CH22 basics of electronics and computer systems STUDENT VERS

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Chapter 22

Basics of Electronics and Computer Systems

• Stores and releases electrical energy

• Can smooth current fluctuations

• Store and release high voltage

• Can block DC voltage

• Can release all stored energy in an instant

• Used as noise filters

Capacitors (cont’d)

• Each terminal is

connected to a plate

• Voltage applies

equally to each plate

but with opposite

charge

• Once charged, has

same voltage as

source

• Can be a conductor or an insulator

• No moving parts

• Often used as a switching device

• Common uses are diodes and transistors

• Do not loose/gain electrons like conductors

• Share outer electrons with each other

P-Type Semiconductor

• Only allow current flow in one direction

• AC in generator is rectified by diodes

• Emit light as current passes through them

• Light color depends on material used to make the LED

• Used as a switching device

• Are made up of three sections:

Integrated Circuits

• One diode or transistor is limited in what tasks can be done

• Many semiconductors combined can

perform complex functions

• Integrated circuits are combinations of diodes, transistors, and other electronic components

Computer Basics

• Once mechanically controlled systems now computer controlled

• Electronic systems made up of sensors,

actuators, and control unit

• Two main control units are the powertrain control module (PCM) and body control

module (BCM)

• All inputs have same basic function – detect

a mechanical condition and change it into

an electrical signal to be used by a

computer

• Each sensor has a specific job

• All sensors are either reference voltage

sensors or voltage generating sensors

Reference Voltage Sensors

• Computer sends a constant voltage to the

sensor

• The sensor reacts and sends a voltage signal back to the computer

• Reference voltage is normally 5 to 9 volts

• Most are variable resistors or

potentiometers

Wheatstone Bridges

• Used to measure temperature

• Also used to measure pressure and mechanical strain

• Common switch inputs:

– Brake pedal position, A/C request, defroster

Voltage Generating Sensors

Magnetic Pulse Generators

• Also called permanent magnet generators

• Use magnetic induction

• Used for speed information:

– Engine RPM

– Crank/cam position

– Wheel speed

– Cruise control

Hall-Effect Switch

• Performs the same function as a PM generator

Communication Signals

• Voltage is used as a signal:

– Differences in voltage levels

– Frequency of change

– Switching from positive to negative values

• Computers can read these signals

• Signals can be analog or digital

• Analog signals must be converted to digital

Duty Cycle versus Pulse Width

• Duty cycle is a measurement of the amount

of time something is on compared to the

time of one cycle and is measured in a

percentage

Pulse Width

• Similar to duty cycle except it is the exact time something is turned on, measured in milliseconds

• Modules, sensors, and other components must communicate correctly

• To eliminate wires to and from each

module, multiplexing is used

• In-vehicle networking

• A serial data bus connects modules

• Each module has an ID

Low or Medium CANs

High Speed CANs

• Engine management

• Antilock brake systems

• Transmission control

• Tire pressure monitoring system

• Vehicle stability control

• The BCM is a common gateway module.

• Each CAN bus uses a different voltage

Protecting Electronic Systems

• Avoid jump starting

• Do not connect/disconnect with key on

• Never touch electrical contacts

• Be aware of electrostatic discharge warnings

• Touch ground to discharge static electricity

• Use static-proof work mats inside vehicles

Protecting Electronic Systems

(cont’d)

• Use grounding wrist straps

• Never allow grease, lubricants, or solvents

to touch sensors or connectors

• Do not damage connectors or terminals

when removing components

• Identify correct terminals for testing

Testing Electronic Circuits and Components

• Lab scope can be used for voltage, pulse and duty cycle

• AC voltages using a DMM

– Most meters display average, some show RMS

• Checking diodes

– Many DMMs can check diodes

– Voltage drop typically 500 – 600 mV

• A one farad capacitor can store one

coulomb at one volt

• One coulomb = 6.25 billion billion (6.25 x

1018 ) electrons

• One amp equals one coulomb per second

• A one farad capacitor can store one second of electrons at one volt