Resistive touch screen

Resistive touch screen

A resistive touch screen is a sensor that converts the physical position of a touch point (X,Y) in a rectangular area to a voltage representing the X and Y coordinates.

Many LCD modules use resistive touch screens, which can use four -, five -, seven - or eight-wire screens to generate screen offset voltage while reading back the voltage at the touch point.

The resistive touch screen is basically the structure of the film and glass, the adjacent side of the film and glass are coated with ITO(nano Indium Tin oxide), and the ITO has good conductivity and transparency.

When touching the ITO in the lower layer of the film, it will touch the ITO in the upper layer of the glass, and send corresponding electrical signals through the inductor, which will be sent to the processor through the conversion circuit and converted into X and Y values on the screen through calculation, and the action of clicking will be completed and presented on the screen.

Principle of touch screen

The touch screen consists of two transparent layers that overlap each other. The four-wire and eight-wire touch screens are composed of two transparent resistive materials with the same surface resistance. The five-wire and seven-wire touch screens are composed of one resistive layer and one conductive layer, usually separated by an elastic material.

When enough pressure is applied to the surface of the touch screen, such as through the tip of a pen or finger, contact occurs between the top and bottom.

All resistive touch screens use the voltage divider principle to generate voltages representing the X and Y coordinates.

To measure a coordinate in a particular direction on a resistive touch screen, you need to offset a resistive layer: connect one side to a VREF and ground the other.

At the same time, connect the unbiased layer to the high impedance input of an ADC.

When the pressure on the touch screen is high enough for the two layers to come into contact, the resistive surface is separated into two resistors.

Their resistance is proportional to the distance from the touch point to the offset edge.

The resistance between the touch point and the ground edge is equivalent to the resistance at the bottom of the voltage divider.

Thus, the voltage measured on the unbiased layer is proportional to the distance between the touch point and the ground edge.