Chapter 6
Fundamentals of Electronics and
Computers
Objectives (1 of 4)
• Outline some of the developmental history of
electronics.
• Describe how an electrical signal can be
used to transmit information.
• Define the term pulse width modulation.
• Define the principle of operation of N- and Ptype semiconductors.
• Outline the operating principles and
applications of diodes.
Objectives (2 of 4)
• Describe the construction and operation of a typical
transistor.
• Describe what is meant by the optical spectrum.
• Identify some commonly used optical components
used in electronic circuitry.
• Explain what is meant by an integrated circuit and
outline its application in on-board vehicle
electronics.
• Define the role of gates in electronic circuits.
Objectives (3 of 4)
• Describe the operating modes of some
common gates used in electrical circuits
including AND, OR, and NOT gates.
• Interpret a truth table that defines the
outcomes of gates in an electrical circuit.
• Explain why the binary numeric system is
used in computer electronics.
• Define the role of an electronic control
module in an electronic management system.
Objectives (4 of 4)
• Outline the distinct stages of a computer
processing cycle.
• Describe the data retention media used in
vehicle ECMs.
• Demonstrate an understanding of input
circuits on a vehicle electronic system.
• Troubleshoot a potentiometer-type TPS.
• Describe the operating principles of the
VORAD collision warning system.
Using Electronic Signals (1 of 3)
• Electronic signals used to manage
information are generally low voltage/low
current circuits.
– They may be classified as:
• Analog
• Digital
Using Electronic Signals (2 of 3)
• Analog signals operate
on variable voltage
values.
Using Electronic Signals (3 of 3)
• Digital signals operate
on specific voltage
values.
• A digital signal
produces a square
wave pattern.
• Digital signals may be
classified as:
– Frequency modulated
– Pulse width modulated
(duty cycled)
Frequency Modulation
• Frequency is the
number of pulses per
second.
• It is expressed in hertz
(Hz).
• Information may be
transmitted by varying
the frequency of the
signal.
Pulse Width Modulation (1 of 2)
• A square wave of fixed
frequency, but varying
duty cycle is achieved
by changing the
percentage of on-time.
• This is known as pulse
width modulation
(PWM).
Pulse Width Modulation (2 of 2)
• Electronic noise is an
unwanted pulse or
waveform interference
that can scramble
signals.
Semiconductors (1 of 4)
• Semiconductors have exactly four electrons
in their valence shell.
• The ones commonly used are:
– Silicon
– Germanium
Semiconductors (2 of 4)
• In crystal form,
semiconductor atoms share
electrons in the outer shell
with adjacent atoms.
• Pure silicon or germanium
must be “doped” before it is
useful.
• The type of doping agent
used defines the electrical
properties of the crystals
produced.
Semiconductors (3 of 4)
• Silicon crystals doped
with boron or some
other trivalent element
will form P-type silicon
crystals.
Semiconductors (4 of 4)
• Silicon crystals doped
with phosphorus or
some other pentavalent
element will form Ntype silicon crystals.
Diodes (1 of 3)
• Diodes have two terminals.
• A diode is used in electrical circuitry as a sort
of one way check valve which conducts
electricity in one direction and blocks it in the
opposite direction.
• When a diode is forward-biased, it should
conduct electricity.
• When a diode is reverse-biased, it should not
conduct electricity.
Diodes (2 of 3)
• The positive terminal is
called the anode.
• The negative terminal
is called the cathode.
• In an electrical
schematic showing a
diode, the arrow points
in the direction of
current flow using
conventional theory.
Diodes (3 of 3)
• Types of diodes
– Small signal diodes
– Power rectifier diodes
– Zener diodes
– Light-emitting diodes (LEDs)
– Photo diodes
Transistors (1 of 10)
• Transistors are three-terminal semiconductor chips
that are used extensively in electronic circuits
primarily for switching and amplification.
• Transistors are active circuit elements capable of
amplifying or transforming a signal level.
• A transistor consists of two P-N junctions.
• A transistor functions in an electronic circuit in much
the same manner that a relay functions in an
electrical circuit.
Transistors (2 of 10)
• The base can be
regarded as a switch.
• The collector can be
regarded as an input.
