Ok so people have been confused over the tech thats behind the Iphone/G1 capacitive dual touch screen, and all WinMo phones resisitive screens. So i thought i would do the great job of researching the tech behind both methods. 10 minutes later i came across this info on how both methods work, as well as a more expensive and even better method using acoustic mumbo jumbo. So for all you out there that are too lazy to do the diggin, heres the info that once and for all puts the rumors to bed about "...i heard its dual touch capable from so and so website..."
PLEASE READ>>>
The resistive system consists of a normal glass panel that is covered with a conductive and a resistive metallic layer. These two layers are held apart by spacers, and a scratch-resistant layer is placed on top of the whole setup. An electrical current runs through the two layers while the monitor is operational. When a user touches the screen, the two layers make contact in that exact spot. The change in the electrical field is noted and the coordinates of the point of contact are calculated by the computer. Once the coordinates are known, a special driver translates the touch into something that the operating system can understand, much as a computer mouse driver translates a mouse's movements into a click or a drag.
In the capacitive system, a layer that stores electrical charge is placed on the glass panel of the monitor. When a user touches the monitor with his or her finger, some of the charge is transferred to the user, so the charge on the capacitive layer decreases. This decrease is measured in circuits located at each corner of the monitor. The computer calculates, from the relative differences in charge at each corner, exactly where the touch event took place and then relays that information to the touch-screen driver software. One advantage that the capacitive system has over the resistive system is that it transmits almost 90 percent of the light from the monitor, whereas the resistive system only transmits about 75 percent. This gives the capacitive system a much clearer picture than the resistive system.
On the monitor of a surface acoustic wave system, two transducers (one receiving and one sending) are placed along the x and y axes of the monitor's glass plate. Also placed on the glass are reflectors -- they reflect an electrical signal sent from one transducer to the other. The receiving transducer is able to tell if the wave has been disturbed by a touch event at any instant, and can locate it accordingly. The wave setup has no metallic layers on the screen, allowing for 100-percent light throughput and perfect image clarity. This makes the surface acoustic wave system best for displaying detailed graphics (both other systems have significant degradation in clarity).
Another area in which the systems differ is in which stimuli will register as a touch event. A resistive system registers a touch as long as the two layers make contact, which means that it doesn't matter if you touch it with your finger or a rubber ball. A capacitive system, on the other hand, must have a conductive input, usually your finger, in order to register a touch. The surface acoustic wave system works much like the resistive system, allowing a touch with almost any object -- except hard and small objects like a pen tip.
As far as price, the resistive system is the cheapest; its clarity is the lowest of the three, and its layers can be damaged by sharp objects. The surface acoustic wave setup is usually the most expensive.
How Stuff Works people, its a great website. heres a picture i made to show you how the tech works, or at least how it appears to me.
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Very informative, thanks.
cool info, thanks for your effort.
but does this mean we may be able to improve drivers for a multi touch on our h/d or on other resisitive screens?
This whole lack-of-multi-touch-on-the-HD thing got me thinking. One problem is obviously the gaming side of things, where you can't push two virtual buttons at once to go at a diagonal say.
If you open up an SMS and use the Transcriber option, then push at two points on the screen, there is a line drawn that stops mid-way between the two pushed points.
Would it not be possible therefore, for a cleverer person than I, to program a virtual D-Pad that could work out when two buttons were pushed simply by triangulating the position of the virtual cursor?
Does that make sense?
That's an interesting point, Major.
Try this also, in the notes app - turn it to drawing mode. Then hold one finger on the screen in one position, and then tap the screen or drag around the screen with your other finger. You see how the touchscreen makes lines that fan out between the two points of contact.
i believe that it may be possible to somehow utilize the fact that something does happen when pushing in on two points of a resistive screen.
the real problem with it is that when you push on two seperate points, the screen makes an indentation that spans across the area between the two. the layer you are pushing on is simply not elastic enough to register two smaller seperate points or indents. its just read as one big indent on the layer between the two points of pressure. this is why the the screen only reads a point between the two. the sensor is just picking up one giant blob that centers at the mid point between your two fingers. this wouldnt really help much because the farther apart your fingers are the more random the point location becomes---this is because the thin layer will be contacting the layer below at multiple random spots between your two fingers. idk. it seems like it wasnt meant for multi touch. and a driver would need to have a more precise input than that.
