I have a Pololu SMC04B board. I plan to mount the board inside an aluminum box which will not be and cannot be grounded.
My question is, can I use metal standoffs on the mount points at the corner of the PCB? Is it just tinned or are they bushings (I’m near certain what it is tinned but it doesn’t hurt to confirm for mechanical reasons) at those corners and if it is just tinned, does it connect to the ground plane (this I doubt but again confirmation is never a bad thing)?
Thanks in advance.
I can’t say for absolute sure since I don’t have a SMC04B on hand, but looking at the high resolution pictures in the PDF of the user’s guide, none of the holes appear to be connected to anything. Pololu boards usually don’t have their mounting holes grounded, and on the single occasion that I’ve noticed (one of the Orangutan X2 mounting holes) there is a clear label on one side of the board.
If you want to check for sure, try connecting a multimeter set to continuity testing between the ground pin and each of the mounting holes.
As for using metal standoffs or not, I do it all the time with no problem, and as you can see, the Pololu guys even ship some boards with metal standoffs included:
Always good to check though, why can’t your metal case be grounded?
The mounting holes on the SMC04B are plated but not connected to any electrical lines.
On the single motor driver carrier (#0705/0706), two of the mounting holes are connected to one of the motor outputs:
In general, if you use metal mounting hardware, make sure it’s not so big that it can cut into the soldermask and short to nearby traces.
Thanks for the help guys, I realized I could do a continuity test later on. But the mounting information was still quite helpful.
The reason it cannot be grounded, is because it is part of an experimental aircraft. The case ends up acting like an antenna and another grounding method must be used for the electrical system. The signals can get rather wonky.