# Electronics Primer: Use a Breadboard to Build and Test a Simple Circuit

## Introduction

Breadboards are often used to test new circuit designs because it is faster and easier to experiment on a breadboard than it is to solder (fuse in to place) circuit components. In this mini electronics project, you will gain hands-on experience building and testing electronic circuits by creating a breadboard circuit with a resistor, a light-emitting diode (LED) , and a battery. The LED will light up when the circuit is closed or completed. This basic exercise will help prepare you for more advanced electronics projects.

## Build an LED Circuit

A circuit diagram (also known as a schematic) is used to plan and communicate the design of a circuit. Circuit components are represented by symbols. These symbols are standardized, but sometimes an engineer will use a nonstandard symbol. It is a good idea to check what the symbols mean in the specific diagram you are using. The symbols will often, but not always, have a label next to them that describes the circuit component and its value. Figure 1, below, shows the diagram for the LED circuit you will build in this project.

 Figure 1. LED circuit diagram. The resistor is indicated by a zigzag line, the LED is indicated by the triangle with a line, with arrows to represent the light that is emitted. Current flows from the positive terminal to the negative terminal of the 9 volt battery. In this case, the LED can be presumed to be a 'standard' LED since no specifics are given.

## Tips for Working with Breadboards

1. Use 22-gauge solid wire.
1. If the wire is bigger, it could permanently deform the spring contacts in the breadboard sockets and make those sockets unreliable in the future.
2. Test probes from multimeters are definitely too big for the holes in breadboards.
2. Some breadboards have bus lines that run all the way from one end of the board to the other. Bus lines are the columns of sockets beneath the + and − signs located at the edges of the breadboard. If you are not sure how your specific breadboard is wired internally, use your multimeter to verify which groups of holes are connected. The breadboard may also come with a map of its connections. This map, if present, can usually be found in the breadboard's instructions.
3. Breadboards are not meant for high-current connections.
4. Breadboards are not meant for high-voltage circuitry.
5. Be careful not to push insulation down into the spring contact in the breadboard sockets, as this can lead to a bad connection. Only put the bare, un-insulated part of the wire into the breadboard socket.
6. Stripping too much insulation or leaving long component leads may create accidental connections in the air above the breadboard, if two wires accidentally touch.
7. Some parts, like diodes, have a direction.
1. Adding a part in the wrong direction might damage it and make the circuit not work.
8. It is good practice to build up a circuit one stage at a time and to check the connections using an ohmmeter (a multimeter set to measure resistance) before applying power.
9. Light-emitting diodes (LEDs) almost always require a resistor in series to protect them from burning out. Online calculators can help you determine the correct resistor to use with a particular LED, such as this LED Calculator.

Figure 2, below, shows some of the parts of a breadboard, including a map of the connections between breadboard sockets.

 Figure 2. A solderless breadboard. The yellow lines on the image show how the sockets are connected. You can see that the vertical columns of holes labeled with a "+" are connected to each other, as are the columns of holes labeled with a "-." The columns labeled with a "+" are called the power bus, and the columns labeled with a "-" are called the ground bus. You will connect the power bus to a positive input voltage, such as the positive terminal of a 9-V battery, and you will connect the ground bus to the negative terminal of the battery. Note that in each row (numbered 1 through 30) sockets "a" to "e" are connected to each other. Sockets "f" to "j" are also connected to each other. These groups of connected sockets form a node.

## Materials and Equipment

Many of these components are available at electronics stores or from online retailers like Amazon.com. Figure 3, at the bottom of this list, shows what each of these items looks like.

