Notes on Electronics for Dummies.
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Notes on Electronics for Dummies

  1. Series = Same I's, different U's. Iin = Iout, Uin = U1 + U2 + ..., Rin = R1 + R2 + ..., 1 / C = 1/C1 + 1/C2 + ...
  2. Parallel = Same U's, different I's. Iin = I1 + I2 + ..., Uin = Uout, 1 / Rin = 1/R1 + 1/R2 + ..., C = C1 + C2 + ...
  3. Silicons is a semiconductor when phosphorus or borus is added, isolator otherwise
  4. Si + B = p-type semiconductor
  5. Si + P = n-type semiconductor
  6. p-type + n-type regions in semiconductors create pn junction where current flows only in one direction, eg., diode
  7. pn junctions generate current when exposed to light, used in solar cells
  8. When you run current through pn junction, it emmits light, like LED
  9. Transistors use 3 adjacent areas, eg., npn = P + B + P
  10. Capacitance is the ability to store a charge in an electric field. This stored charge has the effect of making decreases or increases of voltage more gradual.
  11. Capacitors are used in uC as bypass filters that filter out noises in voltage and act as super-responsive energy storage.
  12. Capactitor can not be used as batteries since they wattage is much lower as well as the ouput voltage drops almost linearly when compared to batteries.
  13. Capactitors initially throughputs infinity current till the inner resistance builds up and the voltage is in level with the overall voltage, eg., 9V. After the voltages are equal, there is no current transmitted between the terminals of the capacitor.
  14. Inductance is the ability to store energy in a magnetic field; this stored energy resists changes in current just as the stored charge in a capacitor resists changes in voltage.
  15. DC electrons flow one way
  16. AC electrons alter the direction
  17. Electrostatic discharge involves very high voltages at extremely low currents. Combing your hair on a dry day can develop tens of thousands of volts of static electricity, but the current is almost so negligible you seldom notice it.
  18. Two resistors joined form what is called a voltage divider. Assuming that you have two identical resistors, that is, they apply their brakes in the same amount, the voltage in between the two is exactly half that of the rest of the circuit. See this . The respective circuit Voltage Divider
  19. The value of a capacitor changes with temperature, which you call its temperature coefficient.
  20. The diode is the simplest form of semiconductor.
  21. Zener: These puppies limit voltage to a pre-determined amount. You can build a voltage regulator for your circuit cheaply and easily with a zener diode.
  22. Rectifier: This basic diode transforms (referred to as “rectifying”) AC current to provide DC current only.
  23. Bridge rectifier: This component consists of four diodes, connected one to the other to form a kind of box shape; it rectifies AC to DC with maximum efficiency.
  24. Diodes are rated by two main criteria: peak inverse voltage (PIV) and current.
  25. The PIV rating roughly indicates the maximum working voltage for the diode.
  26. The current rating is the maximum amount of current the diode can withstand.
  27. If you want a more accurate calculation, you need to know the forward voltage drop through the LED, in addition to the LED’s maximum current rating. Most standard brightness LEDs have a forward voltage drop of about 1.5 volts. The latest crop of ultra-bright LEDs may have forward voltage drops exceeding 3.5 volts.
  28. Two resistors joined form what is called a voltage divider. Assuming that you have two identical resistors, that is, they apply their brakes in the same amount, the voltage in between the two is exactly half that of the rest of the circuit. See this . The respective circuit Forward Current
  29. Two main tasks of transistors are signal amplify and signal switch (on, off)
  30. If the transistor has just two wires, it’s probably the light-dependent type
  31. There are three lead for transistors - base, emitter, collector
  32. A base is wired to a voltage or current and turns the transistor on or off. Emitter and collectors leads connect to a positive or negative voltage source or ground. Which lead goes where varies with the circuit.
  33. Most of the LEDs have nominal current of 20mA if not given otherwise.
  34. Diode Resistor Formula
  35. Transistors qualify as either NPN or PNP devices
  36. Transistor Types
  37. The two main types of transistors that you’re likely to encounter are bipolar and FET.
  38. Bipolar transistors: These transistors are the most common kind. A small input current is applied to the base of the transistor. This in turn, changes the amount of current that flows between the collector and emitter.
  39. FETs (field effect transistors): These transistors also have three connec- tions, but you call those connections gate, source, and drain, rather than base, collector, and emitter. Applying a voltage to the gate controls the current between the source and drain. FETs come in two types: N-chan- nel (similar to NPN) and P-channel (similar to PNP).
  40. Technically, FETs come in two sub types: MOSFET and JFET.
  41. Conversely, if you shine light on diodes they generate an electric current. A solar cell is just a large diode that gener- ates current when exposed to a light source, such as the sun.
