# Tag Info

62

Title of question: Is there a technical reason why most touch screens use glass rather than plastic? Note the word "technical" and not "marketing" What are the reasons that most modern portable touch devices come with a glass panel on their fronts, rather than plastic or something else? Glass (as a cheap and common material) has a good dielectric ...

38

When decisions about consumer electronics are made, many reasons beyond technical come into play. There is no valid reason for a phone to be disassembled in 7 pieces in order to replace a battery, yet that's how one of the most popular phones is made. Mobile phones are as much a product of marketing as they are of electronics, and many design decisions ...

33

You mention cracking as a downside to using glass, but most touchscreens will encounter far more potential scratch-causing events than crack-causing events. Glass is highly scratch-resistant: at a Mohs hardness of 5.5, it's harder than anything else in your pocket (steel is around 4). Synthetic sapphire is even more scratch-resistant: at a hardness of 9, ...

26

I generally resist analogies, but since you're a software-only guy, and since everyone else insists on talking to you about capacitance, I'm going to go for the story. Imagine you are firing paint balls at a wall. Everywhere you hit the wall, there's a splat of paint. Except there's one place you fire at, and when the paint hits it, it makes a little mark ...

16

Glass is hard, and therefore brittle, so it shatters. Plastic (acrylic or polycarbonate) is softer, so more prone to scratches. It's certainly a possibility and some cheap phones have plastic touchscreens. But the underlying LCD behind the transparent touchscreen has to be made of glass, due to high temperature parts of the process. So that's still ...

12

I haven't actually done this, but it seems the problem is the objects you are using are too small and don't have enough ambient capacitance. A human touching something adds capacitive coupling to the environment. Think of the size and surface area difference between a carrot and a carrot+human. You should be able to use something conductive that is ...

12

Touch screens have transmit (Tx) and receive (Rx) electrodes which are drawn in transparent indium tin oxide (ITO), forming a matrix of crossed traces with each Tx-Rx junction having a characteristic capacitance. The human finger is basically a ground that alters the mutual capacitance between the RX and TX electrodes. This network is very sensitive to ...

10

No. The edges of a resistive touch overlay are important. They carry the conductors that connect to the resistive layers. Those white traces around the edge are conductors, and are necessary for the overlay to work. If you look carefully, you can actually see which wire corresponds to which axis and side. Keep in mind that you can always use an overlay ...

8

Okay, it seems to be simpler than I originally thought (I should not have read the marketing first) I now realise most touch screens use mutual capacitance between a grid of electrodes (I was thinking of the case of a single touch pad initially) I think it's just a piece of foil. With mutual capacitance any conductive object should disturb the field, however ...

8

so that means that I should be able to interact with it as long as I can bring a small current to the screen where I want to touch. No. You don't "bring" current to the device. These devices measure capacitance, not current or voltage. The additional capacitance thru your body back to ambient or circuit ground is detected by looking at how the capacitive ...

8

Power consumption is a function of many factors, besides resolution. So, I don't think your question is answerable, in the general case. However, I think it's fair to say that most of the power of an LCD screen goes into the backlight. So as a first order approximation, screens of similar size will have similar power requirements. But also consider other ...

7

One common way is to have a grid of infra-red emitters and receivers around the edge of the screen pointing at each other (say all emitters at left and top, and all receivers at right and bottom). A touch to the screen interrupts the beams, and the intersection of two interrupted beams gives the location of the touch.

7

Basically, a capacitive touch sensor works by detecting the change in capacitance in a "capacitor" that consists of a sensor plate and "ground", where this ground could be your ground plane, or a large nearby conductive plate, or water, or something. The mechanism for capacitance being the ability to hold an electric field means that anything that changes ...

6

It's just the method they use to detect the touch. In capacitive touch they lay down a grid of Indium Tin Oxide (ITO) and connect it to some sensors. Then when your finger which comes either in contact or really close the capacitance of the circuit changes and a touch is detected. For inductive I've seen two kinds, one that's pen based where there are a ...

5

Yes, this is quite possible to do. Simply place a small piece of copper foil on the screen. Connecting the foil to ground will simulate a finger press. You can use an N-channel FET to switch the foil between connected and not connected. The gate of the FET goes to your microcontroller.

