most people see the computer system:
– Screen
– Keyboard
– Mouse
• ‘computers make things interactive’
• Think of COMPUTING rather than computer!
– Computers should take whatever physical form suits our
needs for computing
– Examples…
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Computing as a Medium
• Can store sound and images
– Random access media: non-sequential parts of a computer
memory can be called up as if they were next to each
other
– (vs. linear media – tape, film)
• Reduce the barriers of time and space
– Networking
• Create more complex relationships between sensed events
and caused events
– E.g.: system that lowers the blinds when sunny; system
that turns on the lights when persons enter the room
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Elements of Interaction
• Why do we need interaction?
– Create a rich conversation between the physical
world and the virtual world of the computer
• Transduction – enables this interaction
– Is the conversion of one form of energy into
another
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Transduction
• Physical world: various forms of energy (depending
on the project and system used – e.g., mechanical,
light, pressure, etc)
• Computer system: electrical energy
• Transducers are devices which will convert between
the physical energy and electrical energy
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What is Interaction?
• Interaction is
“an iterative process of listening,
thinking and speaking between
two or more actors”
Chris Crawford – author and game
programmer
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Interaction in Terms of Computing
Listening  Input
Thinking  Processing
Speaking  Output
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Input
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Output
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Transducers for Input and Output
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Input, Processing and Output
Have to do with energy flow
Input: takes less energy than output
• It takes less energy to sense activity than to move things
Processing: requires a computer to read the input, make
decision and activate output
• Requires programming
Output: often requires electrical and mechanical skills
• Light, sound, movement
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Digital and Analog
• Digital: limited number of states (usually 2)
– “whether or not”
• Is the cat on the mat or not?
• Analog: continuous range of multiple states
– “how much”, “stronger”, “faster”, “brighter”
• How heavy is the cat that’s on the mat?
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Parallel and Serial
• How the input/ output flows over time
serial
• Speak analogy:
– Present ideas one after another  serial
– Present many ideas all at once  parallel
• Events happening one after another = serial
• Events happening simultaneously = parallel
parallel
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Application of Serial / Parallel
• Electrical current can flow through components
serially or in parallel.
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Application of Serial / Parallel
• Computers can exchange bits of information
serially or in parallel as well.
serial
parallel
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In Practice – Building a Project
Describe first what you want to happen, from the point of view of the person experiencing the
project
In plain language
What they see
What they hear
What they feel
What they can do
Describe what changes as the person takes different actions
Why the system is engaging to the person
How the events should unfold to keep the person
engaged
Focus the description on what happens, not how it happens
Do not think of the technology at this stage
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In Practice – Building a Project
• Break your project down into the stages of
input, processing and output
• Identify your input and output as analog or
digital
• Begin your search for transducers
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In Practice – Building a Project
• Describe the sequence of events
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Tools of Interaction
Source: “Physical Computing: Sensing and Controlling the Physical World with Computers” (2004) by Dan O’Sullivan and Tom Igoe
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Making the Connection between the Physical
World and the Digital World
Assemble
circuits
Connect
circuits to the
computer
Write
software for
the computer
Enable
computers to
communicate
with each
other
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Electricity Concepts
• Serial and Parallel Circuits
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Serial Circuit
• The defining characteristic of a series circuit is
that there is only one path for electrons to
flow.
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Serial Circuit
• Let’s calculate the total resistance in this
circuit!
• R1 = 820 Ω
• R2 = 1.2 kΩ
• R3 = 150 Ω
• What is the total resistance?
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Serial Circuit
• Re= 820 + 1200 + 150
• Re= 2170 Ω or 2.170 kΩ
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Serial Circuit
• The total resistance of any series circuit is equal to
the sum of the individual resistances.
• This should make intuitive sense: the more resistors
in series that the electronics must flow through, the
more difficult it will be for those electrons to flow.
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Parallel Circuit
• The defining characteristic of a parallel circuit is that
all components are connected between the same set
of electrically common points.
• Note that all resistors as well as the battery are
connected between the top and bottom sets of points.
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Parallel Circuit
• Let’s calculate the total resistance in this circuit!
Source Voltage = 60V
R1 = 6 Ω
R2 = 12 Ω
R3 = 20 Ω
• The current can take any of the 3 paths to go through.
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Parallel Circuit
Source Voltage = 60V
R1 = 6 Ω
R2 = 12 Ω
R3 = 20 Ω
• What is the total current (I) at each path and the total current in
the circuit?
• Hint* We need to use Ohm’s Law.
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Parallel Circuit
• Ohms Law: I = V/R
• Lets use a table to help us with the calculation
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Parallel Circuit
• Ohms Law: I = V/R
• Lets use a table to help us with the calculation
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Parallel Circuit
• Ohms Law: I = V/R
• Lets use a table to help us with the calculation
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Parallel Circuit
Source Voltage = 60V
R1 = 6 Ω | 10 A
R2 = 12 Ω | 5A
R3 = 20 Ω | 3A
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Parallel Circuit
What is the total resistance?
I = V/R > R = V/I
60 / 18 = 3.3 Ω
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Parallel Circuit
What is the total resistance? Version 2 only for parallel circuits
1/ Rtot= 1/R1 + 1/R2 + 1/R3
1/Rtot = 1/6 + 1/12 + 1/20
Rtot= 3.3 Ω
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Parallel Circuit
• Total resistance in a parallel circuit is less than any of the
individual resistances.
• *The more pathways we have the less congested it is for the
current to flow through. This circuit opens up potential
pathways for the electrons to flow.
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In-Class Exercise 3
Source Voltage = 60V
R1 = 5 Ω
R2 = 15 Ω
R3 = 10 Ω
Equivalent resistance in serial connection: ___
Equivalent resistance in parallel connection: ___
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Summary
• What are the elements of interaction?
– Listen, think, speak = input, processing, output
• Input, output and transduction
– Input = sense
– Output = produce some change (motion, sound, light, etc)
• Tools for interaction
– Circuits, microcontroller, transducers, programming, computer system
• Electricity
– Serial and parallel circuits
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Readings
• Physical Computing textbook (ebook available
from the library)
– Introduction
– Chapter 1
– Chapters 2 and 3 selections (follow lecture slides
as guide on what to read)
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Thank you
Questions?
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