• The emitter is the
output.
• A small base current
controls a larger
current through the
emitter/collector.
Transistors (3 of 10)
• Transistors may be categorized as:
– Bipolar
– Field effect (FETs)
• Junction FETs
• Metal-oxide semiconductor field effect
transistors (MOSFETs)
– Thyristors
– Silicon-controlled rectifiers (SCRs)
– Darlington pairs
Transistors (4 of 10)
• Bipolar transistors
– The base emitter junctions will not conduct
until the forward bias voltage exceeds ± 0.6V.
– Excessive current flow through a transistor will
cause it to overheat or fail.
– Excessive voltage can destroy the
semiconductor crystal media.
– A small base current can be used to control a
much larger collector current.
Transistors (5 of 10)
• Field effect transistors
(FETs) are more
commonly used than
bipolar transistors.
• They are cheaper to
manufacture.
• They may be divided
into:
– Junction-type
– Metal-oxide
Transistors (6 of 10)
• JFETs
– JFET gate resistance is very high, so the
device has almost no effect on external
components connected to the gate.
– The gate and channel form a “diode,” and as
long as the input signal “reverse biases” this
diode, the gate will show high resistance.
Transistors (7 of 10)
• MOSFETs
– They have become the most important type of
transistor in microcomputer applications.
– Thousands can be photo-infused onto minute
silicon wafers.
– They can act both as a switch and as variable
resistors.
– They can be switches at very high speeds.
Transistors (8 of 10)
• Thyristors
– Thyristors are solid-state switches.
– They are only capable of switching.
– They fall into two classes depending upon
whether they switch AC or DC current.
Transistors (9 of 10)
• Silicon-controlled rectifiers
are similar to a bipolar
transistor with an additional
layer added.
• SCRs will remain on even
when the gate current is
removed.
• Current will continue to flow
until the anode-cathode
circuit is either opened or
reverse biased.
Transistors (10 of 10)
• Darlington pairs
– A pair of transistors are connected so that the emitter
of one supplies the base of the other through which a
much larger current flows.
– This provides signal amplification.
– They are used extensively in computer control
systems and ignition modules.
Photonic Semiconductors (1 of 5)
• Photonic semiconductors emit and detect
light (photons).
• A photon is a unit of light energy.
• Photons behave like waves.
• All visible light is classified as
electromagnetic radiation.
Photonic Semiconductors (2 of 5)
• The optical light
spectrum includes:
– Ultraviolet
– Visible
– Infrared
Photonic Semiconductors (3 of 5)
• The portion of the
electromagnetic
spectrum that is visible
is very narrow.
• Photonic
semiconductors
operate in this range.
Photonic Semiconductors (4 of 5)
• The importance of optical components in the
electronic age is increasing.
• Data signaling functions will be removed from
hard-wired buses and will be performed using
fiber optics.
• Optical components may conduct, refract, or
modify light.
• The use of optical components in vehicle
technology is increasing.
Photonic Semiconductors (5 of 5)
• Optical components:
– Filters
– Reflectors
– Beam splitters
– Lenses
– Optical fibers
– Solar cells
Testing Semiconductors (1 of 2)
• Diodes should produce
a low resistance when
forward biased and a
high resistance when
reverse biased.
Testing Semiconductors (2 of 2)
• Test a transistor using a
DMM in ohmmeter mode.
• There should be continuity
between the emitter and
base.
• There should be continuity
between the base and the
collector in one direction
and high resistance when
the leads are reversed.
• There should be high
resistance in either direction
between the emitter and
collector terminals.
Integrated Circuits
Gates and Truth Tables
• Digital integrated circuits contain thousands
of gates.
• Gates are only to be either be open or
closed.
• Gates may be categorized as:
– AND gates
– OR gates
– NOT gates (inverter gates)
Gates, Truth
Tables, and Basic Data Processing
Binary System Basics
• The binary system is an arithmetic system with only
two digits, 1 and 0.
• The binary system is used in computers because it
directly corresponds to the on or off states of
switches.
• Digital electronic data is stored in binary code.
