#248 How does a touchscreen work?

I learned this today. A touchscreen works because a tiny electric current is sent to your finger, which allows the device to calculate where your finger is.

There are two different types of touchscreen: resistive and capacitive. The touchscreen in the phone you are probably reading this on is a capacitive touchscreen, so let’s look at resistive first.

Resistive touchscreens are screens that work when pressure is applied to them. They are often used in ATMs, or cash registers, or in restaurants and hospitals. They have a protective layer of plastic on the front of them which makes them stronger and easier to clean than capacitive touchscreens. They are also much cheaper to make and can be used with gloves on. A resistive touchscreen has two resistive layers that are separated by a narrow space of air or nonconductive gas. The top layer has an outer covering of plastic and the resistance circuit on the other side. One layer has horizontal wires on it and the other layer has vertical wires on it. When the device is turned on, power is applied to one of the layers. When you press it with your finger, the plastic screen bends slightly, and the two layers meet at the point where you press them. This creates a circuit, and the device can use the horizontal and vertical wires to work out exactly where it was pressed. These screens are cheap, but they are not as bright as capacitive screens due to the layer of plastic that covers them. They can also not recognize contact in multiple places at the same time.

Capacitive screens are used in the majority of smart devices. They are more expensive, but they are clearer, and they can recognize more than one point of contact at the same time. That is why you can use two fingers to enlarge a picture.

In the capacitive screen, the surface is almost always made of glass. This is why your phone will crack if you drop it and resistive touchscreens are sturdier. Glass is used because it doesn’t conduct electricity. The glass is coated with a transparent conductive material, such as indium tin oxide. When you switch your device on, a tiny charge is applied consistently to the entire screen at the same time. If you touch the screen with your finger, your body attracts some of that charge and there is a minute drop in charge at the point where your finger contacted the screen. The device can recognize this tiny change in voltage and use it to pinpoint your finger. This is why you can’t use your phone if you are wearing gloves. Most gloves don’t conduct electricity. Gloves that are made specifically for use on touchscreens, usually contain some kind of conductive thread so that they can draw some of the charge away from the screen.

The first technical touchscreen was invented in 1946, but it used a stylus and not a finger. It was used for drawing arrows on a TV during a live television broadcast. In 1963, the stylus system was advanced enough to be able to recognize what was drawn on the computer screen. These worked by amplifying the signal on the cathode ray tube in the monitor.

The first finger touchscreen was invented by Eric Johnson in Malvern, England. He was working at the Royal Radar Establishment and he wanted to develop touchscreen for air traffic control. His idea was for a capacitive screen. However, it was not transparent. The first transparent touch screen was invented in the early 1970s. The first resistive touchscreen was invented by accident in the 1970s as well.

In 1983, Bob Boie came up with a new transparent overlay, and was the closest relation to the touchscreens we have today. The first real portable device with a touchscreen was the IBM Simon Personal Communicator in 1993. Apple brought out their Newton PDA at the same time. And the rest, as they say, is history.

Interestingly enough, the future of the touchscreen appears to be a screen that doesn’t need to be touched. It is known as predictive touch. The device has gesture trackers and artificial intelligence that analyzes the gesture and makes a prediction as to what action the person is about to carry out. Then the device carries out that action. The AI system will learn each time you make a gesture and it will become more and more accurate the longer you use the device. Some devices are even able to use eye trackers for more accuracy. And then, of course, the next jump from a touchless touchscreen is no screen at all. Future devices may holographically project an image that you can interact with purely through gestures.

So, touchscreens work in two ways. By using the pressure you apply to a screen to complete a circuit and tell where you touched the screen. Or by using the conductivity of your finger to conduct a small charge from the screen, lowering the voltage and allowing the device to calculate where your finger is. And this is what I learned today.

Photo by Pixabay: https://www.pexels.com/photo/laptop-technology-ipad-tablet-35550/

Sources:

https://en.wikipedia.org/wiki/Touchscreen