1. Resistive Touchscreen The screen of a resistive touchscreen is a multi-layered composite film that matches the display surface. It consists of a glass or acrylic base layer coated with a transparent conductive layer, topped with a hardened, smooth, scratch-resistant plastic layer. Its inner surface is also coated with a transparent conductive layer. Between these two conductive layers are numerous tiny (less than one-thousandth of an inch) transparent insulating dots that separate them. When a finger touches the screen, the normally insulated conductive layers make contact at the touch point. 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. This connection is detected by the controller, converted from digital to digital (A/D), and compared to 5V to obtain the Y-axis coordinate of the touch point. Similarly, the X-axis coordinate is derived. This is the fundamental principle common to all resistive touchscreens. The key to resistive touchscreens lies in materials technology. Resistive touchscreens are classified into four-wire, five-wire, six-wire, and other multi-wire resistive touchscreens based on the number of leads. Resistive touchscreens have two layers of OTI (Optically Oxide) transparent conductive metal oxide coating on a tempered glass surface. The outermost OTI coating acts as a conductor, while the second OTI layer is coated with a precise network of voltage fields ranging from +5V to 0V in both horizontal and vertical directions. The two OTI layers are separated by tiny transparent insulating dots. When a finger touches the screen, a contact point is created between the two OTI conductive layers. The computer simultaneously detects the voltage and current, calculates the touch location, and the response time is 5-15ms. The outer conductive layer of a five-wire resistive touchscreen uses a highly ductile nickel-gold coating material. The use of ductile nickel-gold for the outer conductive layer, due to frequent touches, aims to extend its lifespan, but this increases manufacturing costs. Although the nickel-gold conductive layer has good ductility, it can only act as a transparent conductor and is unsuitable as the working surface of a resistive touchscreen because of its high conductivity and the difficulty in achieving a perfectly uniform thickness. It is not suitable as a voltage distribution layer and can only be used as a probe layer. Resistive touchscreens operate in a completely isolated environment, unaffected by dust and moisture. They can be touched by any object and can be used for writing and drawing, making them suitable for industrial control applications and limited-person use in offices. 2. Surface Acoustic Wave (SAW) Touchscreen The touchscreen portion of a SAW touchscreen can be a flat, spherical, or cylindrical glass plate, mounted in front of a CRT, LED, LCD, or plasma display screen. This glass plate is simply a piece of tempered glass, unlike other touchscreen technologies, it has no film or covering layer. Vertical and horizontal ultrasonic transducers are fixed to the upper left and lower right corners of the glass screen, respectively, while two corresponding ultrasonic receiving transducers are fixed to the upper right corner. The four edges of the glass screen are engraved with highly precise reflective stripes at 45° angles, ranging from sparse to dense. Taking the X-axis transmitting transducer in the lower right corner as an example: The transmitting transducer converts the electrical signal from the controller via the touchscreen cable into acoustic energy, which is transmitted to the left side of the surface. Then, a set of precise reflective stripes on the lower edge of the glass plate reflects the acoustic energy into a uniform upward projection. The acoustic energy passes through the screen surface and is then focused by the upper reflective stripes into a line propagating to the right to the X-axis receiving transducer. The receiving transducer converts the returned surface acoustic energy into an electrical signal. When the transmitting transducer emits a narrow pulse, the sound wave energy travels through different paths to reach the receiving transducer. The rightmost path arrives earliest, and the leftmost path arrives latest. These early and late arriving sound wave energies superimpose to form a wider waveform signal. It's easy to see that the received signal gathers all the sound wave energy that has traveled different paths in the X-axis direction. While their paths on the Y-axis are the same, on the X-axis, the furthest path travels twice the maximum X-axis distance compared to the closest. Therefore, the time axis of this waveform signal reflects the positions of the original waveforms before superposition, i.e., the X-axis coordinate. When there is no touch, the received signal waveform is exactly the same as the reference waveform. When a finger or other object that can absorb or block sound wave energy touches the screen, the sound wave energy traveling upwards along the X-axis through the finger is partially absorbed. This is reflected in the received waveform as an attenuation gap at a certain moment. The received waveform shows a signal attenuation gap corresponding to the area blocked by the finger. Calculating the position of this gap gives the touch coordinate controller, which analyzes the attenuation of the received signal and determines the X-coordinate based on the position of the gap. The Y-axis coordinate is then determined using the same process. Besides the X and Y coordinates that most touchscreens respond to, surface acoustic wave (SAW) touchscreens