Hardware Basics Electricity Electricity is the flow of

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) Ø 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 Extra electrons 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) – 1 A 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/ft 2)

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 5 v • starting to use 3. 3 v, but 5 v 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 5 v source – From power supply, or from output pin of a chip to ground (0 v 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 1 0. 000 001 106 103 100 10 -3 10 -6 10 -9 10 -12

Examples 5 V with 10Ω 5/10 A = 0. 5 A = 500 m. A • For typical chips you will use = Poof! 5 V with 100Ω 5/100 A = 50 m. A • Still Poof! 5 V with 250Ω 5/250 A = 20 m. A • OK for PIC processors, not for lots of other digital electronics 5 V with 10 kΩ 5/10000 A = 0. 5 m. A • 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 Ø 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 R 1 R 2 • Rtotal-series = R 1 + R 2 R 1 R 2 • Rtotal-par = (R 1 * R 2) / (R 1 + R 2)

Series and Parallel Circuits Combining capacitors C 1 C 2 • Ctotal-series = (C 1 * C 2) / (C 1 + C 2) C 1 C 2 • Ctotal-par = C 1 + C 2

Digital Electronics • Computer circuits treat signals as digital values – Consider signals to only have two states: 1 or 0 – +5 v is considered to be “ 1” – 0 v is considered to be “ 0”

Digital Electronics • But need to leave some room for error or fluctuation +5 v 1 – Between VHMin and +5 v considered 1 – Between 0 v 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 0 v