my_text_data/cheatsheets/electronics cheatsheet.txt

Electronics: field studying the controlled flow of electrons using passive and
active components.

component types:
  - active: Can supply power, e.g. voltage/current sources, generators (pulse,
    DC, ...), transistors, diodes, ...
  - passive: Only receive power which they somehow transform, e.g. resistors,
    inductors, capacitors, transformers, ...

current flow:
  By convention electricity "flows" from + to -, but in reality electrons move
  from - to +. Current can be:
  - direct (DC): Constant current in the same direction. DC is what we get e.g.
    from a battery.
  - alternating (AC): Current that changes with time and switches direction,
    normally as a sine function, due to constantly changing voltage. AC is what
    we get e.g. from electricity generators (rotating magnets that induce
    current, this current changes due to the rotation of the generator).

circuit types:
  - short circuit: Circuit without significant load, i.e. one end of source
    connected directly to the other. This creates extreme current and great
    heat, burns the circuit in practice.
  - open circuit: Circuit with a "hole" (infinite resistance), current cannot
    flow.

units:
  C (coulomb): charge which about 6.21 * 10^18 protons have (same amount of
    electrons have the same charge but negative)
  V (volt): J/C, unit of electric potential (or its difference), 1 V between
    two points in electric field means that moving 1 C between these points
    dissipates 1 J (joule) of energy
  A (ampere): current, charge per time, A = C/s
  Omega (ohm): V/A, resistance (attribute of resistor), 1 Omega is the
    resistance that makes 1 V produce 1 A or current
  F (farad): Q/V (charge to voltage), capacitance
  H (henry):      inductance

quantities:
  voltage (V): difference of electric potentials, measured in V
  current (I): measured in A
  resistance (R): measured in ohms, property of resistors
  capacitance (C): mesured in farads, property of capacitors
  inductance (L): measured in henrys, property of inductors, depends on geometry
    and material of the core

laws:
  Ohm's law: I = V / R
  1st Kirchhoff's law: Sum of current to/from a node is zero (currents flowing
    in are positive, currents flowing out are negative).
  2nd Kirchhoff's law: The sum of voltage drops in a circuit is zero (voltage
    sources have positive voltage drops, resistors have negative).
  Thévenin's theorem: Any linear electrical network with two terminals that
    internally consists of only voltage/current sources and resistors can always
    be replaced by a Thévenin equivalent network consisting of one voltage
    source plus a resistor in series (i.e. any "abomination" of resistors and
    voltage sources can always be replaced just by one voltage source and
    resistor).

components:
  voltage source: Active, ideally provides constant voltage (no matter
    the load resistance or current). In practice battery is used as voltage
    source, but battery is not ideal (may not provide constant voltage) and
    behaves like a voltage source with small resistor in series.
  current source: Active, ideally provides constant current (no matter the
    voltage accross it).
  resistor: Passive, provides resistance. There is a voltage drop on a resistor
    (can be computed from Ohm's law, knowing current I in the circuit and the
    resistor's resistance). Many components such as lightbulbs behave like a
    resistor. Used for: adjusting currents/voltages, terminating transmission
    lines etc.
  capacitor: Passive, stores electric energy in an electric field when voltage
    if applied to it, provides capacitance. It consists of two metallic plates
    in close proximity separated by dielectric medium: when a voltage is
    applied, charge accumulates on both plates (negative on one, positive on the
    other), when the voltage is taken away the accumulated voltage stays in the
    capacitator and will dissipate when the capacitator is connected in a
    circuit, until it discharges (it is for a short while like a mini-voltage
    source). No current will pass through capacitor but in the whole circuit a
    current will flow for a short while when chargin/discharging (thanks to the
    electric field). Capacitor can be used to block DC while letting AC pass
    through (from the point of view of DC capacitor is an open circuit) and also
    for other things like waveform generation, singal filtering,
    integration/differentiation etc. Amount of current in capacitor is
    proportional to the voltage change on it.
  inductor (coil, reactor, ...): Passive, stores electric energy in an electric
    field when current flows through it, provides inductance. It consists of a
    long wire wind around a dielectric core. When current flows through it,
    magnetic field is created, and changes to that field create voltage. It
    resists current changes and can be used to block AC while letting DC
    through, they're also used for filters etc. Amount of voltage on inductor is
    proportional to the current change on it.

formulas:
  resistance:
    resistors in series: R = R1 + R2 + ...
    reistors in parallel: 1/R = 1/R1 + 1/R2 + ...
  capacitance:
    capacitors in series: 1/C = 1/C1 + 1/C2 + ...
    capacitors in parallel: C = C1 + C2 + ...
  inductance:

hydraulic analogy:
  Model likening electronics to hydraulics, e.g.:
  - wire = pipe
  - C (coulomb) = amount of water
  - V = pressure
  - A = water flow, amount of water per second
  - resistor = thin pipe
  - capacitator = flexible membrane sealed in pipe
  - inductor = paddle wheel/turbine
  - battery = pump