hardware basics

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

electronsEMF (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

electronsEMF (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 1,000103

one 1 100

milli m thousandth 0.00110-3

micro μ millionth 0.000 001 10-6

nano n billionth 10-9

pico p trillionth 10-12

Examples5V 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

??