原创 Max's service: Zapping things with ESD

Question: Before we leap into this blog with gusto and wild abandon, I have a poser for you to ponder. Suppose you are working on hobby electronics projects on your kitchen table and you've invested in an ESD (electrostatic discharge) wristband as shown below. To what should you attach the crocodile (alligator) clip on the end of the strap to give you a good ground connection? Now, read on...

When I was younger, I was a paragon of virtue with regard to taking preventative measures against ESD (electrostatic discharge). However, I'm ashamed to say that -- over time -- I grew a little blasé about this phenomena. Well, that was until quite recently when things like LEDs and MCU input/output (I/O) pins started to shrug off this mortal coil, helped on their way with an electrostatic "zap" provided courtesy of yours truly (it's just another service I offer).

Now the pendulum has swung and -- as is the way with these things -- I've become something of an ESD zealot. It started with my purchasing a humble ESD wristband similar to the one shown above. (Amazingly enough, you can get these from Best Buy; even more amazing, the folks at Radio Shack don’t know what you're talking about when you say "electrostatic discharge.")

More recently, while rooting around looking for a toolkit to accompany me on my travels, I invested in a rather nice 24" x 48" anti-static mat from those little scamps at iFixit. (This mat is intended for home use, of course -- I don’t plan on carting it around the world with me.)

Based on this, you might assume that all is now well in the Land of Max (where the colors are brighter, the butterflies are bigger, the birds sing sweeter, and the beer is plentiful and cold), but there is one small fly in the soup, as it were. The thing that has been bugging me is the best mechanism to ground my ESD wristband and mat.

The folks in the next bay in the building housing my office have an easy time of this. They have fully grounded anti-static mats at each work area. Also, their ESD wristbands have banana plugs on the end and there are grounding points located in front of each work area as illustrated below.

Obviously, I don’t have these grounding points mounted on my kitchen table at home, and I'm reasonably confident that the radiance of my wife's (Gina the Gorgeous) smile would no longer fall upon me if I were to install such an item. I have tried clipping the crocodile clips to the metal enclosure of my project's power supply, but sometimes I unplug this from the wall while I'm "tweaking" something, in which case I'm SOL (sadly out of luck).

Another approach I've tried is to have one end of a flying lead plugged into the ground strip on my breadboard, and to then attach the crocodile clip on my ESD wristband to the other end of this lead. We can see an example of this in the image below, which is from my blog on constructing my MSGEQ7-Based DIY Audio Spectrum Analyzer.

Observe the green wire that is plugged into the bottom right-hand corner of the breadboard and that exits from the lower right-hand side of this image. While I was working on this project, my crocodile clip was connected to the flying end of this wire (this is not shown in this image). There are several problems with this approach, not the least that it's easy to tug the lead out of the breadboard. Also, for this to really work, it assumes that the breadboard is actually connected to a ground point via a power supply or some other mechanism.

Another alternative would be to replace the crocodile clips with banana plugs, to splay these out a little at the end, and to plug them into the ground pins of wall-mounted power sockets. On the one hand this should ensure a good ground connection (we'd have to check the socket in question first -- experience has shown me that you can't rely on anything); on the other hand, it means that the cable on the ESD wristband would be stretched out to its fullest extent, which somewhat limits one's movements. Also, you'd constantly be bending down to plug yourself in or unplug yourself again.

And then, just this morning as I was mulling things over while driving into work, I had a simple yet (I think) brilliant idea...

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 lowdown on batteries series). 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?