It's a DE9, Not a DB9. (But We Know What You Mean)
You have been misusing the D-sub connector terminology, and we're guilty of it, too.
You’ve seen them everywhere, especially on older computer equipment: the classic 9-pin serial connector. You probably know it as a DB9. It’s an iconic connector for makers, engineers, and anyone who's ever used an RS232 serial device. Here's a little secret, though: calling it a DB9 is technically wrong. The correct name is actually DE9.
With the release of our new DE9 Connector Breakouts, we wanted to address a common misconception and explain why we named our boards as we did.
SparkFun DE9 Breakout - Male BOB-29195 Easily connect with the SparkFun DE9 Male Breakout, a compact board that brings all nine DE9 pins to a convenient 0.1in. spac… $3.95 SparkFun DE9 Breakout - Female BOB-29196 Easily connect with the SparkFun DE9 Female Breakout, a compact board that brings all nine DE9 pins to a convenient 0.1in. sp… $3.95
In the Interest of Fairness: We are omitting the "-" in "DE-9" and "DB-25." We have found that using a "-" is optional in writing this information.
What's in a Name? The D-Subminiature Standard
The connector in question belongs to a family known as D-subminiature, or D-sub for short. To put it simply, the "D" in the name comes from the D-shaped metal shield surrounding the pins, which ensures the plug can only be inserted one way!
The full part number for these connectors follows a specific pattern. The first letter is always D for the D-shape. The second letter, however, is where the confusion starts. It doesn't stand for a feature; it specifies the size of the connector's shell. The number that follows indicates the number of pins in that shell.
Here’s a quick breakdown of the standard D-sub shell sizes:
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