Transcript Slides12-hardware

Hardware Basics
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
-
-
++
+
-
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
Conductors and Insulators
• Materials that allow electrons to flow easily are
conductors
– Most metals are good conductors
• Materials that don’t 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
Basic Law of Charges
• Like charges repel each other
• Opposite charges attract each other
+
+
-
-
• Exert a force
– Can do work: e.g., move something
+
-
Charge
• Charge is measured in Coulombs ( C )
– (A unit we won’t 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
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
electron
s
+
EMF (voltage)
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
Extra
electron
s
Conductor
EMF (voltage)
+
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
Conductor
½ the extra electrons
0 voltage
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
Conductor
½ the extra electrons
0 voltage
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
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
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)
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 ( Ω )
Ohm’s 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
Ohm’s Law
• V = IR
•R=V/I
•I=V/R
V
I
R
Ohm’s 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
Ohm’s 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?
Ohm’s 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!)
Current Limiting
• Important
– This is how you (literally) fry hardware if you don’t 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” ~0Ω
– Current limiting resistor at value needed to stay within
current limits of the device
Aside: Units
• Volts, Amps, Ohms
• Normally use metric system unit prefixes
mega
kilo
M
k
milli
micro
nano
pico
m
μ
n
p
million
thousand
one
thousandth
millionth
billionth
trillionth
1,000,000
1,000
1
0.001
0.000 001
106
103
100
10-3
10-6
10-9
10-12
Examples
5V with 10Ω
 5/10 A = 0.5A = 500mA
• For typical chips you will use = Poof!
5V with 100Ω
 5/100 A = 50mA
• Still Poof!
5V with 250Ω
 5/250 A = 20mA
• OK for PIC processors, not for lots of other digital electronics
5V with 10kΩ
 5/10000 A = 0.5mA
• Good for most digital electronics
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
Schematic Diagrams
AC vs. DC
• DC – Direct Current
– Current flows steadily in one direction
– Most of what we will do is DC
V
• AC – Alternating Current
– Current flows in one direction then another
– Wall current does this
• Alternating 60 times per sec
• 60 Hz
V
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
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
Series and Parallel Circuits
• Series circuit
• Parallel circuit
Series and Parallel Circuits
• Combining resistors
R1
R2
• Rtotal-series = R1 + R2
R1
R2
• Rtotal-par
= (R1 * R2) / (R1 + R2)
Series and Parallel Circuits
Combining capacitors
C1
C2
• Ctotal-series = (C1 * C2) / (C1 + C2)
C1
C2
• Ctotal-par
= C1 + C2
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”
Digital Electronics
• But need to leave some room for
error or fluctuation
+5v
1
– Between VHMin and +5v considered 1
– Between 0v and VLmax considered 0
VHMin
??
– Between VLmax and VHMin is undefined
(and unpredictable)
• Can pass through this but you don’t want
to stay there long
VLmax
0
0v