How Touch Screens Work

But if you guys think I sound a little weird or maybe even sounded weird and past episodes, because the episodes we recorded last week, I was already coming down with it, that's why. And uh, I can report that it kind of is awful. It's very much like the flu. It is, um, except that apparently I now also have the uncontrollable urge to lick pigs. I'll so let's uh and then of course lead Yes, I was about to say,

it leads directly into our topic. UM. Now, I don't have a listener mail for this specifically, we did have a request for this topic, and it was from a listener and it did arrive in mail, but our listener Thomas sit in several requests for different text stuff podcast episodes, right, Like, he had about five or six different lists topics listed, And so we're just gonna tackle one of those today,

and that one is touch screens. And of course touch screens are becoming more and more ubiquitous ever present all over the place because things like smartphones. You got a lot of cell phones out there that now have touch screens. Um. You've got things like the iPod, TOUCHERSK reader right that has a touch screen. Um. So yeah, there are a lot of them out there. And of course then they're always the other ones that have been around for ages a t M S. Yeah, good example, vending machines, Um, yeah,

vending machines. I always think back to, uh, Epcot, the old days of Epcot where they would have a computer screen and you could walk up to it and touch the computer screen and uh and and pull up information about the park and about you know, the different aspects of the park and make reservations. And this was back in the early eighties, you know, when Epcot first opened and uh and back then, a touch screen seemed like

freaking science fiction to me. It was. It was pretty amazing because you didn't have to have like any sort of keyboard to get it. In fact, that was that was even before computer mouse had become really a commonplace item. Yeah, you know, some of those early touch screens, at least the ones that I used, were sort of like touched touch touch touch, touch, touch, touch touch touch touch screens. Punch, punch, cry, mop up blood. Yes, those were the stupid thing doesn't work. Yeah,

that the technology has improved somewhere, it hasnally. Now, there are different touchscreen technologies that that are commonly used today. The two most common when it comes to things like portable electronic devices, so things like NP three players or smartphones or whatever, would be resistive screens and capacitive screens. Yes, all right, so let's talk about the differences between these two systems since these are the most common that you'll

find out there a resistive screen or resistive system. It consists of several layers of screens. It's like an onion of screen. Yes, And the way that the system works is when you press upon the screen, you compress these different layers together and when they touch, it creates an electric circuit. Right. Normally, there are spacers they keep the

two the layers apart. Right, If those spacers were to be damaged and the space the screen were to permanently be fused together, you would lose your resistive UH capabilities. It would it would constantly be detecting a specific point

of pressure somewhere on the screen. So those the spacers are very important because basically where you're touching it, the computer is able to tell basically the coordinates of where you're touching, and you know, maps that up to what's being displayed on the screen, and that's how it knows what you're touching and when. Right, So there's a processor that is um it's receiving this information based upon where the different layers of the screen are touching, and that

way it can it can give the correct response. So, for example, if you have a phone that has a resistive screen touch screen and you're pushing the call feature, then it's going to map out the location of the touch send that information to the processor. The processor says, hey, when this particular area on the screen is touched, that means that this action must be performed, and your phone makes a call. And this all happens very very quickly.

Anklebone is connected to the footphone something like that. And old resist of screens had a few big disadvantages really compared to the other type the capacity of screen. One of those was that the the the different layers would somewhat obscure the light coming from the screen, so you would only get a certain percentage of the light coming out of the screen that you would get if the

if the screen were completely clear or transparent. UM. The layers had to be really thin, yes, in order for this to work properly, right, and some of them could. Some of them could detect things like the amount of pressure that you used, and really the amount of pressure was coming from not how hard you were pushing, but how much surface area of your finger or other whatever

it was was in contact with the screen. UM and that could give it an indication of how hard you're pushing, because the harder you push, the more of your finger is going to be against the screen. So that whole punching thing not really effective. No, that would be a bad idea. It's pretty much a guarantee that you're gonna break your resistive or any other touch screen. UM. The the other disadvantage was that early resistive screens couldn't do

multi touch. Um, they were not capable of of accepting two different points of contact at the same time and could not interpret that as a you know, a legitimate command. Now. Of course, we've got a lot of devices out there that support multi touch now, and most of those are using capacity screens. However, I can report it is possible to create a resistive touch screen that supports multi touch. You have to create a system that specifically supports this.

