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Introduction
Breadboards are often used for testing new designs since they do not involve soldering. The goal of this mini project is to gain hands-on experience building and testing electronic circuts 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. This basic exercise will help prepare you for more-complex electronics projects.
Build an LED Circuit
The components in a circuit have specific symbols that are used in a circuit diagram. The circuit diagram is used to plan and communicate the design of the circuit. The diagram for the LED circuit you will build is shown in Figure 1.
Figure 1. LED circuit diagram. The resistor is indicated by a rectangle, and the LED is indicated by the triangle with a line, and arrows represent the light that is emitted. Current flows from the positive terminal to the negative terminal of the battery.
Wire stripper, any version for small wires will work, from suppliers such as www.radioshack.com, part #: 64-2979
Alligator test leads, 14-inch, insulated test/jumper leads; available at www.radioshack.com, part #: 278-1156
These will be used to help measure the current through the circuit.
Battery, 9-V (1)
Solderless breadboard jumper wire kit; available at www.radioshack.com, part #: 276-173.
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Tips for Working with Breadboards
Use 22-gauge solid wire.
If the wire is bigger, it could permanently deform the spring contacts and render the future reuse of those holes unreliable.
Test probes from multimeters are definitely too big for these holes.
Some breadboards might have splits in their long connections.
Breadboards aren't meant for high-current connections.
Breadboards aren't meant for high-voltage circuitry.
Be careful not to push insulation down into the spring contact, as this might cause a bad connection.
Stripping too much insulation or leaving long component leads subject the circuit to accidental connections up in the air above the breadboard.
Some parts, like diodes, have a direction.
Adding a part in reversed direction might damage it and make the circuit inoperable.
It is good practice to build up a circuit one stage at a time and to check out the connections using an ohmmeter (a multimeter set to measure resistance) before applying power.
Light-emitting diodes (LEDs) usually require a resistor in series to protect them from burning out. There are online calculators that will help you determine the correct resistor to use with a particular LED, such at this LED Calculator.
Figure 2. A solderless breadboard. The yellow lines on the image on the right 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 you will connect one of them to a positive input voltage, such as the positive terminal of a 9-V battery. One of the columns labeled with a "-" (the ground bus) will be attached 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. And "f" to "j" are also connected to each other. These groups of connected sockets form a node.
Figure 3. Material to make and test a simple LED circuit.
Procedure
Connect the components, as shown and described in Figure 4.
Figure 4. Completed LED circuit. Current flows from 1 to 8. The resistor is in the circuit to control the current. Without the resistor, the LED would burn out
Attach the red positive lead from the battery to the power bus, which is the column of sockets near the red line (#1 in Figure 4).
Connect the resistor to the power bus (#2 in Figure 4).
It does not matter in which direction you put the resistor.
The resistor limits the current to the LED. Without the resistor, the LED would burn out.
The resistor has a tolerance of 5%, meaning that its actual resistance is within ± 5% of the stated value.
Connect the other side of the resistor to one of the rows of five sockets (#3 in Figure 4).
Connect the long wire from the LED into the same row as the resistor (#4 in Figure 4).
Orientation matters for LEDs. It will not work if you reverse the wires.
Attach the other (short) wire from the LED into a different row of five sockets (#5 in Figure 4).
Insert a jumper wire into the same row of sockets (#6 in Figure 4).
Insert the other end of the jumper wire into the ground bus.
The ground bus is the column of sockets near the blue line.
The color does not have to be blue.
When the black wire from the battery is attached, the whole ground bus will be connected to the negative terminal of the battery.
Insert the black wire from the battery into the ground bus.
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.
Use this circuit to practice with 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 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.
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