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 female jack connector, “JP” is for jumper, and it doesn’t list a “H.” My board has break away two-row male headers and keyed single-row male 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
Somwhere over the reflow…

http://blog.screamingcircuits.com/

About Duane

Duane is the Web Marketing Manager for Screaming Circuits, an EMS company based in Canby, Oregon. He blogs regularly on matters ranging from circuit board design and assembly to general industry observations.
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3 Responses to Need a Reference for the Reference

  1. Bill Burton says:

    I looked at IPC-T-50H “Terms and Definitions…” and don’t find a definition for “Reference Designator” or “Component Designator”, nor do I see anything in IPC2221A “Generic Standard on Printed Board Design”.
    Most crystals I’ve seen have been called “X”, oscillators have also been “X” or sometimes “Y”, or sometimes “U”. It’s probably more important to be consistent in the designators you use than to focus on choosing the “right” one.

  2. John Lambert says:

    When you find that “standards” book… share it with rest of us.

    My experience.. the standards used in US until the 1980s… were fairly simple / straight forward (as you indicated).
    This is the only period in time that I have expected any real/documented standards.
    Generally, based on standards originating with the US Military.
    International standards for designators? I haven’t seen an universally accepted version (yet).
    This subject is very similar to “living languages”.. a moving target… (nailing jelly to a tree? Herding cats?)

    designators for:
    Relays (R, CR, M,U) confusing depending on type of relay (magnetic contactors , control relays as used in latter diagrams are generally CR, Solid-state relays are often viewed as another IC so “U” or “I” or “IC” is used)
    Crystals another problem child…(as you noted)
    Numerous other examples….

    I have found some Companies define their own (internal) standards.. so, doing work on a professional basis may involve learning your customer’s standards.
    This is often related to the industry where the electronic pcb assembly is going to be used..

    Some companies also define :
    Designator number usage… based on location on assembly (physical – R1 will be near R2) or schematic page number where the component can be found.
    example: all components with “XX 100-199″ are on page 1 of the schematic.

    If you want a happy customer (we can try) .. you need to know what is wanted or expected.

  3. John Lambert says:

    sorry, my mind .. not always working..
    I meant “ladder diagrams” .. not latter diagrams.
    a special form of schematic…

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