I'm developing a board like this FTDI to ESP8266 Adapter that serves as an adapter for a given board that needs to be plugged like this

enter image description here

given that the board size is the same, users tend to plug it the other way, the way the boards are on top of each other. Normally connectors are made the way that physically prevents them to be plugged incorrect way. However the blue board doesn't have such a connector.

What markings should I use on the purple board to indicate that the blue board must be plugged facing away? I designed it to be facing away so the button is accessible and also the pin marking is visible and the antenna should be facing away too. I have no control over the blue board.

  • don't rule out tactile feedback, both for the stated goal but also to help with accessibility
    – Toni Leigh
    Mar 3, 2015 at 17:53
  • Could you add a picture of the other side of the blue board so we can compare its labeling? I'm thinking along the lines of labeling the sockets with pin numbers corresponding to labeling on the blue board? Mar 7, 2015 at 7:12

4 Answers 4


You don't have a lot of space on your board for markings. I'm going to assume the following:

  1. You can't expand the size of the purple board.
  2. You can't force a pairing indicator on the blue board (e.g. it's made by some other party).

In this case, it's hard to convey precise orientation within these hard constraints. But what you can do with the limited space is signal a warning so the user knows they should pay special attention.

One way to do this is to paint one of the connectors red, so there is a clear indication that (a) there is an attention/warning; and (b) there is a polarity to the socket.

It's common for PCB's to indicate a Pin-1 or Pin-0 number to indicate pin orientation, so the visual cue should make sense to users.

The red indicator isn't going to communicate the entirity of the orientation, but given the extreme limitations on space it should be enough to prompt the user to look at the instructions or otherwise confirm the orientation of the blue board before plugging it in. enter image description here

If you have the tools, adding an exclamation mark ! or information i to the red swatch could be additionally communicative.

If you don't want to use red because it may alarm user unnecessarily (e.g. if plugging the boards the wrong way doesn't actually damage them), bright green is a decent alternative.

If you are able to change the markings on the blue board, then it's relatively simple to add clear mating markers to both boards.


A rather drastic solution would be to add a 'sticking-up' metal or plastic spike on the purple board just to the left of the connector which sticks up just high enough to prevent the blue board from being fitted across it.

  • Probably impractical as you suggest, but I really like that out-of-the-box thinking! Creates a hard (literally) constraint on orientation.
    – tohster
    Mar 4, 2015 at 23:15

The way you indicate this commonly for atmega chips is to have the half moon symbol printed on the PCB:

enter image description here

The convention should be familiar to your target audience, so if you were to put some kind of shape on the board that matched up to a similar shape on the secondary board, then you would have something that would be intuitive.

If you don't have control over what is printed on both boards, then perhaps some arrows pointing in the direction the parts should be oriented might work:


download bmml source – Wireframes created with Balsamiq Mockups


If you happen to have the resources to rearrange your layouts, you could arrange the two rows of plugs and pins in an "L"-or "T"–shape – this way there would only be one way how to plug them.

  • Unfortunately I have no control over the blue board.
    – Cano64
    Mar 4, 2015 at 14:44
  • too bad – could have been so easy if you had Mar 4, 2015 at 14:53

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