© Jonathan Bartlett 2020
J. BartlettElectronics for Beginnershttps://doi.org/10.1007/978-1-4842-5979-5_6

6. Constructing and Testing Circuits

Jonathan Bartlett1 
(1)
Tulsa, OK, USA
 

In Chapter 5, we learned how a circuit works. However, the method of putting together a circuit in the chapter doesn’t translate to the real world well. In this chapter, we will learn how to use solderless breadboards to construct circuits in a more robust manner. Additionally, we will put our understanding of Ohm’s law to the test as we learn how to measure voltages in circuits using our multimeter.

6.1 The Solderless Breadboard

The most important piece of equipment to use for making circuits is the solderless breadboard. Before solderless breadboards, if you wanted to put together a circuit, you had to attach them to a physical piece of wood to hold them down and then solder the pieces together. Soldering is a process where two wires are physically joined using heat and a type of metal called solder, which melts at much lower temperatures than other types of metal. So what you would have to do is attach the electrical components to the board, wrap the components’ legs around each other, and then heat them up with a soldering iron and add solder to join them permanantly.

This was an involved process, and, though it was sometimes possible to get your components back by reheating the soldered joints, you were generally stuck with your results. The solderless breadboard is an amazing invention that allows us to quickly and easily create and modify circuits without any trouble at all. Figure 6-1 shows what a solderless breadboard looks like, and Figure 6-2 has the different parts of the breadboard labeled.
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Figure 6-1

A Solderless Breadboard

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Figure 6-2

Parts of a Solderless Breadboard

The solderless breadboard has a number of spring clips (usually about 400 or 800 of them) called connection points which will allow you to insert wires or component leads and will hold them in place. Not only that, the breadboard itself will connect the components for you!

The way that this works is that the breadboard is broken up into little half-rows called terminal strips. Each terminal strip has multiple connection points—usually five. Each connection point on a given terminal strip is connected by wire inside the breadboard. Therefore, to connect two wires or leads together, all you need to do is connect them to the same terminal strip. Any two wires or leads connected to the same terminal strip are themselves connected.

In most breadboards, the two sides of the breadboard are separated by a gulf known as the bridge. The bridge is a visual indication that the two sets of terminal strips are not connected, but it also serves a practical purpose. If you have an integrated circuit (a small chip), the bridge is the right width so that you can place your integrated circuit right over the bridge, and each leg of the chip will receive its own terminal strip for you to easily connect them to what you need. We will cover this in more depth in later chapters.

In addition to the terminal strips, most breadboards have two strips running down each side, one with a red line and one with a blue line. These are known as power rails (some people call them power buses).

Power rails are very similar to terminal strips, with a few exceptions. The main difference is that, in terminal strips, only the five connection points grouped together are connected. On power rails, many more of the connection points are connected together, even when there are short gaps. Some boards will split the power rails at the halfway point, but others go all the way down the board. A split in the power rails is usually visually indicated by a break in the red and blue lines that indicate the power rails.

Note that the positive and negative are not connected to each other (that would create a short circuit) and they are not connected to the power rails on the other side of the breadboard (unless you connect them manually). On some breadboards, even a single side isn’t connected all the way down, but may be broken into sections at the halfway point.

In many projects, many components need direct access to the positive or negative power supply. Power rails make this easy by providing a connection point with positive and negative power a very short distance away from wherever you need it on the breadboard. If you plug your power source’s positive and negative terminals into the positive and negative rails on the breadboard, then any time you need a connection to the positive or negative terminal, you can just bring a wire to the closest connection point on the appropriate power rail.

6.2 Putting a Circuit onto a Breadboard

To see how a simple circuit works on a breadboard, let’s go back to the circuit we first looked at in Chapter 5. Figure 6-3 has the drawing again for ease of reference.
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Figure 6-3

Basic LED Circuit

So how do we translate what we see in the drawing to what we need to put in the breadboard? Well, let’s take a look at what is in the circuit—a 9-volt battery, an LED (we will go with a red LED), and a 1,000 Ω resistor. Let us not concern ourselves with the battery at the moment. So, without the battery, we have a resistor connected to an LED.

