Resistive Touchscreens
The resistive touchscreen is the most common type of touchscreen. Except for modern smartphones, tablets and trackpads, most touchscreens we come in contact with are actually resistive touchscreens. As you’ve probably guessed, the resistive touchscreen relies on resistance. In that respect, it’s pretty intuitive to understand – the pressure you apply causes the screen to respond.
A resistive touchscreen is made out of two thin layers separated by a thin gap. These are not the only layers in the resistive touchscreen, but we’ll focus on them for simplicity. These two layers both have a coating on one side, with the coated sides facing each other inside the gap, just like two pieces of bread in a sandwich. When these two layers of coating touch each other, a voltage is passed, which is in turn processed as a touch in that location.
So when your finger, stylus, or any other instrument touches a resistive screen, it creates a slight pressure on the top layer, which is then transferred to the adjacent layer, thus starting the cascade of signals. Because of this, you can use anything you want on a resistive touchscreen to make the touch interface work; a gloved finger, a wooden rod, a fingernail – anything that creates enough pressure on the point of impact will activate the mechanism and the touch will be registered.
Capacitive Touchscreens
Surprisingly, it was actually the capacitive touchscreen that was invented first; the first one was built almost 10 years before the first resistive touchscreen. Nevertheless, today’s capacitive touchscreens are highly accurate and respond instantly when lightly touched by a human finger. As opposed to the resistive touchscreen, which relies on the mechanical pressure made by the finger or stylus, the capacitive touchscreen makes use of the electrical properties of the human body. A capacitive screen is usually made of one insulating layer, such as glass, which is coated by a transparent conductive material on the inside. Since the human body is conductive, which means electricity can pass through it, the capacitive screen can use this conductivity as input. When you touch a capacitive touchscreen with your finger, you cause a change in the screen’s electrical field.
This change is registered, and the location of the touch is determined by a processor. This can be done by several different technologies, but they all rely on the electrical change caused by a light touch of a finger. This is the reason you cannot use a capacitive screen while wearing gloves – the gloves are not conductive, and the touch does not cause any change in the electrostatic field. Same goes for non-capacitive style. Since capacitive screens are made of one main layer, which is constantly getting thinner as technology advances, these screens are not only more sensitive and accurate, the display itself can be much sharper, as seen on devices such as the iPhone 4S. And of course, capacitive touchscreens can also make use of multi-touch gestures, but only by using several fingers at the same time. If one finger is touching one part of the screen, it won’t be able to sense another touch accurately.
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