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Part 1
Electronics
Conductors and Insulators
All matter is made up of atoms.
Atoms contain:
Protons (positive charge)
Electrons (negative charge)
Neutrons (no charge)
Electronics is the study of how electrons move
from one atom to another
Insulators do not want to give up their electrons,
so electrons don’t move, so current doesn’t
flow
Conductors quite readily give up their electrons,
so electrons will move freely if there is a
force to push them, so current flows with
little resistance under an electromotive force
Copyright © 1971-2002 Thomas P. Sturm
Electronics
Part 1, Page 2
Good Insulators and Conductors
Good insulators are:
a vacuum
air
polytetrafluoroethylene
polyisobutylene
mineral oil
kraft paper
polystyrene
polyethylene terephthalate
polycarbonate
castor oil
halowax
chlorinated diphenyl
ruby mica
aluminum oxide
flint glass
ceramic
polyester
Copyright © 1971-2002 Thomas P. Sturm
Good conductors are:
silver
annealed copper
hard-drawn copper
gold
aluminum
chromium
phosphor bronze
zinc
brass
cadmium
nickel
iron
tin
steel
lead
Electronics
Part 1, Page 3
Voltage, Resistance, and Conductors
To move electrons we need a source of
electromotive force (EMF), a voltage
source.
A battery will work.
It provides a constant force in a constant
direction (over time).
The amount of force, E, is measured in volts.
The schematic for a battery is:
The amount of resistance to the flow of electrons
is resistance, R, measured in ohms.
The schematic for a resistor is:
Connections of negligible resistance (copper
wire) are drawn as solid lines.
Copyright © 1971-2002 Thomas P. Sturm
Electronics
Part 1, Page 4
Circuits
A circuit is a collection of components
connected together with the intent of
conducting a signal or current from a source
to a destination.
The closing line of the circuit is frequently
omitted in favor of using a “ground” symbol
to indicate a common return connection.
Copyright © 1971-2002 Thomas P. Sturm
Electronics
Part 1, Page 5
Circuit Values and Calculations
The battery has a voltage, the resistor has a
resistance, and the current has a magnitude
that are related by Ohm’s law:
E  IR
So if we have a 1.5 Volt D-cell battery, and a 10
Ohm resistor, than the current will be:
I = E/R = 1.5/10 = .15 Amperes = .15 Amp = .15 A =
150 mA
If we wanted to instead draw 50 mA, then we
would need a resistor that would be:
R = E/I = 1.5/.05 = 30 Ohms = 30 
The power consumed by each circuit can be
calculated using the Power law:
P  EI
So using the D-cell battery and the 10 Ohm
resistor, the resistor would consume (and the
battery would provide)
P = E x I = 1.5 x .15 = .225 Watts = .225 W = 225 mW
We could safely use a ½ watt resistor.
Using the 30 Ohm resistor, the resistor would consume
P = E x I = 1.5 x .05 = .075 Watts = .075 W = 75 mW
We could safely use a ¼ watt resistor (as small as you can buy in discrete components).
Copyright © 1971-2002 Thomas P. Sturm
Electronics
Part 1, Page 6
Resistor Color Coding
Resistors, as components, are color coded to
display their resistance. They use the
following coding:
Color
black
brown
red
orange
yellow
green
blue
violet
grey
white
silver
gold
Color
black
brown
red
orange
yellow
green
blue
violet
grey
white
silver
gold
Value
0
1
2
3
4
5
6
7
8
9
-2
-1
The resistor code is read from left to right,
orienting the resistor so that leftmost band is
closest to the edge.
A resistor code NEVER starts with silver or gold, so if
you have that color at the left, you are holding it
backwards.
The leftmost color represents the first significant digit of
the resistance.
The next color represents the second digit of the
resistance.
The third color represents the power of 10 to multiply
the above 2-digit number by.
Copyright © 1971-2002 Thomas P. Sturm
Electronics
Part 1, Page 7
Decoding the Resistor Color Code
So:
red, violet, orange would be:
2, 7, 3
or
27 x 10**3
or
27 x 1000
or
27000 Ohms
blue, grey, black would be:
6, 8, 0
or
68 x 10**0
or
68 x 1
or
68 Ohms
Copyright © 1971-2002 Thomas P. Sturm
Electronics
Part 1, Page 8
Resistors in Series
When resistors are placed in series, the
resistances add.
The same current flows through both resistors.
The voltage is divided across the resistors in
proportion to their resistance.
Let’s suppose we have a 9 Volt battery, that the resistor
on the left, R1, is 8 ohms, and the resistor on the
right, R2, is 10 ohms.
Then the total resistance, R = R1 + R2 = 8 + 10 = 18 Ohms.
The current is then, I = E/R = 9/18 = .5 A through each resistor.
The voltage drop across R1 is E = I x R1 = .5 x 8 = 4 Volts
The voltage drop across R2 is E = I x R2 = .5 x 10 = 5 Volts
The power consumed by R1 is P1 = E x I = 4 x .5 = 2 Watts
The power consumed by R2 is P2 = E x I = 5 x .5 = 2.5 Watts
The total power consumed by the circuit is P = E x I = 9 x .5 =
4.5 Watts = P1 + P2
Copyright © 1971-2002 Thomas P. Sturm
Electronics
Part 1, Page 9
Resistors in Parallel
When resistors are placed in parallel they each
consume the current they would otherwise
consume without the other resistor present,
so, in a sense, their conductivities (1/R) add.
So to calculate the equivalent resistance, we need to
convert to conductivity, add the conductivities, and
then convert back to resistance.
This gives us the formula:
R
1
1
1