Let us start out by simply placing our components onto the breadboard. What you will want is to place them on the breadboard so that each of their legs is on a different terminal strip. It doesn’t matter which terminal strips you use—just make sure the legs all get plugged into different ones. Figure 6-4 shows how your breadboard should look so far. Note that the longer leg of the LED is closer to the resistor. The longer leg is depicted in the diagram as having an extra bend in the leg.
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Figure 6-4

Putting the Components onto the Breadboard

Figure 6-5 shows the wrong way to do it. In that figure, the legs of both the components are on the same row, which is the same thing as placing a wire between the legs, creating a short circuit. Don’t do that! Make sure each leg goes into its own row.
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Figure 6-5

The Wrong Way to Put Components onto the Breadboard

Now, to connect the resistor to the LED, we need to add a wire. So all we need to do is connect a wire to any empty connection point that is on the same terminal strip of the right leg of the resistor and connect the other side of that wire to the left leg of the LED as shown in Figure 6-6.
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Figure 6-6

Adding a Wire to Connect the Components

Note that wires used on breadboards are often called “jumper wires.” The difference between these and other kinds of wires is that jumper wires usually have solid, hard ends, making them easier to push into the breadboard. If you use regular wire or speaker wire, the ends are flexible, and it is almost impossible to get them into the breadboard properly to connect.

A common mistake that people will make is to connect the wire to the row right before or after the component. Take some time and be extra certain that the wire is connected to the very same row as the leg of your components.

Now, we need to connect our project to the power rails. So take a red wire from the left leg of the resistor to the positive power rail (remember, as long as it is in the same terminal strip as the resistor, they will be connected). Likewise, take a black wire from the right leg of the LED to the negative power rail. I always use red wires for connecting to the positive power rail and black wires for connecting to the negative/ground rail, as it makes it more clear when I am looking at my project what wire carries what. Your project should look like Figure 6-7.
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Figure 6-7

Adding Wires to the Power Rails

Now your project is almost done. All you need to do now is to connect your power rails to a power supply. Connect a T-connector to a 9-volt battery, and then connect the red (positive) wire to the positive power rail on the breadboard.1 You can plug it in anywhere on the rail, but I usually connect the power to the edge of the rail to leave more room for components. Then, connect the black (negative) wire to the negative power rail on the breadboard. As soon as you do this, the LED should light up! Figure 6-8 shows the final circuit.
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Figure 6-8

Final LED Circuit with Power Connected

Note that many T-connectors for 9-volt batteries have very flimsy wires that are difficult to insert into a breadboard. Usually, as long as you can get both terminals in far enough to touch the metal within the connection point, it will work. We will move to using power regulators shortly, which makes the process a bit easier.

If your circuit doesn’t work, here is a list of things to check:
  1. 1.

    Make sure your battery is properly connected to the breadboard—the red should go to positive and the black to negative.

     
  2. 2.

    Make sure there are no wires directly connecting positive to negative on the board. Any direct pathway from positive to negative without going through a component will cause a short circuit and can destroy your components and battery.

     
  3. 3.

    Make sure that your wires are connected to the same terminal strip as the component lead that they are supposed to be connected to. If they are on a different row, they are not connected !

     
  4. 4.

    Make sure the LED is inserted in the right way. The longer leg should be connected to the resistor, and the shorter leg should be connected to the negative power supply.

     
  5. 5.

    Make sure your components are good. Try replacing your LED with another LED to see if it works.

     
  6. 6.

    If all of those things fail, take a picture of your project and post it to an online forum. Someone will likely be able to spot your problem and/or lead you in the right direction. Many forums are also available on the Web for this.

     

6.3 Using Fewer Wires

In the previous section, we used three wires to connect our components, plus two more wires from the battery. We can improve our project by reworking it so that most of the wires are not necessary.