  42. Normally closed (NC): This push-button switch disconnects the wire only when you push the button. Normally open (NO): This push-button switch connects the wire only when you push the button.
  43. A relay is simply an electrically powered switch.
  44. Inductors and crystals both have a relationship with frequency. Inductors are used to weed out all but a desired frequency (this is one of the pieces of the process when a radio tunes into only one station; more about this shortly). Crystals, on the other hand, are often used to generate specific frequencies in a circuit.
  45. Circuits use inductors (you may hear inductors also called “coils” or “chokes”) along with capacitors (which we discuss in Chapter 4) to filter out all but one frequency.
  46. When you use a remote control for your TV you are using a photodiode in the remote to send infrared signals to a phototransistor in your TV.
  47. There are two types of thermistor: Negative temperature coefficient (NTC) thermistors: The resistance of this type of thermistor decreases with a rise in temperature. Positive temperature coefficient (PTC) thermistors: The resistance of this type of thermistor increases with a rise in temperature.
  48. The positive and negative terminals of the battery connect so that each end of the electromagnet has the same polarity as the permanent magnet next to it. Like poles of magnets repel each other. This repelling action moves the electro- magnet and causes the axle to spin. As the axle spins, the positive and negative connections to the electromagnet swap places, so the magnets continue to push the axle around. A simple mechanism consisting of a commutator (a segmented wheel with each segment connected to a different end of the elec- tromagnet) and brushes that touch the commutator cause the connections to change. The commutator turns with the axle and the brushes are stationary, with one brush connected to the positive battery terminal and the other brush to the negative battery terminal. As the axle, and therefore the commutator, rotates, the segment in contact with each brush changes. This in turn changes which end of the electromagnet is connected to negative or positive voltage.
  49. The piezoelectric effect, the ability of certain crystals — quartz and topaz to name a few — to expand or contract when you apply voltage to them.
  50. In a series setup, you calculate R t by finding the sum of all the resistances. In a parallel circuit, the R t of the circuit is a smaller value than the smallest resistor (in Figure 7-5, 7.2 Ω versus 10 Ω for the smallest resistor).
  51. A capacitor stores electrons, and a resistor controls the flow of electrons. Put these two together, and you can control how fast electrons fill (or charge) a capacitor and how fast those electrons empty out (or discharge) from a capacitor.
  52. The larger the value of a resistor, the less current flows through it for a given voltage, which means it takes more time to fill a capacitor. Likewise, larger capacitors require more electrons to fill them up, which means they take a longer time to charge. By picking the combination of capacitors and resis- tors, you can determine your project’s charge or discharge time. Turning things on and off It turns out that the voltage out (V out) depends on how full the capacitor in your circuit is. The closer to full, the higher V out . The closer to empty, the lower V out.
  53. Filling the capacitor to two-thirds of its capacity often gives a high enough V out to turn on the next component in the circuit. If it doesn’t, try a smaller resistor so that the capacitor fills up faster.
  54. You can calculate the time to fill a capacitor to two-thirds of its capacity using something called an RC time constant. Simply multiply the values of the resistor, in ohms, by the capacitor, in farads, and you get the time it takes to fill the capacitor up to two-thirds of its capacity.
  55. RC time constant = R x C = 2,000,000 ohms x 0.000015 farads = 30 seconds
  56. You can use the ability of capacitors to gather and release electrons to smooth out voltage fluc- tuations. A given voltage level across a capaci- tor produces a certain number of stored electrons. When the voltage starts to rise, the capacitor stores more electrons, which dampens any rise in voltage. When the voltage drops, the capacitor releases some of its trapped electrons, which dampens the drop in voltage.
  57. Super nice video about how vacuum tubes work
  58. How Amplifiers Work: Rectifiers and Filter Capacitors:
  59. Simply put, a transistor controls the flow of electric current by opening and closing a kind of valve within it.
  60. A super nice video about how transistors work
  61. Bandwidth is the highest fre- quency signal that you can reliably test with your oscilloscope, measured in megahertz (MHz).
  62. Another important specification is resolution. The resolution of the scope has to do with its accuracy. The X (horizontal) axis on an oscilloscope displays time, and the Y (vertical) axis displays voltage. The horizontal amplifier indi- cates the X-axis resolution. Most scopes generally have a resolution of 0.5 microseconds (millionths of a second) or faster.
  63. So how do you calculate the time constant for a resistor-capacitor circuit? These circuits combine a resistor and a capacitor. Note that the capacitance value is in farads. Typical capacitor ranges are in microfarads and even smaller units, so the capacitance value is a fractional number. T = RC In this formula, T represents time (in seconds), R stands for resistance (in ohms), and C signifies capacitance (in farads). For example, with a 2000-ohm resistor and a 0.1-uF capacitor, the time con- stant is 0.002 of a second, or two milliseconds.