The screen of a resistive touchscreen is a multi-layered composite film adhered to the display surface. It consists of a glass or acrylic base layer coated with a transparent conductive layer (ITO, indium oxide), followed by a hardened, smooth, scratch-resistant plastic layer. The inner surface of this plastic layer is also coated with ITO. Numerous tiny (less than one-thousandth of an inch) transparent insulating dots separate and insulate the two conductive layers. When a finger touches the screen, a contact point appears between the two ITO conductive layers. Because one conductive layer is connected to a uniform 5V voltage field along the Y-axis, the voltage of the sensing layer changes from zero to non-zero. The controller detects this connection, performs an A/D conversion, and compares the obtained voltage value with 5V to obtain the Y-axis coordinate of the touch point. Similarly, the X-axis coordinate is derived. This is the fundamental principle of resistive touchscreens. Resistive touchscreens are classified into four-wire, five-wire, and other multi-wire resistive touchscreens based on the number of leads. The A-side of a five-wire resistive touchscreen is conductive glass, not a conductive coating. The conductive glass manufacturing process significantly improves its lifespan and light transmittance.
The ITO coating on resistive touchscreens is relatively thin and brittle. Applying it too thickly reduces light transmission and causes internal reflections, decreasing clarity. Although a thin plastic protective layer is added over the ITO, it is still easily damaged by sharp objects. Furthermore, due to frequent touches, the surface ITO layer develops tiny cracks and may even deform after a period of use. If one point of the outer ITO layer is damaged and breaks, it loses its function as a conductor, resulting in a short lifespan for the touchscreen. However, resistive touchscreens are unaffected by dust, water, or dirt.
This type of touchscreen uses pressure sensing for control. It consists of two highly transparent conductive layers, with a distance of only 2.5 micrometers between them. When a finger presses on the touchscreen, the two conductive layers make contact, causing a change in resistance and generating signals in both the X and Y directions, which are then sent to the touchscreen controller. This type of touchscreen can operate in harsh environments, but its feel and light transmittance are relatively poor, making it suitable for situations where gloves are worn or direct hand contact is not possible. The key to resistive touchscreens lies in materials technology; commonly used transparent conductive coating materials include:
A. ITO, indium oxide, is a weak conductor. Its characteristic is that when the thickness is reduced to below 1800 angstroms (1 angstrom is one hundred billionth of a meter), it suddenly becomes transparent with a light transmittance of 80%. As it becomes thinner, the light transmittance decreases, but it rises back to 80% at a thickness of 300 angstroms. ITO is the main material used in all resistive and capacitive touchscreens. In fact, the working surface of resistive and capacitive touchscreens is the ITO coating.
B. Nickel-Gold Coating: The outer conductive layer of a five-wire resistive touchscreen uses a highly ductile nickel-gold coating material. Due to frequent touches, the use of this ductile material extends the lifespan of the outer conductive layer, but the manufacturing cost is relatively high. While the nickel-gold conductive layer has good ductility, it can only be used as a transparent conductor and is unsuitable as the working surface of a resistive touchscreen because of its high conductivity. Furthermore, it's difficult to achieve a perfectly uniform thickness with metal, making it unsuitable as a voltage distribution layer; it can only be used as a probe layer. Resistive touchscreens are a new type of touch technology that has been widely used in consumer electronics products due to their unique advantages. This article will introduce its principles and applications to help readers better understand this new touch technology.
Touchscreens work by detecting the effect of human body charge on capacitance, and are generally classified into the following types:
Resistive touchscreens consist of two conductive thin films separated by an insulating layer. When a user presses a finger or stylus on the screen, the two conductive films come into contact, creating an electric current. The coordinates of the touch point are determined by measuring this current.
Capacitive touchscreen: The surface of a touchscreen is covered with a layer of capacitive material, such as glass or a conductive film. When a user touches the screen, the human body's charge changes the capacitance of the touched area. By measuring this capacitance change, the location of the touch point can be determined.
Surface acoustic wave (SAW) touchscreen: A set of transmitters and receivers are arranged on the screen. The transmitters emit ultrasonic signals, and the receivers receive the reflected signals. When a user touches the screen, the touch point causes the ultrasonic waves to scatter, which are captured by the receivers and their positions are determined through calculations.
Touchscreens have a wide range of applications, mainly focusing on the following aspects:
Smartphones and tablets: Touchscreens are the primary input method for smartphones and tablets, allowing users to perform gesture operations, text input, and more.
Computers and laptops: Some computers and laptops are equipped with touchscreens, allowing users to operate them directly, similar to using a smartphone or tablet.
Public information kiosks and self-service terminals: Touch screens are widely used in information kiosks and self-service terminals in public places, such as banks, airports, and train stations, to facilitate users in accessing information and conducting business.
Digital signature pad: Touch screens are also used for digital signature pads, allowing users to write or sign on the screen using a stylus to achieve functions such as electronic signatures.
Industrial control and interactive interfaces: Touch screens are widely used in industrial control and interactive interface design, providing convenient operation and monitoring methods.
I. The Principle of Resistive Touchscreens
1. Introduction
It is a touch technology that uses a closed resistive circuit formed between the touch surface and the driving surface, and uses the resistance change generated when the fingernail touches the surface to obtain the coordinates of the touch point.
2. Working principle
When a fingertip touches the touchscreen, the contact creates a closed resistive circuit at the point of contact, which changes the resistance value in the circuit, thereby altering the current and voltage, and ultimately changing the coordinates of the touch point.
3. Structure
A resistive touchscreen basically consists of two parts: a touch surface and a driving surface. The touch surface is composed of a layer of glass and a thin film, while the driving surface is composed of a layer of glass and a thin film. When the touch surface and the driving surface come into contact, a resistive closed circuit is formed, which generates changes in current and voltage, thereby detecting the coordinates of the touch point.
II. Applications of Resistive Touchscreens
1. Mobile phone
As a new type of touch technology, resistive touchscreens have been widely used in the mobile phone industry due to their good sensitivity and resistance to external interference. Currently, almost all mainstream mobile phone brands use resistive touchscreen technology to achieve touch operation.
2. Computer
Computers are also a common application scenario for resistive touch screens. Resistive touch screens are highly sensitive, not easily affected by external interference, and can support multi-touch. Therefore, some laptops and desktops on the market now use resistive touch screens as the main input device for touch operation.
3. Automobile
Resistive touchscreens have also been widely used in the automotive industry. Multimedia systems and electronic dashboards in automotive electronics use resistive touchscreen technology to achieve different operating functions.
In summary, resistive touchscreens are a new type of touch technology that has been widely used in consumer electronics products such as mobile phones, computers, and automobiles due to their unique advantages, providing users with a comfortable touch experience. Its working principle is that when a fingertip touches the touchscreen, the contact creates a closed resistive circuit at the point of contact, changing the resistance value in the circuit, thereby altering the current and voltage, and ultimately changing the coordinates of the touch point. Resistive touchscreens are an indispensable part of modern consumer electronics products. A correct understanding of its working principle can provide users with a better touch experience, thus improving the user experience of the product.
