Capacitive touch screen introduction

Tantalum Capacitor

1. Introduction The capacitive touch screen is designed with a transparent conductive layer deposited on a glass panel, followed by a protective glass layer on top. This dual-glass structure ensures the conductor and sensor layers are well protected from external damage. The capacitive screen uses narrow electrodes placed around the edges of the display to create a low-voltage alternating electric field across the conductive layer. When a user touches the screen, their body forms a coupling capacitor with the conductive layer, causing current to flow from the four electrodes toward the point of contact. The intensity of this current is proportional to the distance between the finger and the electrode. A controller behind the screen calculates the position based on the current ratio and strength, allowing for precise touch detection. The dual-layer design not only safeguards internal components but also minimizes interference from environmental factors like dirt, dust, or oil. However, the performance of capacitive screens can be affected by temperature, humidity, and grounding conditions, leading to instability and drift. This makes them more suitable for early-stage system development rather than long-term use in production environments. 2. Disadvantages of Capacitive Touch Screens While capacitive screens offer better clarity and transmittance compared to four-wire resistive screens, they still fall short when compared to surface acoustic wave or five-wire resistive technologies. One major issue is that capacitive screens are highly reflective, which can reduce visibility under bright lighting. Additionally, multi-layer capacitive screens may suffer from uneven light transmission, resulting in color distortion and blurred images due to reflections between layers. Another significant drawback is the susceptibility to false triggers. If a large object such as a hand or palm comes close to the screen without actually touching it, it can cause unintended responses. This is especially problematic in humid conditions, where even a small distance—like 7 cm—can lead to malfunctions. Furthermore, capacitive screens do not respond to gloved fingers or non-conductive objects because the added insulation disrupts the capacitive coupling. Drift is another critical issue. Changes in ambient temperature or humidity can alter the electric field around the screen, leading to inaccurate touch readings. For example, when a user touches the screen, their other hand or body part near the display might cause drift. Even distant objects or people can influence the screen’s performance. This drift is inherent to the technology and often requires frequent recalibration at the site. Moreover, the capacitive touch screen's coordinate system lacks a fixed origin, making it difficult for the controller to adjust for drift. The conversion process from four-point current measurements to Cartesian coordinates is complex, and any shift in the system can lead to cumulative errors over time. The outermost layer of the capacitive screen is scratch-resistant, but it is vulnerable to impact from sharp objects like nails. If the ITO layer inside is damaged during installation, transportation, or accidental knocks, the screen may stop functioning properly. 3. Usage Precautions for Touch Screen Products - The touch-sensitive area is the front of the product, while the back is a non-touchable glass surface. - Handle the touch screen with care, wearing gloves or finger sleeves during assembly to avoid injury from sharp edges. - Avoid applying excessive force or impact during installation, as the glass is fragile. - Do not pull directly on the cable; instead, lift the product carefully. - Do not bend or fold the cable reinforcement plate. - Ensure the cable is inserted horizontally and not at the root of the reinforcement plate. - Handle each unit individually to prevent scratches from collisions. - Clean the surface using a soft cloth and petroleum ether. Avoid using corrosive solvents like industrial alcohol. - Do not stack the touch screens; use a tray for storage. - In assembly and frame design, ensure that all mounting points are outside the visible area. - The frame should not exert pressure on the operational zone of the screen. - It is recommended to use a plastic frame with a soft padding on the front side. - Avoid using adhesive materials that could damage the screen surface.