1. Electronics and Computer Systems Fundamentals
Chapter 45

2. 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

3. 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

4. Semiconductors Can be a conductor or insulator Doping
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

6. Diodes One-way electrical check valve P-N junction Clamping diode
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

7. 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

8. Transistors (cont'd.) Biases Transistor never shuts off Zener diode
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

9. 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

10. 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

11. On-Board Computer Functions Hardware and software
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

12. Information Processing
Logic circuits: turn signals into output or store them in computer memory
Sensor information may be digital or analog

13. 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)

14. 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

15. Thermistors and Voltage Dividers
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

16. 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

17. Heated Resistive Sensors and Variable DC Frequency Sensors
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

18. 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

19. Wheatstone Bridges and Switches
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

20. 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

21. 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

22. Motor Actuators and Actuator Switches/Modules
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

23. Adaptive Strategy Keep alive memory (KAM) Adaptive fuel trim
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

24. 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

25. Electronic Throttle Control/ Drive-By-Wire
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

26. On-Board Diagnostics and Diagnostic Trouble Codes
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

27. 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

28. 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

29. Network Sizes and Types and CAN Systems
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

30. 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

31. 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