Four-wire resistive touch screen

Four-wire resistive touch screen

The screen body of the resistive touch screen is a multi-layer composite film that fits well with the surface of the display. A layer of glass or plexiglass is used as the base layer. The surface is coated with a transparent conductive layer and covered with a layer of hardened and smooth outer surface. The scraped plastic layer, its inner surface is also coated with a transparent conductive layer. There are many small (less than one thousandth of an inch) transparent isolation points between the two conductive layers to isolate them. When the finger touches the screen , The two conductive layers that are usually insulated from each other have a contact at the touch point. Because one conductive layer is connected to the Vref uniform voltage field in the Y-axis direction, the voltage of the detection layer changes from zero to non-zero. After detecting this connection, perform A/D conversion and compare the voltage value obtained with Vref to get the Y-axis coordinate of the touch point. Similarly, the X-axis coordinate is obtained. This is common to all resistive technology touch screens. The most basic principle. The key to resistive touch screens is the material. The resistive screens are classified into four-wire, five-wire, six-wire and other multi-wire resistive touch screens according to the number of lead wires.

Four-wire resistive touch screen control

The interface between the touch screen and the built-in A/D single-chip microcomputer can be realized by applying voltage to the X and Y directions through 4 triodes or MOS tubes, and reading the voltage values in the Y and X directions through the A/D channel, and input A/D to the touch screen The data reading control can adopt timing query mode and interrupt mode.

Four-wire resistance physical structure

The bottom layer of the screen is a general glass plate or tempered glass plate. There are two layers of ITO Film on the glass. The upper layer is used to read the y-axis voltage value, and the lower layer is used to read the x-axis voltage value. The two layers of Film are close together and coated The sides with ITO face each other, and the two layers are separated by tiny transparent insulating "separators".

Working principle of four-wire resistance

In the standby state, the CPU alternately supplies +5v voltage to the upper y-axis and the lower x-axis at a very fast frequency.When one layer is conductive, the other layer is grounded to read the voltage value, and the voltage value on the Film is continuously changed by A The /D converter does the conversion and is monitored by the CPU on the control card.

When the screen is touched, the ITO on the upper film and the lower film are connected. After the CPU detects the above action, the following processing is performed: the CPU first supplies the lower x axis + 5v, and the upper y axis is grounded. When touched, the upper layer will The voltage value of the x-axis of the lower layer is sent out, and the A/D converter digitizes the voltage value to calculate the coordinates of the x-axis. Then the CPU supplies the y-axis +5v, and the lower x-axis is grounded. When touched, the lower layer will turn the upper y-axis Send the voltage value on the A/D converter to digitize the voltage value, Calculate the coordinates of the y axis.