Ahh, but consider a simple d-pad arrangement, with 4 direction buttons and maybe 2 action buttons (à la SNES or similar?). Diagonals would be easy enough with the point of contact appearing between the 2 buttons pushed. A move-and-fire combo could be detected with clever placement of the virtual action buttons giving the device a good clear area of detection.
If I get time today, I'll try to draw a simple graphic. A picture speaks a thousand words and all that.
Edit: OK, excuse my laughable drawing, but you get the idea. With better placement, the buttons could be made quite in-sensitive to where the fingers/thumbs are pushing on them.
My thoughts on the matter.
I think it would do emulator or even virtual d pad developers well to add this option into their d pad. When you press on two points the screen reads in between right? So if you're playing mario and you're trying to run and jump over a hole, just have a setting that allows right button to continue if suddenly the pointer reads in the middle of the screen. In otherwords, it would make no sense for a nintendo player to suddenly press the middle of the screen, so the d pad would read that as a whichever butten first pressed, plus button now being pressed.
If it reads exactly between both points, then the software should be able to guess which button you're pressing by calculating which buttons are exactly in line with eachother. There will be a beginning reference set by the first point pressed, so it is only a matter of auto executing o---^---0. I hope this idea makes some sense to someone other than me.
Just think of Orion's belt and it's symetry to get the right idea of what I'm talking about.
Caid.
Just a bit more clarity, if the d pad developers set up a reference of center screen points, the could technically program their pads to be multitouch souley off the basics that each two buttons pressed together would have a center point at an exact or near exact point in between the left and right side of the d pad. This wouldn't work for diagnal, but for any direction plus ABXYLR there would be a center point between each of them, a place in between them that the phone would register the touch.
Is this exploitable?
Sorry for constantly editing, but ideas keep crystalizing.
Beyond the first idea, to register an A+b, have slide vs tap settings on the d pad. That means, if I slide from a to b, the d pad will hold a and activate b as opposed to just switching between the two. Once again, this should technically be possible with the first idea as the middle reference point should also read a shift. In fact, if you're pressing on both sides of the screen at once (d pad and abxy) then all the actually pressing action would be happening in the center of the screen or rather between both pads.
tazbo28 said:
the real problem with it is that when you push on two seperate points, the screen makes an indentation that spans across the area between the two. the layer you are pushing on is simply not elastic enough to register two smaller seperate points or indents.
Click to expand...
Click to collapse
I seriously doubt that it's technically any more difficult than calculating the two touch positions on a capacitive digitizer (keeping in mind that in reality "multi" means "dual").
it's actually hysterical raisins (historical reasons) that resistive is single touch only - when PDAs were first developed, the designers had to cater for both stylus (very precise) and finger use. Finger use is spread over the fingertip so the designers hard-coded algorithms that would average out the touch coordinates so the middle of the touch events.
The mentality basically went along the line of "why would you want to touch two points on the screen at the same time? Nothing uses that! Can you think of a use for that? No? Ah well, we don't need that then"
This has held until Apple decided to use the more battery draining capacitive method (resistive only uses battery when the two layers touch, capacitive has a constant charge and therefore constant drain) and decided to use multi-touch as a gimmick (and, lets be completely blunt here it IS a gimmick - pinching is NOT easier than running a circle around the point of interest and it's certainly more clumsy than a slider for zooming!) under the pretense of a new and awesome feature for mobiles (it does have practical use in laptop trackpads though)
Resistive technology does support multi-touch, but it's a bigger issue to code the function because the touch events are processed by the touch controller then sent to the operating system as x/y coordinates. The operating system can't do anything about this. To get resistive technology to support multi-touch you'd have to re-code the controllers...
Major_Sarcasm and Caid444, I agree 100%. If I just had the time, given that I can develop applications using .Net Framework, I should be able to replicate this in a simple application. Will try and get back to you... I'll start with a Win XP app, just the concept, and then I will deal with Compact Framework (if it's still called 'Compact'). Making drivers to work in any application is another story, though.
tazbo28 said:
Ok so people have been confused over the tech thats behind the Iphone/G1 capacitive dual touch screen, and all WinMo phones resisitive screens. So i thought i would do the great job of researching the tech behind both methods. 10 minutes later i came across this info on how both methods work, as well as a more expensive and even better method using acoustic mumbo jumbo. So for all you out there that are too lazy to do the diggin, heres the info that once and for all puts the rumors to bed about "...i heard its dual touch capable from so and so website..."