also respond to a third axis, the Z-axis, which senses the user's touch pressure. This is calculated based on the attenuation at the point of signal attenuation. Once the three axes are determined, the controller transmits them to the host computer. One characteristic of SAW touchscreens is their impact resistance. Because the working surface of a SAW touchscreen is an invisible, indestructible layer of acoustic energy, and the base glass has no interlayer or structural stress (SAW touchscreens can even be directly mounted on CRT surfaces, eliminating the need for a separate "screen"), they are highly resistant to violent use and suitable for public places. A second characteristic of SAW is its fast response speed; it is the fastest of all touchscreens, providing a smooth user experience. A third characteristic is its stable performance. Because the SAW technology is based on stable principles, and the controller calculates the touch position by measuring the position of the attenuation point on the time axis, SAW touchscreens are extremely stable and highly accurate. Currently, the accuracy of SAW touchscreens is typically 4096×4096×256 levels of pressure. The fourth characteristic of surface acoustic wave (SAW) touchscreens is that the control card can distinguish between dust, water droplets, and fingers, and how much is being touched. This is because a finger touch, with a pressure precision of 4096×4096×256 levels, generates 48 touches per second, which cannot be perfectly constant. Dust or water droplets, however, remain completely constant. If the controller detects a touch that remains unchanged for more than three seconds, it automatically identifies it as interference. The fifth characteristic of SAW touchscreens is their third axis, the Z-axis, or pressure axis response. This is because the greater the force of the user's touch, the wider and deeper the attenuation gap in the received signal waveform. Currently, only SAW touchscreens possess the ability to sense touch pressure. With this function, each touch point is no longer simply a matter of being touched or not touched, but becomes an analog switch capable of sensing force. This function is extremely useful; for example, in multimedia information retrieval software, a single button can control the playback speed of animations or videos. The disadvantage of surface acoustic wave (SAW) touchscreens is that dust and water droplets on the touchscreen surface can block the transmission of surface acoustic waves. Although intelligent control cards can detect this, the signal attenuates significantly when dust accumulates to a certain level, causing the SAW touchscreen to become sluggish or even malfunction. Therefore, SAW touchscreens are being developed with dustproof versions, and it is recommended to clean the touchscreen regularly each year. 3. Infrared Screens Infrared touchscreens are simple to install, requiring only a dot-matrix frame on the display, without the need for a coating or controller on the screen surface. Infrared emitters and receivers are arranged along the four sides of the dot-matrix frame, forming an infrared grid on the screen surface. When a user touches a point on the screen, the horizontal and vertical infrared rays passing through that point are blocked, allowing the computer to instantly calculate the touch point's location. Any object can alter the infrared rays at the touch point, enabling touchscreen operation. Early on, infrared touchscreens suffered from limitations such as low resolution, restricted touch methods, and susceptibility to environmental interference leading to malfunctions, causing them to fade from the market for a time. The second generation of infrared screens partially solved the problem of light interference, and the third and fourth generations also improved resolution and stability, but none achieved a qualitative leap in key indicators or overall performance. However, those familiar with touchscreen technology know that infrared touchscreens are unaffected by current, voltage, and electrostatic interference, making them suitable for harsh environmental conditions. Infrared technology represents the ultimate development trend for touchscreen products. Touchscreens using acoustic and other materials science technologies have insurmountable barriers, such as damage and aging of individual sensors, susceptibility to contamination and destructive use of the touch interface, and complex maintenance. Once infrared touchscreens truly achieve high stability and high resolution, they will inevitably replace other technologies and become the mainstream in the touchscreen market. The resolution of past infrared touchscreens was determined by the number of infrared photocells in the frame, resulting in lower resolution. The main domestic products on the market were 32x32 and 40x32. Furthermore, it was said that infrared screens were sensitive to lighting conditions, potentially misinterpreting or even crashing under significant changes in light. These are precisely the weaknesses of infrared screens that domestic distributors of foreign non-infrared touchscreens tout. The latest fifth-generation infrared screen technology achieves a resolution of 1000x720, depending on the number of infrared photocells, scanning frequency, and interpolation algorithm. Regarding the issue of instability under certain lighting conditions, this weakness has been largely overcome since the second generation of infrared touchscreens. The fifth-generation infrared touchscreen is a new generation of intelligent technology products, achieving a high resolution