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Topic: Wiring an 2.1mm DC Barrel Jack (Read 19167 times) previous topic - next topic


Hello everyone,

how do I need to wire a simple 2.1mm DC Barrel Jack? So where do I need to connect the three legs?

It's for an external power source for a DC motor, and I don't know where to connect the three pins of the 2.1mm jack.



I had my issued with them, often experienced corrosion on older ones, and ruined a few commercial appliances using the wrong wall adapter (I can recall two label printers, one game console, one photo frame).

Use a DMM, or use screw terminals.


The back pin is generally connected to the barrel center pin (usually V+ although you should always check your source you plug into it.)  On the ones I bought a pack of, the front pin is connected to the outer barrel lead (usually GND) and the side is connected to that as well and is used as a "connected" indicator.  From what I understand, the last two are sometimes switched.  If you check your data sheet, whichever of the other two can handle more current should be used as GND.  I checked which pins were which on mine by lightly clamping it in an insulated vise, plugging a low power wall wart into it, and checking the leads with my multi-meter.


As used in an Arduino:

The far back terminal is the positive voltage terminal. The other two comprise a switched ground contact. As the arduino doesn't use a switch ground arrangement you can just connect both to ground.



Mar 13, 2012, 08:10 pm Last Edit: Mar 13, 2012, 08:12 pm by MarkT Reason: 1
The best answer to problems like this is "measure it" - unless you have a link to the a known correct datasheet the only sure way to get the right answer is to stick multimeter leads on the pins and see which is connected to what.  There may be identical looking connectors with different internals from the same manufacturer's range even...

(BTW the "jack" is the plug, you have a 2.1mm socket.  Its a coaxial power connector, not normally called a jack)
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]



Mar 14, 2012, 07:06 pm Last Edit: Mar 14, 2012, 07:13 pm by TiboJ Reason: 1
I used my multimeter to look which one is the positive leg, and it is one of the back pins. The front pin is the negative leg.


BTW, which size is the one on Arduino Uno ?

There are lots of different sizes, most of the mobile phone chargers have too small plugs.

2.1 mm inner hole, 5.5 mm outer diameter seems the most common plug size. correct? did not find it on  www.arduino.cc  yet.
Up to now I use a wall socket to USB adapter when my new Arduino runs in standalone mode...

This plug should fit:


which size is the one on Arduino Uno ? ... did not find it on  www.arduino.cc  yet.

Thanks for not answering too quickly. ( better than a "search and you'll find " type reply )

Selecting "Hardware" on the ain page, then the board type, leads me to
which says rather clearly:

External (non-USB) power can come either from an AC-to-DC adapter (wall-wart) or battery. The adapter can be connected by plugging a 2.1mm center-positive plug into the board's power jack.
Leads from a battery can be inserted in the Gnd and Vin pin headers of the POWER connector.


Mar 15, 2012, 05:01 pm Last Edit: Mar 15, 2012, 05:16 pm by TiboJ Reason: 1
I go to school, that's why I can't answer during the day...

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