You know. It's not just like any resistive screen could do this with a firmware update. You'd actually have to go through the manufacturing process. But engadget has a video on their site of a pretty cool device. Um. It really was a concept of prototype where it's resistive screen, it can detect pressure, and it is uh, it can detect multi touch. One of the advantages of the resistive system to the capacitive system is that you don't have to You can use pretty much anything to contact the

screen and and give a command. So it doesn't have to be your finger. It could be a stylist, right, it could be anything, because it could be a dog. Yes, it could be a rock, it could be some play doh. Um, it really doesn't matter because as long as it is able to make that pressure against the screen, that's going to count as a an input. Now, capacity of screens are different. Now they actually have a layer that stores

an electrical charge in them. That would be the capacitance layer. Yes, Thus the name kind of makes sense now, doesn't it amazing, isn't it. I mean the capacitive layer is uh, you know, storing a like Tron's right, So it's storing these electrons right there on the screen. When your finger comes in contact with the screen, this actually ends up transferring the charge to you. So technically you are kind of getting a very mild shock. I find that revolting. Do you

do you get a charge out of it? We can do this all day, palass oh, I know, and and our listeners are depart like lightning was especially a shocking kind of experience as long as you stay current. But you know, I could tell that my iPod Touch has a capacity screen because I'm stopping because you know, sitting out and waiting for the bus or the train to bring me to work here in the morning in the wintertime,

and having gloves on. You can't change you know, the volume on your iPod because you know, my bears get you know, the gloves won't because they start for the chart. If they don't, they don't, they won't pick up the charge like your skin would if you are But otherwise, if you if you are outside on a really cold, dry day, you might have problems getting a capacity of screen to work at all. Uh. Capacity screens work best when there's at least a little bit of humidity to

help conduct that electricity. Right. Yeah, but if it were really called dry day, you might find that your touch screen is not very responsive. It's not necessarily because your phone is cold. It may be because you don't have the moisture on your finger that helps create that that electrical connection. And um, we'll see. That's good because I like licking my iPod, So that explains why it always works pretty well. Also explains why I have the swine flu.

So anyway, the capacity of screens actually do support multi touch if you create the right hardware and software around it. They don't automatically. It's not like magically supports it. You have to build the system around it. Um. And of course, if you were to build the system around it, you could very possibly engender the wrath of Apple because they patented it. They patented multi touch for for mobile devices.

That was really smart of them. It's also incredibly mean because the Android operating system actually supports multi touch, but it is not um enabled in any Android device that

I know of. Specifically, I assumes the patent I should have. Yeah, I should assume it's because of this patent, and if if the phones were to support multi touch, then it could very well be Even if it's not directly in violation of the patent, I'm sure that an argument could be made and then you've got a costly legal battle. So that would be why the iPhone is this great multi touch device and most other devices don't support multi touch in the same way. Um, some of you may

be yelling, hey, what the Microsoft surface. We'll get to that. It's a it's a totally different animal. But the capacitive system, so you know, like I said, it's it's it detects this electrical uh connection, and that it's in a way does the same sort of thing as the resistive screen in the sense that it finds out you know, it says where the connection happens on the screen, it maps that to a specific command, and then the processor executes

that command. So the big difference between the two systems is how it how the electrical connection is made. Yeah, basically the one Once the the circuit or you know, is completed and an electrical connection is made, the computer on the other end figures out where it is and what it's supposed to be doing at that point, right, and and again with capacity of screens, you would have to use something like a finger or you know, your nose or you know, something that could create could accept

