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I recently started doing hardware projects with Arduino. Those projects involve custom-made enclosures to hide (and protect) the actual components. Those enclosures should have plugs in order to be able to connect the components.

If this is too abstract, here's a concrete example. One case contains the transformer, an Arduino, a resistor and a bunch of wires needed to power a LED strip. The LED strip itself is assembled with another case which hides its wiring. Two cases should then be connected together for the LED strip to work.

My idea was to use ordinary 3.5 mm TRS or TRRS connectors where tiny cables (22 AWG) are largely enough, and XLR connectors where I need thick 14 AWG cables. The benefit of using those standard connectors is that there is a broad range of cables, and that connectors are easy to find as well. Another benefit is that I already have a lot of 3.5 mm cables and a few XLR cables at home.

This causes, however, a problem. Since those connectors are familiar to everyone (well, XLR is a bit less), and since those connectors are used by many other devices, it is easy to make a mistake and plug something which is not expected to be plugged: for instance connect an audio recorder to an XLR intended to be used for a LED strip, or connect a headset to where one would expect a device which monitors the temperature in the room.

There are, potentially, two risks:

  • I myself, by inadvertence, connect the wrong thing.
  • Someone who either comes to my home or, for some unknown reason, acquires a device I created (they are made for my own personal usage, not for sale), tries to connect the wrong thing.

When the wrong thing is connected, the worst thing which could happen is that it will damage either the thing (very likely in the case of a 3.5 mm connector) or the electrical components I've used in my devices (very likely in the case of a XLR if using 12 V or more), and possibly start a fire.

How should I proceed in order to avoid those two risks (given that having custom connectors is obviously the best thing to do, but as I explained, it is not an option here)?

From the UX perspective, should I put specific labels? Use specific colors? Something else?

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Obviously, as you've mentioned, the main issue is familiarity.

The TRS/TRRS cables have a distinct shape and are very commonly recognized, so people will assume it's safe to plug into their phone.

Oh sweet! I can control LEDs from my phone?! Let me try!  *BZZZAP* *fizzle*

The XLR cables are not quite as common, and most people don't walk around with devices that have XLR connectors, so I'd wager that's probably less of a concern.

So, essentially, you have to alter it in one of two ways:

  1. Change it such that someone would not recognize it as a familiar cable
  2. Physically prevent them from using it in the way they usually would.

I'd guess (no data to back this up) that simply changing the color of the connector, or adding a label could be pretty easily ignored. The connector is still the same shape, so it'll still seem like any other "audio cable" or "headphone cable".

I'm not sure what's possible for you to do, but I'll throw out a couple ideas (I'll add more if I think of any others).

  • Use less common cables that can satisfy your requirements.
  • Modify the connectors to add a hard "sheath" around the end of the cable, so it fits only in a connector that also allows that sheath to pass over, similar to how an audio coaxial cable fits on its connector. This would serve as a physical barrier so people cannot use the cables to connect devices that are not designed to be connected. The image below shows a rough idea of what I mean. Example image, showing audio coaxial cable connector up close Image courtesy of Mediabridge, edited. (Source)

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