• Breadboard, such as this one available on Amazon.com
• Multimeter
• Digital multimeters can be easier to use than analog multimeters.
• Some multimeters, like this one, require you to choose the range you expect your measurements to be in.
• Autoranging multimeters, like this one, are a bit more expensive, but they automatically adjust to the range your measurements are in.
• Many kinds of multimeters can work for this project.
• LED, standard red
• Tip: You can substitute a yellow, green or orange LED for the red one.
• Resistor, 220-Ω, 1/4-W, 5% carbon film
• Most resistors have colored bands on them, which tell you value of the resistor and its tolerance. The CSGNetwork.com website explains the resistor color code and has a nifty calculator that can help you interpret the colored bands correctly. The FAQ for this project also has information about the resistor color code.
• Wire stripper, any version for small wires will work, like this one available on Amazon.com
• 22-gauge wire, 60 centimeters (cm) about (2 feet)
• Tip: To make custom jumper wires, cut a piece of wire to your desired length (a strong pair of scissors will do this, since the wire in the kit is so narrow). Then, use wire strippers to remove the insulation from both ends of the jumper wire. Remove enough insulation so you have about 0.5 cm of bare copper wire on each end of the jumper wire.
• Battery connector, 9-V
• Battery, 9-V
 Figure 3. Materials to make and test a simple LED circuit.

## Experimental Procedure

1. Connect the components, as shown in Figure 4, below, and described in the following steps.
 Figure 4. Completed LED circuit. Current flows from 1 (the red, positive lead from the battery) to 8 (the black, negative lead from the battery). The resistor limits the current in the circuit. Without the resistor, the LED would burn out.
1. Attach the red, positive lead from the battery to the power bus, which is the column of sockets beneath the "+" sign, near the red line (#1 in Figure 4).
2. Connect the resistor to the power bus (#2 in Figure 4).
1. It does not matter which and of the resistor connects to the power bus.
2. The resistor limits the current to the LED. Without the resistor, the LED would burn out.
3. The resistor has a tolerance of 5%, meaning that its actual resistance is within ± 5% of the stated value.
3. Connect the other side of the resistor to one of the rows of five sockets (#3 in Figure 4).
4. Connect the long wire from the LED into the same row as the resistor (#4 in Figure 4).
1. Unlike resistors, orientation matters for LEDs. The LED will not work if you reverse the wires.
2. Check that the lead you inserted is NOT the lead on the flat side of the LED.
3. Tip: You can identify which lead from an LED goes towards positive and which goes towards negative by looking at the length of the leads and by looking for a flat side on the otherwise round LED. The lead on the side with the flat edge always goes towards the negative and is called the cathode. The longer lead goes towards the positive and is called the anode.
5. Attach the other (short) wire from the LED into a different row of five sockets (#5 in Figure 4).
6. Insert a short piece of 22-gauge wire, with the insulation removed about ½ cm from each end, into the same row of sockets as the short wire from the LED (#6 in Figure 4).
7. Insert the other end of the wire into the ground bus.
1. The ground bus is the column of sockets beneath the "-" sign, near the blue line.
2. The color of the line on your breadboard might not be blue.
8. Insert the black wire from the 9-V battery connector into the ground bus.
1. When the black wire from the battery connector is attached, the entire ground bus will be connected to the negative terminal of the battery.
9. Attach the battery to the 9-V battery connector. At this point, the LED should light up. If it does not, check the wiring carefully.
1. Tip: You can use a multimeter to help you isolate the problem with your circuit. For more details on how to do this, take a look at the Frequently Asked Questions page for this mini-Project.
10. Use this circuit to practice using your multimeter. Detailed directions for testing the circuit with your multimeter can be found on the Science Buddies page Using a Multimeter.

Congratulations! You've built your LED circuit!

## Variations

• Reverse the LED and see what happens.
• Add a switch to the circuit.
• Does it matter if the resistor is on the positive or negative side of the LED?
• Try different-colored LEDs. You will have to determine the correct resistance to use. This is easy to do. To determine the correct resistor to use with an LED, look on the LED package for the "forward current" and "forward voltage." Plug these numbers into one of several online LED resistance calculators, like this one, to get the correct resistance.
• Use two jumper wires to check which sockets are connected to each other on the breadboard. Set the multimeter to read "resistance." If the resistance between the two wires is zero, the sockets are connected.

Q: The LED is not turning on or emitting light, and it has never turned on or emitted light. What do I do?
A: If your LED has never lit up, then your circuit is probably incomplete; electric current is not able to flow through the circuit. This could be because the circuit's connections are incorrect or because of a faulty circuit component. Check that all of the circuit components are connected to the correct holes in the breadboard. Check your circuit against steps 2–10 of the procedure and against Figure 4 in the Project Idea.