this charge from the screen. You couldn't use something that was passive like a stylus or the rock four mentioned rock. Right, you could possibly use a dog, depending on what part of the dog was touching the screen. Yeah, yeah, you know, or nose or something. But well yeah, well some of us can leave a lot of finger smudges already, so um. But yeah, if you wanted to use a stylist with a capasity screen, you would have to have a stylist had an active point on it that could accept that charge,

otherwise you wouldn't get anything out of it. So that actually makes me wonder what the Microsoft Courier tablet, the prototype that we we We've seen a video that was more or less an animation of this prototype tablet that Microsoft is coming out with. It's got two screens and it has a touch screen interface, and it shows people flicking through with their wealth. It shows an animation of a finger flicking through pages UM and it also shows an animation of like a stylist writing on a page.

So I kind of wonder what kind of touchscreen technology it's playing on using if if they're using going to use resistive or they're going to use capacitive UM. There is another choice, but you don't see it that often in in smaller devices. Is the surface acoustic waves system. Yeah. Now this is something that you would see in and more often in things like a t M S and

bigger displays. But what this uses is a couple of transducers and they are placed along the X and y axes of the glass plate of the monitor, and whenever it sends an electrical signal, one transducer sends it to another transducer, and there are reflectors on there to kind of reflect the signal from one to the other. When something makes contact with the screen, it disturbs that electrical wave, and by measuring the disturbance, the touchscreen knows where it

was touched that. When I say knows, of course, we're talking about a processor that that that the screen. Yeah, the screen itself does not know. Um, it's not magic, and it doesn't it's not sentient. It's once touch screens become sentient, sexual harassment lawsuits will go through the roof because of inappropriate touch screen interface. Let's we'll see if

that stays in the right. At any rate, the surface acoustic wave system UH is not often Now, for one thing, the equipment that you need in order to make this thing work is kind of um big. It wouldn't really be easy to miniaturize this into a mobile format, right, So you wouldn't want to try and use this kind of technology in your in your general mobile device because it would make it too fat, too heavy. Um. And

of course we all want sleek and stylish. Well, I mean, you know, the iPod pretty much proves that the sleek and stylish approaches is really popular. I mean, it's a good product anyway, but I think that the style is definitely a large contributing factor to the popularity of the iPod line. So at any rate, uh, capacity of resistive, that's the two that you're going to see the most often in your in your average mobile devices. Um, the iPhone uses a capacity of screen, and like we said before,

it actually can detect multi touch. So that means that you can use gestures instead of just touching. Two give commands things like pinching, you know, like if you pinch. No, not, I'm not actually pinching, Pillette. I want to make that clear. I've already made one sexual harassment. I am not. I am not even within pinching range of palette. Um, he has barricaded himself in the corner and he's perfectly safe.

I got my blanky. Yes, he does have his blankie. No. But but you know, like like when you wanna when you want to squish or enlarge a photo doing various pinching motions, or if you're panning or whatever, these are gestures. Okay, But so these are commands that your phone should or m P three player or whatever should be able to recognize as a very general command as opposed to open

up this application I want to use it. It's more of a you know, I'm I'm manipulating something, rotating a picture, or you know, scrolling from one screen screen to another, that kind of thing. And UM. I mean, regular touch screens can identify some gestures as well. It's just multi touch can identify more complex gestures. Uh. So that's pretty much the the basis there. I mean, the the both kinds of display are both kind of touch screens are

fairly accurate if they're done well. The execution has to be there. But there's nothing about either u I Their technology that makes one far more accurate than the other. UM. They're both challenging to do well. But if you do uh, you know, if you do the good work, then either one should be more than accurate enough for the average user. UM. The resistive screens are much cheaper than capacitive screens. UM capacity seems to have the probably more support among the

technology savvy crowd. They seem to like the capacity screens more, probably because of things like the old resistive screens were harder to it's harder to see the images they were scratched. They weren't scratch proof that they could get scratched pretty easily because the screens had to be soft enough for