Remember that any two leads or wires plugged in next to each other on the same terminal strip are connected. Therefore, we can remove the wire that goes from the LED to the resistor simply by moving the LED and resistor so that the right leg of the resistor is on the same terminal strip. Figure 6-9 shows what this looks like.
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Figure 6-9

Joining Components by Putting Their Leads on the Same Terminal Strip

However, that middle wire is not the only redundant wire. If you think about it, we could also save a wire by actually using the LED’s own lead to go back to the negative rail. Figure 6-10 shows how this is set up. Now, in order to make the LED fit better, it is now on the other side of the resistor in the terminal strip. Remember that this does not matter at all! No matter where a component is connected on the terminal strip, it is joined with a wire to every other component on the same terminal strip.
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Figure 6-10

Directly Connecting the LED to the Negative Rail

Now, there is one last wire that we can get rid of. Can you think of which one it is? If you said the wire going from the positive rail to the resistor, you were right.

What we can do is to directly connect the resistor to the positive rail. Doing this gives us what is shown in Figure 6-11.
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Figure 6-11

Connecting the Resistor Directly to the Positive Rail

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Figure 6-12

A Low-Cost Multimeter

Therefore, as you can see, there are any number of ways that you can arrange parts on a breadboard to match a given schematic. All of these arrangements we have seen match the schematic given in Figure 6-3. As long as your circuit matches the configuration in the schematic, the specifics of where you put the wires and components is up to you. Some people like to place the components on their breadboard first, spaced out, and then add wires to connect them as needed. This works, though it does make for a messier board, with lots of wires going every which way. Other people like to use as few wires as possible and have their layouts as clean as possible (i.e., they don’t like a tangled mess).

Some people like to use flexible jumper wires that go up and over the board. Other people like to use rigid jumper wires that lie down close to the board and are the exact length needed. The flexible wire allows more flexibility in building your circuits (they are easier to move around and reconfigure), while the solid, rigid wire makes the final result a lot cleaner and easier to follow.

You can also trim the legs of your components to make them fit better, if you want. Some people like to leave their components as intact as possible, while others like to trim the legs of their leads to be the exact right size for their project. However, if you do trim the leads on your LEDs, be sure to keep the positive leg longer!

However you like to work with electronics is up to you. There are lots of options, and they all end up with the same circuit.

6.4 Testing Circuits with a Multimeter

Now that we know how to put circuits together, we need to know how to test our circuits. The main tool used to test simple circuits is the multimeter. It is called a multimeter because it measures multiple different things about a circuit. Figure 6-12 shows a typical low-cost multimeter.

There are a lot of different multimeters around which have a lot of different functions. However, almost all of them will measure voltage, current, and resistance. Each of these values is measured by testing two different points on the circuit. Most multimeters have a red lead and a black lead. The red lead should connect to the more positive side of the circuit, and the black lead should connect to the more negative side of the circuit. However, if you get it reversed, it is usually fine—the multimeter may just report negative values if you are measuring for voltage or current.

To illustrate how to use a multimeter, we will start out measuring the voltage in a 9-volt battery. Remember from Chapter 4 that there is no absolute zero voltage—voltages are merely measured with reference to each other. Therefore, a multimeter doesn’t tell you the exact voltage of something—there is no exact voltage. Instead, a multimeter allows you to choose two points on your circuit and measure the voltage difference (also known as the voltage drop) between them.

Now, remember that a 9-volt battery means that the battery should have 9 volts between its positive and negative terminals. Don’t try it yet, but when we measure voltage, we will expect that the multimeter will tell us that the voltage difference is near 9 volts.

When using your multimeter, you must set what you are going to test before you test it. Otherwise, you can easily damage your multimeter or your circuit. Therefore, since we are going to measure voltage, select the DC Voltage setting on your multimeter (do not select the DC Current or DC Resistance setting!). If you are using a high-quality auto-ranging multimeter , that is all you need to do. However, when starting out, most people buy the bottom-of-the-line multimeter. That’s not a problem, but just know that you will probably accidentally break it at some point.

If you are using a lower-quality multimeter, you will need to select not only what you want to measure but the estimated range of values that you want to measure. On my multimeter, the DC Voltage has five different settings—1000, 200, 20, 2000 m, and 200 m. These are the upper boundaries (in volts) that these settings can read.

