Hardware Basics

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Hardware Basics
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Electricity

• Electricity is the flow of electrons
• Atoms contain
• In the nucleus (center)
• Protons with a positive charge
• Neutrons with no charge (no consequence here)
• Orbiting around the nucleus
• Electrons with a negative charge

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Charged Atoms

• Atoms with more protons that electrons
• Positively charged
• Try to acquire additional electrons to get back
  in balance
• Atoms with more electrons than protons
• Negatively charged
• Want to give up electrons to get back in balance
• If you set up an imbalance, electrons will try to
  jump (flow) between atoms to correct this
• This flow is electricity

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Conductors and Insulators

• Materials that allow electrons to flow easily are
  conductors
• Most metals are good conductors
• Materials that dont allow electrons to flow
  easily are insulators
• E.g., plastic, rubber, glass
• Some materials can be influenced to change from
  conducting to insulating (a very useful property)
• Semiconductors

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Basic Law of Charges

• Like charges repel each other
• Opposite charges attract each other
• Exert a force
• Can do work e.g., move something

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Charge

• Charge is measured in Coulombs ( C )
• (A unit we wont use much)
• Measure of how many more protons than electrons
  in a substance
• 1 Coulomb 2.15 x 1018 excess protons

2.15 x 1018 extra electrons -1 C
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Electromotive Force(Voltage)

• Charge has the ability to do work
• A potential to e.g. move something in one
  direction or another
• Difference in potential (in charge) provides a
  force Electromotive Force (EMF) Voltage

Extra electrons

EMF (voltage)
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Flow of electrons
Conductor

• If this is a conductor then ½ the excess
  electrons will very rapidly flow to the other end
  to balance the charge

Extra electrons

EMF (voltage)
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Flow of electrons
Conductor

• If this is a conductor then ½ the excess
  electrons will very rapidly flow to the other end
  to balance the charge

½ the extra electrons
0 voltage
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Flow of electrons
Conductor

• If this is a conductor then ½ the excess
  electrons will very rapidly flow to the other end
  to balance the charge
• And then things are not very interesting

½ the extra electrons
0 voltage
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Flow of electrons

• If this is a conductor then ½ the excess
  electrons will very rapidly flow to the other end
  to balance the charge
• And then things are not very interesting
• Hence we set up circuits (cycles, loops) to keep
  this going

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Flow of Electrons

• Current is the flow of electrons
• Measured in Amperes (Amp, or A)
• 1A is 1 Coulomb of charge flowing past a point
  per second

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Current vs. Voltage

• Water analogy
• Useful, but only goes so far
• Coulombs analogous to quantity (gallons)
• Amps analogous to flow rate (gallons / sec)
• Voltage analogous to pressure (lbs/ft2)

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Resistance

• Can have a lot of flow at low pressure or a lot
  of pressure but low volume
• Depends on the size of the pipe
• Resistance is analogous to the size of the pipe
• Resistance is the opposition to current flow
• Measured in Ohms ( O )

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Ohms Law

• Relates current, voltage, and resistance
• Current normally denoted by variable I
• Voltage normally denoted by variable V
• Resistance normally denoted by variable R
• V I R

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Ohms Law

• V IR
• R V / I
• I V / R

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Ohms Law

• In the electronics we will do, we tend to (try
  to) hold the voltage constant (or zero)
• Typically 5v
• starting to use 3.3v, but 5v still most common
• I V / R I 5 / R
• Raise the resistance, current drops
• Lower the resistance, current rises

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Ohms Law

• I V / R I 5 / R
• Raise the resistance, current drops
• Lower the resistance, current rises
• What happens if we lower the resistance towards
  zeros?

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Ohms Law

• I V / R I 5 / R
• Raise the resistance, current drops
• Lower the resistance, current rises
• What happens if we lower the resistance towards
  zeros?
• Current goes towards infinity
• Power V I (related to heat)
• Boom! (or Poof!)

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Current Limiting

• Important
• This is how you (literally) fry hardware if you
  dont pay attention (trust me, I know)
• Always think carefully (and check!) that the path
  from 5v source
• From power supply, or from output pin of a chip
• to ground (0v location) has appropriate
  resistance
• Not a short circuit 0O
• Current limiting resistor at value needed to stay
  within current limits of the device

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Aside Units

• Volts, Amps, Ohms
• Normally use metric system unit prefixes
• mega M million 1,000,000 106
• kilo k thousand 1,000 103
• one 1 100
• milli m thousandth 0.001 10-3
• micro µ millionth 0.000 001 10-6
• nano n billionth 10-9
• pico p trillionth 10-12

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Examples

• 5V with 10O ? 5/10 A 0.5A 500mA
• For typical chips you will use Poof!
• 5V with 100O ? 5/100 A 50mA
• Still Poof!
• 5V with 250O ? 5/250 A 20mA
• OK for PIC processors, not for lots of other
  digital electronics
• 5V with 10kO ? 5/10000 A 0.5mA
• Good for most digital electronics

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Schematic Diagrams xx

• Wire, connection, cross, hop-over
• Resistor, variable resistor (pot, rheostat)
• Battery, switch
• Capacitor, electrolytic capacitor
• Diode, LED
• Transistor (PNP, NPN)
• Inductor, transformer
• Integrated circuit

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Schematic Diagrams
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AC vs. DC

• DC Direct Current
• Current flows steadily in one direction
• Most of what we will do is DC
• AC Alternating Current
• Current flows in one direction then another
• Wall current does this
• Alternating 60 times per sec
• 60 Hz

V
V
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Capacitance

• Capacitor
• Device with two conducting plates separated by
  insulating material (called dielectric)
• Stores electric charge in the dielectric
• Water metaphor
• Consider a pipe with a rubber balloon blocking it
• DC current bulges out the balloon (charges the
  capacitor)
• But then stops flowing
• Release the pressure the charge drains back out
  over time
• AC current can go back and forth continuously
• Capacitor blocks DC but allows AC to pass

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Capacitance

• Capacitance is measured in Farads ( F ) and
  denoted by variable C
• Amount of charge divided by voltage across plates
• Charge (in Coulombs) denoted by Q
• C Q / V

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Series and Parallel Circuits

• Series circuit
• Parallel circuit

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Series and Parallel Circuits

• Combining resistors
• Rtotal-series R1 R2
• Rtotal-par (R1 R2) / (R1 R2)

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Series and Parallel Circuits

• Combining capacitors
• Ctotal-series (C1 C2) / (C1 C2)
• Ctotal-par C1 C2

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Digital Electronics

• Computer circuits treat signals as digital values
• Consider signals to only have two states 1 or 0
• 5v is considered to be 1
• 0v is considered to be 0

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Digital Electronics
5v

• But need to leave some room for error or
  fluctuation
• Between VHMin and 5v considered 1
• Between 0v and VLmax considered 0
• Between VLmax and VHMin is undefined (and
  unpredictable)
• Can pass through this but you dont want to stay
  there long

1
VHMin
??
VLmax
0
0v
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