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DC Power Coupler for 3 5mm Barrel Jack - Gav Tries To Build (with video)

By Gavin Davies

Where I build a DC power coupler for a very unusual adapter.

My friend Richard has a camera that has a curious method of powering. The camera has a USB Mini jack but takes 3 volts, not the standard 5 that USB outputs.

Richard presented me with an adapter that has a micro USB connector on the left, and a barrel jack that is 8mm long and 3.5mm wide with an inner size of 1.35mm. This is a standard size barrel jack, albeit not a common one.

The problem to solve is inverting the barrel jack so that Richard can connect his power adapter, which presumably also has a 3.5mm x 1.35mm DC barrel jack.

It is my belief that a DC Power Coupler will solve this (although may not be the optimal solution; I’d have to know more about the problem). I was unable to source a prebuilt unit so I elected to build one.

Risks: It is not clear to me why the camera is designed this way. I’d like to ask a few questions including the camera model, whether this is factory, why they didn’t step down the voltage within the camera, et cetera. It also feels like with enough force I could pull apart the unit Richard presented me with, but I don’t want to risk destroying it. However, I didn’t have Richard’s contact details so I elected to continue with the assumptions I have stated in the brief. A risk of building a DC coupling is accidentally inverting polarity and damaging the camera. I have designed the coupler to avoid this.

Bill of materials:

  • 2 x PCB mount 1.35mm x 3.5mm female DC barrel sockets
  • 1 x heatshrink tubing
  • 1 x short wire
  • Solder

Testing: I metered the connections, which seem good. I get continuity through the sleeve to the ground pin of the USB connector, and from the center pin to the hot pin of the USB connector. All looked good.

Download DC-Power-Coupler-for-3-5mm-Barrel-Jack—Gav-Tries-To-Build.mp3