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This question is related to part with part number PJ-102AH (CUI Devices).

Digikey link: https://www.digikey.com/products/en?keywords=PJ-102AH

Datasheet: https://www.cuidevices.com/product/resource/pj-102ah.pdf

The datasheet shows this:

enter image description here

For this, I understand that pin 1 is positive.

What is really the negative? 2 or 3?

And how the remaining pin work? Does it connected to negative when the cable is plugged-in?

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Pin 1 is "positive" if your system is setup like that. THERE IS NO REASON IT COULDN'T BE NEGATIVE! "Positive Tip" is something of a common standard, but there are examples where this is not true (for example - guitar pedals pretty much are all negative-tip, positive shield)

Pin #3 is a switch that is 'normal closed'. When no plug is in the jack, pins #2 and #3 are shorted together. When you insert a plug, pin #3 actually moves and becomes disconnected from pin #2. In this state, there is no electrical connection between pin #3 and the plug.

This is useful when the device has both batteries and wall-power input. When you insert the plug, it automatically disconnects the batteries (thus preventing your wall-power from charging the batteries)

Most likely, in your case, you would make pin #1 "positive", pin #2 "negative" and pin 3 not connected. But only you can know if this is right or not as we don't have access to the rest of your circuit or understanding of what you're trying to accomplish.

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Pin 1 is negative for guitar effects pedals.

Pin 1 is positive for almost all other applications.

Don't ask me how I discovered the difference, but my son now has one fewer working effects pedal.

In both cases, pin 2, and pin 3 if used, are the other sign.

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  • 2
    \$\begingroup\$ It is surprising how many center pin negative devices there are (usually not in a good way). \$\endgroup\$ – DGB Jun 11 at 18:09

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