you to press them in a little bit. UM. But if you're concerned with manufacturing a device that's going to be an inexpensive one for your customers than the resistive screen is a more attractive approach because it's less expensive for those components. If you're doing a premium product, capacitive it is probably the way to go. Yeah, well, it seems like, you know, over the past few years, with the ubiquitous nous of these devices, it's you know, it's

harder to find the implementation done poorly. He thinks that more and more people are getting it right, which is what's making you know, applications for these devices more and more common. And a lot of the problems with touch screens have more to do with the underlying operating system than the technology of the screens themselves. So like older operating systems for smartphones are tend to tend to have a little more trouble with touch screens than the more

recent ones. You might have an older phone that's running an older version of Windows Mobile, for example, that UH is not as responsive as newer versions. UM. I think Microsoft philosophy right now is from now on going forward, smartphones running running Windows Mobile will have resistive screens. Smartphones that will run the Windows Mobile or the Windows seven modified modified UH operate system for mobile devices will have

multi touch and will be capacitive screens. So that's kind of interesting that they've actually developed two different strategies that and each one focuses on a specific technology. Well, it makes sense that they would try to keep the cost down by using a resistive screen in a you know, more consumer device and higher end screens. Yeah, it's it's actually a pretty clever approach. I think it'll be interesting

to see how that plays out. The only thing I could think of that might cost them more money down the road is by having the complexity of having another system and another device, and it's another thing they have to tool up for and another thing they have to support. Yeah. Well, they've also got issues with their their Windows Mobile store, and there there are a lot of things that the issues, a lot of things Microsoft look at. Yeah, never any

issues with technology. I was going to mention also that Research in Motion also known as risk Yes, the the company behind BlackBerry. They filed a patent in January two thousand eight for a hybrid resistive capacitive screen would have both resistive and capacitive layers. I tried reading this patent to figure out how it would work for this podcast, and I think I would need another three or four

days to really get through it to understand it. Um. I can't even pretend to go into the science behind it because part of it is written in Martian. Well, it's written in patent ease and okay, so it's a level of difficulty above Martia. It's slightly more difficult than Martian UM. And then I said, we were going to talk about the Microsoft Surface very quickly. So the surface, it doesn't use a capacitive resistive It does not. It is if you don't know what it is. It is

a table like device. It has a monitor on the top of it, so you would sit down at one of these things, and it has a big screen that you can touch and manipulate things on the screen. You can have images there, you can play games, and it can detect dozens of different touch points, so it's not

just you know, two finger touching. You could have a game where five people are sitting around this table and are playing a little pinball game or whatever, and each one's controlling a set of flippers, you know, or tons of other different implications. It does not use capacity or resistive touch screens. Instead, it uses cameras and an image recognition UH software that is in the infrared spectrum. So

these cameras are pointing up from inside the device. They're pointing up at the screen, the screen surface, and they detect the points of contact and then send that information to the processor, which then you know, translates into a command. The neat thing about this is you can use multiple objects on the surface and and automatically transmit commands. So let's say that you have a an MP three player

that can wirelessly sink with a computing device. So let's say you've got a Microsoft Zoom and you lay this down on the surface, the surface, the surface of the surface. Yes, you could lay it on the screen of the surface, and you could sink your device with the surface automatically just by laying it on the screen, because it would detect the shape and size of that Say, hey, you know what that is. That's a zoom uh, and it just automatically has the command that when that device is

placed on there, it'll sink. Yeah. So there are a lot of interesting swine flu interesting um applications for this device. So anyway, that was one thing I wanted to bring up because technically that's not even if you think of it as a touch screens. It's not really a touch screen.

It's really all because the camera. You had a similar device you wanted to mention briefly, right, Well, yeah, because uh, you know, as we were talking before hand, I started thinking about other devices like that UM and uh one of the ones that our friends that stuff from the B side uh recorded And actually John Fuller wrote about the React table, which uses a series of acrylic shapes on a Microsoft surface like surface UM to control music.

