Getting in Touch with Touchscreens

the sets for Star Trek. The Enterprise, which is the flagship of the Federation, used physical buttons and switches, not touch screens. Now, that should not come as a surprise. The set designers were taking their inspiration from electronic devices and mainframe computers of the time and then just saying, how can we make that look more futury? And you can't blame them for failing to predict that in the future people would interact with technologies through other means, including

voice and touch. By the time we get up to Star Trek the next generation, things had changed quite a bit. The controls on the new Enterprise were these sort of touch sensitive panels. They had control surfaces that were built directly into walls and consoles in such a way that I bet it was someone's full time gig on the set to just wipe down the surfaces to get rid of all the smudges. They also had voice commands built into their computer system at that point, so that was

pretty cool too. They kind of had both of those blossoming technologies involved in Star Trek next generation. And there are actually several different methods that you could follow to

create a touch screen or touch surface. So for example, you could have a rear projection screen and you're projecting image is from behind the screen onto the screen, and also behind the screen, you could have a bunch of near infrared cameras, and these near infrared cameras could detect when a fingertip or some object makes contact with the surface that's on the other side and then map that

to a program that creates the appropriate response. The original Microsoft surface, which later would be called the Pixel Sense, had something like this and used multiple near infrared cameras I think five of them behind the screen to detect and track objects that make contact with the screen. If you don't recall, the pixel Sense had sort of a table form factor. It was quite a large display, bigger

than what you would have with like a tablet. But I wanted to talk about the differences between the two most common touchscreen technologies that consumers typically encounter. So first up is actually capacitive touch. This is really the type of screen you're most likely to encounter these days. Most touch screen technology falls back on this, and capacitive touch predates the other technology that we'll talk about by about

five years or so. So back in nineteen sixty five, there was a British engineer named E. A. Johnson who developed capasitive touch technologies while working for the Royal Radar Establishment. He wrote up his work in a paper he titled Touch Displays a Programmed Man Machine Interface in nineteen sixty seven. A capacitive screen consists of several layers, So we're going to work from the bottom up, and by up, I mean like at the top layer will be the surface

that you would interact with. So at the base you have your actual display, right, this is what is generating the image that you're going to see through the other layers. So all the layers on top of this need to be transparent, because otherwise you wouldn't be able to see the stuff that's on the display, and you've kind of eliminated the purposes of having a touchscreen device. Now, typically you would have a thin glass substrate that would be on top of the display, and then the next layer

up would be a conductive layer. So this is a layer that creates an electrostatic field across it. On top of that layer is a thin transparent layer, and this is the layer that you could actually touch. So if something conductive makes contact with this top layer, then some of the electrostatic charge on the layer beneath the top layer will transfer to that conductive material. So let's just say it's your finger. Make it easy. So you touch

your finger to the surface of a screen. Your finger is conductive, and once you touch the screen, some of the charge on the surface underneath that top layer transfers to your finger, and the charge decreases at the point

of contact. So you've got circuits that are built into the edge of the screen, often at the corners, and they detect where precisely that charge decrease in the capacitive layer happens and registers this as a contact and then that translates into an action based on whatever it is

you're doing so. Like if you're playing a game and you move your finger across the screen, it says, all right, well, the point of contact started at this position, it ended at that position, and that means we need to reflect that in moving a character from one point to another

or whatever it may be. Now, this is why if you're wearing non conductive gloves, you can't interact with a touch screen, a capacitive touch screen properly, unless you, you know, carry around something like a hot dog around that would work. I've actually seen people or pictures of people in Japan doing that when the weather was really darn cold. Hot dog phone. But also like anything that hasity, a conductive

rather a conductive surface would work. It's just that if you're wearing gloves that insulate you, then that doesn't work. That's why some gloves come with a little conductive mesh at the fingertips so that you can still interact with your capacitive touch screen devices while wearing the gloves. Now, the version that Johnson invented way back in nineteen sixty five was understandably limited. It could only detect the presence of a touch. It couldn't tell the difference between one

finger or two fingers or anything like that. I don't think it could even detect where on the screen the touch happened, just that there was a touch. So in other words, it was kind of an on off or binary system. Either something conductive was in contact with the screen or it wasn't. But this served as the foundation

for the capacitive touch screens we used today. The problem is they were expensive, so while it was possible, it didn't really proliferate because the use cases were fairly limited, and it didn't make any sense to try and incorporate that into consumer technology because whatever you made would be way too expensive. The other common touch screen technology is

called resistive touch. In nineteen seventy, an inventor named G. Samuel Hurst was trying to figure out a way to more efficiently make use of a vandograph accelerator, and so

he came up with the idea of using electrically conductive paper. Essentially, these papers would have like a grid along the X and y axis of the paper, and you could detect a change in voltage along those grids, so you could you could plot a specific point of contact by the way a vandograph generator, you know, a vandograph accelerator is what Hearst was referring to, but that's because a vandograph generator was used as a very primitive particle accelerator back

in the day. It is an electrostatic generator. You've probably at least seen pictures of these, if not actually seen one in use. So typically you're using a belt mounted on some rollers that turn very quickly. This makes the belt move very quickly, and the moving belt actually typically makes contact with another surface, but it generates this electrostatic charge and carries that charge to a hollow metal globe.

