Electronics and Computer Systems Fundamentals

© 2012 Delmar, Cengage Learning

Electronics and Computer Systems Fundamentals

Chapter 45


Objectives• Describe the operation of various

semiconductors• Understand how computers operate• Explain the operation of various types of

sensors and actuators• Compare the different types of computer

memory• Summarize the various guidelines of on-board

diagnostics


Introduction• Electronics is the science of using small

amounts of electricity to control larger amounts– All laws of basic electricity apply

• Emphasis of this chapter is the operation of:– Semiconductors– Computers– Sensors– Actuators


Semiconductors• Can be a conductor or insulator

– Crystalline structure• Doping

– Small amount of impurity added to crystal• Circuit can pass through• N-type: five or more electrons in outer valence ring• P-type: three electrons in outer valence ring

• Electrons flow from negative to positive– Semiconductors are designed to handle a limited

amount of current



Diodes• One-way electrical check valve

– P-type and N-type crystals placed back-to-back• P-N junction

– Allows current to pass when voltage greater than 0.5 to 0.7 volt

• Forward bias diodes allow current to flow• P-N junction empty: current flow stops

• Clamping diode – Installed parallel to coil– Provides an alternate electrical path


Transistors• Turn electrical circuits on and off

– Controlled by another electrical circuit• Semiconductor crystal layers

– Emitter, base, and collector• Bipolar transistors

– Used in automobiles– Polarities: electrons and holes

• Electrical current – Cannot move across transistor layers unless

voltage applied to base


Transistors (cont'd.)• Biases

– Forward bias: allowing current to flow– Reverse bias: voltage removed from base

• Transistor never shuts off– Current flows from base or collector– Can regulate at 10,000 times per minute

• Zener diode – Crystals are more heavily doped – Halt current below a certain voltage– Controls backwash or double bounce of voltage


Electronic Instrument Displays• Light emitting diodes

– Crystal glows when current flows through it• Use more power than other display types• Less power than ordinary bulbs

• Liquid crystal displays– Liquid and glass with conductive coating

• Light can pass through when voltage is applied• Vacuum fluorescent displays

– Glass tubes filled with argon or neon gas• Current causes tube to glow


Automotive Computer Systems and Parts of a Computer System

• Integrated circuit – Complete miniature electric circuit

• Chip– Tiny sandwiched silicon wafers of P-type or N-

type material– As many as 30,000 transistors placed on a chip

• Main parts to computer systems– Computer– Sensors– Actuators


On-Board Computer• Functions

– Gather input– Make decisions and process information– Store information– Take action by way of output command

• Hardware and software– Items that make up a computer system

• Computer electrical control– Ground and logic side switching


Information Processing• Logic circuits: turn signals into output or store

them in computer memory– Sensor information may be digital or analog


Computer Memory and Communication Rate

• Microprocessor reads and writes to memory– Temporary information: stored in random access

memory (RAM)• Volatile: erased when ignition turned off

– Read-only memory (ROM): permanently programmed into chip during manufacturing

– Programmable read-only memory (PROM): specific program for one function of vehicle

• Time between one crystal pulse– One bit of information is transmitted (i.e., baud rate)


Sensors, Actuators, and Types of Sensors

• Sensors monitor engine functions – Modify voltage signals that return to computer

• Actuator – Electronic or magnetic relay

• Transducer – Converts energy from one form to another

• Types of sensors– Variable resistors and variable DC frequency– Variable voltage generators and switches– Variable AC voltage/frequency generators


Thermistors and Voltage Dividers

• Thermistor – Variable resistor made from semiconductor

material• Resistance changes with temperature

• Voltage dividers – Variable resistors that produce variable DC

voltage signal– Potentiometer: three-terminal variable resistor

• Measures linear or rotary motion– Rheostat: carries current


Piezoelectric and Piezoresistive Sensors

• Piezoelectric crystals: develop voltage on their surface when pressure applied– Used as switches for measuring pressure in

engine oil, power steering, or air-conditioning• Piezoresistive sensor: used in MAP sensors

– Silicon diaphragm sealed to a quartz plate– Doping creates four resistances around edges of

diaphragm– Pressure deflected from diaphragm– Causes a change in resistance of resistors


Heated Resistive Sensors and Variable DC Frequency Sensors• Heated resistive sensor

