Electrical Engineering I Laboratory Exercise #2 Page 1 of 9

Name: _________________________ Lab Partner: ____________________ Lab Instructor: __________________ Date: __________________________

United States Coast Guard Academy Department of Engineering

EE1 (1218) Fall 2010 Laboratory Exercise 2

1.0 OBJECTIVE: To introduce students to the instruments used to measure DC circuit parameters and verify the theoretical behavior of electrical laws and circuits discussed in class. 2.0 PREPARATION: Read this lab exercise and complete the theoretical calculations for each of the three circuits shown in Figure 4, Figure 5, and Figure 6. 3.0 EQUIPMENT: At each student lab station there should be:

K & H IDL-800 Digital Lab Breadboard (1) Agilent Digital Multimeter 34410A (1) Assorted resistors with color bands (6) Resistors: 5.1 k, 1.0 k, 3.9 k Various banana cables Assorted wires and alligator clips

3.1 Notes on the IDL-800 Digital Lab Breadboard The IDL-800 combines a breadboard, many different voltage and waveform sources, several binary devices, banana jacks to wire socket adapters, a digital volt meter (DVM), LED (pronounced el-ee-de) bit displays, and a two digit display for onboard measurements. Figure 1 shows a picture of the IDL-800 breadboard and Figure 2 is a diagram of the IDL-800 with the various components labeled. The following sections will describe some of these components.

Figure 1. IDL-800 breadboard.

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3.1.1 Breadboard - The breadboard simplifies the construction of circuits in an electronic laboratory. It is a plastic board full of holes somewhat like a cribbage board. Each hole provides access to a metal contact imbedded in the board. Electrical connections are made by inserting the end of a wire or a circuit component lead into a hole. Figure 3 is a top view of the IDL-800 breadboard insert. The holes in each horizontal row at the top and middle of the board are connected together except for a break at the center. These rows are usually connected to ground or a voltage supply. The entire half row of holes can then be used to distribute ground or voltage wherever needed in your circuit. In each numbered row (top half) or column (bottom half), the holes (lettered A through F) are connected together. These are used to connect the resistors, capacitors, and other elements in your circuit.

1. Power Switch with Indicator 11. Pulse Switches 2. F.G. Output Amplitude Adjuster 12. Data Switches 3. F.G. Output Frequency Range

Selector 13. Removable Solderless Breadboard in 1896 Tie

Points 4. Fine Tune of F.G. Output Frequency 14. Point Tip/Banana Socket/BNC Socket

Exchange Adapters 5. F.G. Output Wave Form Selector 15. Buffered Single Lamp LED Displays 6. BCD Input of 7-Segment Decoder 16. Output of 7-Segment Decoder 7. DC 0 to +15V Adjuster 17. Range Selector of Digital Voltmeter 8. DC 0 to –15V Adjuster 18. Input of Digital Voltmeter 9. Fixed DC +5V 19. Display of Digital Voltmeter 10. Function Switches, –5V / 0 / +5V

Figure 2. IDL-800 Digital Breadboard Lab Switches and Controls.

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3.1.2 Signal Supplies - The IDL-800 provides many different sources. Remember that every source requires a ground connection in addition to the signal connection. The sources on the IDL-800 are already internally connected to ground. That is, the ground sides on the sources have already been internally connected to the ground terminals (GND). A circuit may be connected to the ground side of any source by connecting to any of the ground terminals (GND).

CAUTION: Never connect the signal side of the voltage supply directly to a

ground terminal. This will short circuit your voltage supply and cause fuses in the IDL-800 breadboard lab to burn out.

3.1.3 DC Voltage Sources - Fixed positive and negative 5 volt DC voltage is supplied at the wire jacks labeled +5V and -5V, respectively (Figure 2, number 9). Ground connection is available at all of the wire sockets marked with the ground symbol, (GND). Variable DC voltage (0 to +15V or 0 to -15V) is also available (Figure 2, numbers 7 and 8 respectively). Switched voltage sources are provided at the two switches SWA and SWB (Figure 2, number 10). The two connect to +5V in the up position and to -5V in the down position.

3.1.4 Time Varying Voltage Sources - The IDL-800 provides sine, triangle, and square wave signals from the appropriately marked wire jack in the FUNCTION GENERATOR section at the top. The function is selected with the knob (Figure 2, number 5). The frequency of these waveforms is adjusted by the frequency and range controls at the top left portion of the IDL-800 (Figure 2, numbers 4 and 3). The amplitude can be varied using the amplitude control knob (Figure 2, number 2).

3.1.5 Binary devices - The IDL-800 has binary power supplies, a flip flop, and binary pulse generators. These devices will be explained and used when they are needed.

Figure 3. IDL-800 Breadboard Insert.

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3.1.6 Output Displays - The IDL-800 has several display devices. The LED, bit, and digit displays will be used in future labs. In this exercise you will use the Digital Voltmeter (DVM) display (Figure 2, number 19). The (+) and (-) wire jacks under the DVM (Figure 2, number 18) are used to connect this device to the points to be measured. The display is positive when the point in the circuit connected to the + is at a higher potential than the point connected to the - wire socket. The range scale of the DVM is controlled with the knob (Figure 2, number 17).

3.1.7 Adapters - The IDL-800 has two adapters for connecting banana plugs to wires (Figure 2, number 14). To use these adapters, insert a banana plug in any of the two large banana jacks and a wire in the wire jack next it. The two are then electrically connected. You should use these adapters to connect the Agilient multimeter to the circuit for measurements.

