Hand machined mechanical pencils

USB connector panel insulator (13/06/13)

I have never been able to figure out exactly what best to do with the shield on USB connectors - whether it should be left floating, connected to ground directly or via a capacitor, whether it should contact the case or insulated from it (which depends on whether the case is metal or plastic) etc. For the particular product in question (my temperature controller) I had various discussions with the tech people at FTDI and eventually decided to connect the shield to circuit ground via a 470nF capacitor, but keep it insulated from the enclosure (an anodised aluminium box). My initial attempts were to just wrap some Kapton tape around the connector, which worked fine but didn't look very professional.

Here's what I ended up making. It's a plastic "surround" which fits tightly inside the panel cutout and provides support for the connector. A small flange prevents it from being pushed through the panel during installation, and a cutout allows the PCB to butt up against the inside of the panel as before. The material is 2mm thick black Delrin sheet. It's all milled out using a little jig which I've currently lost, hence no photos! A blank rectangle is clamped in the middle with a single screw, the perimeter and flange are machined, then the piece is removed, flipped, re-clamped, and the inside milled out. The spacer is held to the remaining stock with some small tabs which are easily removed. A quick sandblast removes any burrs and gives it a nice matt texture.

View from outside of panel

View from inside of panel. Note cutout for PCB.

PCB with connector installed behind panel