Capacitive touch screen introduction

Tantalum capacitor

1. Introduction The structure of the capacitive touch screen is mainly to deposit a transparent film body layer on the glass screen, and then add a protective glass outside the conductor layer. The double glass design can completely protect the conductor layer and the inductor.
The capacitive touch screen is plated with narrow electrodes on all four sides of the touch screen to form a low voltage alternating electric field in the conductive body. When the screen is touched, due to the electric field of the human body, a coupling capacitor is formed between the finger and the conductor layer, and the current from the four electrodes flows to the contact, and the current intensity is proportional to the distance from the finger to the electrode, and the controller located behind the touch screen is The ratio and strength of the current are calculated to accurately calculate the position of the touch point. The dual glass of the capacitive touch screen not only protects the conductors and sensors, but also effectively prevents external environmental factors from affecting the touch screen. Even if the screen is stained with dirt, dust or oil, the capacitive touch screen can accurately calculate the touch position.
Since the capacitance varies with temperature, humidity, or grounding conditions, its stability is poor, and drift often occurs. This kind of touch screen is suitable for the debugging phase of system development.
Second, the capacitive touch screen defect capacitive touch screen transmittance and clarity is better than the four-wire resistive screen, of course, can not be compared with the surface acoustic wave screen and five-wire resistive screen. The capacitive screen is seriously reflective. Moreover, the four-layer composite touch screen of the capacitor technology has uneven transmittance for light of various wavelengths, and there is a problem of color distortion. Due to the reflection of light between layers, image characters are also blurred.
(1) The current capacitive screen is used in principle as an electrode of a capacitor component. When a conductor is coupled to a capacitor with a sufficient capacitance between the working surface of the ITO and the interlayer, the current flowing away is sufficient to cause the capacitor. Screen malfunction. We know that although the capacitance value is inversely proportional to the distance between the poles, it is proportional to the relative area and also to the insulation coefficient of the medium. Therefore, when a large area of ​​the palm or hand-held conductor is close to the capacitive screen instead of touching, it can cause the malfunction of the capacitive screen. In humid weather, this situation is particularly serious. The hand holds the display and the palm is close to the display 7 cm. Within 15 cm of the display or the body close to the display can cause malfunction of the capacitive screen. Another disadvantage of capacitive screens is that they do not respond when touched with a gloved hand or a non-conductive object, because of the addition of a more insulating medium.
(2) The main disadvantage of the drift capacitive screen is drift: when the ambient temperature and humidity change, the environmental electric field changes, causing the drift of the capacitive screen, resulting in inaccuracy. For example, the temperature rise of the display after power-on will cause drift: when the user touches the screen, the other hand or the side of the body will drift near the display; the larger object near the capacitive touch screen will move back and drift, and if someone touches it, It will cause drift; the drift of the capacitive screen belongs to the technical congenital deficiency. Although the environmental potential surface (including the user's body) is far away from the capacitive touch screen, it is much larger than the finger area, and they directly affect the measurement of the touch position. .
(3) Others In addition, in theory, many linear relationships should be nonlinear. For example, the total amount of current drawn by people with different body weights or different finger wetness is different, and the total current amount changes and four points. The change of the electric current is nonlinear. The custom polar coordinate system of the four corners used in the capacitive touch screen has no origin on the coordinates. After the drift, the controller can not detect and recover, and after the four A/Ds are completed, The calculation process from the values ​​of the four partial flows to the X, Y coordinate values ​​of the touch points on the Cartesian coordinate system is complicated. Since there is no origin, the drift of the capacitive screen is cumulative and calibration is often required at the job site. The outermost bauxite protection glass of the capacitive touch screen is very scratch-resistant, but it is afraid of the nail or hard object knocking. If a small hole is knocked out, the interlayer ITO will be damaged, whether it is the injury of the sandwich ITO or the installation and transportation. The inner surface of the ITO layer, the capacitive screen will not work properly.
Third, touch screen products use precautions
1. The touch screen surface is the touch surface, that is, the front of the product; the glass surface is the non-touch surface, that is, the back of the product
2, the touch screen part is glass products, the glass corner is sharper, please wear gloves / finger sleeves when assembling
3, the touch screen part is glass fragile, do not exert a strong impact on the touch screen during assembly.
4. Avoid taking the lead directly and pick up the touch screen to avoid pulling the lead wire.
5. The bending line of the lead wire reinforcement plate cannot be bent.
6. No folding is allowed in any part of the lead wire.
7. When the lead wire is assembled, it must be inserted horizontally. Do not insert it at the root of the reinforcing plate.
8. When handling the product, it needs to be handled by a single piece. Handle it gently to avoid the product colliding with each other and scratching the surface of the product.
9. When cleaning the surface of the product, wipe it with a soft cloth (deer skin) and petroleum ether.
10. Do not wipe the surface of the touch screen film with a corrosive organic solvent. Such as industrial alcohol.
11, do not stack the touch screen, use the tray.
12. In the assembly design and frame design, please pay attention to the following items:
a. The pillars of the frame of the fixed touch screen must be outside the visible area of ​​the touch screen.
b. The edge of the frame shall be outside the operation area of ​​the touch screen, and the frame side shall not have pressure action in the visible area to the operation interval.
c. It is recommended that the material of the fixed touch screen be a plastic material, and the front part of the touch screen is padded with a soft material.
d. Do not stick the corrosive adhesive to the surface of the touch screen.