Circuit Breadboarding
Saturday, 21 July 2018
6:46 PM
Once a circuit has been designed, it must be tested. To do this quickly and reliably, a good breadboarding system is needed. It should allow for the easy interconnection and removal of the analog ICs, discrete components, power supplies, and test equipment. It is absolutely critical that connections between the breadboard, the components, the power supplies and the test equipment be mechanically and electrically sound. Most beginners spend more time running down poor or wrong breadboarding connections than they spend actually evaluating the circuit they have built. In this section you will find breadboarding hints that will help you minimize problems and errors in building your circuit for testing. 
Figure 1 – Breadboard with ICs and other components inserted 
The universal breadboard illustrated in Figure 1 provides a popular and convenient technique for circuit prototyping. Typically they give two to four busses (rails) for power supplies and ground, running along the edges. The body provides an array of solderless connections properly spaced and sized for most analog and digital ICs, transistors, diodes, small capacitors, 1/4 W resistors, and 22 AWG solid hook-up wire. Using it, you can construct circuits quickly, compactly, and reliably. These breadboards are available in a variety of styles and qualities from most electronic component suppliers.
The connection diagram of a typical breadboard is shown below: 
Figure 2 – Connection diagram of wire sockets (holes) on a breadboard
The breadboard consists of two regions – rows and columns: 

There are two sets of 64 columns each of 5 interconnected holes (A-E and F-J), to plug in components and connection wires. 

There are four sets of 2 rows each of 31 interconnected holes, called ‘rails’. The two rails on each side are for connecting the power supply(ies). Typically, the rails are for the positive supply +V, the negative supply -V and for 0 V (common). 
The universal breadboard provides a good interface between the components of the circuit, but care must be taken when you connect it to power supplies and test equipment. The breadboard is usually mounted on some larger, sturdier base (an aluminium plate). 
Just as a chain is only as good as its weakest link, test equipment can perform no better than the technique used to connect it to the circuit under test. Excellent standard leads supplied with banana plugs, BNC connectors, or probes are common. Use them. 
Hours of careful design and breadboarding can literally go up in smoke because of a shorted or open wire to a power supply or from two alligator clips which accidentally touch, or jump off at just the wrong time. Alligator clips are a major source of trouble. They are often too large for use on a breadboard, short together, or fail to hold adequately. 
Instead of connecting test equipment to the breadboard with alligator clips, we use binding posts (that have a socket for 4mm banana plugs) mounted on the side of the base plate. There are 5 binding posts: three for a dual power supply: +V, 0 (common) and –V, and the other two for the input and output signals. 
Connect signals and supply sources from the test instrument to the breadboarding system, and from breadboard to instruments using standard leads with 4mm banana plugs. Then wire from the binding posts to the breadboard with 22 AWG wire, inserting the wire into the desired connector. This technique will provide an electrically and mechanically sound and professional way to build circuits, eliminating the cause of most breadboarding headaches, bad connections. 
Use only standard connectors to connect test equipment to the breadboard. Never use alligator clips. 
Find a suitable box to contain the breadboard with its base and the components you have plugged into it, to enable you to carry the breadboard around from home to the Lab without unplugging components and disturbing the assembled circuit. 
An example of a properly assembled breadboard is shown below: 
Figure 3 – Neatly and correctly assembled circuit on breadboard 
Observe the two sets of decoupling capacitors (one electrolytic, one ceramic in each set) connected as explained below: 

One set of two capacitors connected between the +V rail and upper 0 V (common) rail. 

The other set of two capacitors between the –V rail and lower 0 V (common) rail. 

Of course, the upper and lower ground rails are interconnected with a wire strap. 
Probes must also be used carefully. It is far too easy, when you are trying to touch a pin on an IC, for the probe to slip between two pins, shorting them together. This could damage the IC or supporting equipment. Instead of probing IC pins directly, you should connect a wire from the point you want to probe to a vacant part of the socket, where it can be secured and safely probed. 
Never probe IC pins directly. 