My first big design attempt in OnShape.com. Focused on style and minimal hardware requirement. Only six screws and one nut needed. There's channels through the arm and base to route the contact point wires for a cleaner look. A printed spring can be adjusted by a through screw from the top. Snap-fit hinge and knob also.
Be sure to print the arm on it's side. The spring may stick to the bottom of the arm, break it loose before assembly if so.
If you like and use it, please feel free to toss me a tip through the tip button.