What is wire wrap?
The wire wrap technique and tools facilitate semipermanent electrical connections for low current applications. As shown in Figure 1, small gauge wire is wrapped around square posts such as the 0.1 in pitch headers attached to this used Arduino PORTENTA Pro breakout board. The result is a fast heat- and chemical-free joint with good mechanical stability on par with a soldered joint.
The square pin is an important stipulation for the wire wrap technique as it ensures a solid oxygen resistant connection. This physical joint is formed as the wire is wrapped around the pin using a tool such as the Jonard WSU-30M shown in Figure 2. As the wire is wrapped the pin’s square corners distort the 30 AWG wire providing a low resistance cold weld. The fact that there are four cold welds per turn provides mechanical stability against vibration and further ensures a low resistance.
Figure 1: Secure connections to the Arduino PORTENTA Pro breakout board are facilitated by wire wrap connection to Würth Elektronik pin headers.
Tech Tip: The historical importance of the wire wrap technique cannot be overemphasized. Wire wrap was once the backbone for our telephones, communications, and early computers. A prime example is the mission critical Apollo guidance computer as shown in Video 1. At time index 2:45 and 4:40 we see the maze of small gauge wire terminated with wire wrap. Note that the twilight of wire wrap era included machines to route the ever-increasing wire complexity.
Video 1: The Apollo guidance computer uses a wire wrap backplane. This can be seen at time index 2:45 and 4:40.
How do I complete a wire wrap connection?
A proper wire wrap connection demands the use of a wire wrap tool. Understand that the pin, wire, and tool work together as a system. When properly selected they ensure a tight wrap with low resistance oxygen free connection. Please see Video 2 for a detailed video introduction to wire wrap. You may appreciate the opening historical information along with the detailed examples in the latter half of the video.
Video 2: This HACKADAY video show how to perform the wire wrap along with a variety of historical applications.
Figure 2: Picture of the author’s well used Jonard Tools WSU-30M along with a bundle of precut and stripped 30 AWG wires.
What wire wrap tools and supplies should I use?
One popular tool is the Jonard Tools WSU-30M as shown in Figure 2 and Video 2. Other tools including wire wrap guns are available here.
DigiKey offers a large variety of wire suitable for wire wrap applications. This includes 30 AWG spools along with precut wires such as those pictures in Figure 1 and 2.
Please visit the wire wrap product selection guide.
Conclusion
Wire wrap is an old circuit construction technique that still finds application for prototyping and even final production. An example is the opening picture showing the new Arduino PORTENTA Pro break out board which will be featured in an upcoming article involving PID control.
Wire wrap has a to-the-moon reliability. The precut wires save save time and heartache by reducing the need to troubleshoot those loose wires.
Best Wishes,
APDahlen
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About the Author
Aaron Dahlen, LCDR USCG (Ret.), serves as an application engineer at DigiKey. He has a unique electronics and automation foundation built over a 27-year military career as a technician and engineer which was further enhanced by 12 years of teaching (interwoven). With an MSEE degree from Minnesota State University, Mankato, Dahlen has taught in an ABET accredited EE program, served as the program coordinator for an EET program, and taught component-level repair to military electronics technicians. Dahlen has returned to his Northern Minnesota home and thoroughly enjoys researching and writing articles such as this.