SECTION 1:
ELECTRONIC FUNDAMENTALS
MAE 2055 – Mechetronics I
2
K. Webb
Introduction
MAE 2055 – Mechetronics I
Electricity – what is it?
3

Fundamental form of energy
 Results
from differences in charge from one location
to another

Electrons are the carriers of electrical charge
 Electron
is negatively charged
 Hole – absence of an electron – is positively charged

May occur naturally
 Lightning,

static electricity
May be produced
 Generator,
K. Webb
battery
MAE 2055 – Mechetronics I
Electricity – why do we care?
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
Electricity can do work for us
 Mechanical,

Efficient means of energy transmission
 Large

heat, light, etc.
regions supplied by a single power plant
Used to process and transmit information
 Computers,
mobile phones, TV, radio, etc.
 Instrumentation and measurement
K. Webb
MAE 2055 – Mechetronics I
Electrical Energy
5


Energy is conserved, but may be transferred from
one form to another
Electrical energy – charge differentials – produced
from other forms of energy
 Generator
– mechanical energy
 Battery – chemical energy
Electrical Generator
Mechanical
Energy In
Electrical
Energy Out
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K. Webb
MAE 2055 – Mechetronics I
Electrical Energy
6

Electrical energy can be transformed into other
useful forms of energy
 Motor
– mechanical energy
 Heater – thermal energy
 Charged battery – chemical energy
Electric Motor
Electrical
Energy In
Mechanical
Energy Out
http://www.trimainternational.com/Products/de.htm
K. Webb
MAE 2055 – Mechetronics I
Energy Transmission
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
Electricity is an efficient means of energy
transmission
 Energy
is transmitted broadly from a single power
plant
 No longer need to grind our wheat at the windmill

Imagine other modes of energy transmission
 Hydraulic,
pneumatic, rotating shafts!
 Pneumatic was proposed for transmission of energy
from Niagara to Buffalo in late 19th century
K. Webb
MAE 2055 – Mechetronics I
Relevance for Mechanical Engineers
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
Very few purely mechanical systems
 Aircraft,


automobiles, etc. rely heavily on electronics
Need to understand impact of mechanical design
on electronics and vice versa
Instrumentation and measurement
 Mechanical
products and systems must be tested,
measured, and evaluated
 Electronic measurements are fast, accurate,
repeatable, and can be automated
K. Webb
MAE 2055 – Mechetronics I
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K. Webb
Where We Are Going
MAE 2055 – Mechetronics I
Electronic Photo Flash Circuit
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






Electronic photo flash
circuit
An interesting example of
the type of circuit whose
function you’ll be able to
analyze and explain by the
end of the course
4V rechargeable battery
Flash tube requires 100s of volts, ~1000W
How can a single 4V battery trigger the flash?
How do we determine an appropriate model for the battery?
How long will the battery last? How many flashes can it provide?
K. Webb
MAE 2055 – Mechetronics I
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K. Webb
Fundamentals of Electronics
MAE 2055 – Mechetronics I
Electrical Potential
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++
+++++++
++++++++++
++++++++++
+++++++
++
+
V
–
---------------------------------
Electrical potential is a measure of electrical energy.
 The unit of electrical charge is the coulomb (C)
 The unit of electrical potential is the volt (V)


Positive charge wants to move from high potential to low potential


V = J/C – required energy per unit charge moved across that potential
Think of voltage as the force that drives this movement
Voltage is analogous to



K. Webb
Pressure that drives fluid flow
Temperature that drives heat flow
Gravity
MAE 2055 – Mechetronics I
Electric Field
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Positively-charged
metal plate
+
+
+
+
+
+
+
+
V
E
-
Negatively-charged
metal plate
Electric field vectors
The electric field is a field of force experienced by a positively-charged
particle.
 Positive charge wants to move in the direction of the E-field, toward
negative charge
 The electric field has units of newtons per coulomb (N/C) or volts per
meter (V/m)
 Electrical energy is stored in the electric field
 The E-field is the negative gradient of the electrical potential
K. Webb
MAE 2055 – Mechetronics I
Electrical Current
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Conductor (e.g. wire)
Current
I
V1> V2
V1
V2
- - -
- - - -
- - - -
Electrons
Electrical current, denoted as I, is defined as the flow of positive charge
 Voltage is the force that drives charge to flow – current is the result
 The unit of current is the ampere or amp (A), or coulombs per second
 Electrical current is analogous to a fluid flow or heat flow
 Current flows from high to low voltage


