As I was saying before we were so rudely interrupted by that page break, while driving to work this morning, I had an idea that was both simple and cunning at the same time -- what about using a USB cable as my ground point?
The thing is that I always have a notepad computer powered up on the table while I'm working on my projects. In fact, I actually purchased a cheap-and-cheerful second-hand notepad running Windows 7 from the local technology recycling center for just this purpose. Most of my projects feature Arduino or chipKIT microcontroller boards, and I use my notepad to program them. Even if I'm not programming a microcontroller, I almost invariably need to access the Internet to check something or other.
As soon as I arrived at work, I ambled into the bay next to mine to bounce this idea off my chum Ivan (the guy who's writing the All About Batteries series here on EETimes). If there was any reason why I shouldn’t do this, Ivan would be the man to know.
Happily, Ivan gave me the green light. Even better, he happened to have a battered USB keyboard lying around, so he snipped the USB cable off the end and presented it to me with a flourish.
A standard USB-A connector has four pins as illustrated below. If you look closely at the cable, you will see that it contains four individually insulated wires. These are surrounded by uninsulated braided shielding, and the whole thing is then encapsulated by the outermost insulation.
The braided shielding -- shown pulled back from the inner wires, twisted together, and sticking out of the right-hand side of the cable in the image above -- is connected to the outer metal case at the tip of the USB connector. In turn, this case will be connected to a good ground inside the notepad computer.
I obviously have a little tidying up to do. This will include applying solder to the end of the twisted braided wire and then adding some heat-shrink to cover the area between the non-soldered and soldered parts to provide some strain relief.
The bottom line is that I think this is a jolly efficacious solution. When I'm working on my projects, the notepad computer is always plugged into the wall and powered up, so I'll always have a good ground. It's also always mounted close to the project I'm working on, so my ground connection will be easy to access, my ESD cables won’t have to stretch too far, and it will be easy to attach and detach the crocodile clips from the ground point.
The only thing I'm wondering now is why no one sells ESD wristbands with USB plugs on the end. Another alternative would be to have a USB plug with a socket for a banana connector. Maybe there's a business opportunity here for someone. What do you think of my solution? Is this a good idea, or am I about to make a horrible mistake?
— Max Maxfield, Editor of All Things Fun & Interesting