So, for a 9-volt battery, using the 1,000-volt setting is probably unwise. It may give a reading, but it probably won’t be accurate. However, if I try it on too low of a setting (say, 2000 m), it either won’t read, or it will blow out my multimeter. So the safe thing to do is to start with the highest reasonable setting (or just the highest setting if you don’t know what’s reasonable) and test it and then reduce the setting until it gives you a good reading.

So, for instance, for my 9-volt battery, let’s say I didn’t know the voltage. Therefore, I’m going to measure the battery using the 1,000-volt setting. After setting the multimeter to 1,000 volts, I will put the red lead on the positive terminal of the battery and the black lead on the negative terminal. Be sure that you firmly press the tip of your leads against the positive and negative terminals. If it is not firm or if you use the sides of your terminals, you will not get a good reading.

When I do this, my multimeter reads 9.

Now, notice that this reading is significantly less than our 1,000-volt setting. Therefore, it may not be entirely accurate. So I will reduce the setting to the 200-volt setting and measure again. This time, my multimeter reads 9.6. This is definitely a more accurate reading—it is giving me an extra digit of accuracy! However, this reading is still significantly below the setting.

Therefore, I will reduce the setting again to the 20-volt setting and remeasure. This time, the measurement is 9.66. Again, it is more accurate. Now, can I reduce the setting even more? Well, the next setting is 2000 m, which is basically 2 volts. Our reading is 9.66 volts, so it is above the cutoff point for the next setting. Therefore, I should not try it on a lower setting, both for the sake of accuracy and for the sake of my multimeter’s lifespan.

However, I should note that if I did use a lower setting, since the setting is listed as being in millivolts (i.e., 2000 m), then the reading would also be in millivolts. That is, if we were to read the value of the battery on that setting, it would say 9660, because that is how many millivolts the battery has.

Now, you could be wondering, why is a 9-volt battery anything other than exactly 9 volts? Well, it turns out that in electronics, no value is exact, and no formula works perfectly. When we talk about a 9-volt battery, we are actually talking about a battery that runs anywhere from 7 volts to 9.7 volts. In fact, my battery that started out at 9.66 volts will slowly lose voltage as it discharges. This is one of the reasons why measurement is so important.

Also, this means that in our circuits, we will have to find ways to compensate for varying values. Our circuits should work across a wide range of possible values for our components. We will discuss strategies for this as we go forward.

The next thing we will measure is resistance. Pull out a resistor—any resistor. The resistor datasheet in Appendix E shows you how to find the resistor values based on the color bands on the resistor. I don’t know about you, but my eyes are not that good at looking at those tiny lines on the resistor and figuring out which color is which. Many times, it is easier just to test it with the multimeter.

The process is the same as with measuring the voltage, except that you start at the lowest setting and work up. First, find the resistance settings on your multimeter (perhaps just marked with the symbol for ohms—Ω). Start with the smallest value (200 in my case). On this setting, the multimeter read 1, which means that it didn’t pick up a signal. So I turned it up to the next setting, 2000. This time, it read 1002. Remember that if the value that the meter is set to includes a metric suffix (i.e., m, k, or M), that suffix gets applied to the value that is displayed on the screen.

Note that you should never test for resistance in a live circuit. The multimeter uses power to measure resistance, and if there is already power in the circuit, it can damage the multimeter and/or the circuit. However, to test for current and voltage the circuit must be powered.

6.5 Using a Multimeter with a Breadboard

We can use our multimeter with our breadboard too. Let’s say that we wanted to measure the voltage between the positive and negative rails of the breadboard.

There are two ways to do this. The first, if the size of your multimeter probes and the size of your breadboard connection points allow it, is to simply shove the probes of your multimeter into connection points on the positive and negative rails. Since these will be connected to the power by a wire, these will be at the same voltage levels as the battery itself.

Second, if your breadboard/multimeter combination does not support this, you can do the same thing by simply connecting two jumper wires into the positive and negative rails and then testing the voltage on the other end of the wires.

Also, if you are testing components for voltage, you can also use your multimeter on the exposed legs of the component. This is often easier than either trying to push your probes into the breadboard or running extra wires to your multimeter.