of 1000*720, multi-level self-adjustment and self-recovery hardware adaptability, and highly intelligent discrimination and recognition. It can be used for extended periods in various harsh environments. Furthermore, it can be customized with expanded functions such as network control, sound sensing, human proximity sensing, user software encryption protection, and infrared data transmission. Another major drawback of infrared touchscreens, previously touted in the media as poor impact resistance, can actually be addressed by using any impact-resistant glass that meets customer satisfaction without significantly increasing costs or affecting performance—a feature unmatched by other touchscreens. Infrared touchscreens are inexpensive, easy to install, and capable of effectively sensing both light and rapid touches. However, because infrared touchscreens rely on infrared sensing, changes in external light, such as sunlight or indoor spotlights, can affect their accuracy. Furthermore, infrared touchscreens are not waterproof and are susceptible to dirt; even small foreign objects can cause errors and affect their performance, making them unsuitable for outdoor and public use. 4. Capacitive Touchscreens Capacitive touchscreens are constructed by depositing a transparent thin film layer on a glass screen, followed by a protective glass layer over a conductor layer. This double-glass design thoroughly protects the conductor layer and sensors. Additionally, narrow electrodes are deposited on all four sides of the touchscreen, creating a low-voltage alternating current field within the conductor. When a user touches the screen, a coupling capacitance is formed between the human body's electric field, the finger, and the conductor layer. The current emitted from the four electrodes flows to the touch point, and its strength is proportional to the distance between the finger and the electrodes. The controller behind the touchscreen calculates the current ratio and strength to accurately determine the touch point's location. The double-glass design of capacitive touchscreens not only protects the conductor and sensors but also effectively prevents external environmental factors from affecting the touchscreen. Even if the screen is dirty, dusty, or oily, the capacitive touchscreen can still accurately calculate the touch position. Capacitive touchscreens offer better light transmittance and clarity than four-wire resistive touchscreens, though they still lag behind surface acoustic wave (SAW) and five-wire resistive touchscreens. Capacitive screens suffer from severe glare, and the uneven light transmittance of four-layer composite touchscreens with varying wavelengths leads to color distortion. Reflection between layers also causes blurring of images and characters. In principle, a capacitive screen uses the human body as an electrode of a capacitor. When a conductor approaches the ITO (Ionometallic oxide) working surface, creating a sufficient capacitance, the resulting current can cause the screen to malfunction. While capacitance is inversely proportional to the distance between electrodes, it is directly proportional to the relative area and also depends on the dielectric constant of the medium. Therefore, even a large hand or a handheld conductive object near the screen (not just touching it) can cause malfunctions. This is particularly pronounced in humid weather; holding the monitor, having the palm within 7 cm, or the body within 15 cm can all trigger malfunctions. Another drawback of capacitive touchscreens is that they don't respond when touched with a gloved hand or a non-conductive object, due to the added insulating medium. A more significant drawback is drift: changes in ambient temperature, humidity, and the surrounding electric field can all cause drift, leading to inaccuracies. For example, the monitor's temperature rise after powering on can cause drift; the user touching the screen while another hand or part of their body is near the monitor can cause drift; moving large objects near the touchscreen can cause drift; and people watching while you're touching it can also cause drift. The drift of capacitive touchscreens stems from inherent technical limitations. Although the ambient potential surface (including the user's body) is relatively far from the touchscreen, it is still much larger than the area of ​​a fingertip, directly affecting the determination of the touch position. Furthermore, many relationships that should theoretically be linear are actually non-linear. For example, the total current drawn by people with different weights or varying degrees of finger moisture differs, and the change in total current and the changes in the four component currents are non-linear. The custom polar coordinate system used by capacitive touchscreens lacks an origin, so the controller cannot detect or recover from drift. Moreover, after four A/D conversions, the calculation process from the values ​​of the four component currents to the X and Y coordinates of the touch point in the Cartesian coordinate system is complex. Due to the lack of an origin, the drift of the capacitive screen is cumulative, and calibration is frequently required in the workplace. The outermost silica protective glass of the capacitive touchscreen has excellent scratch resistance, but it is susceptible to damage from fingernails or hard objects. Even a small hole can damage the ITO interlayer. Whether the damage is to the ITO interlayer or the inner surface ITO layer during installation and transportation, the capacitive screen will not function properly.