5

I'd use an analog multiplexer in combination with a 2D matrix. An example: Matrix of 64 sensors in an 8*8 configuration An eight-channel analog multiplexer with three-bit address input, each input channel connected to a row of the matrix A means of applying a voltage to each column in turn (for example, an 8-bit shift register and some transistors) A ...

4

Capacitive sensors react to the polarization of a conductor or dielectric that touches (or is close enough to) its surface, so the size or connection to the water should be taken into account. An isolated drop might not affect it, while a stream of water will. I have a large trackpad for my computer, and an app that visualizes its input. I put a fairly large ...

4

If I had to choose a touchscreen for my project I rather prefer a capacitive one. Resistive touch screens may be cheaper but have some disadvantages comparing with capacitive ones: They need calibration Are less sensitive Have shorter life cycle One of the downsides of the capacitive touch screens used to be the complexity of the required software and ...

4

I have seen inductive sensing systems offered by Microchip. They consist of a PCB trace coil covered by a metal plate or dome. When the plate is pushed towards the coil, it causes a slight change in the inductance of the coil which can be measured.

4

FFC/FPC, like Oli says. There are common connectors, or ZIF "Zero Insertion Force" connector. In the latter you first insert the FFC, then click the top part in the bottom part to fix it. ZIF connectors may be handy, since otherwise the FFC may get crooked when inserting; in my experience the insertion force can be rather high. On one occasion we had our ...

4

Square touchscreen displays are not common; search for 4.3" touchscreens to obtain approximately the same screen area, typically in a rectangular 4:3 or widescreen format. If you are not experienced in microcontroller programming, a serial touchscreen (SPI or I2C connection) would be easier to use than one designed for parallel data. Also, touchscreen and ...

4

The normal process for applying ITO is vapor deposition: like 'fogging' a mirror with steam, but using a boiling metal alloy. The challenge in doing that with thermoplastic would be not melting it in the process. (There are some references on google to doing this at room temperature with a plasma instead, though). Recent advances in glass hardness mean that ...

4

Well you do measurement same way as on Arduino. The MCP3008 has 8 channels, so you can easily do 8 measurements. You'd normally connect two channels of the ADC to the X+ and Y+ leads. The connectors of the ADC are in high-impedance input mode, so you can treat them as disconnected as far as power supply is concerned. Then you also need to connect two GPIO ...

4

They basically aren't interested in a flow of current, at least not from your actual body, that is why it works through a plastic or glass insulator. It measures the capacitance on several sensors, generally by charging them with a constant current and time, then measuring the resulting voltage. It registers a capacitance change because your body works to ...

4

Most touch screens are capacitive - meaning they detect the change in capacitance that is introduced by touching them. Insulators generally do not introduce a large enough change in capacitance to trigger the touch screen. So if your fingers are turning to papery stumps somehow, you wont be able to trigger it. This has nothing to do with the temperature of ...

4

I expect the high-resolution display to use slightly more, but roughly the same amount of power as the lower-resolution display. Most of the power consumed by the display in a tablet like this goes to two primary components: the backlight and the LCD. Typically the backlight consumes very roughly 75% of the energy going to the screen. Most tablets like ...

4

Some data as what the excitation signals for the screens are would help. But even without that you could design a powered stylus with a fine tip. The basic setup would be a simple metal wire connected with one end to a voltage source. The other end of voltage source should be insulated. Now you have a artificially generated electric field around the wire. ...

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I was about to file a query to Samsung Support. To ask better questions, I re-study the webpage again, and I came across this post having the table below: In the row of "Sub-Pixels Per Inch", we can see that only green pixels are having 432 ppi. Both red and blue pixels are at only 305 ppi. Doing a few maths:  Closest\ (inclined)\ distance\ between\ red\...

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There is really no way to do what you ask. Each copper plate is a single electrode. You therefore have a single capacitor. Something disturbing the field or coupling to the plates can be detected as a change in capacitance of the capacitor, but there is no way to tell where on a plate. You can only measure a single value. How do you suppose you get the ...

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