PLEASE READ>>>
The resistive system consists of a normal glass panel that is covered with a conductive and a resistive metallic layer. These two layers are held apart by spacers, and a scratch-resistant layer is placed on top of the whole setup. An electrical current runs through the two layers while the monitor is operational. When a user touches the screen, the two layers make contact in that exact spot. The change in the electrical field is noted and the coordinates of the point of contact are calculated by the computer. Once the coordinates are known, a special driver translates the touch into something that the operating system can understand, much as a computer mouse driver translates a mouse's movements into a click or a drag.
In the capacitive system, a layer that stores electrical charge is placed on the glass panel of the monitor. When a user touches the monitor with his or her finger, some of the charge is transferred to the user, so the charge on the capacitive layer decreases. This decrease is measured in circuits located at each corner of the monitor. The computer calculates, from the relative differences in charge at each corner, exactly where the touch event took place and then relays that information to the touch-screen driver software. One advantage that the capacitive system has over the resistive system is that it transmits almost 90 percent of the light from the monitor, whereas the resistive system only transmits about 75 percent. This gives the capacitive system a much clearer picture than the resistive system.
On the monitor of a surface acoustic wave system, two transducers (one receiving and one sending) are placed along the x and y axes of the monitor's glass plate. Also placed on the glass are reflectors -- they reflect an electrical signal sent from one transducer to the other. The receiving transducer is able to tell if the wave has been disturbed by a touch event at any instant, and can locate it accordingly. The wave setup has no metallic layers on the screen, allowing for 100-percent light throughput and perfect image clarity. This makes the surface acoustic wave system best for displaying detailed graphics (both other systems have significant degradation in clarity).
Another area in which the systems differ is in which stimuli will register as a touch event. A resistive system registers a touch as long as the two layers make contact, which means that it doesn't matter if you touch it with your finger or a rubber ball. A capacitive system, on the other hand, must have a conductive input, usually your finger, in order to register a touch. The surface acoustic wave system works much like the resistive system, allowing a touch with almost any object -- except hard and small objects like a pen tip.
As far as price, the resistive system is the cheapest; its clarity is the lowest of the three, and its layers can be damaged by sharp objects. The surface acoustic wave setup is usually the most expensive.
How Stuff Works people, its a great website. heres a picture i made to show you how the tech works, or at least how it appears to me.
Click to expand...
Click to collapse
Thanks tazbo28
Very usefull info here!
Here what the guys working on android have been able to produce with a capacitive screen:
http://gizmodo.com/5097166/android-multitouch-proof-of-concept-aint-pretty-but-it-works
Multi-touch that works "not-so-well-but-at-least-it-does"
tazbo28 said:
the real problem with it is that when you push on two seperate points, the screen makes an indentation that spans across the area between the two. the layer you are pushing on is simply not elastic enough to register two smaller seperate points or indents.
Click to expand...
Click to collapse
Your source?
I don't think so...
Just a little comment about the two points creating a crease down the screen. The distance between the metalic layer and the plastic screen is minimal at best, not to mention the material on the top layer is very flexible. I don't think it's likely at all that the screen would have a crease or ridge between the two points, there's just not enough indent to create this scenario.
One more thing, I'm not 100 percent sure, but I get the impression that the space between the two layers isn't actually filled with air but in fact some sort of non conductive fluid or gel. It would help the two laters to retain their space and elasticity from eachother.
But what do I know without poking holes in my screen (and I'm not about to do that.)
Caid.
just got this from wikipedia
Resistive touchscreens are composed of two flexible sheets coated with a resistive material and separated by an air gap or microdots. When contact is made to the surface of the touchscreen, the two sheets are pressed together, registering the precise location of the touch.
For example, during operation of a four-wire touchscreen, a uniform, unidirectional voltage gradient is applied to the first sheet. When the two sheets are pressed together, the second sheet measures the voltage as distance along the first sheet, providing the X coordinate. When this contact coordinate has been acquired, the uniform voltage gradient is applied to the second sheet to ascertain the Y coordinate. This operation occurs instantaneously, registering the exact touch location as contact is made.
Resistive touchscreens typically have high resolution (4096 x 4096 DPI or higher), providing accurate touch control. Because the touchscreen responds to pressure on its surface, contact can be made with a finger or any other pointing device.
the part about "microdots" is true i can see the grid of super tiny dots on my 8125 touch screen