PCB Assembly Services - Screaming Circuits: Need a Reference for the Reference


Need a Reference for the Reference

Not long ago, I wrote a short post about non-standard use of reference designators. After doing that, I've been looking at some of my own microcontroller and motor driver boards with an eye for how close to standards I am.

All of the R's, C's, D's and U's are okay, but there are some differences. For example, the Eagle library I've been using calls crystals "X" instead of the more standard "Y." I have seen crystals designated as "X", "Y" and "Q." LEDs seem to go by "LED" instead of "D" as indicated in the Wikipedia list. Headers go by "J", "JP", or "H." Wikipedia says "J" is for a socket (AKA jack) connector, "JP" is for jumper, and it doesn't list a "H." My board has break away two-row headers and keyed single-row headers. Wikipedia does note that its list is a set of commonly used designators. Not necessarily standard.

We probably do have the specific standards document laying around here someplace, and if I were doing real work on a professional basis, I'd hunt it down and make sure I followed the actual standards. But I'm not doing real work with my controllers and drivers, so I just do the best I can. I wonder how often that happens everywhere. The standards books are "somewhere" but no one really knows where.

Duane Benson
Somewhere over the reflow...


The LED itself is not a display or lamp but can be part of it. It is a diode (Light Emitting Diode) in the first place. DS for LED is simply wrong interpretation of IEEE Std 315.

IEEE Std 315 ("Graphic Symbols for Electrical and Electronics Diagrams") has section 22.4 "Class Designation Letters" which is a comprehensive list of one- and two-letter designators and all the items they apply to. There is also an index that does the reverse; lists all electrical components and tells you which designator to use. This is the closest thing to an official standard that I know of.

@CADSTARGuy: Y is indeed specified for crystals, and DS ("display") for LEDs.

It's true, i usually works with different softwares and they all called the components different. It's frustrating

The new IPC-2612-1 has a list of component stem names.

Although I do not agree with it - a crystal has always been shortened to "Xtal" and then "X" in my book
so why "y" :)

And an LED can simply be LD - not DS as it does not even sound like LED.

There is still a requirement for a modern standard component stem name list however these are usually company specific.

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