And I started thinking about how that worked, and you said, basically, it's the same, you know, a similar situation of cameras underneath the table. And I remember from editing that that yes, it's got UM, it's got a screen on which the shapes said, and it's you know, the cameras tracking where those those different pieces are. And it says, okay, well this is a this is a circle. I know, you know when his circle it controls the beat is you know,

the square does this. So that's uh yeah, So depending on the position of those and the position and configuration right those different objects, it'll create a different set of sounds and you can rotate things in it, you know it because it's the shape and the position of the

uh implement that it has to do a certain thing. Yeah, I've seen similar applications which would do things like even incorporate stuff like colors, so you might have a one circle that's blue and one circle that's red, and it actually translates to two different commands, so you can have multiple circles on the same sort of surface and and it would Yeah. Again, mostly it's it tends to be

things for like music performance art. I think Byork toured with one of these, so, um, the thing is, my question is if you, you know, have an instrument that's using you know, reds and yellows, can it help you play the blues? Let's move on. I'm glad that we have exhausted touch screen, or at least I'm exhausted. But then again, I've got puns aren't helping, I'm sure. Let's move on to a little listener mail. This listener mail comes from Chase, and Chase is an Oregonian living in Osaka, Japan.

He's also very verbose. Chase, I loved your email, and I responded to Chase already, so I'm gonna have to sort of summarize Chase's email here um, but he said they had an He has an iPod Touch and he got an application called Anti Young Free, which emits a sound that only young people or people who took very

good care of their ears can hear. Because I work in a high school, so I decided to test it out on the class of fifteen to sixteen year old I got them all to stand up and then push the button to turn the sound on and told everyone to sit down and they could hear something. To my surprise, eight of the forty students remain standing and mystified. According to the descriptions for this app, people who people should be able to hear it until they are around twenty

to thirty years old. I'm twenty five years old and cannot hear it, but my wife, who was twenty four freaked out when I turned the sound on. That aside, I also discovered a number of other absolute things like repel mosquitoes or act as dog whistles. And you wanted to know, one, how does it work? And two is it doing any damage to his speakers? Let's take the second one. First, most speakers can emit sounds that are well beyond the range of human hearing, and so they're

perfectly capable of doing this. Nothing bad is going to happen, um, you know, on its own, because that's what speakers do. They're capable of emitting these sounds. It's not not like it's suddenly ripping itself apart. But the first part about how does it work? Well, humans can hear in a range of of sound frequencies that it's between about twenty hurts and twenty thousand hurts, give or take a few thousands. All depends on who you ask, really, but whether you're

male or female. And of course, as we get older, we start to lose the capability of hearing that complete range, and in general we lose the upper ranges first. And so if you are in your late twenties, early thirties, you may only be able to hear up to fourteen thousand hurts or sixteen thousand hurts or sixteen killer hurts if you prefer. But um so, anything above that frequency you just you don't, you don't hear it. But younger people could still hear that. And in general, human beings

don't like high pitched noises. They tend to irritate us um, which is you know why Chris likes to drown me out, I guess at any rate. So that's how that really works, is that as we age, we just naturally begin to lose that ability, and some of us lose it more slowly than others. So you may find someone who's thirty two who can hear the same thing that a sixteen year old can hear, or you may find you know a fourteen year old kid who can't hear anything at

all from that particular range. Um, it's very subjective. There are no hardened past rules, but in general, if you're talking about big numbers, that's kind of how it works. So thanks for writing in Chase. If any of you have any questions, concerns, criticisms, suggestions per episodes, you can write us tech Stuff at how stuff works dot com. Remember we have a live show every Tuesday at one pm Eastern. You can find that if you go to the blogs over at how stufforks dot com and Crispy

and I will talk to you again. Hopefully I will be talking without a raspy voice really soon. For moral thiss and thousands of other topics, does it how stuff works dot com and be sure to check out the new tech stuff blog now on the house Stuff Works homepage, brought to you by the reinvented two thousand twelve camera. It's ready, are you