Pay particular attention to the LED; make sure it is inserted correctly. Look at the leads coming from the LED and then look at the LED body itself. You should see one flat edge on the base of the LED that lines up with the shorter lead. This is the cathode and should go towards the negative or minus side of the battery. The longer lead then goes towards the positive or plus side. Remember that direction matters for a diode like an LED. In addition, if you pushed a stripped connection wire too far into the breadboard, then the insulation will lead to a bad connection.

If your components are connected in the correct places and there is no insulation in the breadboard sockets, but the LED still does not turn on, then rebuild the circuit and check each of the connections with a multimeter as you do so. By this systematic approach, you should be able to find out where the problem is:

1. Start by disconnecting the battery from the battery connector and removing all of the components from the circuit board.
2. Starting with step 2 of the Experimental Procedure, add each component to the breadboard.
3. As you add each component, use a multimeter to check the connectivity between the first component (the red battery lead, in this case) and the component you added.
1. To do this, turn the dial on the multimeter so that it measures resistance and touch the two probes of the multimeter to the two circuit components you are testing.
2. If the resistance between the two components is 0 (or very close to it), then the two components are connected and the circuit is complete between the two points.
1. If the circuit is complete between these two points, add the next component and check the connectivity between the first circuit component and this new circuit component.
2. Once you have added the resistor, the resistance of the circuit should be about 220 Ω. If the resistance is about 220 Ω, then the circuit is wired correctly and the components are connected correctly.
3. If the circuit is incomplete, then there is a problem between the beginning of the circuit and the component.
1. Once you know where the problem is, recheck those connections and circuit components. One of the odd things about circuits is that sometimes just taking things apart and putting them back together again can fix a problem!
Q: The LED was lighting up, but it suddenly stopped working. What should I do?
A: This could happen for a few reasons. If your LED was lit and then suddenly turned off, then the LED may have burned out. Double check your wiring to make sure you have the resistor connected in series with (in between) the battery and the LED. Make sure the resistor is the correct value. For a 9 volt battery, a 220 ohm resistor (red-red-brown) will light the LED safely.

To identify the source of the problem, start by using the multimeter to measure the voltage coming from the battery. To do so, turn the dial on the multimeter so that you are measuring DC volts (a 10 volt scale would work if you have to set a range). Touch one multimeter probe to each of the battery terminals. If the reading is much less than 9 volts, then the battery could be the problem. Try a new battery. If the voltage is ~9 volts, then the battery probably is not the problem. Use the steps 3a-c in the previous FAQ answer to check the connection between the resistor and LED.
Q: What do the colored bands on a resistor mean?
A: The colored bands indicate the value of the resistor and its tolerance. That is, they tell you how much resistance the resistor nominally provides, in ohms (Ω), and how close the actual resistance of your particular resistor is to the stated resistance value. For example, if the colored bands indicate a value of 220 Ω and a tolerance of ±5%, then the actual resistance of that resistor will be within 5% of 220 Ω, or somewhere between 209 and 231 Ω.

There are 10 possible colors on a resistor. Each color has a value from 0 to 9. You can think of the handy mnemonic "Bright Boys Rave Over Young Girls But Veto Getting Wed". It is a nonsense phrase, but the first letter of each word gives the colors in order from 0 to 9: Black, Brown, Red, Orange, Yellow, Green, Blue, Violet, Gray, and White.

On a standard resistor there are 4 colored stripes. One is a metallic stripe such as silver or gold. Start at the other end of the resistor, which will be one of the non-metallic, colored bands. The first two bands are digits of the resistor value. The third is a multiplier and tells you how many times to multiply the first two digits by 10. The fourth colored band indicates the precision, or how accurate the resistor value is likely to be.

In this project, we used a resistor with red-red-brown stripes. Red means 2, and we have two red bands, so the value so far is 22. The multiplier stripe is brown which means 1. Multiply 22 by 10 one time, to get 220. The fourth stripe is gold which means the resistor will be within 5% of the stated value. Precision bands of silver (10%) or no 4th band (20%) are uncommon.

You can read more about the resistor color code on the http://www.csgnetwork.com/resistcolcalc.html website, which has a table explaining what each band and each color means, along with a nifty resistance color code calculator.