Intro to Electronics November 2010

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First class: Monday, November 8, 2010 7-9 PM

Concepts discussed:

  • Current (Measured in Amps, usually represented with I)
  • Voltage (Measured in Volts, usually represented with V)
  • Power (Measured in Watts, usually represented with P)
  • Nets, also known as nodes. Can be thought of as wires.
  • Voltages must always add up when you go around the circuit
  • Currents must add up in/out of a node. (Water in pipes analogy.)

Components covered:

  • Batteries
    • Battery as a voltage source
    • Total power (mAh) supplied by a battery - varies but can be calculated.
    • Battery parasitic (internal) resistance (LED powered by coin cell with no series resistor)
  • Resistors
    • Series combination of resistors: R(total) = R1 + R2
    • Parallel combination of resistors: R(total) = 1/(1/R1 + 1/R2)
    • Calculating current through a resistor given voltage and resistance: I = V/R
    • Calculating voltage across resistor given current through it: V = I*R
    • Calculating resistance required to produce a chosen current given the voltage across the resistor: R = V/I
  • Diodes
    • Discussion of forward voltage of a diode, finding it on a datasheet
    • Diodes in a circuit are either on (voltage drop is equal to forward voltage) or off (voltage drop must be less than forward voltage for this to happen).
    • LEDs: Higher Vf than regular diodes - see datasheet
    • Look up Vf and If of LED from datasheet
      • Design to never run quite at If (Component tolerances etc.)
      • Use resistor in series to prevent burnout of LED
      • Whatever voltage is in the circuit that is greater than Vf is dropped by the resistor. (In that simple circuit.)
      • LEDs in parallel need separate resistors due to manufacturing variability.

First homework for Intro to Electronics November 2010

File:Intro_elec_nov_2010_homework_1.png

For homework_1, calculate:

  1. ) The current through the entire circuit
  2. ) The voltage at the upper right corner of the circuit
  3. ) The power dissipated in R1
  4. ) The power dissipated in R2

File:Intro_elec_nov_2010_homework_2.png

For homework_2, calculate:

  1. ) The equivalent resistance of R6, R8, and R9 combined. Trick: I only showed you how to combine two resistors in parallel, but that's all you need. Try to figure it out without asking me.  :-)
  2. ) The current through the entire circuit
  3. ) The voltage at the upper right corner of the circuit
  4. ) The current through R6
  5. ) The current through R8

File:Intro_elec_nov_2010_homework_3.png

For homework_3, calculate:

  1. ) The equivalent resistance of R11 and R12 combined
  2. ) The current through the entire circuit
  3. ) The power dissipated in R12
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