EE215   Lab #1   Introduction to Circuit Analysis

 

Objectives

 

The object of this laboratory is to introduce fundamental concepts of circuit analysis using DC (Direct Current) sources of energy, such as batteries. These concepts coincide with those explored in your EE215 Homework and Lecture topics and include:

 

 

In addition to these concepts, you will be able to do the following after completing Lab 1:

 

 

The circuits covered in this laboratory and laboratories 2 and 3 are part of an area of electrical engineering called Electronic Circuits, Devices and Transducers. You can find a summary of this area of specialization within electrical engineering in your supplemental notes for this course. The notes are part of your reading assignment.

 

Materials and Supplies

 

For this EE215 laboratory, you will need to purchase some equipment and a multimeter or you will have to do the lab in the Open Physics Lab Fridays from 9 – 11 AM (then you can use the school’s equipment-- which cannot be taken home).Groups may choose to purchase one multimeter and move it from person to person to take measurements, although I suspect you may find that it is more convenient for each individual to get their own meter. Every student serious about becoming an electrical engineer should have their own multimeter, and a breadboard plus a jumper kit.

 

Lab Parts: I will supply most of the parts needed for the labs. Things like resistors, capacitors and op-amps. You may have to purchase small items such as batteries.

 

Multimeter: You need a multimeter that can measure ac and dc voltage, dc current and resistance. Ones that measure ac current, frequency and/or capacitance can be useful in the long run, but are not required for the course. A good multimeter costs $40-50, and you can spend more if you want to.

 

Before you buy a cheap multimeter, think about this: a good multimeter will be with you for years and is a useful part of a house, apartment or automotive toolkit, as well as essential for any electronics work. Of course you are free to purchase your multimeter from any source, these include:

 

Local electronics stores:

 

·         Radio Shack: 4505 California Ave., West Seattle  (206)-935-0900

·         Active Electronics: 13107 Northup Way, Bellevue (425) 881-8191, has a 5-10% student discount

·         Radar Inc: 168 Western Ave. W., Seattle (206) 282-2511

·         Supertonix Inc: 18650 68th Ave. S., Kent (425) 251-8484

 

You can also find multimeters at Sears! Or from the Web (allow enough time for delivery!):

 

·        www.jameco.com

·         www.newark.com

·         www.elexp.com

·         www.digikey.com

·         www.mouser.com

·         www.radar21.com

 

Breadboard and Jumper Kit: You must buy a breadboard and a jumper kit. The cheapest ones will do—I will show you examples in class.

 

Optional Stuff: If you get a multimeter that does not have clips at the end of at least one set of leads (sometimes these are an option), you might want to invest in a pair of wires with alligator clips on either end. This can make taking measurements much more convenient, and they're cheap. Needle nose pliers, wire strippers, screwdriver and soldering iron are part of any good tool kit. You may want to start collecting these items.

 

Parts for This Lab

 

·         Breadboard—you provide this.

·         Jumper Wire Kit—you provide this. Note: you could also buy thin wire and strip it by hand.

·         30 W 1/4 Watt, 5% tolerance resistor (Orange Black Black Gold) –I provide this.

·         ? W 1/4 Watt, 5% tolerance  (mystery) resistor –I provide this.

·         1 kW 1/4 Watt, 5% tolerance resistor (Brown Black Red Gold) –I provide this.

·         1.5W 1/4 Watt, 5% tolerance resistor (Brown Green Red Gold) –I provide this.

·          Diode (1N4148) –I provide this.

·         0.1 μ Farad Ceramic Disc Capacitor–I provide this.

·         100mH Inductor–I provide this.

·         1000 W potentiometer (1/4 Watt) –I provide this.

·         Potentiometer adjustment tool (a small screwdriver)—you provide this.

·         9V battery connector–I provide this.

·         9V battery—you provide this.

 

The breadboard is typically a white piece of plastic with lots of tiny little holes in it. You stick wires and component leads into the holes to make circuits. Some of the holes are already electrically connected with each other. The holes are 0.1 inch apart, which is the standard spacing for leads on integrated circuit dual in-line packages (DIP). You will investigate the breadboard internal connections in this lab.

 

 

The arrowed green lines on the above drawing indicate how the holes are connected internally in the breadboard. Each of the two outer rows of holes on each side of the breadboard, marked with the + and  – symbols are connected together. These are commonly used as the power supply bus, because they run the length of the breadboard and have polarity markings. The central section of the breadboard is split into two. Each half consists of 63 columns of 5 holes. The 5 holes in each of these columns are connected together. The gap between each set of 63 columns allows a DIP package integrated circuit to be used on the breadboard without its opposing pins being connected together.

