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A breadboard (or protoboard) is a construction base for a one-of-a-kind electronic circuit, a prototype. In modern times the term is commonly used to refer to a particular type of breadboard, the solderless breadboard (or plugboard).
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| Modern Solderless Breadboard |
Because the solderless breadboard does not require soldering, it is reusable, and thus can be used for temporary prototypes and experimenting with circuit design more easily.
In the early days of radio, amateurs would nail bare copper wires or terminal strips to a wooden board (resembling a cutting board for bread) and solder electronic components to them. Sometimes a paper schematic diagram was first glued to the board as a guide to placing terminals, then components and wires were installed over their symbols on the schematic. Using thumbtacks or small nails as mounting posts was also common.
The now common, classic, usually white, plastic pluggable (solderless) breadboard, was designed by Ronald J Portugal of EI Instruments Inc. in 1971.
A modern solderless breadboard consists of a perforated block of plastic with numerous tin plated phosphor bronze or nickel silver alloy spring clips under the perforations.
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| Solderless Breadboard Connections |
The spacing between the clips (lead pitch) is typically 0.1". Integrated circuits (ICs) in dual in-line packages (DIPs) can be inserted to straddle the centerline (gutter) of the block. Interconnecting wires and the leads of discrete components (such as capacitors, resistors, inductors, etc.) can be inserted into the remaining free holes to complete the circuit. Typically the spring clips are rated for 1 ampere at 5 volts and 0.333 amperes at 15 volts (5 watts).
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| Solderless Breadboard with Circuit. They can get messy[1]. |
The jump wires for solderless breadboarding can be obtained in ready-to-use jump wire sets or can be manually manufactured. The latter can become tedious work for larger circuits. Ready-to-use jump wires come in different qualities, some even with tiny plugs attached to the wire ends. Jump wire material for ready-made or home-made wires should usually be 22 AWG (0.33 mm²) solid copper, tin-plated wire - assuming no tiny plugs are to be attached to the wire ends. The wire ends should be stripped 3/16" to 5/16" (approx. 5 mm to 8 mm). Shorter stripped wires might result in bad contact with the board's spring clips (insulation being caught in the springs). Longer stripped wires increase the likelihood of short-circuits on the board. Needle-nose pliers, tweezers and hemostats are helpful when inserting or removing wires, particularly on crowded boards.
Wire wrap is a technology used to assemble electronics. It is a method to construct circuit boards without having to make a printed circuit board. Wires can be wrapped by hand or by machine and can be hand-modified afterward. It was popular for large-scale manufacturing in the 60s and early 70s and continues to be used for short runs and prototypes. It is unusual among prototyping technologies in that very complex assemblies can be produced by automated equipment, and then easily repaired or modified by hand.
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| Closeup of a wire wrap connection[3]. |
Wire wrap construction can produce assemblies which are more reliable than printed circuits — connections are less prone to fail due to vibration or physical stresses on the baseboard, and the lack of solder precludes soldering faults such as corrosion, cold joints and dry joints. The connections themselves are firmer and have lower electrical resistance due to cold welding of the wire to the terminal post at the corners.
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| A wire wrap tool and wire[4]. |
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| End of a wrapping tool showint the post hole and the wire hole.[5]. |
A correctly made wire-wrap connection is seven turns of wire with 1.5 turns of insulated wire at the bottom for strain relief. The square hard-gold-plated post thus forms 28 redundant contacts. The silver-plated wire coating cold-welds to the gold. If corrosion occurs, it occurs on the outside of the wire, not on the gas-tight contact where oxygen cannot penetrate to form oxides. A correctly designed wire-wrap tool applies up to twenty tons of force per square inch on each joint.
The sockets have square posts. The usual posts are 0.025 inches square, 1 inch high, and spaced at 0.1 inch (2.54 mm) intervals. Premium posts are hard-drawn beryllium-copper alloy plated with 0.000025 inches of gold to prevent corrosion. Less-expensive posts are bronze with tin plating.
30 gauge silver-plated soft copper wire is insulated with a fluorocarbon that does not emit dangerous gases when heated. The most common insulation is "Kynar". The 30 AWG Kynar is available that is cut into standard lengths, then one inch of insulation is removed on each end.
A "wire wrap tool" has two holes. The wire and one-quarter inch (6.35 mm) of insulated wire are placed in a hole near the edge of the tool. The hole in the center of the tool is placed over the post.
The tool is rapidly twisted. The result is that 1.5 to 2 turns of insulated wire are wrapped around the post, and atop that, 7 to 9 turns of bare wire are wrapped around the post. The post has room for three such connections, although usually only one or two are needed. This permits manual wire-wrapping to be used for repairs.
The turn and a half of insulated wire helps prevent metal fatigue where the wire meets the post.
A manual wire wrap tool resembles a small pen. It is convenient for minor repairs. Wire wrap is one of the most repairable systems for assembling electronics. Posts can be rewrapped up to ten times without appreciable wear, provided that new wire is used each time. Slightly larger jobs are done with a manual "wire wrap gun" having a geared and spring loaded squeeze grip to spin the bit rapidly.
The Apollo Guidance Computer with its short production run and stringent reliability requirement was one of the early applications of wire wrap to computer assembly.
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| A wire wrapped circuit board[6]. |
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