Introduction to the working principle of touch screen

Recently, I heard a woman on the subway utterly bitterly complaining to her friend: The kid in her family who just learned to walk, I want to “dump” everything in the house-coffee table, books, plates and even her mother, Just like the picture on the touch screen, All slipped and disappeared. Hearing this makes me think, How much do most of us users know about the knowledge behind the display screen?

Before I started to really study how the touch screen works, I think there is a common technology behind the “swipable” phenomenon (referring to the sliding screen). But the fact is just the opposite. As far as I know, there are almost 6 kinds, And most of them are still under constant research. The two most commonly used systems are resistive and capacitive touch screens. For simplicity, I will focus on these two systems here, It is easy for everyone to understand.

1. Resistive touch screen—— Resistive Touch Screens
This is the most basic and common touch screen, It is often used in ATM machines and electronic signature devices at supermarket checkouts. These screens actually “resist” your contact, Unless you make it big enough, And feel the screen bend slightly. This is how the resistive touch screen works, As you can see in the figure below: Two conductive layers, Bending after being touched.

Introduction to the working principle of touch screen

Resistive touch screen technology

Thin yellow layer, One piece is a resistor and the other piece is conductive, It is separated by spacers in the middle Until you press it down. (The outside is completely covered by a very thin, scratch-resistant blue film layer.)An electric current runs through those yellow layers all the time, But when the finger touches the screen, When the two pressed tablets are squeezed, The current changes at the contact point. And the software will recognize the current changes in these coordinates, Start to execute the function corresponding to this point.

Although the resistive touch screen is durable, However, due to a large number of layers, the light transmittance is poor, Not suitable for the user’s reading experience. And they only have a single touch, For example, if you want to use two fingers to zoom the picture on the iPhone, it can’t be achieved. This is one of the reasons why high-end electronic devices are more inclined to use capacitive touch screens.

2. Capacitive touch screen—— Capacitive Touch ScreensUnlike resistive touch screens, The capacitive touch screen does not rely on finger pressure to create or change the power flow.On the opposite of, They work through any object that holds an electrical charge, including human skin. (Yes, the human body is also made up of positive and negatively charged yards!)Capacitive touch screens are made of materials such as alloys of indium tin oxide (ITO), Electric charge is stored in tiny electrostatic nets that are thinner than hair.

Introduction to the working principle of touch screen

Capacitive touch screen technology

There are two main types of capacitive touch screens-Surface Capacitive and Projective Capacitive. “The surface capacitive type uses sensors located in the four corners and a thin film evenly distributed across the surface (as shown in the picture), Projected capacitors use independent chips that are interleaved in rows/columns and have sensing functions at the same time.”Matt Rosenthal, the embedded project director responsible for Touch Revolution explained.

In both cases, When the finger taps the screen, it Will draw a small amount of current from the contact point, Cause the voltage drop of the corner electrode, Use the method of sensing the weak current of the human body to achieve the purpose of touch control. (This is why there is no response when you put on gloves and touch the screen.)And the software will handle the stressed position, Command the next action. (If you are still confused, why not take a look at the video demo.)

3. Next target? Zoom in and zoom in
The emerging touch screen technology is still under constant research and development, But the capacitive touch screen is still the current industry standard. The biggest challenge for the touch screen is how to graft it into a larger screen. Larger also means high requirements for sensing capabilities.
From Perceptive Pixel, Software engineers engaged in multi-touch, Is using a technology called FTIR (Frustrated Total Internal Reflection), Developed an 82-inch screen. When the finger touches the FTIR touch screen, There will be light reflected, At the same time, the infrared camera at the bottom of the screen captures the reflected bright spot, Just as the capacitive touch detects the change in current.

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