Operating Principle of Resistive Touch Screen

Operating Principle of Resistive Touch Screen Touch screen is a data input device. It is a screen which responses to a touch. There are various types of touch screens which work according to different physical principles. Let’s consider operating principle of a resistive touch screen. A resistive touch screen consists of a glass board and a flexible plastic membrane. Both the board and the membrane are covered with resistive coating. Space between the glass and the membrane is filled with micro insulators which are evenly distributed along the screen’s active area. They insulate conducting surfaces. When you touch the screen the board and the membrane close up. The controller registers change in resistance with the help of analog-to-digital converter and converts it into coordinates of the touch. There are also 5- and 8-wire touch screens. They improve tracking accuracy but do not increase reliability. Initially all 4 electrodes are earthed and the membrane is “pulled” by the resistor up to +5V. Membrane voltage level is constantly tracked by the analog-to-digital converter. When the screen remains untouched the voltage equals 5V. As soon as the screen is touched the microprocessor detects the membrane’s voltage change and starts calculating touch coordinates. A five-wire screen is more reliable as the membrane’s resistive coating is replaced with a conductive layer. A 5-wire screen continues working even with a cut membrane. The back glass has a resistive coating with 4 electrodes along the corners. Resistive touch screens are cheap and have a maximum pollution resistance. Resistive screens respond to a touch by any smooth solid object. This can be a hand, a feather, a credit card, or a scalpel’s blunt end. One of the disadvantages of resistive screens is their low light transmittance – no more than 85% for 5-wire models and lower parameters for 4-wire models. They also have a short lifespan – no more than 35 mln touches per one point. Touch screens are used in payment terminals, information kiosks, sales automation equipment, handheld computers, and operator boards in industry.

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