670 likes | 954 Views
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.
E N D
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 P-type 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 N-type 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 ± 0.6V. • 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)
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
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 piezo-resistive sensors.
Potentiometers (1 of 2) • A potentiometer is a three-wire 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.