20 SEPTEMBER 2022 WorldWide Drilling Resource® You’ve Got the Touch by Britt Storkson Owner, P2FlowLLC There are many types of HMI - Human Machine Interface (systems) - out there. These are devices that take input from the human operators and convert this information into a code the computer can “understand” and respond to. This HMI can be anything from a simple mechanical switch - touching two pieces of metal together - to a sophisticated touch screen. But one must be careful when using any type of switch because it can “switch” when you don’t want it to, or when it is not supposed to. The key fob on my car allows me to lock and unlock the doors remotely, but sometimes a wrinkle in my pants pocket holding this key fob will press on the key fob and either lock or unlock the car without my input. Lately, there are many touch-activated devices that do a wide variety of things. Some years ago, my sister bought a touch-activated lamp for her living room. To turn the lamp on or off and select the lamp brightness, you just touch any metal part of the lamp. It worked great except for her dog. Often the dog would walk by and touch the lamp with his nose and the lamp would turn on. So it was only a matter of time before the dog turned on the lamp even when she didn’t want it on. One type of touch-activated device is a touch screen (HMI), and they’re everywhere these days. They’re on virtually every computer device made and have a lot of advantages. These touch screens can be made waterproof and resistant to a lot of environmental hazards and can be redefined to present many choices for the user to interface with a wide variety of applications. While touch screens have many advantages, there are downsides as well. For one, it is difficult to know if the function you selected has actually been recognized because there is no tactile feedback. Tactile means “touch” in that one cannot tell by touch if the command has been received. Also, various things brushing up against the screen can create false inputs the user may not be aware of. How does a touch screen work? It works by detecting a change in capacitive charge on the touch screen surface. What is capacitive charge? The short answer: Electricity is basically the flow of electrons, and capacitive charge is the storage of these electrons. Electrons flow through electrical conductors like copper, silver, gold, etc., but are stored on the surface of electrical insulators like paper, plastic, ceramics, etc. Given this dynamic, it’s possible to store electrons on the surface of insulators. The number of these electrons stored on these surfaces is called capacitance, and this can be measured as a voltage. While the surface of the touch screen has a capacitive value, the object touching this screen adds capacitive value, which changes the voltage detected. The controlling microprocessor continuously “samples” and a change in the voltage measured indicates something or someone is touching the screen. The touch screen is laid out in a grid/pad pattern so the voltage can be measured relative to the pads next to it, so the microprocessor operating all of this can note where the touch occurred and determine what the touch screen operator wants to do. All of this activity happens several hundred or even thousand times every second, so they can be very fast. In fact, the touch screen on my phone is a bit too fast sometimes. I’ll be watching a video and just briefly moving my finger near the display area often switches to another video I wasn’t interested in. One way to prevent this problem is to provide a longer delay before switching or generate a confirmation routine that will ask the user to confirm they really want to switch to another video. As for me, I’m for whatever works, and works well. Mechanical switches have been greatly improved over the years both in operational and durability functions and will be with us for a long time. Time delays can be programmed in to make switch press confirmation consistent and reliable and even adjustable in another area of the code. Like a lot of things, one wants it to react quickly, but not so fast it’s a problem for the user. Britt Britt Storkson may be contacted via e-mail to michele@worldwidedrillingresource.com
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