Electronics and Computer Systems Fundamentals

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 • 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-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 • 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 • 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 • 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

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 • 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

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 • 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

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 • 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

23. 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

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 • 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

26. 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

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 • 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

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