1. IEEE’s Hands on Practical Electronics (HOPE) Lesson 2: Voltage, Current, Resistance

2. Last Week Course Introduction Safety Soldering Terminology

3. Last Week’s Circuit Consisted of a 9V battery, 1 resistor, and 1 or more LEDs 9V Battery Resistor LED

4. This Week History Lesson Voltage Current Resistance Digital Multimeter (DMM)

5. History Lesson The common units: Volts, Amps, Ohms, Coulombs are all named after people VoltaAmpereOhmCoulomb

6. Voltage Definition: Difference of electrical potential between two points of an electrical circuit Units: Volts (V) 1 V = 1 Joules per Coulomb (J/C) Example: The electrical potential difference between the + and – ends of a battery is 9 V

7. Voltage Sources Two ways to represent a voltage source Current flows from + to -

8. Voltage There is no absolute number or quantifiable value for voltage. Remember integrals? The integral of f(x) is equal to F(x) + C. The + C allows us to choose whatever number is most convenient for our calculations.

9. Voltage We will assign a point on our circuit to have 0 volts. We will call this ground. We will use this symbol to represent ground.

10. Ground We will not spend too much time on this. Just know that it is the place on our circuit that we choose to be 0V. For more reading see http://www.ese.upenn.edu/rca/instruments/misctut orials/Ground/grd.html http://en.wikipedia.org/wiki/Electrical_ground

11. Current Definition: Flow (movement) of positive electric charge Units: Amperes (A) 1 A = 1 Coulomb per second (C/s) Example: The rate that a stream of water flows is analogous to the amount of current flowing through a circuit

12. Coulombs Symbol: Q Unit: Coulomb 1 coulomb is the amount of electrical charge in 6.241×10 18 electrons Amps = C/s, current is the amount of electrical charge flowing per second We will revisit Coulombs when we study Capacitors

13. p+p+ Electron Flow –However, in reality, electrons move in the opposite direction! Current Convention Conventional Current –Current is conventionally defined as the movement of positive charge It doesn’t matter which way define current flow -Current behaves the same regardless of convention. -But, it is important to use the same convention consistently e-e-

14. Resistance Definition: Measure of the degree to which an object opposes the passage of an electric current Units: Ohms (Ω) 1 Ω = 1 Volt per Ampere (V/A) Example: Hurdles serve as obstacles to a runner, so it requires more energy to overcome them

15. Circuit Symbols Battery LEDResistor

16. Resistors Resistors are manufactured and labeled with another convention. There are bands of colors used to indicate the resistance of the particular resistor. See: http://en.wikipedia.org/wiki/Resistor

17. Calculating Resistance It’s possible to calculate resistance of a resistor using the color bands on it –AB represent a 2 digit number –C represents the magnitude –Resistance = AB * 10 C + D However, we will mainly be measuring resistances with a multimeter

18. Example: Calculating Resistance The first two bands correspond to 4 and 7. The third band tells you the number of zeros following. 47*10 3 = 47,000 Ω + 10%

19. Example Resistor Usage LEDs are designed to work for approximately 1-2 Volts of power. Too much voltage across the LED will cause it to burn out from overheating Always put a resistor before (or after) an LED to limit the current. You do not want to burn out your LEDs

20. LED Introduction LED = Light Emitting Diode Lights up when current flows through it LEDs only allow current to go through it in one direction Current FlowsLED’s have 1 lead that is longer than the other. The longer lead is the positive side. Current flows from the longer lead to the shorter lead.

21. Putting it all Together Battery provides energy to the charges so that they can travel through the circuit Resistor opposes the movement of these charges, thus slowing them down. Current through the LED provides energy to the LED, which transforms into light.

22. Example 1: Last Week’s Circuit i i 9V 1V 0V 1V drop 8V drop

23. Example 2 9V 0V i i2 9V 1V 9V 8V 1V i3

24. Using the Multimeter To measure current: -Turn dial to “20mA” -OPEN the current circuit -Complete the circuit with the two wires of the multimeter To measure resistance: -Turn dial to “2K” - Touch the 2 wires of the multimeter to the two ends of the resistor To measure voltage: -Turn on multimeter by turning dial to “20V” -Touch one of the wires to the first point in the circuit to measure -Touch the other wire to a point across the circuit element

25. Everyday Use Multimeters are used to measure voltages and currents at different points on the circuit. They are used to diagnose a circuit to see if current is flowing or not (potentially an open circuit or short draining the current) A soldering iron can then be used to fix the damage (Week 1)

26. Digital Multimeter (DMM) Combination of –Ammeter: measures current –Voltmeter: measures voltage –Ohmmeter: measures resistance We will go into more detail on how to use multimeters next week

27. DMM Usage A Digital Multimeter is a measurement device commonly used as a diagnostic tool. Fancier multimeters can measure more quantities such as frequency, temperature, conductance, inductance, capacitance and so on.

28. Today’s Lab More practice on soldering You can continue building on your last week’s device If you feel comfortable soldering, try using the real soldering irons.

29. Today’s Lab Build the following circuit that consists of 1 battery, 2 resistors and 6 LEDs: 9V