1. HOPE- Hands On Practical Electronics Lesson 1: Introduction and Voltage, Current, and Resistance

2. HOPE Is Brought To You By: The SEC  Student Engineers’ Council  Check Out Their Website at http://www.sec.vt.edu/  Next GAM: IEEE Student Branch @ Berkeley

3. This Week Today’s Goals are:  Discuss underlying principles such as Voltage, Current, and Resistance  Become Familiar with some basic EE components  Build 2 simple circuits

4. History Lesson The Common Units: Volts, Amps, Ohms, Coulombs are all named after people VoltaAmpereOhmCoulomb

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

6. Voltage: Sources Two Ways to Represent a Voltage Source Current flows from + to -

7. Voltage: Ground We will assign a point on our circuits to have 0 Volts We will call this ground We will use this symbol to represent ground

8. Current: Introduction Definition: Flow (movement) of positive electric charge Units: Amps (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

9. 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

10. Current Convention Conventional Current  Current is conventionally defined as the movement of positive charge  However, in reality, electrons move in the opposite direction! p+p+ e-e-

11. Conventional Current (Cont.) It doesn’t matter which way we define current flow  Current behaves the same regardless of convention  But, it is important to use the same convention consistently

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

13. Circuit Symbols BatteryResistorLED

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

15. 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

16. 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%

17. 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

18. 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.

19. 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.

20. Circuits Closed loop – There is a path for the current to flow back to the other end of the battery Circuits will only work if there is a closed loop The following circuit diagram contains a closed loop starting from the battery to the resistor, through the first LED and then back to the battery

21. Circuit Example 1: Tonight’s Lab 1 i i 9V 1V 0V 1V drop 8V drop

22. Circuit Example 2 0V i2 9V 1V 9V 8V 1V i3

23. Digital Multimeter (DMM) Combination of  Ammeter: measures current  Voltmeter: measures voltage  Ohmmeter: measures resistance 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

24. Using The Multimeter 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 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

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)

26. Breadboards A reusable, solderless device used to build a prototype of an electric circuit Power and Ground Busses on either sides Horizontal connections (terminal strips) with break in center We will learn more with practice

27. Move the battery around to see where the current flows. The LEDs will turn on when current flows through them. Test what happens when you connect 1 lead of the battery to the first LED, the 2 nd LED etc. Questions to consider:  Will the first LED light up?  Will the second? Connect the battery lead behind the 2 nd LED. Does it light up? Today’s Lab: Circuit 1

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