1. Basic Electricity/Electronics
Computer Maintenance
Basic Electricity/Electronics
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2. Summary Slide Parts of an Atom Types of Electrical Materials
Measuring Electricity
Using a Multimeter to Make Resistance Measurements
Using a Multimeter to Make Voltage Measurements
Signals and Noise in Communication Systems
Measuring Analog Signals
Digital and Analog Signaling
Simplex, Half-Duplex, and Full Duplex Transmission
Baseband and Broadband
Signaling and Communications Problems
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Computer Maintenance: Electronics/BasicElectricity

3. Parts of an Atom
nucleus - the center part of the atom, formed by neutrons and protons
protons - particles have a positive charge, and along with neutrons, form the nucleus
neutrons – particles have no charge (neutral), and along with protons, form the nucleus
electrons - particles have a negative charge, and orbit the nucleus
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Computer Maintenance: Electronics/BasicElectricity

4. Types of Electrical Materials
Insulators - high resistance to electrical current
plastic, glass, air, wood, paper, rubber
Conductors - conducts the flow of electrons
Copper, silver, gold
Semiconductors - control the flow of electrons
carbon, silicon
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Computer Maintenance: Electronics/BasicElectricity

5. Measuring Electricity
Voltage (V) - electrical force or pressure that occurs when electrons and protons are separated
The force that is created pushes toward the opposite charge and away from the like charge.
Voltage can also be created by friction (static electricity), by magnetism (electric generator), or by light (solar cell).
unit of measurement is VOLT
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Computer Maintenance: Electronics/BasicElectricity

6. Measuring Electricity
Current (I)—the measurement of electron flow in an electrical circuit
unit of measurement is AMPERE (amp)
Resistance (R)—amount of opposition to current
unit of measurement is the OHM ()
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Computer Maintenance: Electronics/BasicElectricity

7. Measuring Electricity
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Computer Maintenance: Electronics/BasicElectricity

8. Measuring Electricity
Electricity is brought to your home, school and office by power lines.
The power lines carry electricity in the form of alternating current (AC).
Another type of current called direct current (DC), can be found in flashlight batteries, car batteries, and as power for the microchips on the motherboard of a computer.
It is important to understand the difference between these two types of current.
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Computer Maintenance: Electronics/BasicElectricity

9. Measuring Electricity
Alternating Current (AC)
Flows in two directions
Direct current (DC)
Flows in one direction only
Impedance (Z) – measured in ohms (Ω)
Total opposition to current flow (due to AC and DC voltages)
Resistance – generally used when referring to DC voltages.
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Computer Maintenance: Electronics/BasicElectricity

10. Measuring Electricity
Current flows through closed loops called circuits.
These circuits must be composed of conducting materials and have sources of voltage.
The three required parts of an electrical circuit are
Source or battery
Complete path
Load or resistance
Voltage causes current to flow while resistance and impedance oppose it.
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Computer Maintenance: Electronics/BasicElectricity

11. Measuring Electricity
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Computer Maintenance: Electronics/BasicElectricity

12. Measuring Electricity
For AC and DC electrical systems, the flow of electrons is always from a negatively charged source to a positively charged source.
For the controlled flow of electrons to occur, a complete circuit is required.
Electrical current generally follows the path of least resistance.
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Computer Maintenance: Electronics/BasicElectricity

13. Measuring Electricity
Because metals such as copper provide little resistance, they frequently are used as conductors for electrical current.
Materials such as glass, rubber, and plastic provide more resistance; they are not good conductors and are generally used as insulators.
The purpose of connecting the safety ground to exposed metal parts of computing equipment is to prevent such metal parts from becoming energized with a hazardous voltage from a wiring fault inside the device.
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Computer Maintenance: Electronics/BasicElectricity

14. Using a Multimeter to Make Resistance Measurements
A multimeter can be used to measure:
Voltage
Resistance
Continuity
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Computer Maintenance: Electronics/BasicElectricity

15. Using a Multimeter to Make Resistance Measurements
If you intentionally make a path into a low-resistance path for use by two connected electrical devices, then the path has continuity.
If a path is made unintentionally into a low-resistance path, then it is called a short circuit.
The unit of measurement for both is the OHM (Ω).
Continuity refers to the level of resistance of a path.
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Computer Maintenance: Electronics/BasicElectricity

16. Using a Multimeter to Make Resistance Measurements
You can perform measurements on the following:
CAT 5 cable
Terminated CAT 5 cable
Terminated coaxial cable
Telephone wire
CAT 5 jacks
Switches
Wall outlets
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Computer Maintenance: Electronics/BasicElectricity

17. Using a Multimeter to Make Voltage Measurements
Two types of voltage measurement exist: DC and AC.
The meter must be set to DC when measuring DC voltages. This includes the following:
Batteries
Outputs of computer power supplies
Solar cells
DC generators
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Computer Maintenance: Electronics/BasicElectricity

18. Using a Multimeter to Make Voltage Measurements
Two types of voltage measurement exist: DC and AC.
The meter must be set to AC when measuring AC voltages.
If you measure a wall socket, you must assume that line voltage is present.
Line voltage is 120 V AC in the US and 220 V AC in most other places around the world
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Computer Maintenance: Electronics/BasicElectricity

