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26 October 2001

Electronics for the Amateur Scientist: Breadboard Basics

by Paul Dito
Illustrated by Brian Mansfield

This column is intended for the amateur scientist who is familiar with basic electronics concepts, but lacks an understanding of the (sometimes cryptic) fundamentals of building and debugging electronic prototypes. You've come across an experiment you'd like to try, but the project involves building some electronics to control or monitor the experiment. You have the scientific method down pat, but maybe your understanding is a little fuzzy where anodes and cathodes are concerned.

Unless you are pursuing a career in electrical engineering, most disciplines are exposed to little beyond passive DC circuit analysis, if at all. Amateur scientists are more likely to find themselves wandering down the self-taught path, which can be very daunting. There are few texts that explain basic prototyping techniques, and many circuit diagrams are laid out with the assumption that the user understands certain conventions. I intend to convey some of those techniques and describe those conventions.

One of the fundamental skills necessary for electronic experimentation is breadboarding. The term breadboard long predates my initial exposure to electronics, but my understanding is that it refers to the wooden base upon which circuits were laid out in the "early days" of electronics. These days, breadboards are typically white plastic boards, generally referred to as ‘solderless breadboards’, with a grid of holes into which leaded components are inserted. There are strips of metal clips under these holes, allowing for quick interconnection of relatively simple circuits.

As most circuits involve the use of ICs, the typical breadboard is laid out in such a way that leaded integrated circuits fit nicely in the center of the board and connections can be made between individual pins. Most typical breadboards allow for four or five simultaneous connections on one column of holes. Generally, there will be a row at the top and bottom of the board, electrically isolated from the columns, allowing for bus connections. These busses are usually used to supply power and a common ground to the circuit (see figure 1).

figure 1.

Interconnections between columns or busses are made either by the leads of the components themselves (as in the case with resistors and LEDs, for example) or by lengths of solid wire, generally 24 gauge. When assembling a circuit care must be taken to ensure the connections are made between the proper holes and that no bare leads are touching. I have let the smoke out of many components because of bare leads shorting!

There are a few other issues to be aware of when using breadboards. They are primarily used for circuits that are low voltage, low current, and (relatively) low frequencies. Keep this in mind when it comes to troubleshooting an intermittent or non-functioning circuit. In addition, the metal clips in these boards do wear out, especially if you use the same portion of board repeatedly.

Interpreting circuit diagrams is more straightforward, but there are still some ‘gotchas’ to look out for, the most common being related to the voltage supplies to the circuit. Schematics are usually simplified by giving common points names. It can be assumed that all points with the same name are electrically connected. This is often the case with input/output lines associated with various parts of digital circuit, but almost every diagram will use this approach with power supplies.

Most diagrams will not include the power supply itself, but will simply refer to the voltages necessary to power the circuit. The main supply can be called out several different ways, most often by the term ‘Vcc’ or by the nominal voltage, for example ‘+5V’. There is sometimes a ‘B+’ line providing higher voltages to certain parts of the circuit. Keep in mind this would be a completely different bus from other supply busses. Historical note: the term ‘B+’ dates back to early radio days when radios had multiple batteries to supply different voltages throughout the circuitry. Analog circuitry often has negative voltages to provide biasing for various active devices. Negative supplies can be referred to as ‘Vee’ or again by the nominal voltage.

The same holds true for the ground bus. This can be represented by various symbols (see figure 2) or names on a schematic, but they all provide the same basic purpose: provide the power supply current a return path to complete the circuit. Depending on the circuit there can be different grounds in a circuit. This occurs most often with so-called ‘mixed-signal’ circuitry that combines analog and digital subcircuits in the same design. There will often be grounding advice included with the schematic, but most often analog ground and digital ground are treated as separate busses and connected only at one physical point, generally close to the supply (or as instructed on the schematic). Also worth noting is the chassis ground, where the structure of the equipment upon which the circuit is mounted is used as the return path.

figure 2.

Once you have your circuit breadboarded, you can power it up, test it, and make changes as necessary. When all is working properly, you rebuild the circuit on more permanent etched copper boards, or use it as-is, depending on your needs. More on constructing permanent prototypes at a later date.....