 

 

 

 

Jumper Wire Kit: This kit contains assorted lengths of pre-stripped wire. (Stripping means removing the insulation from an end of a wire.) Working with pre-cut and pre-stripped wire is much easier than cutting and stripping your own wire.  The wire lengths are color-coded using the same colors as the resistor color code. For example a short yellow jumper wire will connect two holes that are four holes apart. Similarly a long orange jumper wire will connect two holes that are thirty holes apart.

 

 

Resistors are the small light brown tubular things with wires (leads) sticking out of each end and four colored rings on the body. The colored rings correspond to the resistors value. Use the resistor color code handout to determine a resistor value.

 

               

 

 

 

 

 

 

 

 

The ceramic disc capacitor is the light brown circular component with two wires. It is marked in black with the numbers “104”. These numbers represent its value in pico (1x10-12 ) Farads. The third number 4 represents the number of zero’s, so 104 is equal to 100,000 x 10-12 Farads or 0.1 x 10-6 Farads or 0.1 micro Farads (0.1 μF). There are several different types of capacitors each with there own characteristics. Selections of which are shown in the photograph below. The ceramic disc types are on the right hand side. Electrolytic capacitors have a clearly marked + and – terminal. These must be hooked up correctly or they will explode. The capacitor in the upper left hand corner is an electrolytic capacitor.

 

               

 

 

 

 

 

 

 

 

The diode is shaped sort of like a resistor, only smaller. It may have a tubular glass body with orange insides and one end will have a black band on it. They can also be all black with a silver band. The number (1N4148) is a standard part number. Diodes with different numbers will have different characteristics. The band on a diode indicates the cathode end. The other end is called the anode.

 

               

 

 

 

 

 

 

 

 

The 1000 W potentiometer (sometimes called a "pot") is the rectangular or cubed blue devise. It is a variable resistor that can be adjusted with a small screwdriver or adjustment tool.

                 

 

 

 

 

 

 

 

 

 

The 100 mH inductor is the blue cylindrical device with two wires. It is marked in black with LJ 410. Inside the blue plastic case will be an enameled copper wire coil. A practical inductor will typically also have a resistance of several ohms dependant upon the size of copper wire used.

 

                 

 

 

 

 

 

 

 

 

 

 

The 9V battery connector is the black plastic cap with two snaps mounted on it and a couple of wires coming out of its side. The snaps fit with the snaps on the top of the 9V battery. The red wire is from the positive terminal of the battery, the black from the negative terminal.
Laboratory Procedures, Measurements and Questions

 

Record your data and the answers to questions on a separate sheet (or sheets) of paper and hand it in when the lab is due. You will also have to bring your breadboard with designated circuits on it to me the week the lab is due.

 

Procedure 1 (15 points)

 

Use your multimeter to verify the connections in your breadboard in the first 5 columns and the top two rows of the breadboard as indicated on the diagram below.

 

 

 

Sketch enough of the holes on your breadboard to illustrate its connectivity. (Do NOT sketch the entire breadboard! Just enough so the pattern of connections is clear.) Set your multimeter on resistance. To find out if any two holes are connected, measure the resistance between them with the multimeter. This is called a continuity check.

 

a.        (2 points) What will the resistance be between connected holes?

 

b.       (2 points) What will the resistance be between unconnected holes?

 

c.        (1 point) Does it make a difference which probe goes in which hole?

 

d.       (10 points) Draw the connections you find into your sketch of the breadboard holes.

 

Some hints on measuring resistance:

 

Never try to measure resistance in energized circuits (ones with the power on). You won't get an accurate value and you could damage your multimeter or the circuit.

 

Your multimeter probes probably don't fit into the breadboard holes. Stick the stripped end of a wire into each hole, and touch the other stripped ends of the wires with the multimeter probes. If you have clips at the end of your multimeter leads, or you bought those optional alligator clips, you can clip on to the ends of the wires and move the wires from hole to hole. Resistor leads also work for this purpose, but make sure you are not measuring the resistor resistance as well as the breadboard resistance!

 

Because the multimeter uses a low voltage to measure resistance, you can safely use your fingers to press the wires to the multimeter probes to be sure you have a good contact. If you do, though, you will put your body in parallel with the resistance you are measuring. This can be important for certain values of resistance, those near your body resistance. It's usually not a problem for continuity checks.

