Today’s Agenda

1. Today’s Agenda More on potentiometers Introduction to AC signals 1

2. What Potentiometers Look Like: EGR 101

3. Trimmer potentiometers. EGR 101

4. Potentiometer construction. EGR 101

5. The effect of turning the control shaft on the component resistances. EGR 101

6. Potentiometer in Multisim Found in Basic category EGR 101

7. Pressing the ‘a’ key increases percentage • Pressing ‘Shift a’ decreases percentage EGR 101

8. Note, in Multisim, if you place the potentiometer with the arrow angled down, the resistance will change in the opposite direction EGR 101

9. EGR 101

10. EGR 101

11. Information on Lamps in Multisim • The lamp you’ll need for the prelab can be found under Indicators/Virtual_Lamp EGR 101 11

12. Chapter 9 Alternating CurrentDC & AC Circuits 12

13. DC: Direct CurrentA DC current is a current that does not change direction in time. 13

14. Example of DC circuits: • Portable flashlight circuit. • Internal circuit inside a DMM to measure resistance. • Circuit to control a dimmer light using a potentiometer, as you will on Thursday. EGR 101 14

15. AC: Alternating CurrentAn AC current is a current that changes direction in time. 15

16. Imagine you take a battery with one polarity between times t0 and t1 (top schematic). • Flip polarity between t1 & t2 (bottom schematic). EGR 101 16

17. Flipping batteries is unrealistic. However, you can built an AC circuit using two batteries and a SPDT switch, as shown below. • When the switch is flipped to the right you get +15 V. • When the switch is flipped to the left you get -15 V. EGR 101 17

18. In-Class Activity 1 • Working in pairs, simulate the circuit below in Multisim. The single pole, double throw (SPDT) switch can be found in the Basic, switch category. • Flip the SPDT switch using the space key and watch how the meter reading alternates between +15 V and -15 V. EGR 101 18

19. Oscilloscope – piece of equipment that provides a visual representation of a voltage waveform EGR 101 19

20. In-Class Activity 2 • Repeat simulation using an oscilloscope (4th instrument down on right column). • Watch on the scope how fast the voltage alternates: • click the space bar slowly. (see slide 21) • click the space bar fast. (see slide 22) EGR 101 20

21. Slow Clicks (Low Frequency AC) EGR 101 21

22. Fast Clicks (High Frequency AC) EGR 101 22

23. AC using 555 timer • Although you can easily create the previous AC circuit using two batteries and SPDT, you can automate the circuit using a 555 timer, as you are going to do in your semester projects, as shown in the next slide. EGR 101 23

24. Switching between two batteries automated using 555 timer two batteries SPDT replaced with Relay 555 timer EGR 101 24

25. How do we characterize the differences in the waveforms we generated? For periodic rectangular waves: Insert Figure 9.39 EGR 101 25

26. Rectangular Waves- Terminology and Time Measurements EGR 101 26

27. Rectangular Waves- Duty Cycle – ratio of pulse width to cycle time where PW= the pulse width of the circuit input T= the cycle time of the circuit input EGR 101 27

28. In-Class Activity 3 • For the following waveforms, specify the pulse width, space width and period: a) 2 ms 5 ms 10 ms EGR 101

29. One of the most important AC signals is the periodic sinusoid, as shown below. Power generation power plants. Design of radios and radio stations. EGR 101 29

30. Difference between AC & DC Demo. Loss of DC power over long distance. AC power transport is more efficient. http://www.pbs.org/wgbh/amex/edison/sfeature/acdc.html EGR 101 30

31. Generating a Sine Wave EGR 101 31

32. EGR 101 32

33. Alternations and Cycles Alternations – the positive and negative transitions Cycle – the complete transition through one positive alternation and one negative alternation Half-Cycle – one alternation Insert Figure 9.3 EGR 101 33

34. Cycle Time (Period) – The time required to complete one cycle of a signal EGR 101 34

35. In-Class Activity 4 Calculate T in ms Calculate T in ms EGR 101 35

36. Frequency the rate at which the cycles repeat themselves Unit of Measure – Hertz (Hz) = cycles/second T = 200 ms = 0.2sf = 1/0.2 = 5 cps = 5 Hz EGR 101 36

37. Relation between Cycle Time (Period) and Frequency where T = the cycle time (period) of the waveform in seconds Another way to describe periodicity of the wave is through the angular frequency defined as where  = angular velocity, in radians per second 2 = the number of radians in one cycle f= the number of cycles per second (frequency) EGR 101 37

38. Note that is not the same thing as What is a radian? EGR 101 38

39. 1 Radian – the angle formed within a circle by two radii separated by an arc of length equal to the radii when ra = r1 EGR 101 39

40. Instantaneous Value – the value of a sinusoidal voltage or current at a specified point in time can be expressed as: where Vpk is the magnitude of the voltage. In terms of f, EGR 101 40

41. In-Class Activity 5 An AC voltage in volts is given by what is the unit of the number 10? what is the unit of the number 377? what is the angular frequency in rad/s? what is the frequency in Hz or cps? what is the period in ms? EGR 101 41

42. In-Class Activity 5 A device emits a sinusoidal signal that has a magnitude of 1 volt and a frequency of 690 kHz. what is the angular frequency in rad/s? what is the period in ms? Express this signal as (i.e. fill in the values for A and w) Express this signal as EGR 101 42