What is a Surface Capacitive Touch Screen
A Surface Capacitive Touch Screen is a type of touch screen technology that operates by detecting changes in the electrical charges on the surface of the touch screen caused by the touch of a finger or stylus. It consists of several layers, including a scratch-resistant top coat, hard coat with anti-glare, electrode pattern, conductive coating, and a bottom layer of glass. A uniform electric field is created over the panel by applying the same phase voltage to the electrodes on the four corners. When a finger touches the panel, electrical current flows from the four corners through the finger, and the ratio of the electrical current flowing from the four corners is measured to detect the touch point. The location of the point of contact is then calculated by the controller and transmitted to the PC.
However, Surface Capacitive Touch Screens are no longer widely used, as they have been replaced by more advanced touch screen technologies, such as Projected Capacitive Touch Screens. The main reasons for this are that Surface Capacitive Touch Screens are easily affected by environmental factors, such as temperature, humidity, dust, and greasy dirt, leading to miscalculated and shifted touch points. Additionally, they are not responsive to gloved hands or pen writing and do not support multi-touch. There is also a problem of color distortion and light reflection in each layer, which can cause image blur.
Overall, Surface Capacitive Touch Screens are considered obsolete, as they have been largely replaced by more advanced touch screen technologies that offer better performance and reliability.
Dr Pan: Welcome to DISPLAY Museum. I am Dr Pan, the curator of Museum.
Greg: Hello, Dr Pan. I am Greg. I came here to learn about surface capacitive touch screen.
Dr Pan: Hello, Greg. Surface capacitive touch screen is rarely used today.
It is low cost, simple working principle and simple design circuit, but difficult to achieve multi-touch.
Let’s look at the structure. From top to bottom, scratch resistant top coat, hard coat with anti-glare, the first two layers are protective layers, they provide a good working environment; electrode pattern, conductive coating, the third and fourth layers are functional layers, the bottom layer glass is supporting layer.
The same phase voltage is applied to the electrodes on the four corners, then a uniform electric field will be forming over the panel.
When a finger touches on the panel, electrical current will flow from the four corners through the finger.
Ratio of the electrical current flowing from the four corners will be measured to detect the touched point.
The measured current value will be directly proportional to the distance between the touch point and the four corners.
The location of the point of contact is calculated by the controller and transmitted to the PC.
Greg: Dr Pan, from my experiences, we can’t see surface capacitive touch screen very often. Is it true?
Dr Pan: That is right. Surface capacitive touch screen is obsolete. It is replaced by projected capacitive touch screen and there are 4 reasons.
- It is the most important reason. The uniform electric field is easily affected by the environments, such as temperature, humidity, dust, greasy dirt and so on. Therefore, the touched points will be miscalculated and shifted from time to time.
- It is not responsive to gloved hand or pen writing.
- It can not support multi-touch.
- There is a problem of color distortion due to the uniformity of each wavelength in four layers of composite materials and it causes image blurred because of light reflection in each layer.
Greg: Thank you, Dr Pan. Now I got it.
Dr Pan: Welcome to contact us if you have any question.
