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.