– Monitors the amount of air taken into the engine– Computer applies current to maintain wire

temperature– From the current, the computer calculates

amount of airflow into engine• Frequency sensors

– Used for same things– Produce digital signal


Voltage Generators• Voltage generating sensors

– Have no reference voltage but create their own– Variable AC voltage generator

• Magnetic pickup generates an AC analog signal– Pulse generators

• Signal generators– Oxygen sensor

• Variable CD voltage generator– Knock sensor

• Piezoelectric crystal senses vibration and creates voltage signal


Wheatstone Bridges and Switches

• Wheatstone bridges– Two simple series circuits connected in parallel

across battery power on its way to ground– Used by a hot wire MAF sensor

• Switches– Switch-to-power– Switch-to-ground– Hall-effect


Types of Actuators• Act upon processed signals received from the

computer– Solenoids– DC motors– Relays– Switches– Control Modules

• Output drivers: supply actuators with ground – Without ground the actuator does not work

• Quad driver: controls up to four transistors


Solenoid Actuators and Relay Actuators

• Solenoid: magnetic switch– Uses for solenoids

• Fuel injectors• Electronic transmissions• EGR vacuum control

• Relay actuators– Trigger operation of high-current load devices– Normally open relay: open until energized– Computer controls ground side of relay

• Current can pass through when grounded


Motor Actuators and Actuator Switches/Modules

• Motor actuator– Example: idle speed control motor – Types of idle motors

• Fuel injection with idle air control motor• Actuator switches/modules

– Example: ignition module – Other modules control the operation of cruise

control and the air-conditioning compressor


Adaptive Strategy• Keep alive memory (KAM)

– Computer maintains power to RAM when ignition switch is off

• Keeps information as long as battery connected• Computer compensates for wear and aging

• Adaptive fuel trim – Varies fuel system to operate at correct ratio

• Short-term fuel trim: short-term correction in air-fuel mixture during closed loop

• Long-term fuel trim: makes long-term corrections


Knock Sensor• Computer advances timing until engine knocks

– Retards the timing until knock goes away• Searches for best timing settings

– Rpm, load, temperature, and fuel– Stores the best setting in memory


Electronic Throttle Control/Drive-By-Wire

• Electronic throttle control – Module receives accelerator pedal position

signal• Controls electric motor attached to throttle plate• Inputs include how fast pedal depressed or

released– Provides better drivability, fuel economy, and

lower emissions– Cruise control may be part of the system


On-Board Diagnostics and Diagnostic Trouble Codes

• On-board diagnostics– Computer has diagnostic capabilities

• Universal data link connector (DLC) for reading trouble codes

• Universal generic scan tool • Diagnostic trouble codes

– Universal diagnostic trouble codes (DTC)• Stored in computer’s non-volatile RAM• Battery supplies power to computer for memory


Computer Self-Diagnostics• Computers diagnose the majority of electronic

system faults– MIL comes on while car is running: fault code is

stored – Hard faults: present and stored in memory during

self-test– Intermittent fault code: only occurs occasionally

for a short time and is not present in the system at the time of the fault test


Multiplexing• Average vehicle has 16 electronic control units

– Multiplexing (MUX) allows control modules to communicate

• Twisted pair wiring – Reduces interference from other circuits

• Protocol – Language used by modules to communicate– Gateway module allows communication from

slower to faster modules


Network Sizes and Types and CAN Systems

• Networks– Wide area network (WAN)– Local area network (LAN)– Controller area network (CAN)

• CAN systems– Messages: diagnostic mode and normal mode– Manufacturers use different CAN system designs– Topology describes the physical network

makeup– CAN chip manages information transfer


Supplemental Data Bus Networks

• Provide additional support to main bus network– Media-oriented system transport (MOST)

• Connects audio and video components• Lowers manufacturing costs• Minimizes wiring harnesses

– System information carried by fiber optics• Capable of higher speeds than ordinary networks• Plastic or glass fibers• Transmits light waves free of electrical noise• Light signals transmitted between LED, photodiode,

and transceiver


Telematics and Wireless Networks

• Telematics blends computers and wireless communications– Example: General Motors OnStar

• Wireless networks transmit without wires– Tire pressure information monitor – Bluetooth™: wireless personal area network

• Allows communication between modules using standard radio transmissions

– DSRC: dedicated short range communications• Links vehicles to each other and roadside access

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Electronics and Computer Systems Fundamentals