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

electrons

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 Extra

electrons

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

0 voltage

½ the extra electrons

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

0 voltage

½ the extra electrons

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 M million 1,000,000 106

kilo k thousand 1,000 103

one 1100

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

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

• AC – Alternating Current– Current flows in one direction then another– Wall current does this

• Alternating 60 times per sec• 60 Hz

V

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 continuouslyCapacitor 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

• Rtotal-series = R1 + R2

• Rtotal-par = (R1 * R2) / (R1 + R2)

R1 R2

R1

R2

Series and Parallel Circuits

Combining capacitors

• Ctotal-series = (C1 * C2) / (C1 + C2)

• Ctotal-par = C1 + C2

C1 C2

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– 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 don’t want to stay there long

+5v

0v

VHMin

VLmax

1

0

??