Comparison of four-wire resistive touch screen and five-wire resistive touch screen

OneTouch -4W four wire resistance

In the standby state, the CPU alternately supplies the +5 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. The voltage value on the film is continuously converted by the A/D converter and 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 checks it, the following processing is performed. The CPU first supplies the lower x-axis +5v and grounds the upper y-axis; when touched, the upper layer digitizes the voltage of the lower x-axis and calculates the x-axis coordinates. Then the CPU supplies the y-axis +5v, and the lower x-axis is grounded; when touched, the lower layer will send the voltage value on the upper y'axis, and the A/D converter digitizes the voltage value to calculate the y-axis coordinate.

OneTouch -5W five-wire resistor

In the standby state, the four lines on the Glass will send out +5 volts, the voltage value on the ITO Film is 0, and the voltage value on the ITO Film is continuously converted by the A/D converter, and the CPU on the control card Monitoring. When the screen is touched, a line on the Film will send out the voltage at that point. After the microprocessor detects it, it performs the following conversion processing. The microprocessor first supplies the x-axis +5v and grounds the y-axis. When touched, the adc digitizes the voltage value and calculates the x-axis coordinate position. Next, the microprocessor supplies the y-axis +5v and grounds the x-axis. When it touches the city, Film will send the voltage value of the point on the y-axis, and the ACD digitizes the voltage value to calculate the coordinate position of the y-axis.

The resistive touch screen uses pressure sensing for control. The main part is a resistive film screen that fits well with the surface of the display. This is a multilayer composite film. It uses a glass or hard plastic flat plate as the base layer, and the surface is coated with a transparent metal oxide (ITO) conductive layer. Layer, covered with a layer of hardened outer surface, smooth and scratch-resistant plastic layer (the inner surface is also coated with a layer of ITO coating), there are many small (about 1/1000 inch) transparent spacing points between them Separate and insulate the two ITO conductive layers. When a finger touches the screen, the two conductive layers that are normally insulated from each other make a contact at the touch point. Because one conductive layer is connected to a 5V uniform voltage field in the Y axis direction, the voltage of the detection layer changes from zero to Non-zero, after the controller detects this switch on, it performs A/D conversion and compares the voltage value obtained with 5V to get the Y-axis coordinate of the touch point. Similarly, the X-axis coordinate is obtained. The most basic principle common to all resistive technology touch screens.

The key to resistive touch screens lies in material technology. Commonly used transparent conductive coating materials are:

1. ITO, indium oxide, weak electrical conductor, the characteristic is that when the thickness drops below 1800 angstroms (angstroms = 10-10 meters), it suddenly becomes transparent, the light transmittance is 80%, and the light transmittance becomes thinner. When the thickness reaches 300 angstroms, it rises to 80%. ITO is the main material used in all resistance technology touch screens and capacitive technology touch screens. In fact, the working surface of resistance and capacitance technology touch screens is ITO coating.

2. Nickel-gold coating, the outer conductive layer of the five-wire resistive touch screen uses a nickel-gold coating material with good ductility. Due to frequent touches, the purpose of using a good ductile nickel-gold material is to extend the service life. , But the process cost is relatively high. Although the nickel-gold conductive layer has good ductility, it can only be used as a transparent conductor. It is not suitable for the working surface of the resistive touch screen because of its high conductivity and the metal is not easy to be very uniform in thickness. It is not suitable for the voltage distribution layer and can only be used as a probe. Floor.

Five-wire resistive touch screen: The base layer of the five-wire resistive technology touch screen adds voltage fields in two directions to the conductive working surface of the glass through a precision resistance network. We can simply understand that the voltage field in two directions is time-sharing, and the work is added. On the same working surface, the outer nickel-gold conductive layer is only used as a pure conductor, and the position of the touch point is measured by the method of time-sharing detection of the X and Y axis voltage values of the inner ITO contact point after touch. The five-wire resistive touch screen requires four leads on the inner layer of ITO, and only one conductor on the outer layer. There are 5 lead wires for the touch screen.

Another proprietary technology of the five-wire resistive touch screen is to correct the linearity problem of the inner layer of ITO through a precise resistor network: the uneven thickness of the conductive coating may cause uneven voltage distribution.

Resistive screen performance characteristics:

1. They are a working environment completely isolated from the outside world, not afraid of dust, moisture and oil

2. It can be touched with any object, can be used to write and draw, which is their big advantage

3. The accuracy of the resistive touch screen only depends on the accuracy of the A/D conversion, so it can easily reach 4096*4096. In comparison, the five-wire resistance is better than the four-wire resistance in ensuring the resolution accuracy, but the cost is high , So the price is very high.