The easiest way to get started building electronic circuits is by using a solderless breadboard. A breadboard is a tool for holding the components of your circuit, and connecting them together. It’s got holes that are the right size for hookup wires and the ends of most components, so you can push wires and components in and pull them out without much trouble. This lab shows how to set up a breadboard with an independent power supply (9-12V) through a 5V Voltage Regulator (7805).
What You’ll Need to Know
To get the most out of this lab, you should be familiar with the following concepts beforehand. If you’re not, review the links below:
- What is a Voltage Regulator
- Batteries and Power Supplies
- All about DC Power supplies – this page will introduce you to DC power supplies. You probably have several in your house already, and this lesson will tell you more about how they work and how you can use them.
Safety Warning: When inserting components on or removing components from a breadboard always unplug power supply first!
Things You’ll Need
Setting up the Breadboard
Figure 8 shows a typical breadboard with a 7805 5-Volt voltage regulator mounted on it. There are several rows of holes for components. The holes on the breadboard are separated by 0.1-inch spaces, and are organized in many short rows in the center, and in two long rows down each side of the board. The short horizontal rows in the middle are separated by a center divider. The pattern varies from model to model; some breadboards have only one strip down each side, others have multiple side rows, and some have no side rows at all.
On each side of the board are two long rows of holes, with a black or a red line next to each row (on many boards, you’ll see a blue row instead of black). All the holes in each of these lines are connected together with a strip of metal in the back. In the center are several short rows of holes separated by a central divider. All of the five holes in each row in the center are connected with a metal strip as well. This allows you to use the holes in any given row to connect components together. To see which holes are connected to which, take a multimeter and a couple of wires, set the multimeter to measure continuity, stick the two wires in two holes, and measure them with the multimeter. If the meter indicates continuity, then the two holes in question are connected.
What’s Inside A Breadboard?
The image below (Figure 9) of the back of a breadboard may help to clear up how the holes on the front of the board are connected. The backing of the board has been removed (don’t remove the backing on your own board! It will make the board useless) to expose the metal strips connecting the holes. You can clearly see the short strips in the center separated by the divider, and the long strips down the side. The detailed photo in Figure 10 illustrates how the holes and strips are related.
The reason for the center divider is so that you can mount integrated circuit chips, like a microprocessor, on the breadboard. IC chips in a DIP package (Dual In-line Package) have two rows of pins that to which you need to connect other components. The center row isolates the two rows from each other, and gives you several holes connected to each pin, so that you can connect other components.
Powering the Breadboard
Avoid adding, removing, or changing components on a breadboard whenever the board is powered. You risk shocking yourself and damaging your components.
The regulator in Figure 11 is used to supply 5 Volts to the two red side rows of the breadboard. You’re looking at the back of the regulator, so that the pins are, from left to right: voltage out, ground, voltage in. Notice that the regulator’s voltage out pin on the left is connected to the red row with a wire. The two black side rows are connected to ground pin of the regulator. These will be your voltage and ground bus rows. They give you lots of convenient places to connect to voltage or ground as needed.
Note: The pin functions for the LD1117 regulator (datasheet) differ from the 7805. The pins are (left to right, as seen from the front of the board):
7805: 1) V in 2) Ground 3) V out
LD117: 1) Ground 2) V out 3) V in
If using the LD1117 instead of the 7805, adjust your breadboard accordingly. Also note that the board will be using 3.3V instead of 5V, so adjust things like LED resistors accordingly as well.
With your board connected like this, you’ll be able to build many different 5-Volt circuits on the board. The last thing you need to add is a power connector to connect 9 – 12 volts DC to supply power for the voltage regulator. Figure 12 below shows a power connector connected to the voltage input and ground pins of the voltage regulator.
Will it Light? Test Your Understanding
Figures 13-23 below show an LED and a resistor connected in a breadboard. Some are connected correctly and others are not. Take a guess as to whether the LED will light or not, then click the links below the image to find out. All of the circuits below should realize the same circuit, shown in the schematic below:
As in Figure 14, will the LED below light up when you power the board? Take a guess, then click the link below the image to find out.
As in Figure 14, the LED will light up because the circuit is wired correctly. The power flows from bus row through the resistor to row twelve of the board. The LED’s anode connects to the same row, and the cathode is in another row, row fourteen. Then the black wire connects that second row to the ground bus, completing the circuit. The LED will light.
Try another one. As in Figure 16, will the LED below light up when you power the board? Take a guess, then click the link below the image to find out.
The photo above, Figure 16, is wired incorrectly. The power flows from bus row through the resistor to row thirteen of the board. The LED’s anode connects to the same row, but on the other side of the center divide, so there is a break in between the resistor and the LED. The LED will not light.
Here’s a third one, Figure 17. Will the LED below light up when you power the board? Take a guess, then click the link below the image to find out.
The photo above, Figure 18, is wired correctly. It’s almost the same as Figure 16, but now the two sides of the junction row are connected by a wire, completing the circuit. The LED will light up.
Here’s another test. In Figure 19, will the LED below light up when you power the board? Take a guess, then click the link below the image to find out.
The photo above, Figure 18, is wired incorrectly. Both of the LED’s connections are in the same junction row as the end of the resistor, so the LED is bypassed by the conductor under the row. The schematic below, Figure 20, shows what’s happening electrically. The LED will not light. This is a short circuit. The schematic below shows it.
Here’s a final test. In Figure 21, will the LED below light up when you power the board? Take a guess, then click the link below the image to find out.
The photo above, Figure 21, is wired correctly. The resistor connects to power on the right, the resistor spans the center divider, and the black wire connects to ground on the left. The LED will light.
If you connected an LED and resistor just as it’s shown in Figure 22, and it didn’t light, check to make sure that the anode (the long leg) of the LED is connected to the resistor, and the cathode (the short leg) is connected to the ground wire.
Below, as shown in Figure 23, the three LED’s are connected in parallel using two rows. They are then connected to power and ground by connecting the rows to the voltage row and the ground row. These three LEDs are in parallel with each other.
Many options are possible using a breadboard, which is what makes them very useful and convenient for building circuits. Once you understand which holes are connected to each other (and which ones are not), you can build any circuit very quickly.
It’s a good idea to keep your circuits neat. When possible, shorten the leads on components so there is no bare metal sticking up from the breadboard. Make sure no wires cross each other with metal touching (this is the biggest source of short circuits on a breadboard). Lay things out as sensibly as possible, so each component of the circuit is near the components it needs to connect to. Use wires when needed to separate parts of the circuit that are crowded together. Use consistent colors of wires when possible; for example, use green or black for ground connections, red for power connections, white or blue for data connections, and so forth. This will make your troubleshooting much easier.