The D-Sub connector: the most versatile connector?

Today, we’re used to seeing small connectors, with the likes of micro-USB and mini-HDMI catering for devices that continue to shrink in size. While the D-Sub connector may seem large in comparison by today’s standards, when it was first created it was designed, as its name suggests, to be the Subminiature answer to the miniature connectors of the time.

The D-Sub was invented by Cannon engineers in 1952 for aircraft radio systems. According to the company: “The D-Subminiature was designed as a smaller, lightweight, rectangular alternative to larger, heavier connectors at the time. At up to one inch wide by one quarter inch tall, the first D-Subs featured a 1500 V rating, a shell of cold rolled steel and an insert made of moulded nylon.”

However, while it started life in a highly specialised environment, it quickly gained popularity in more everyday applications — gaining some commendable firsts. The D-Sub was used in the first colour television, the first mainframe computers, as well as early video game consoles and PCs and printers.

This versatility meant it was quickly adopted for use in a variety of consumer and industrial applications. After its introduction, Cannon rolled out the D-Sub with five shell sizes containing anywhere from 9-78 contacts in various layouts. The concept was eventually picked up and replicated by other manufacturers and the D-Sub took off.

Today it’s used in everything from aerospace, communications and defence to industrial, transport, medical and consumer electronics. Its versatility means that it is equally at home on the International Space Station as it is on a high-speed train or in food manufacturing.

A versatile champion

So, what makes the D-Sub so appealing? At its heart, the connector can transmit data, power and radio frequency signals. On the outside, the D shape of the shell means the connector can only be plugged in one way round — a useful design that, unlike other polarised connectors including USB-A, prevents the user from forcing the connector in upside down.

The metal shell also adds a robust housing for the rows of contacts inside and offers shielding against electromagnetic interference, which can be improved by adding a dedicated backshell.

For applications where the connector is subject to vibration that could cause accidental disconnect, mounting hardware options including jack screws, slide locks or spring latch systems, ensure a secure connection between D-Subs.

Stability

Stability is especially important in space applications where the cost of failure could bring a multi-billion-dollar project to a halt. While it’s cheaper to transport lightweight plastics into space, the high-vacuum conditions of space can cause plastics and elastomers to outgas, releasing volatile compounds trapped within the material.

Outgassing can damage the connector and compromise electronics and connected equipment. D-Subs for space applications undergo a bake-out process to release the volatile compounds prior to assembly, or they can use specialised polymers that do not outgas.

However, stability doesn’t just come from the connector material, it also comes from how those materials interact with their surroundings, in the form of magnetism. The permanent magnetic field present in ferromagnetic metals like steel can cause sensors to lose calibration and produce erroneous measurements.  As such, D-Sub connectors supplied for space and some medical applications use shells with a low level of residual magnetism.

A versatile connector

Space isn’t the only demanding application. Thanks to modern automated assembly techniques, D-Subs can now be sourced to suit almost any application, while staying low cost. PEI-Genesis can assemble connectors to order in as little as 48 hours and offers a variety of standard products including those with higher pin densities ranging from 15-78 pins in five shell sizes.

In a world where technological innovations come and go, the fact that the D-Sub has been in continuous production for nearly 70 years is testament to its versatility and popularity. Now, modern automation techniques have injected further life into the connector for years to come, making it perhaps the most versatile low-cost connector of all time.