Chapter 10

Fun with solderless breadboards

When building a circuit for the first time, it is often very useful to have a way to quickly change connections or parts placement.

In the early days of electronics, quick, temporary circuits were sometimes built on a piece of wood, similar to the boards that bread is sliced on. Building a first prototype came to be known as breadboarding.

Back when components like tubes and transformers were large and long wires were common, it was easy to solder and unsolder connections. Modern circuits, made with small transistors or many legged integrated circuits, are much harder to solder and especially to unsolder.

To make life easier, solderless breadboards were invented. These are blocks of plastic with holes into which wires can be inserted. The holes are connected electrically, so that wires stuck in the connected holes are also connected electrically.

The connected holes are arranged in rows, in groups of five, so that up to five parts can be quickly connected just by plugging their leads into connected holes in the breadboard. When you want to rearrange a circuit, just pull the wire or part out of the hole, and move it or replace it.

Click on photo for a larger picture

In the photo above, we have a complete radio, with an antenna coil, a tuning capacitor, a three-legged integrated circuit, a battery, and earphone, two resistors, and three capacitors. This radio is the Three Penny Radio kit from the Scitoys Catalog, which is usually soldered, using three pennies as convenient places to connect the various parts.

The three-penny radio needs these parts:

Click on photo for a larger picture

In the closer view, you can see that the parts we want to be electrically connected are plugged into one of the five holes marked A, B, C, D, or E, (or in this case, where we used the second half of the board, marked F, G, H, I and J) in rows marked 1 through 63.

Along each side of the breadboard are two strips of power supply rails, making it convenient to connect a battery when many parts need power. In our simple radio, only one part needs power, so it is convenient to simply plug the battery wires directly into the main circuit area.

The solderless breadboard is designed to accept the leads from parts such as resistors, integrated circuits, transistors, and other parts with round solid wire for leads. Some of the parts for the radio have thin, stranded wire that is not stiff enough to poke into the holes, or (like the variable capacitor) have flat strips of metal that are too big to fit into the holes.

For these parts, we solder their leads to pieces of wire cut from the leads of other parts, such as resistors or capacitors. Most such parts have leads that are longer than we needed anyway, so they will fit more snuggly onto the board with shorter leads. In the photo you can see that the antenna coil, the variable capacitor, and the piezoelectric earphone have wires soldered to their leads to make it easy to plug them into the breadboard.

Click on photo for a larger picture

Having the holes arranged in a labeled grid is convenient for describing the parts layout. We can list each part, and the letter and number of each lead:

This makes it very simple to build the circuit, and easy to double check all of the connections.

Making the circuit permanent

Solderless breadboards are great for building circuits the first time, and getting them to work, or experimenting with design changes. But when you get the circuit working the way you want it to work, you will want to copy it to a more permanent form, by soldering it onto a circuit board.

The printed circuit boards we carry in our catalog also have five holes that are electrically connected. The holes are grouped into 3 holes and 2 larger holes, to make it convenient to connect larger wires leading out from the board, for power connections and other external parts.

The radio shown below was built by a student as a first exercise in soldering:

Here is the back side:

It worked the first time!

Next: A simple audio amplifier.

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