Research And Implementation Of Infrared Touch Screen Based On HID Class

Nowadays, the technology of touch and multi-touch has been applied to various electronic products. From small mobile internet device to the large display screen in showroom, more and more devices are about to meet demands of users for more natural and more intuitional on the hardware. Due to its simple installation, low cost, good translucency and hard to lower the image quality, infrared touch screen has the particular advantage in the application of medium and large screen. In this paper, we study the implementation principle and the advantages and disadvantages of all kinds of common touch technology, and then we design and implement an infrared touch screen, which is based on USB HID protocol and is applied to large touch screen.In order to support multi-touch recognition, two groups of radiation tubes and incept tubes are arranged around the traditional infrared touch screen. Some infrareds are developed to form three axes through adding an extra layer of radiation tubes and incept tubes, so the infrared touch screen can eliminate the false contacts consequently. Those technologies not only make the structure of infrared being more complex and take longer to scan, but also effect the normal induction of infrared receiving tube, when the infrared ray sent from the infrared decay seriously because of the large distance between radiation tubes and incept tubes, which located a super-large screen. Owing to the user’s operation is limited by his height, about2miters, which is in the effective transmission distance range of infrared light, one group of radiation tubes and incept tubes are installed on the up and bottom of the system in this paper, we also propose a new multi-touch identification algorithm accordingly, thus the infrared system would be applied to the super-large display screen.Usually, the traditional infrared touch screen communicates with the host by RS-232serial port. So they not only need additional power, but also need to develop relevant driver for them. Although some infrareds communicate with PC by USB and work by USB bus power, the developer also need to develop relevant driver about the USB device. The system in this paper is developed based on USB HID protocol without developing extra driver. Starting with the operation system of Windows98, the drivers of HID class devices are included in Windows OS. When the HID devices insert the host, it should return the descriptors requested from the host according to the HID protocol. As a result, the host will recognize the device, and then USB bus driver will automatically load the driver included in the OS and make the device work normally. The touch devices based on HID protocol can realize the plug and play function really without installing any other drivers.The designer and producers of infrared touch screen have to consider the problem of high resolution and the ability of resisting the optical interference. The resolution of traditional infrared is low, and generally, the way of improving the resolution is simply increasing the number of infrared diodes. In this system, we will quantified and classify the infrared light intensity to subdivided one original pixel into more pixels, so we can improve the resolution per inch effectively.The infrared receiving tubes of the infrared touch screen are easily affected by the infrared light in environment. So according to the feature of the infrared light in environment, we present three ways to improve the system’s ability of resisting optical interference. Firstly, the infrared light in the environment is stable, so we can enable the infrared transmitting tube to launch high frequency infrared light, and then the low frequency and stable infrared ray in the environment can be effectively filtered by RC high-pass filter. Secondly, as the intensity of infrared light in environment may be different in different time, we add optional different multiples of amplifying circuits to the circuits. Therefore, we can map the input voltage values to the range of ADC’s input voltage uniformly to achieve better A/D conversion. Finally, considering the most of the infrared light in the environment shine from top to bottom, we placed the infrared receiving tubes on top of the screen so that can reduce the receiving of the ambient light to some extent and can improve the ability of resisting the optical interference of the system.