R1 R2
Note that the voltage across the two resistors will be the
same.
Also note that the total current through the circuit will be
the sum of the currents through each of the two
resistors.
Copyright © 1971-2002 Thomas P. Sturm
Electronics
Part 1, Page 10
Calculating with Parallel Resistors
So…
Suppose we have a 5 Volt DC power supply from our
trainer, and we place a left resistor R1 of 10 Ohms
and a right resistor R2 of 25 Ohms.
Then the left resistor draws a current of I1 = E/R1 = 5/10
= .5A
and the right resistor draws a current of I2 = E/R2 = 5/25
= .2A
The total current drawn from the power supply is I1 + I2
= .5 + .2 = .7A
The equivalent resistance is 1/((1/10) + (1/25)) = 1/(.1 +
.04) = 1/.14 = 7.1429 Ohms
The equivalent current is I = E/R = 5/7.1429 = .7A
The power consumed by the entire circuit is P = E x I =
5 x .7 = 3.5 Watts
The power consumed by R1 is P1 = E x I1 = 5 x .5 = 2.5
W
The power consumed by R2 is P2 = E x I2 = 5 x .2 = 1
W
Copyright © 1971-2002 Thomas P. Sturm
Electronics
Part 1, Page 11
AC Electronics
Alternating current (AC) represents the situation
where the sign and magnitude of the EMF
changes over time.
The most common type of AC in the US is 60
Hz sine wave current, and is the standard
against which other AC current is measured.
For circuits containing only resistance, Ohms
law and the power law apply. (The laws are
“calibrated” to apply by the way the voltage
of an AC source is measured.)
Copyright © 1971-2002 Thomas P. Sturm
Electronics
Part 1, Page 12
Capacitance
A capacitor consists of two insulated conductors
in close proximity with each other.
A capacitor blocks the flow of DC. Some
current initially flows when power is applied
to charge the capacitor.
The schematic for a capacitor is:
The curved end indicates the negative side. The
+ sign is used when capacitor polarity
MUST be observed in the installation of the
capacitor. Sometimes just two parallel lines
are shown (bottom line is straight like the
top line).
When AC is applied to a capacitor (any
waveform), it acts as a variable resistor with
frequency (lower resistance at higher
frequencies)
Capacitance in measured in Farads. 1 Farad is a
huge amount of capacitance. Most practical
capacitors have a capacitance in
microFarads or picoFarads
Copyright © 1971-2002 Thomas P. Sturm
Electronics
Part 1, Page 13
Calculating with Capacitance
Capacitors in parallel ADD capacitance.
C  C1  C2
So in the above circuit, the total capacitance between
points A and B would be C = 1uF + 2uF = 3uF
Capacitors in series add impedance, which is the
reciprocal of capacitance
C
1
1
1

C1 C 2
The total capacitance between points A and B is now:
C = 1((1/1) + (1/2)) = 1/(1 + .5) = 1/1.5 = .667 uF
Copyright © 1971-2002 Thomas P. Sturm
Electronics
Part 1, Page 14
Capacitive Reactance
The capacitive reactance (which works like
resistance in a circuit with ONLY
capacitance) is calculated by the formula:
X C  21fC
So a 1uF capacitor acts like an infinite resistance at DC.
At 60 Hz the reactance would be:
XC = 1/((2)*(3.1416)*(60)*(.000001)) = 2653 Ohms
At 1 MHz the reactance would be:
XC = 1/((2)*(3.1416)*(1000000)*(.000001)) = .159 Ohm
When a capacitor and a resistor are placed in
series, the resistance to current flow is now
called impedance. The formula for
impedance is:
Z  R2  X C 2
So in the following circuit:
The impedance at 60 Hz would be:
Z = sqrt((1000*1000) + (2653*2653)) = 2835 Ohms
Copyright © 1971-2002 Thomas P. Sturm
Electronics
Part 1, Page 15
Inductance
An inductor consists of a coil of wire.
An inductor permits the flow of DC, subject
only to the resistance of the wire. An
inductor supplied a steady DC current also
acts as an electromagnet.
At AC the resistance of the inductor increases
with frequency.
Inductors don’t like current change, so they will
resist not only increases in current but
decreases. When current in an inductor
ceases, the stored magnetic energy “kicks
back” a back EMF in an attempt to keep
current flowing.
Relays contain inductors to act as magnets.
These magnets attract an iron bar connected
to the contacts in the relay. When a relay is
de-energized, the back EMF can destroy
nearby semiconductors unless proper
precautions are taken.
The schematic for an inductor is:
Inductance is measured in Henrys.
Copyright © 1971-2002 Thomas P. Sturm
Electronics
Part 1, Page 16
Calculating with Inductance
Inductors in series add inductance.
L  L1  L2
So in the following circuit:
The inductance between points A and B is:
L = .001 + .0005 = .0015 H = 1.5 mH
Inductors in parallel behave like resistors in
parallel.
L
1
1
1