To try out using your multimeter with your breadboard, configure your breadboard similar to Figure 6-8. Use this layout, and not one of the ones with fewer wires (you will see why in a minute). With the battery connected to the breadboard, set your multimeter to the highest voltage setting, and put the red lead in any empty hole in the positive rail. While that lead is there, put the black lead in any empty hole in the negative rail.

This should give you the same reading that you received for the battery terminals. Remember that the power rails are connected all the way across—that is why putting your probes in any hole on the line works! If you work your way down the ranges on your multimeter, you should find that you get the same value that you did when you measured directly on the battery’s terminals. Again, if your probes do not fit inside the connection points, you can also use wires to connect out from your breadboard to your multimeter probes.

You can now do the same to any component on your board. Let’s find the voltage difference between one side of the resistor and the other. To do this, find an empty hole on the same terminal strip as the left-hand side of the resistor, and put the red lead from your multimeter in that hole. Then, find an empty hole on the same terminal strip as the right-hand side of the resistor, and put the black lead from your multimeter in that hole. Now you can measure the voltage difference. Note that to measure voltage differences, the circuit must be active. If the power is gone, the voltage difference will likely drop to zero. Use the same ranging procedure to find the voltage drop between the left-hand and right-hand sides of the resistor.

Even though we have not discussed diodes, this doesn’t prevent you from measuring the voltage difference between the legs of the diode in your circuit. Use the same procedure as before to measure the voltage drop.

6.6 Measuring Current with a Multimeter

Now we will learn to measure current using the same circuit layout from Figure 6-8. Like voltage, measuring current requires that the power to your circuit be on. To measure current, use the DC Amperage (sometimes called DC Current) settings on your multimeter.

Measuring current is a little different than measuring voltage in a circuit. Instead of just placing your probes in the breadboard as it is, you are going to use your probes to replace a wire. You will remove a wire and then place your probes in the holes (connection points) where the wire used to be. Alternatively, if your multimeter probes do not fit into the connection points, you can again run two wires, one from each hole, from the breadboard to your multimeter probes.

Using either of these approaches, the circuit will then use your multimeter as the wire that was removed, and the multimeter will then measure how much current is running through it and report it to you on the screen. You will need to use the same ranging technique as you used before with voltages to get an accurate report.

Let’s say that you wanted to measure the current going through the wire that connects the resistor to the LED. To do this, we will start by removing that wire, and connecting the red lead to where the wire used to be on the left (since it is more positive) and the black lead to where the wire used to be on the right (since it is more negative). The multimeter should now report back how much current the circuit is using. This will vary for a number of reasons, but should be about 17 mA.

Now, put the wire back, and remove another wire and measure current there. No matter which wire you choose, they should all measure the same current. The reason is that, since all of these components are in series (one right after the other), they must all have the same amount of electricity flowing through them (otherwise, where would the electricity be going?).

6.7 Using a Power Regulator

So far, we have discussed several problems of using batteries in electronics projects. First, with batteries, we don’t know exactly how much voltage they will deliver. A 9 V battery will deliver between 7 V and 10 V, and the actual amount will vary across its life. Additionally, the connectors available from batteries usually don’t have the solid jumper wire ends, so it is hard to connect them to breadboards.

Both of these problems can be solved with a power regulator module. A power regulator module will take power from other sources (such as a battery) and reduce the voltage to a value which, while lower, will be constant. The power regulator we will use is the YwRobot breadboard power supply.

This low-cost device will take an input between 6.5 and 12 volts and deliver a constant voltage at the output of either 3.3 or 5 volts (we will use the 5 V setting). This device can be connected to a battery with an appropriate battery clip.2 Figure 6-13 shows what this looks like.
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Figure 6-13

Breadboard with a Power Module

As you can see, the power module clips onto the power rails of the breadboard. The most important thing is to make sure that the power module is oriented correctly so that the positive and negative markings on the power module line up with the positive and negative power rails. Additionally, this power module has a shunt which, depending on where it is placed, sets whether it outputs 3.3 V or 5 V or is switched off. You need to be sure that the shunts on both sides are set to the 5 V position.

