It might not fully register, but we all know there are two types of touchscreens. There are those we find on expensive smartphones and tablets, which respond to the slightest touch, allow multi-touch and are generally highly responsive (unless you’re wearing gloves); and then there are those that have slightly longer response time, that require some pressure or a stylus, that don’t have multi-touch abilities but work no matter what you touch them with.
Whether you know what the difference is or not, you’ve probably experienced these differences yourself. When that happened, you might have wondered what causes them; why doesn’t your iPhone work when you’re wearing gloves? Why do touchscreens on feature phones behave differently from those of high-end smartphones? Why can’t you use just any old stylus on your iPad?
All these questions can be answered by two words: resistive and capacitive. The difference between these two touchscreen technologies answers all the above questions. Curious? Read on to find out exactly how it works. Note, however, that this is a simple explanation, and is not meant for engineers. Don’t expect to be able to build one of these by the end of the article!
Touchscreens in a Nutshell
Although touchscreens are becoming increasingly popular, they are by no means a new invention. The first touchscreen was invented back in the 1960s, and has gone through many changes and iterations to become the touchscreen we use today.
Touchscreens are not limited to smartphones and tablets, they are literally everywhere; from ATM machines, point-of-sale terminals, and navigation systems, to game consoles and even touchpads on laptops. Touchscreens are popping up everywhere, and are slowly taking over our lives, so the least we can do is know a bit more about how they work!
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.
For this very same reason, resistive touchscreen require slight pressure in order to register the touch, and are not always as quick to respond as capacitive touchscreens such as the iPhone’s. In addition, the resistive touchscreen’s multiple layers cause the display to be less sharp, with lower contrast than we might see on capacitive screens. While most resistive screens don’t allow for multi-touch gestures such as pinch to zoom, they can register a touch by one finger when another finger is already touching a different location on the screen.
Resistive screens have been improving greatly over the years, and today many lower-end smartphones boast a resistive screen which is no less accurate than high-end devices. Some recent devices using resistive touchscreens are the Nokia N800, the Nokia N97, the HTC Tattoo and the Samsung Jet. Another well-known device using resistive technology is the Nintendo DS, which was the first popular game console to make use of it.
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. So how does it work?
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 styluses.
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.
Which type of screen do you prefer? Do you like being able to use your touchscreen with any type of stylus or instrument, or do you value speed and accuracy over anything else? Share your opinions in the comments.