The globe itself is also mounted on top of a column that's made of some sort of insulator material, so this isolates the metal globe. Right, You're building up this electrostatic charge in the metal globe and there's nowhere for the charge to go because you've isolated the globe. And then you can bring something conductive in you know, general proximity of the globe, and as you get close enough, the difference in electric potentials will cause a spark to form.

Like you essentially create a circuit very very briefly, and then you get this zap of a spark and you've probably seen, like I said, one of these, either in video or maybe even in person. You're likely to find it in like science classrooms to help demonstrate the principles of electrostatics. But back in the day they were used as particle accelerators in physics research. Yes, today it's a toy and a science classroom, but back in the day,

it was a particle accelerator. Anyway, doctor Hurst used the electrically conductive paper to plot charge on X and y axis, and only a bit later did he realize that what he was doing could potentially have other applications outside the lab. I'll explain more, but first let's take a quick break. So doctor Hurst and his team figured that they might actually have some applications for this conductive paper beyond the plotting of charges using a vandograph accelerator. And he thought

that he could make this into a touchscreen interface. So this would be a resistive touch screen. They actually have more layers than capacitive touch screens. That also means they block a little more light than capacitive touch screens do, so resistive screens tend to be dimmer than capacitive ones. So let's go through those layers again and again, we're going to start from the display side up to the

surface where you would make contact with the screen. So at the very base you've still got your display, just like with capacitive. On top of the display, you've got a glass substrate. Above that you have a transparent conductive layer, so again similar to what you would have with the capacitive screen. But next you would have a layer of what are called separator dots. So these are our little supports that are non conductive. They are there to act

as a separator. They keep the first transparent conductive layer separate from a second transparent conductive layer, so they're there to keep space between those two layers. So again above these separator dots is that second transparent conductive layer, and then on the very top you have a flexible transparent film on top. This is where you would make contact

with the screen. So when you push down on the screen, whether it's with a conductive surface or not, what you're doing is you're deforming the top most transparent layer to push down and come into contact with the next transparent conductive layer. That creates a circuit. So as long as you're pushing down with enough force, you're creating the circuit

and it will detect that touch. So typically you've got other circuits in the device that detect drops in voltage or changes in voltage, and that's how they can detect the precise location where the touch happened. So again, doesn't matter if it's your finger, if you're wearing gloves, if you're using a stylus, it doesn't really matter. What matters is that that top transparent conductive layer comes into contact with the bottom transparent conductive layer and creates a circuit.

So the capacitive screen actually came first, but the resistive screen was more popular. It got more popular, and it did so faster than capacitive. So why is that, Well,

mostly it comes down to cost. Also, like the fact that you didn't have to have a conductive material to work with it meant that you could actually use it for lots of other stuff, including stuff where you might have to do something like wear gloves, but you could use a stylus like That's a useful part of that technology is the fact that you can still work with it even if you aren't able to, you know, use

your fingers directly on the screen. But it was much cheaper and that was really the big thing, so capacitive sort of took a back seat for a while, and it would require a lot more innovation in the space to make capacitive screens more attractive than resistive screens. However, these days, most consumer devices you're going to come in to contact with use capacitive touch screens, largely because, I mean, they're still more expensive than resistive touch screens, but they

can display brighter images, so that's definitely a positive. They tend to be more durable as well as you can imagine if you've got a resistive touch screen, which is it works based upon you pushing the screen hard enough to make contact between two layers. I mean, you don't have to push super hard, but it does have to be enough pressure so that the system detects there's a

touch there. Well, as you might imagine, this eventually deforms the upper transparent conductive layer, and that you can eventually get to points where it's already close to or making contact with the lower layer. Just kind of like having a short circuit, right, and it makes it more difficult to have an accurate experience. Using resistive touch screens. Doesn't happen overnight, but over time it does happen, So that's one of the other benefits capacitive touch screens have over resistive.

It's also easier to use capacitive touch screens for multi touch functions in general, not that you couldn't do it with resistive touch screens, but it's just it's easier when you're not focusing on using pressure to make that point of contact. You will still find resistive touch screens, however, in devices that are aimed at lower price points, So if you're looking at like a budget tablet, there are a lot of industrial uses for resistive touch screens to

this day. And keep in mind, as I said at the beginning of this episode, there are other types of touch screen technologies besides these two. There's some that use acoustics, there's some that use infrared lasers. Like I said with the surface, there are the kinds that use you know, cameras that are mounted behind the screen itself. It's not like these two are the only two. There are lots

of other technologies. It's just those two are the ones you're most likely to come into contact with, both figuratively and literally. So I hope that this was interesting and informative. A little tech Stuff Tidbits episode, and I'm trying to do more of these because it's fun to do these short ones. It's just a challenge because you know, I'm a chatty Kathy. This episode probably could have been eight

minutes long and instead of going twice as long. So but hey, I like your company, hope you like mine, And if you have any suggestions for little things that you would like explained in the tech space, even if it's something like, hey, can you give a quick rundown on logic gates and what those do or something along those lines, let me know and I'll look into it. And I hope you are all well, and I'll talk to you again really soon. Tech Stuff is an iHeartRadio production.

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