PRACTICAL ELECTRONICS

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PRACTICAL ELECTRONICS

• MASTERCLASS
• (Mr Bell)

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Fault finding

• A fault is when a piece of equipment does not
  work the way it had been intended too.
• Fault finding is a job in itself, in which
  electricians need to dismantle broken equipment
  and find the fault and fix it.
• Faults can occur due to many reasons, such as-
• Broken components
• Surge in power
• Poorly soldered joints (dry-joint)

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Open and Closed Circuits

• Open circuit is when the normal electrical path
  of current in a circuit has been interrupted or
  broken. This can be caused by
• Faulty solder joints (dry joint)
• Broken wires or tracks
• Components missing or placed in incorrectly
  (LED?)
• Wrong value of components (resistors)
• Fuses blown
• Closed circuit When the electrical path of
  current can flow in an uninterrupted path and
  works like it was intended.

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Short Circuit

• Short circuit When the electrical path of
  current crosses over onto another unintended
  path. This can cause a higher level of current to
  flow in to components that could then damage it.
  
• Hence why we incorporate fuses, circuit breakers
  and earth wire in to electrical appliances, to
  prevent overloads in current.

• This circuit shows a blue track which has crossed
  over the circuit, bypassing the globe and
  decreasing the resistance in the circuit and
  increasing the current to a dangerous level,
  which could cause overheating and a fire. However
  the fuse would prevent this by breaking the
  circuit.

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Testing checklist what to do

• First understand how the circuit works, i.e. what
  each part does.
• Is the power supply switched on and is the
  polarity of the power supply correct.
• Inspect the circuit for obvious concerns, like-
• - Broken wires
• - missing components
• - fuses blown
• Is their power at each part of the circuit? (use
  multimeter)
• Check each component to see if current is
  travelling through it
• If it is a component, then replace one at a time
  and re-test after each replacement.
• Always keep a log of what you have done and think
  logically

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Multimeter

• Multimeters are very useful test instruments.
  They are multi, in that they can measure voltage
  (voltmeter), current (ammeter), resistance
  (ohmmeter) and be used as a continuity tester
  (establishing if an electrical path can be
  established).

LCD
Power button
Rotary switch
Red ammeter jack
Banana jacks
Black COM jack
Red voltmeter jack
Testing probes
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AC and DC settings

• Multimeters can measure both AC and DC
  current/voltage, but what does AC DC mean? And no
  its not the band.

AC means Alternating Current , which is current
or Voltage that changes direction, usually many
times in one second. This is used in wall
outlets in your house and power sockets. The
symbol on the multimeter is a wave symbol.
DC means Direct Current, which is current or
Voltage that always flows in one direction ( to
-). This is what batteries use and it is what we
will use in the classroom. The symbol on the
multimeter is a straight line with a dotted line
below it.
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What is resistance?

• Resistance is how difficult it is for electricity
  to flow through something.
• The higher the resistance the more difficult it
  is for electricity to flow.
• A resistor is used to resist current to an LED.
• Resistance is measured in ohms.
• Named after Georg Ohm (German physicist and
  mathematician) in 1854.
• The symbol for ohms is ? (the capital Greek
  letter for omega).

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What is voltage?

• Voltage is how hard electricity is being pushed
  through a circuit.
• The higher the voltage, the harder the
  electricity is being pushed.
• Voltage is measured in volts.
• It is named after Alessandro Volta (Italian
  physicist) in 1880.
• The symbol for volts is V.
• Alessandro also invented the first battery.

Circuit Symbol
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What is current?

• Current is how much electricity is flowing
  through the circuit.
• The higher the current, the more electricity is
  flowing.
• Current is measured in amperes.
• Named after André-Marie Ampère in 1836
  (mathematician and physicist)
• The symbol for amperes is A.

Circuit Symbol
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Measure the current for resistor A, B and C

• Keep the crocodile clips and battery connected
• Record your measured values in your log book
• Remember to write in your units

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Continuity tester

• The multimeter can also be used as a continuity
  tester.
• This allows you to determine if an electrical
  path exists.
• Used to help test for open, closed and short
  circuit conditions.

• Turn the rotary switch to
• Insert the black lead into the COM socket
• Insert the red lead () into the V? socket