Short Distance Capacitive Location And Direction Sensing System

Capacitive touch button technology originated in the 90's of last century. In the past ten years,it has been developed rapidly, covering a large number of areas. At present, it has been more mature touch key detection technology, mainly mechanical contact button. But the traditional mechanical contact key service life by mechanical switch limited restrictions on the use of the number. Up to meet the service life of 10 million times and need a mechanical switch by a large current, the switch contact can cause great load and damage. In some failure modes of the fault may produce high current and burn the contact switch failure phenomenon, also may cause burning of module. At the same time, the mechanical switch mode can not be applied to the occasion of high comfort requirements. Therefore, this kind of touch detection technology has certain defects, such as high cost, high loss rate, and so on. It is not easy to be used in the large-scale application of consumer products.This paper presents a design method of a close non-contact measurement of the position and moving direction, which is a new type of button. Among them, near distance refers to the measurement without contact, and generally between the contact of the vertical distance is less than 2cm, in order to ensure measurement capacitance volume change. The capacitance sensor has the advantages of simple structure, high sensitivity, high resolution, non-contact measurement,stability and dynamic response characteristics of a good, low cost and other advantages. In order to determine the location of the human finger, it can penetrate a few millimeters of insulating materials by detecting human body induction mobile charge. To solve the ordinary mechanical contact key oxidation and the bad contact, the service life is greatly improved.This system mainly uses the ADI company's capacitance digital conversion(CDC) chip ADUX1050 and the digital signal processor Blackfin as the core measuring device. The overall framework of the system is mainly composed of capacitance acquisition module, I2 Ccommunication module, DSP processor, USB communication module and Win Form display module and so on. System based on capacitive sensing principle, measuring the amount of change in the three blocks between the capacitor plates capacitance value, the conversion measured the position of the object in the plane, and the Win Form GUI software shows the measured object location and direction of motion. The system is mainly applied to the large size panel with low positioning accuracy. Experimental results show that the system can not only achieve real-time positioning, but also achieve scaling, rotation and other functions.