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

2. EGR 1012 What Potentiometers Look Like:

3. EGR 1013 Trimmer potentiometers.

4. EGR 1014 Potentiometer construction.

5. EGR 1015 The effect of turning the control shaft on the component resistances.

6. EGR 1016 Potentiometer in Multisim Found in Basic category

7. EGR 1017 Pressing the ‘a’ key increases percentage Pressing ‘Shift a’ decreases percentage

8. EGR 1018 Note, in Multisim, if you place the potentiometer with the arrow angled down, the resistance will change in the opposite direction

9. EGR 1019

10. 10

11. EGR 10111 Information on Lamps in Multisim The lamp you’ll need for the prelab can be found under Indicators/Virtual_Lamp 11

12. 12 Chapter 9 Alternating Current DC & AC Circuits

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

14. EGR 10114 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.

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

16. EGR 10116 Imagine you take a battery with one polarity between times t 0 and t 1 (top schematic). Flip polarity between t 1 & t 2 (bottom schematic).

17. EGR 10117 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.

18. EGR 10118 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.

19. EGR 10119  Oscilloscope – piece of equipment that provides a visual representation of a voltage waveform

20. EGR 10120 In-Class Activity 2 Repeat simulation using an oscilloscope (4 th instrument down on right column). Watch on the scope how fast the voltage alternates:  click the space bar slowly. (see slide 10)  click the space bar fast. (see slide 11)

21. EGR 10121 Slow Clicks (Low Frequency AC)

22. EGR 10122 Fast Clicks (High Frequency AC)

23. EGR 10123 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.

24. EGR 10124 Switching between two batteries automated using 555 timer 555 timer SPDT replaced with Relay two batteries

25. EGR 10125 How do we characterize the differences in the waveforms we generated? Insert Figure 9.39 For periodic rectangular waves:

26. EGR 10126 Rectangular Waves - Terminology and Time Measurements

27. EGR 10127 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

28. EGR 10128 In-Class Activity 3 a) For the following waveforms, specify the pulse width, space width and period: 2 ms5 ms10 ms

29. EGR 10129 One of the most important AC signals is the periodic sinusoid, as shown below.  Power generation power plants.  Design of radios and radio stations.

30. EGR 10130 Difference between AC & DC Demo. Loss of DC power over long distance. AC power transport is more efficient. AC power transport is more efficient http://www.pbs.org/wgbh/amex/edison/sfeature/acdc.html

31. EGR 10131 Generating a Sine Wave

32. EGR 10132

33. EGR 10133 Insert Figure 9.3 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

34. EGR 10134 Cycle Time (Period)  – The time required to complete one cycle of a signal

35. EGR 10135 In-Class Activity 4 Calculate T in ms

36. EGR 10136 Frequency  the rate at which the cycles repeat themselves  Unit of Measure – Hertz (Hz) = cycles/second T = 200 ms = 0.2s f = 1/0.2 = 5 cps = 5 Hz

37. EGR 10137 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)

38. EGR 10138 Note that is not the same thing as What is a radian?

39. EGR 10139  1 Radian – the angle formed within a circle by two radii separated by an arc of length equal to the radii when r a = r 1

40. EGR 10140 where V pk is the magnitude of the voltage. In terms of f, Instantaneous Value – the value of a sinusoidal voltage or current at a specified point in time can be expressed as:

41. EGR 10141 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?

42. EGR 10142 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  ) Express this signal as