Actually a very good question, it's hard to tell by eye.
You can measure the outside diameter of the plug barrel to verify it is 5.5mm with a micrometer, but all other measurements are difficult.
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I have 2.5mm jack (such as would be mounted on the board), if the plug does not fit into that jack it is probably 2.1mm.
I also have a 2.1mm plug, if it fits into an unknown jack, then that jack is probably 2.1mm.
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Most plugs and jacks of approximately this appearance are either 2.1 or 2.5mm.
Some plugs have longer barrels than others (and some jacks accept longer barrels), but that usually doesn't matter too much.
Poorly manufactured jacks and plugs may not be exactly 2.1 or 2.5mm.
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The majority of jacks and plugs for consumer electronics are 2.1mm.
The QMX+ uses a 2.1mm jack, and most 12v supplies I have laying about the house can plug into it.
The down side is that it is possible to plug a 2.5mm plug into it and get a dicy connection.
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None of this matters much on most equipement, a flakey power connector just causes a reboot.
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Jerry, KE7ER
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On Wed, Jan 22, 2025 at 03:25 PM, Grant wrote:
This may be a stupid question but how can you tell by looking at the plug if it is a 2.5 or 2.1mm plug? Having read this discussion I thought it prudent to make sure the plug I am using is the right one. Mine has no markings regarding size.