L1 L2
So in the following circuit:
The inductance between points A and B is:
L = 1/((1/.001) + (1/.0005)) = 1/(1000 + 2000) = 1/3000
= .000333H = 333uH
Copyright © 1971-2002 Thomas P. Sturm
Electronics
Part 1, Page 17
Inductive Reactance
The inductive reactance (which works like
resistance in a circuit with ONLY
inductance) is calculated by the formula:
X L  2fL
So a 1mH inductor acts like 0 resistance at DC.
At 60 Hz the reactance would be:
XL = (2)*(3.1416)*(60)*(.001)) = .377 Ohms
At 1 MHz the reactance would be:
XL = (2)*(3.1416)*(1000000)*(.001)) = 6283 Ohms
When an inductor and a resistor are placed in
series, the resistance to current flow is now
called impedance. The formula for
impedance is:
Z  R2  X L2
So in the following circuit:
The impedance at 1 MHz would be:
Z = sqrt((1000*1000) + (6283*6283)) = 6362 Ohms
Copyright © 1971-2002 Thomas P. Sturm
Electronics
Part 1, Page 18
Capacitive and Inductive Reactance
When capacitors and inductors are placed in
series, the net reactance is
X  X L  XC
So in the following circuit:
At 60 Hz the reactance is: X = .377 – 2653 = -2653
Ohms, indicating a capactive reactance
At 1 MHz the reactance is: X = 6283 - .159 = 6283
Ohms, indicating an inductive reactance
When capacitors and inductors are placed in
parallel, the net reactance is
X
1
1
1

X L XC
So in the following circuit:
At 60 Hz the reactance is: X = 1/((1/.377) – (1/2653)) =
1/(2.653 - .000377) = 1/(2.653) = .377 Ohms
At 1 MHz the reactance is: X = 1/((1/6283) – (1/.159))
= 1/(.000159 – 6.289) = 1/(-6.289) = -.159 Ohms
Copyright © 1971-2002 Thomas P. Sturm
Electronics
Part 1, Page 19
Impedance
When reactance and resistance are in series, the
impedance, Z, is calculated as follows:
Z  R2  X 2
When reactance and resistance are in parallel,
the impedance, Z, is calculated as follows:
Z
1
1
R
2

1
X2
Copyright © 1971-2002 Thomas P. Sturm
Electronics
Part 1, Page 20
Semiconductors
Conductors – give up electrons (exchange
electrons) freely
Insulators – hold electrons (do not change
energy levels) tightly
Semiconductors – behave as insulators until the
electrons receive enough energy to jump to
the next electron orbit, then behave as
conductors.
Copyright © 1971-2002 Thomas P. Sturm
Electronics
Part 1, Page 21
Diodes
A semiconductor diode is comprised of a PN
junction.
-
+
N
P
The N-type material has excess electrons.
The P-type material is deficient in electrons, it
has “holes”. It is a + charge carrier.
-
+
current flows
N
P
+
Current flows AFTER the voltage has overcome
a junction voltage barrier
Copyright © 1971-2002 Thomas P. Sturm
Electronics
Part 1, Page 22
Reverse Biased Diode
-
+
charges, but no current
N
+
P
A circuit containing a diode:
Note that the “arrow” in the diode symbol points
to the direction of current flow.
The line in the diode symbol is the negative end,
the cathode, the banded end of a real diode.
This diode is forward biased, so current will
flow.
Copyright © 1971-2002 Thomas P. Sturm
Electronics
Part 1, Page 23
Junction Voltage
In all semiconduction junctions, current flows
AFTER the voltage has overcome a junction
voltage barrier.
The magnitude of this barrier depends upon the
material used in the manufacture of the
junction.
For silicon diodes, transistors, and integrated
circuits this voltage is nominally .7 Volts.
For germanium diodes, this voltage is nominally
.3 Volts.
So no current flows until the applied voltage is
in the proper direction and reaches the
barrier voltage. Once current flows the
voltage across the barrier remains constant
(within reasonable values of current).
Copyright © 1971-2002 Thomas P. Sturm
Electronics
Part 1, Page 24
Transistors
Transistors are comprised of 2 semiconductor
junctions in either a PNP or an NPN
configuration.
Copyright © 1971-2002 Thomas P. Sturm
Electronics
Part 1, Page 25