• Digital signals may be transmitted:
– Serial data link
– Parallel data link
Serial and Parallel Data Links
Microprocessors (1 of 2)
• A microprocessor is a solid-state chip
containing many hundred of thousands of
gates per square inch.
• The microprocessor is the core of both
personal and vehicular computer systems
• On-board computers are referred to as
ECMs.
• Truck technicians must have a basic
understanding of both personal computers
and vehicle ECMs.
Microprocessors (2 of 2)
• Information processing
requires:
– Data input
– Data processing
– Data output
Data Input
• Most data input devices are sensors.
– Thermistors
– Variable capacitance sensor (pressure)
– Piezo-resistive sensor
– Potentiometers
– Hall-effect sensors
– Induction pulse generator
– Switches
Thermistors
• Thermistors precisely
measure temperature.
• If the resistance decreases
as temperature increases, it
is an NTC thermistor.
• If the resistance increases
as temperature decreases, it
is a PTC thermistor.
• Coolant temperature,
ambient temperature, and
oil temperature are
measured using thermistors.
Variable Capacitance Sensors
• These sensors are
provided with a
reference voltage and
return a signal voltage
based upon pressure.
• Oil pressure, boost
pressure, and fuel
pressure can be
measured using
variable capacitance
sensors.
Piezo-Resistive Pressure Sensor
• Piezo-resistive sensors are sometimes referred to
as wheatstone bridges.
• A doped silicon chip is formed in a diaphragm
shape with the center much thinner. A set of
sensing resistors are attached around the perimeter
and measure the amount of flexing in response to
pressure.
• An electrical signal proportional to pressure is thus
obtained.
• Manifold pressure may be measured using piezoresistive sensors.
Potentiometers (1 of 2)
• A potentiometer is a threewire voltage divider that
varies its resistance in
response to mechanical
movement.
• Throttle position is
commonly measured using
a potentiometer.
• This sensor may be referred
to as the TPS (throttle
position sensor) or APP
(accelerator pedal position)
sensor.
Potentiometers (2 of 2)
• Zero accelerator pedal angle:
– Signal output is ± 0.2 volts.
– 0.0 volts would indicate an
open circuit.
• Maximum accelerator pedal
angle:
– Signal voltage is ± 4.8 volts.
• Between zero and full pedal
travel:
– Actual mechanical position will
produce a signal in proportion
to reference voltage.
• Loss of potentiometer ground:
– Signal voltage will equal
supply voltage. This is
interpreted as a short circuit.
Hall-effect Sensors
• A digital signal is produced
as windows and vanes on a
rotating pulse wheel pass
through a magnetic field.
• The pulse wheel
incorporates one narrow
window for relaying position
data.
• The frequency and width of
the signal provides the ECM
with shaft speed and
position data.
Induction Pulse Generator
• A disc known as a reluctor
with evenly spaced teeth is
rotated through a magnetic
field produced by a
permanent magnet.
• As the field alternately
builds and collapses, an AC
voltage is produced.
• The voltage changes in
frequency and amplitude in
proportion to speed
changes.
Switches
• Switches produce a digital signal by being
either open or closed.
• Toggle switches and coolant level sensors
are examples of switches used as sensors.
Data Processing Cycle (1 of 2)
Data Processing Cycle (2 of 2)
• Functions of the ECM
– Uses a CPU to clock and manage the processing
cycle
– Arithmetic logic unit (ALU) performs numeric
calculations
– Contains in memory banks the data required to
manage the system
– Conditions the processor circuit voltage
– Manages the reference signal
– Converts analog input data into a digital format using
an ADC (analog to digital converter)
– Converts digital output to analog voltages required to
actuate electrical components
Outputs
• The results of data processing are converted
into action by switching units (drivers) and
actuators.
• Examples of actuators are solenoids, relays,
lights, and displays.
SAE Hardware and Software Protocols
• SAE J1587
– Electronic data exchange protocols used in data exchange
between heavy-duty, electronically managed systems
• SAE J1708
– Serial communications and hardware compatibility protocols
• SAE J1939
– The set of standards incorporating both J1587 and J1708
• Separate J1939-compatible electronic systems can share
rather than duplicate common hardware using a common
language.
• J1939 will be updated by simply adding a suffix.
