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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. 6 V. – 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.
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 J 1587 – Electronic data exchange protocols used in data exchange between heavy-duty, electronically managed systems • SAE J 1708 – Serial communications and hardware compatibility protocols • SAE J 1939 – The set of standards incorporating both J 1587 and J 1708 • Separate J 1939 -compatible electronic systems can share rather than duplicate common hardware using a common language. • J 1939 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.