Intro to Electronics November 2010

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

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

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

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