4.0 PROCEDURE: At each lab station you will find at least six resistors of different values, together with a resistor color code chart. For six of the resistors, record the color code, the value as specified by the color code bands, and the specified tolerance. Measure the resistance of each resistor using the Agilent Digital Multimeter and record the value obtained. Follow any instructions given by your laboratory instructor for resistance measuring techniques.

Color Code (List colors left to right)

Value from Color Code

Specified Tolerance +/– %

Measured Resistance

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5.0 SERIES CIRCUIT: Calculate and measure the voltages and currents in the series circuit shown in Figure 4 as directed in the following steps.

(Show your calculations below.)

5.1 Transfer your calculated values to the appropriate spaces below. Label your units! VA (The voltage potential between point A and ground) ____________ VB (The voltage potential between point B and ground) ____________ I (The current in the 5.1 k resistor) ____________ 5.2 Construct the circuit shown in Figure 4. Measure the actual values for these voltages and currents. Use the methods described by your lab instructor for measuring voltage and current. VA (The voltage potential between point A and ground) ____________ VB (The voltage potential between point B and ground) ____________ I (The current in the 5.1 k resistor) ____________ 5.3 Comment on the measured values as compared with your calculated values.

Were there any major discrepancies? YES / NO Were there any minor discrepancies? YES / NO

5.4 Explain why the measured values were not EXACTLY the same as the theoretical. (May we suggest that you consider the resistance of the wire compared to the value of the resistances in the circuit before you tell us that the wire resistance is the reason your measured values differ from the calculated values.)

+_10 V 3.9 k

5.1 k 1 k

I VA VB

Figure 4. Series circuit.

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5.4 Hypothesize what effect shorting out the 3.9 k resistor in Figure 4 will have on the voltage and current measurements? (You may want to draw a schematic of the new circuit and/or make some calculations to support your answer.)

5.5 Now try it (short out the 3.9k resistor) and record the results. Comment on what you observe. VA (The voltage potential between point A and ground) ____________ VB (The voltage potential between point B and ground) ____________ I (The current in the 5.1 k resistor) ____________ Was your hypothesis correct? YES / NO Explain why you got the above results.

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6.0 PARALLEL CIRCUIT: Calculate and measure the voltages and currents in the parallel circuit shown in Figure 5 as directed in the steps below.

(Show your calculations below.)

6.1 Transfer your calculated values to the appropriate spaces below. VA (The voltage potential between point A and ground) ____________ IA (The current in the 5.1 k resistor) ____________ IB (The current in the 1.0 k resistor) ____________ IC (The current in the 3.9 k resistor) ____________ ITOTAL (The total current supplied by the 10 V source) ____________ 6.2 Construct the circuit shown in Figure 5. Measure the actual values for these voltages and currents. Use the methods described by your lab instructor for measuring voltage and current. VA (The voltage potential between point A and ground) ____________ IA (The current in the 5.1 k resistor) ____________ IB (The current in the 1.0 k resistor) ____________ IC (The current in the 3.9 k resistor) ____________ ITOTAL (The total current supplied by the 10 V source) ____________ 6.3 Comment on the measured values as compared with your calculated values.

Were there any major discrepancies? YES / NO Were there any minor discrepancies? YES / NO

6.4 Explain why the measured values were not EXACTLY the same as the theoretical.

+_10 V

3.9 k5.1 k 1 k

ITOTAL VA

IA IB IC

Figure 5. Parallel circuit.

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7.0 COMPLEX CIRCUIT: Calculate and measure the voltages and currents in the parallel circuit shown in Figure 6 as directed in the steps below.

(Show your calculations below… Hint: Find the REQ for 5.1k and 1k in ||…)

7.1 Transfer your calculated values to the appropriate spaces below. VA (The voltage potential between point A and ground) ____________ VB (The voltage potential between point B and ground) ____________ IA (The current in the 5.1 k resistor) ____________ IB (The current in the 1.0 k resistor) ____________ ITOTAL (The total current supplied by the 10 V source) ____________ 7.2 Construct the circuit shown in Figure 6. Measure the actual values for these voltages and currents. Use the methods described by your lab instructor for measuring voltage and current. VA (The voltage potential between point A and ground) ____________ VB (The voltage potential between point B and ground) ____________ IA (The current in the 5.1 k resistor) ____________ IB (The current in the 1.0 k resistor) ____________ ITOTAL (The total current supplied by the 10 V source) ____________ 7.3 Comment on the measured values as compared with your calculated values.

Were there any major discrepancies? YES / NO Were there any minor discrepancies? YES / NO

7.4 Explain why the measured values were not EXACTLY the same as the theoretical.

+_10 V

3.9 k

5.1 k 1 k

ITOTAL

IA IB

VA VB

Figure 6. Complex circuit.

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8.0 SUMMARY QUESTIONS: 8.1 Describe what would have happened if we had short circuited the 3.9 k resistor in Figure 5 instead of short circuiting the 3.9 k resistor in Figure 4. (Again, you may want to redraw the circuit with the short and make some calculations.) Specifically, discuss the VA, i1, i2, i3, ishort, and Req. 8.2 Describe why we could have put a 2.0 M resistor in parallel with the other three resistors in Figure 5 and this action would have had almost no effect on all voltages and currents we measured for the circuit. 8.3 In class, we made the statement that resistors connected in parallel have the same voltage across them. How did this statement hold up in your experiments in Section 7 of this exercise? Why? 8.4 Voltmeters should always be connected in SERIES/PARALLEL with the element whose voltage is being measured. Circle the correct answer. 8.5 Ammeters should always be placed in SERIES/PARALLEL with the circuit whose current is being measured. Circle the correct answer.