Finally, you need to plug the battery in. A 9 V battery can be plugged into the power module using a battery clip designed for CCTV cameras. They have a 9 V clip on one side and a barrel plug on the other side, which plugs nicely into the power module. You can see one in Figure 6-14.
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Figure 6-14

9 V Battery Clip

After that is set up, don’t forget to turn it on! The power module has an LED that lights up when the power module is turned on. This is really convenient because you don’t have to include an on/off switch or an on light on your project, because the power module has one for you.

So how does the power module show up in the schematic? Well, actually, it doesn’t directly. The combination of battery and power module basically just yields a 5 V battery in the schematic. So we will just represent it with the normal battery symbol, but set to 5 volts.

There are other power modules available as well, and they all basically work the same way. Just be sure that the voltage is set to 5 volts.

6.8 Review

In this chapter, we learned the following:
  1. 1.

    Solderless breadboards can be used to quickly create circuits.

     
  2. 2.

    Solderless breadboards allow circuits to be easily constructed and destructed in such a way that the components are reusable from one project to the next.

     
  3. 3.

    Both wires and the legs of a component are attached to connection points on the breadboard.

     
  4. 4.

    Connection points in the same terminal strip are connected by a wire behind the breadboard.

     
  5. 5.

    To connect two components together, all you have to do is put their legs on the same terminal strip of the breadboard.

     
  6. 6.

    The power rails on a breadboard extend either all the way down the board or sometimes split at the halfway point.

     
  7. 7.

    The bridge of a breadboard divides and separates different groups of terminal strips. This allows a chip to be placed over the bridge, allowing each of its pins a separate terminal strip.

     
  8. 8.

    The schematic drawing of a circuit can be assembled onto a breadboard, giving a definite implementation of the drawing.

     
  9. 9.

    There are multiple different ways to place a given circuit drawing onto a breadboard.

     
  10. 10.

    Components on a breadboard can be connected by wires, or they can be connected by placing their legs in the same terminal strip.

     
  11. 11.

    There are many different styles of placing components onto breadboards, which have tradeoffs between how easy it is to reconfigure and how clean the result is.

     
  12. 12.

    A multimeter allows you to measure several important values on a circuit, including resistance, voltage, and current.

     
  13. 13.

    If your multimeter is not auto-ranging, you must test your value several times, starting with the highest range setting for the value you are looking for and decreasing it through the settings until you find a precise value. For resistance values, this is reversed—we start with the lowest range setting and move upward.

     
  14. 14.

    Always be sure your multimeter is set to the right setting before measuring.

     
  15. 15.

    Always turn your circuit off before measuring resistance.

     
  16. 16.

    Your circuit must be on to measure voltage or current.

     
  17. 17.

    Voltage is measured by connecting your multimeter to empty connection points in the terminal strips that you want to measure. This can be done either by putting your multimeter leads directly into the relevant connection points or by running wires from those connection points to your multimeter leads.

     
  18. 18.

    Current is measured by using your multimeter to replace a wire that you want to measure current running through.

     
  19. 19.

    Many circuit values vary much more than what you might think, so it is good to design circuits in a way that will handle these variances.

     
  20. 20.

    Power modules can deliver consistent voltages even when the components feeding into them (such as batteries) may have a significant amount of variance.

     

6.9 Apply What You Have Learned

All measured values should be measured using the ranging technique discussed in this chapter:
  1. 1.

    Start with the circuit you built in Figure 6-8. Measure the voltage drop across the resistor, and then measure the voltage drop across the LED. Now, measure the voltage drop across both of them (put the red multimeter lead on the left side of the resistor and the black multimeter lead on the right side of the LED). Write down your values.

     
  2. 2.

    Using the same circuit, change the LED from red to blue. Measure the values again and write them down. Measure the current going through the circuit using any wire. Is it the same or different than before?

     
  3. 3.

    Add another LED in series with the one you have already. Measure the voltage drops on each side of each component in the circuit. Measure the current going through any given wire. Write down each value.

     
  4. 4.

    Take the new circuit you built in the previous problem and draw the schematic for the circuit.

     
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