What is a Breadboard?

Notice the nails hammered right into the board, and how they are used as solder connection points for the circuit's components.

An early breadboard.

Way back in the early 1900’s, when hobbyists were just getting started in electronics, experimenters needed a way to quickly get a circuit up and running.  Nearly every kitchen had a small piece of wood for cutting the bread (remember, pre-sliced bread did not come out until 1928, so this was before sliced bread.)  This piece of wood was about one foot long by about eight to ten inches wide and about ½” thick.  It was about the perfect size to set up for experimenting with electronic circuits.  The aspiring engineer could just take a few nails and hammer them in to the wood and then solder his components right to the nails.  Quick, easy, simple…, and it left your circuit wide open for hooking up meters and other test equipment.  You could also easily extend your circuit by just adding more nails and soldering your components on.  Thus the name for our rapid prototyping system: a breadboard.  The only down side came about when Mom went to get her breadboard to slice the bread which just came out of the oven.  She usually disapproved of the shape of her poor cutting board, sometimes vehemently so.

The breadboards we have are usually not found in the kitchen and are specialized tools meant to quickly set up new circuits on a temporary basis.  Once you have completed your experiments on the breadboarded circuit, you just pull the components and hook-up wires out of the board and you are ready to begin building your next circuit.

Take a look at the partial breadboard drawing shown here.  Each of the squares in our sample drawing represents a small hole in the plastic breadboard.  These holes are just the right size to insert a single pin of a DIP IC (Dual In-line Pin Integrated Circuit – this is what we call the chip or carrier for ICs), or a single lead of a component such as a resistor, diode, capacitor or transistor.  Notice the columns of five holes numbered 1, 2, 3 and so on.  There are two columns for each number.  The first column, numbered 1 consists of two sets of five holes.  These are labeled A through E and F through J.  See, in the drawing, how the squares are connected together by small black traces?  In the same way, the holes in each set are connected together.  So any pin or lead plugged into a column of holes is electrically connected to any pin or lead plugged into any other hole in that column.  This is how you will be connecting the components of your circuit.  Also, you will notice that the columns are separated from each other by exactly 0.1”; this is the distance between adjacent pins on a standard DIP IC.

In addition, notice that there is a trough down the middle of the breadboard, between the two parts of each column.  This not only separates the two sets of holes physically, it also separates them electrically.  There is no connection between row E and row F of each column.  This trough is exactly 0.3” wide, which is just wide enough to fit a single “slim” DIP IC across with one set of pins plugged into row E and the opposite set of pins in row F.  See the drawing with the DIP IC plugged in for a better idea of how this looks.  When inserting a DIP IC, you will need to be careful not to bend the pins under the IC and into the trough.  This is like plugging an IC into a socket; use the same precautions.  Once the IC is plugged in like our drawing, each pin is electrically connected to four additional holes for extending the circuit.  For example, look at our drawing: notice that pin 1 of the IC is plugged into hole 3E of the breadboard.  Pin 2 is plugged into hole 4E, and so on.  If you wanted to connect a wire to pin 1 of the IC, you would simply plug it into any other hole from 3A through 3D, they are all electrically the same.

Finally, most breadboards also include either one or two additional rows of holes above and below the area which I described above.  These are called the Power Rails and are most often used to provide the positive voltage and ground along the entire circuit.  This can make it more convenient to tap into the power anywhere in your circuit that you wish.  Notice that while these are physically grouped in sets of five, the groups are actually connected to each other all the way down the length of the breadboard (as long as you have the short boards – about 3” long, longer breadboards may have each power rail split into two sets).  Many engineers will use the top rail for +5V and the bottom for ground.  If they have two rails on top and two on bottom, they may pick one rail on each side for +5V and the other side for ground.  These rails are often color coded and you may want to pick the red for +5V and the blue or black for ground.  This will make it even easier to tap into power anywhere in your circuit.  This is where the red and black wires from your development kit’s battery pack, or power supply, will plug in.

To test your breadboard system, take the battery box, or power supply, and plug the power wires into the power rails of your breadboard.  Be careful with the strands of the wire and keep them tightly twisted together.  The red, or positive lead, from the battery pack should plug into the end of the +V power rail.  The black lead then should plug into the end of the Negative or ground power rail.  Be careful to get the polarity correct or you may burn out the LED (later when you plug in the controller and other components, you may burn them out as well.)

Next take a 330Ω (this is not too rigid, 470Ω, or 220Ω, will work just as well) resistor and bend it’s leads 90˚ to the body of the resistor, so that both leads are parallel and point the same way.  Plug one lead of your resistor into the ground power rail and the other lead into hole 1A of the breadboard.  Next, take an LED and spread the leads apart a little bit.  Plug the cathode lead (negative, the shorter lead) in to hole 1E and the anode lead (positive, the longer lead) into hole 1F.  Last, take a short piece of (preferably red) hook-up wire (about 1”-1½” long) and strip about ¼” of the insulation off each end.  Plug one end into hole 1J and the other end into the positive rail of the breadboard.

Turn on the power switch on your battery pack, or power supply, if it has one, or plug the power supply into your wall outlet.  The LED should burn fairly brightly; you should be able to see it light even in bright indoor lighting.  If your LED does not light up, check the wiring of your power leads, the red and black power wires going to the rails of your breadboard and the LED, resistor and wire; also check that you have a good set of charged cells in your battery pack.  If the LED lights, but is dim, replace or recharge your battery.  Start off with freshly charged cells and your set should give you hours of experimenting before needing to be recharged.

Here is a picture from an experimenter kit:

Notice that the leads on the resistor and the LED have been shortened a bit to allow them to sit directly against the breadboard.  You can then put a small amount of glue (maybe hot glue) to hold them in place, if you want your power indicator circuit to be permanent.  Also, although you cannot see it in this photo, the top and bottom power rails are connected together with hook-up wires.  The additional wires are off the picture, on the right side of this breadboard.

Jessica, one of the engineers at Parallax did a great video presentation on breadboards.  You can see it on YouTube at: http://www.youtube.com/watch?v=q_Q5s9AhCR0. Many thanks to [hover1] over at Chris’ Savage Circuit forum (Savage Circuits no longer has their forum) for reminding me of this great video (yeah, there are other good videos on this, look around – but I like Jessica’s version.)

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