Embedded LEDs in a flexible 3D print (Patreon)

Last minute Reddit Secret Santa gift for a dog owner: 3D printed flexible LED collar

Besides the LEDs there's also a battery and a charge controller embedded in the infill structure. I've just paused the print for 5 minutes and squeezed it all in. Then I've epoxied magnets on both ends so that they only fit together in the right orientation.

The magnets of one side are connected to the battery+/- and charge +/-, the magnets on the other side are connected to the LEDs +/- and nothing. When the collar is closed the LEDs light up.

A USB charge adapter also has a "magnetically coded connector", so that it only fits on the battery side.

In retrospect I should have permanently connected all GNDs together through the collar to reduce the magnet number to 3. Because of that old wobbly table theorem "There always is a plane through 3 points." In reality 4 points are never coplanar, so the LEDs are flickering a bit. But commercial LED collars are blinking intentionally, so we'll call it a feature :)