19. Signals and Noise in Communication Systems
The term signal refers to a desired electrical voltage, light pattern, or modulated electromagnetic wave.
Signals can be created as:
Electrical pulses that travel over copper wire.
Pulses of light that travel through strands of glass or plastic.
Radio transmissions that travel over the airwaves.
As laser or satellite transmissions.
As infrared pulse.
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Computer Maintenance: Electronics/BasicElectricity

20. Signals and Noise in Communication Systems
Two main types of signaling (Analog and Digital).
Analog
Change gradually and continuously (will have a continuously varying voltage – versus – time graph).
Typical of things in nature
Used widely in telecommunications for more than 100 years
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Computer Maintenance: Electronics/BasicElectricity

21. Signals and Noise in Communication Systems
Two main types of signaling (Analog and Digital). (Continued)
Digital
Change one state to another almost instantaneously, without stopping at an in-between state.
Discrete or jumpy
Typical of technology instead of nature
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Computer Maintenance: Electronics/BasicElectricity

22. Measuring Analog Signals
Analog signals are measured in cycles, with one cycle representing the change from high to low and back again.
Three characteristics are measured:
Amplitude
Frequency
phase
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Computer Maintenance: Electronics/BasicElectricity

23. Digital and Analog Signaling
Digital signaling is the most appropriate format for transmitting computer data, and most networks use digital signaling methods for that reason.
Because it is a simpler technology, digital signaling has some advantages over analog:
Generally less expensive to make digital equipment
Generally less vulnerable to errors caused by interference because the discrete state of on and off is not as easily affected by a small distortion as is a continuous wave form.
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Computer Maintenance: Electronics/BasicElectricity

24. Digital and Analog Signaling
Analog signals also have advantages:
Signals can be easily multiplexed; that is signals can be combined to increase bandwidth.
Signals are less vulnerable to the problem of attenuation (signal loss due to surroundings), because of distance so they can travel farther without becoming too weak for reliable transmission.
However, when an analog signal is amplified, the noise is amplified with the signal.
Digital connectivity solutions generally offer better security, faster performance, and higher reliability.
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Computer Maintenance: Electronics/BasicElectricity

25. Simplex, Half-Duplex, and Full Duplex Transmission
Simplex Transmission
Unidirectional – signal travels in only one direction.
Television is an example.
Half-Duplex Transmission
Signal can travel in both directions but not at the same time.
Full-Duplex Transmission
Signal can travel in both directions at the same time
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Computer Maintenance: Electronics/BasicElectricity

26. Baseband and Broadband
The entire capacity of an Ethernet cable is used for transmitting the data in one channel. This makes Ethernet a BASEBAND technology.
A channel is an allocated portion of the media’s available bandwidth.
The signal has the benefit of having the entire bandwidth to itself.
BASEBAND is usually associated with digital signaling (although it can be used with analog).
Most computer communications are baseband.
BASEBAND signal is bidirectional; the signal can flow both ways so you can transmit and receive on the same cable.
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Computer Maintenance: Electronics/BasicElectricity

27. Baseband and Broadband
BROADBAND technologies allow for dividing the capacity of a link into two or more channels, each of which can carry a different signal.
All channels can send simultaneously.
ISDN is an example of BROADBAND technology because multiple signals can be carried over separate channels on a single wire.
DSL is another example of a BROADBAND technology because date and voice can travel simultaneously over the same line.
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Computer Maintenance: Electronics/BasicElectricity

28. Signaling and Communications Problems
Propagation
Travel time; speed depends upon medium.
As data transmission rates increase, you must sometimes take into account the amount of time it takes the signal to travel.
Attenuation
Loss of signal over distance due to surroundings.
Can affect a network because it limits the length of network cabling over which you can send a message.
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Computer Maintenance: Electronics/BasicElectricity

29. Signaling and Communications Problems
Reflection
Caused by discontinuities in the medium
Occurs in electrical signals; can be result of kinks in cable or poorly terminated cables.
Networks should have a specific impedance to match the electrical components in the Network Interface Cards (NICs).
The result of impedance mismatch is reflected energy.
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Computer Maintenance: Electronics/BasicElectricity

30. Signaling and Communications Problems
Noise
Unwanted additions to optical/electromagnetic signals.
Crosstalk – electrical noise from other wires in a cable.
EMI (electromagnetic interference) can be caused by electric motors.
Cancellation of signals can be avoided through the twisting of wire pairs to provide self-shielding within the network media.
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Computer Maintenance: Electronics/BasicElectricity

31. Signaling and Communications Problems
Timing problem
Dispersion – signal broadens in time.
Can be fixed by proper cable design, limiting cable lengths, and finding the proper impedance.
Jitter – source and destination not synchronized.
Can be fixed through hardware and software including protocols.
Latency – delay of network signal.
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Computer Maintenance: Electronics/BasicElectricity

32. Signaling and Communications Problems
Collisions
Occurs when two bits from different communicating computers are on a shared medium at the same time.
Excessive collisions can slow the network.
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Computer Maintenance: Electronics/BasicElectricity

33. Summary Slide Parts of an Atom Types of Electrical Materials
Measuring Electricity
Using a Multimeter to Make Resistance Measurements
Using a Multimeter to Make Voltage Measurements
Signals and Noise in Communication Systems
Measuring Analog Signals
Digital and Analog Signaling
Simplex, Half-Duplex, and Full Duplex Transmission
Baseband and Broadband
Signaling and Communications Problems
UNT in partnership with TEA, Copyright © . All rights reserved.
Computer Maintenance: Electronics/BasicElectricity