I confirmed both the 3.5mm socket described in Luc’s schematic (JY039-5P) and the one I used are identical for what pins are used in the board and which part of the 3.5mm jack they correspond to. I just buzzed out a 3.5mm stereo cable and the top/tip is not connected to the optoisolator but the ring/mid terminal (shown as not connected in the schematic) is along with the base/sleeve. Again not a big deal, just something to be aware of to verify when making your cables.