Multiplexing
• Multiplexing is used to network multiple
electronically managed systems.
– This avoids hardware duplication and
synergizes the operation of the system.
Data Retention
• Random access memory (RAM)
– Designed not to be overwritten
• Read-only memory (ROM)
– Sometimes described as a “personality
module” which calibrates the ECM to each
truck’s configuration
• Electronically erasable PROM (EEPROM)
– Contains customer data options and
proprietary data that can be altered using a
variety of electronic service tools
Collision Warning Systems
• Doppler effect
• Pulse radar
• VORAD collision detection system
–
–
–
–
–
–
–
Antenna assembly (AA)
Blind spot sensors (BSS)
Turn sensor assembly (TSA)
Central processing unit (CPU)
Driver display unit (DDU)
Blind spot display (BSD)
The VORAD cab
Summary (1 of 8)
• Data can be transmitted electronically by means of
electrical waveforms.
• Semiconductors are by definition elemental
materials with four electrons in their outer shells.
• Silicon is the most commonly used semiconductor
material.
• Semiconductors must be doped to provide them
with the electrical properties that can make them
useful as electronic components.
• After doping, semiconductor crystals may be
classified as having N or P electrical properties.
Summary (2 of 8)
• Diodes are two-terminal semiconductors that often
function as a sort of electrical one-way check valve.
• Zener diodes are commonly used in vehicle
electronic systems.
– They act as a voltage-sensitive switch in a circuit.
• Transistors are three-terminal semiconductor chips.
• Transistors can be generally grouped into bipolar
and field effect types.
Summary (3 of 8)
• Essentially, a transistor is a semiconductor
sandwich with the middle layer acting as a control
gate. A small current flow through the base-emitter
will ungate the transistor and permit a much larger
emitter-collector current flow.
• Many different types of transistors are used in
vehicle electronic circuits, but their roles are
primarily concerned with switching and
amplification.
• The optical spectrum includes ultraviolet, visible,
and infrared radiation.
Summary (4 of 8)
• Optical components conduct, reflect, refract, or
modify light. Fiber optics are being used
increasingly in vehicle electronics, as are optical
components.
• Integrated circuits consist of resistors, diodes, and
transistors arranged in a circuit on a chip of silicon.
• A common integrated circuit chip package used in
computer and vehicle electronic systems is a DIP
with either 14 or 16 terminals.
• Many different chips with different functions are
often arranged on a primary circuit board, also
known as a motherboard.
Summary (5 of 8)
• Gates are switched controls that channel flows of data through
electronic circuitry.
• AND, OR, and NOT gates are three commonly used means of
producing an outcome based on the switching status of
components in the gate circuit.
• The binary numeric system is a two-digit arithmetic system that
is often used in computer electronics because it directly
corresponds to the on or off states of switches and circuits.
• A bit is the smallest piece of data that a computer can
manipulate. It has the ability to show one of two states, either on
or off.
• A byte consists of 8 bits.
Summary (6 of 8)
• A byte of data can represent up to 256 pieces of coded data.
• Almost all current on-highway trucks use computers to manage
the engine and usually other chassis systems as well.
• A truck with multiple ECM-managed systems can network them
using a chassis data bus; this is known as multiplexing.
• A vehicle ECM information processing cycle comprises three
stages: data input, data processing, and outputs.
• RAM or main memory is electronically retained and therefore
volatile.
Summary (7 of 8)
• The master program for system management is
usually written to ROM.
• PROM data is used to qualify the ROM data to a
specific chassis application.
• Some OEMs describe their PROM component as a
personality module.
• EEPROM provides an ECM with a read/write/erase
memory component.
• Multiplexing is the term used to describe a system
where two or more ECMs are networked to reduce
input hardware and optimize vehicle operation.
Summary (8 of 8)
• Input data may be categorized as command data
and system monitoring data.
• A potentiometer is a common input component: It is
a three-terminal voltage divider.
• Collision warning systems (CWS) use a
combination of Doppler radar and motion sensors to
alert drivers to imminent collision hazards.
• A CWS such as VORAD processes data received
from radar and microwave motion/proximity sensors
into three categories of warning based on
programmed potential to cause an accident.