K. Webb
Just as fluids flow from high to low pressure
or as heat flows from high to low temperature
MAE 2055 – Mechetronics I
Current – what’s really flowing?
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Conductor (e.g. wire)
Current
I
V1> V2
V1
V2
- - -
- - - -
- - - -
Electrons
Electrical current is defined as the flow of positive charge


Really, current is due to the flow of negatively-charged electrons
Electrons flow in the opposite direction of what we call current


K. Webb
Electrons flow from low to high voltage
Negative charge flowing in one direction is equivalent to positive charge
flowing in the opposite direction
MAE 2055 – Mechetronics I
Conductors and Insulators
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

Electrical current flows more easily in some
materials (conductors) than in others (insulators)
Good conductors
 Copper
 Aluminum
 Gold
 Silver

All have a single valence electron
 Easy

http://elpaso.apogee.net/foe/fbbr.asp
for electrons to move from one atom to the next
Insulators have full valence bands
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MAE 2055 – Mechetronics I
Electricity – mechanical analogies
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
Electrical systems are analogous to fluid systems
Electrical current flows through circuits just as fluids flow
through pipes
 Current (positive charge) flows from high to low voltage
just as fluids flow from high to low pressure



Current always flows toward lower voltage just as a mountain
stream always flows down hill
Analogous to thermal systems
Voltage is the driving potential that creates electrical
current
 Temperature is the driving potential that creates heat flow


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Like electrical current flowing from high to low voltage, heat
flows from high to low temperature
MAE 2055 – Mechetronics I
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Electrical Circuits
MAE 2055 – Mechetronics I
Electrical Networks – schematics
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Schematics are diagrams of electrical circuits or networks
 Schematic symbols represent circuit elements
 Schematics detail connections between circuit elements
 Schematics describe paths for the flow of electrical current
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MAE 2055 – Mechetronics I
Electrical Networks – branches & nodes
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

Nodes are connection points
between circuit elements
Node voltages given with respect
to a reference (0 V, ground) node





Current flows into and out of
nodes
Branches are paths for current to flow – connections between nodes
Current flows through branches
Current may not flow in the direction of the arrow shown on the schematic



V3 = 0 V in the circuit shown
Current is positive if it flows in the direction shown
Current flow opposing the arrow on the schematic is negative
Voltage across a branch is the difference in node voltages at either end
K. Webb
MAE 2055 – Mechetronics I
Power
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
Energy can be supplied or absorbed (dissipated) by components in an
electrical network


Power is the rate at which energy is supplied or dissipated


The unit of energy is the joule (J)
The unit of power is the watt (W) or joule per second (J/sec)
Power supplied (or dissipated) by a branch element is given by the
product of current through the branch and voltage across the branch

Sign convention is critical

P=I∙V
P=
P > 0  Power dissipated
P < 0  Power supplied
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

Positive current flows into the
positive voltage terminal
Power absorbed or dissipated by an
element is positive
Power supplied by an element is
negative
MAE 2055 – Mechetronics I
Circuit Components
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

Voltage Source

Schematic symbol:

Description: a circuit element that generates a voltage or electrical potential.
May be DC (constant voltage) or AC (time varying). Examples are batteries,
generators, and power supplies. The units of potential are volts.
Current Source

Schematic symbol:

Description: a circuit element that generates a flow of electrical current. May
be DC or AC. The units of current are amps (A).
K. Webb
MAE 2055 – Mechetronics I
Circuit Components
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

Resistor

Schematic symbol:

Description: a circuit element that resists the flow of electrical current. May
be an intentional or a parasitic resistance (even wires are resistive). Units of
resistance are ohms (Ω). Resistors are denoted as R.
Ground

Schematic symbol:

Description: a voltage reference for a circuit. A ground node is assumed to be
at a potential of 0 V.
K. Webb
MAE 2055 – Mechetronics I
Circuit Components
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

Capacitor

Schematic symbol:

Description: a circuit element that stores electrical energy. Capacitors consist of two
electrodes separated by a dielectric. An open circuit to DC voltage. Voltage across a
capacitor cannot change instantaneously. Units of capacitance are farads (F).
Capacitance is denoted as C.
Inductor

Schematic symbol:

Description: a circuit element that stores magnetic energy. A short circuit to DC voltage.
Current through an inductor cannot change instantaneously. Units of inductance are
henries (H). Inductance is denoted as L.
K. Webb
MAE 2055 – Mechetronics I
Circuit Components
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
Switch

Schematic symbol:

Description: switches control connections between two or more nodes in a
circuit. The symbol on the left is a single-pole single-throw (SPST) switch. The
symbol on the right is a single-pole dual-throw (SPDT) switch.
K. Webb
MAE 2055 – Mechetronics I
Circuit Components
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
Diode

Schematic symbol:
anode


cathode
Description: a two-terminal semiconductor device that allows current flow in
one direction only. Current flows from the anode to the cathode.
Light-Emitting Diode (LED)

Schematic symbol:

Description: a diode that emits photons when electrical current flows through
it.
K. Webb
MAE 2055 – Mechetronics I
Circuit Components
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
Transistor

Schematic symbol:

Description: a three-terminal device. A small voltage on or current into one
terminal controls current flow between the other two terminals. Transistors
may be used as switches or to provide amplification of electrical signals.
Transistors can be thought of as valves.
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MAE 2055 – Mechetronics I
Short Circuits & Open Circuits
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
A short circuit is a direct electrical connection between two
nodes in a circuit



A direct path for current to flow
Often refers to an unintentional connection
An open circuit is the lack of any electrical connection
between two nodes

K. Webb
No path for current to flow
MAE 2055 – Mechetronics I
Complete Circuits
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
Electrical current always flows in a complete circuit
 Current
flows out of the wall, through a cord, into a
lamp, through the bulb, and back through the cord to
the wall
 Grab a power line while on a ladder: current flows
through you, through the ladder, into the earth, and
back to the power plant
 The
earth completes the circuit
 Birds
can sit safely sit on a power line because there is
no path for current to flow through them in a
complete circuit
K. Webb
MAE 2055 – Mechetronics I
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Electrical Signals & Waveforms
MAE 2055 – Mechetronics I
Electrical Signals
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
Voltage and current are the two properties of
electrical circuits that we are most often
concerned with
 Node
voltages and branch currents may be constant as
a function of time
 Direct
 Or
current or DC
they may be time-varying
 Alternating current

or AC
Voltages and currents can be plotted as functions
of time – waveforms
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MAE 2055 – Mechetronics I
DC vs. AC
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
DC (direct current) electrical signals (voltages, currents) do
not vary over time

AC (alternating current) electrical signals vary periodically in
time
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MAE 2055 – Mechetronics I
Some typical waveforms
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Sinusoid
Square wave
Triangle wave
Noise
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MAE 2055 – Mechetronics I
Frequency
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

The period (T) of an AC
waveform is the duration
of one cycle
Frequency is the number
of periods per unit time
 f = 1/T
 May be measured in
hertz, Hz = cycles/sec


K. Webb
T = 0.333 msec
Denoted as f
May be measured in
radians/sec


𝑣 𝑡 = 𝑉𝑝 ∙ sin 𝜔𝑡 + 𝜙 = 𝑉𝑝 ∙ sin 2𝜋𝑓𝑡 + 𝜙
Denoted as ω
ω = 2πf
f = 1/T = 3 KHz
MAE 2055 – Mechetronics I
Amplitude
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

Amplitude of a sinusoid
is its peak voltage, Vp
Peak-to-peak voltage,
Vpp, is twice the
amplitude


𝑣 𝑡 = 𝑉𝑝 ∙ sin 𝜔𝑡 + 𝜙 = 𝑉𝑝 ∙ sin 2𝜋𝑓𝑡 + 𝜙
Vp = 1V
Vpp = 2∙Vp
Vpp = Vmax - Vmin
Vpp = 2V
K. Webb
MAE 2055 – Mechetronics I
Phase
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

Phase is the ф term
in the waveform
expressions
Phase shift between
two waveforms is
the difference in
their phase angles

K. Webb
We’re typically more
concerned with relative
phase than absolute
phase
𝑣1 𝑡 = 𝑉𝑝 ∙ sin 2𝜋𝑓𝑡 + 𝜙1
𝑣2 𝑡 = 𝑉𝑝 ∙ sin 2𝜋𝑓𝑡 + 𝜙2
t 
(2  1 )
(   )
T  2 1
2

MAE 2055 – Mechetronics I
RMS Voltage
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
RMS (root mean square)
voltage is the square root
of the time-average of the
voltage squared.

Time-varying voltage
waveform dissipates equal
power in a resistor as DC
voltage, where VDC = Vrms

For a sinusoid:

Useful for characterizing
noise signals
K. Webb
Vp = 1 V
Vrms = 0.707 V
MAE 2055 – Mechetronics I