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For example, in the RS232 here:

enter image description here

or here:

enter image description here

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    \$\begingroup\$ For RS232, for those not old enough to remember, the protocol is to start out with two devices and a cable, a stack of 9 to 25 converters, a stack of gender changers in 9 and 25 pin configs, and a null modem or two. Then, you switch things around until they work, never change it again, and slowly reassemble the collection of parts you used up. \$\endgroup\$ Nov 28 '12 at 23:32
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    \$\begingroup\$ Incidentally, that spark-fun schematic is a great example of how to draw a horrible nearly unreadable schematic, because you hate other engineers/everyone. \$\endgroup\$ Nov 29 '12 at 5:40
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No. Different people draw schematics differently. Sometimes it is obvious, but usually not. In the examples you gave, it is not obvious.

When it is marked, it is usually a text note next to the connector. Or sometimes it is in the part number, like "DB-9F" for a female connector.

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Here's one general guideline. It applies to connectors on the outside of the instruments. If the connector supplies power or signal, it's usually a female (F). This is done prevent shorting the signal (to something in the outside environment). A female pin is harder to accidentally short than a male pin. One can figure out from the schematic what's input and what's output.
A mnemonic for this rule is Source Side Socket (SSS).

I would deduce that DB-9 connectors on your schematic are F. The common use of RS232 is for talking to PCs (directly or through USB-to-RS232 adapter). Connector on the PC side is M. Typically, the cable is F-to-M. So, the connector on the other side is F.

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The definition of jack and plug is a common source of problems.

Basically, the jack is the female part and the plug is the male part. Officially, the reference designator for jack is "J" and and the designator for plug is "P". "CONNx" could be either I think, but I'm guessing it's the male connector looking at the schematic, as the female symbols tend to have filled circles. It's a bit of a minefield ;-)

enter image description here

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There are many ways to indicate the polarity when drawing a schematic. Unfortunately the guy who drew yours doesn't seem to have used any of them:

  • Draw the symbol in a way that indicates the polarity.
  • Use a standard for the designators, for example "J1" is a jack, "P1" is a plug.
  • Include some indication like "m", "f", "j" or "p" in the annotation describing the connector. (Like in David's example, "DB-9(f)")
  • Give a part number for the connector so that at least you can look it up.

That said, for some connectors there isn't even a perfect way to describe the part: the outer shell might be an "outie" while the inner pins are "innies" so that the male/female, jack/plug designations are somewhat ambiguous (you may know there's a standard for whether to desgnate by the shell or the pin, but does everyone who has to read your schematic know the standard?). Then only the part number gives a totally clear spec.

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  • \$\begingroup\$ I've seen only the last method used in the industry. The details for the connectors are tracked down from schematic to BOM to p/n to datasheet. Wiring diagrams (not to be confused with schematics) show more details about connectors, though. \$\endgroup\$ Nov 29 '12 at 1:29
  • \$\begingroup\$ @NickAlexeev, If I'm writing a schematic, I try do all 4 (maybe not the third). If I'm reading a schematic, I don't trust anything except the part number. \$\endgroup\$
    – The Photon
    Nov 29 '12 at 2:20
  • \$\begingroup\$ @NickAlexeev - I agree with your point - I always add the part number for pretty much everything in my schematics. Most decent software has the ability to add a link to the datasheet too, so you can just (do something like) right click on the part and go straight to the datasheet URL. \$\endgroup\$
    – Oli Glaser
    Nov 29 '12 at 4:46
  • \$\begingroup\$ @ThePhoton - Also agreed about designation ambiguity - try figuring out which is which with stuff like MCX connectors that have the outie/innie problem you mention. \$\endgroup\$
    – Oli Glaser
    Nov 29 '12 at 4:49
  • \$\begingroup\$ @OliGlaser, sometimes I can't even tell what's what when I'm reading the datasheet. \$\endgroup\$
    – The Photon
    Nov 29 '12 at 5:09
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Either add description 25P or 25S or 2x10S 1x20P or use standard arrows --> pin , ----< socket

This should not be confused with Plug (floating) P1, P2, P3 and Receptacle (fixed J1, J2, J3) which can either use P or S contacts or both.

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