 

Switch the multimeter to off or to the voltage setting when you are not actively measuring resistance. This minimizes battery use in the multimeter and is also safer. (Electrical safety will be covered more thoroughly in later labs. This lab is safe.)

 

Procedure 2 (15 points)

 

Construct the following circuit on your breadboard with R1 = 30 Ω and R2 = Yellow Orange Black (Mystery resistor).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


  1. (2.5 points) Draw the circuit schematic diagram using standard symbols for resistors and batteries.

 

  1. (2.5 points) Measure the voltage v2 (across R2) with respect to the smallest voltage in the circuit (negative terminal of the battery). Note the value.

 

  1. (2.5 points) Measure the current I using your multimeter. Note the value.

 

(Hint: Insert multimeter into circuit to measure current. See below.)

 

  1. (2.5 points) Calculate the value of the mystery resistance R2 using Ohm’s law.

 

  1. (2.5 points) Take R2 out of the circuit and measure its resistance with your multimeter. Write down the calculated value, the measured value, and the value according to the color code. Are they within the resistor accuracy tolerance?

 

  1. (2.5 points) What is the error between the coded value and the measured value

               

(Hint)

                %Error =

 

 

Construction hints:

 


Bend the resistor leads at right angles near the resistor body to make a U-shape with a flat bottom, and then insert the leads directly into breadboard holes. Make sure they go in to the spring clips in the holes. Sometimes the springs don't want to let the leads in. With a little experience you will be able to tell when you have the leads in, and when you don't.

 


You can do the same thing with wires.  If you really like being neat, you can use a pair of needle-nosed pliers to make neat, precise bends, a pair of diagonal cutters to snip the leads and wires to length, and a wire stripper to remove the insulation from the newly cut wire ends. Neatness can improve your clarity of understanding of the circuit. However, you will be graded on the function of your circuits, not their appearance.

 

Your breadboard has vertical rows of connected holes that run the length of the breadboard, often with red and blue stripes marking them. They are usually used for the positive and negative terminals of the battery or other power supply voltage.

 

 

The diagram above shows how to lay out the components on the breadboard for procedure 2. The magenta lines represent the breadboard internal connections.

 

 

Procedure 3 (15 points)

 

Construct the following circuit on your breadboard using a 30 Ω resistor for R1 and a 0.1μF ceramic disc capacitor for C1.

 

a.        (3 points) What is the basic relationship between current and voltage in the capacitor? Refer to Chap 6 of your textbook.

 

b.       (3 points) In this DC (steady state) circuit, what happens to the current through the capacitor? Why?

 

c.        (4 points) Measure the voltage across R1. Use this value to calculate the current through R1 and the capacitor? Is this the value you expected from part b?

 

(hint: See diagram.)

 

d.       (5 points) Can the capacitor be modeled as an open circuit or a short circuit?

 

 

Procedure 4 (15 points)

 

Construct the following circuit on your breadboard using a 30 Ω resistor for R1 and a 100mH inductor for L1.

 

 

  1. (3 points) What is the basic relationship between current and voltage in the inductor? Refer to Chapter 6 of your textbook.

 

  1. (3 points) In this DC (steady state) circuit, what happens to the voltage across the inductor? Why?

 

  1. (4 points) Measure the voltage across the inductor. Is this the value you expected from part b?

 

  1. (5 points) If the inductor were “ideal” and produced the voltage you found in part b, would you model it as an open circuit or a short circuit?

 

 

Procedure 5 (30 points PLUS 10 points for correct demo. Total of 40 points)

(Make this circuit on the board and demonstrate it your instructor.)

 

 

 

Construct the following circuit on your breadboard using a 30 Ω resistor for R1 the 1000 ohm (1k Ω) potentiometer for P1 and a 1N4148 diode for D1. The black band denotes the cathode.

 

(Hint: The pot has three leads, the middle connection is the movable wiper and is represented by the arrow on the schematic)

 

 

 

  1. With the potentiometer removed from the circuit, adjust the resistance to 100 ohms using a screwdriver. Return the pot to the circuit and measure the voltage across the 30-ohm resistor R1. Calculate the current through the diode.

 

  1. (8 points) Measure the voltage across the diode.

 

  1. What is the current through the diode?

 

  1. Repeat parts a. with the pot set to 300, 600, and 1000 ohms.

 

  1. (8 points) Plot the voltage across the diode (x-axis) vs. the current through the diode (y-axis). Is the diode a linear device? Why or why not? If it is not linear, what does the I-V relationship look like? (Hint: exponential, square, square root etc)