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Chapter 17

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  1. Chapter 17 Computer System Fundamentals

  2. Contents • Cybernetics • Computer advantages • Digital electronics • Integrated circuits • Computer signals • Computer system operation • Sensors • Computers • Actuators

  3. Computer • Complex electronic device that will produce programmed electrical output signals after receiving specific electrical input signals • Computers monitor and control all major systems of a modern vehicle

  4. Cybernetics • Study of how electrical-mechanical devices can duplicate the action of the human body • Comparing the human body to a computer system is an easy way to explain this subject

  5. Cybernetics

  6. The Nervous System • Uses chemical-electrical signals to control the body • If you touch a sharp needle, nerve cells in your finger “fire” and send a signal through a strand of nerve cells in your hand, up your arm, and into your brain • Nerve cells in your finger are comparable to a sensor, or input device, in a computer system

  7. The Brain • Uses billions of cells interconnected by linking cells called neurons • When the brain “thinks”, minute electrical impulses travel from neuron to neuron • Cells in the brain can be either charged (on) or not charged (off)

  8. The Brain • By connecting all the brain cells, the brain can decide what to do in each situation • Computers produce logical outputs in a similar fashion

  9. The Reflex Action • Specific brain cells are activated by the needle prick (pain) signal, and a reflex output is produced • The brain sends a signal to your arm to pull back • This is similar to the action of an actuator, or output device, in a car’s computer system

  10. Computer Advantages • There are several reasons that computers are being used in modern vehicles • Computers can provide several advantages

  11. Computer Advantages • Fewer moving parts to wear and go out of calibration • Reduced fuel consumption • Lower emissions • Increased engine power • Reduced vehicle weight

  12. Computer Advantages • On-board diagnostics • Increased driver convenience • Improved passenger safety • Compensation for component wear

  13. Digital Electronics Field of study dealing with the ways a computer uses on-off signals to produce “artificial intelligence”

  14. Binary Numbering System • Uses only two numbers, zero and one • Key to how computers operate • Zero (0) and one (1) can be arranged in different sequences to represent other numbers, letters, words, an input, an output, or a condition

  15. Binary Numbering System • To use the binary system, a computer turns switches (transistors) on or off • Off represents zero • On represents one

  16. Binary Numbering System

  17. Binary Numbering System Binary numbers can be converted into decimal (base ten) numbers

  18. Binary Language • A single zero or a one is called a bit • Four bits make a nibble • Eight bits make a byte or word

  19. Gating Circuits • Gate • electronic circuit that produces a specific output voltage for given input voltages • Common gate types: • NOT • AND • NAND • OR • NOR

  20. NOT Gate

  21. AND Gate

  22. NAND Gate

  23. OR Gate

  24. NOR Gate

  25. Truth Table Shows what the output of a gate will be with different inputs

  26. “Thinking” with Gates If an AND gate is compared to two switches wired in series, both switches must be on to activate the starter motor

  27. Using Gates • Logic gates can be connected together to form super-complex circuits • Millions of gates can be interconnected to produce thousands of programmed outputs from numerous inputs • This is how a computer works, or thinks

  28. Integrated Circuits Electronic circuits that have been reduced in size and etched on the surface of tiny semiconductor chips

  29. Integrated Circuit • Different semiconductor substances are deposited on a silicon chip and then etched to produce resistors, diodes, and transistors • Metal conductors on the top of the chip connect these various electronic components to form the circuit • Wire leads allow for input and output connections

  30. Integrated Circuit Wire leads connect the chip to the metal pins. The pins plug into or are soldered to other parts of the circuit.

  31. Integrated Circuit A digital IC uses logic gates. An analog IC increases output strength or alters output.

  32. IC Construction The circuit has been photographically reduced in size, etched on a silicon chip, and placed in a protective plastic case

  33. Computer Signals • Computer signal • voltage variation over short periods of time • specific arrangement of pulses or waves used to carry data, or information • Computer signals can be digital or analog

  34. Digital Signal On-off signal like that is produced by a rapidly flipping switch

  35. Digital Signal A digital waveform as seen onan oscilloscope

  36. Analog Signal Gradually changes in strength like the output from a dimming switch

  37. Analog Signal An analog waveform as seen onan oscilloscope

  38. Scoping a Magnetic Sensor

  39. Electrical Waveforms

  40. Signal Frequency • How fast a signal changes over time • High-frequency signal • short pulse width • Low-frequency signal • long pulse width

  41. Signal Frequency Measured in cycles per second (hertz)

  42. Signal Amplitude Voltage level present in the waveform

  43. Duty Cycle Percentage of on-time comparedto total cycle time

  44. Computer System Operation • There are three stages of computer system operation: • input • processing and storage • output

  45. Inputs and Outputs

  46. Computer System Block Diagram • Service manual drawing that shows how the sensors, the actuators, and the computer interact • Useful when trying to find out what types of sensors are used and what conditions are controlled

  47. Computer System Block Diagram Fig 18

  48. Sensors • Most vehicle sensors, or transducers, change a physical condition into an electrical signal • Transduce: • to change from one form to another

  49. Sensor Locations • Sensors can be found almost anywhere on a vehicle: • on the engine • on or in the transmission or transaxle • in the exhaust system • on the wheel hubs • on and in the fuel tank • on the suspension • in the trunk

  50. Sensor Locations Some of the sensors located on the engine and transaxle