Research On Multi-touch Control Technology Based On Capacitive Sensor

Capacitive sensor refers to the capacitors in various forms as sensing components,will be measured into the capacitance value changes of the measurement equipment.In recent years,with the development of capacitive sensor related technologies,touch control devices based on capacitive sensors have been widely used in human-computer interaction scenes such as mobile phones,tablets,instrument control panels and so on,with the advantages of high sensitivity,high reliability and support for multi-touch control,becoming one of the most common touch devices at present.Conventional capacitive multi-touch devices often require a large amount of scanning and data processing workload to realize multi-touch functions,and these workload will increase with the increase of the size of the touch panel,resulting in a decline in the frame rate of touch.Therefore,multitouch technology based on capacitive sensor still has a broad research prospect.Combined with the working principle of capacitive sensors in touch control system,this thesis analyzes the working principle of different capacitive sensor structures and capacitive scanning strategies in detail,and analyzes the feasibility of their application in multi-touch control system,so as to determine the multi-touch system based on mutual capacitive scanning strategy projective touch screen as capacitive sensor as the research object of this thesis.This project focuses on building a multi-touch system based on capacitive sensor through FPGA and the integrated soft-core processor,and making use of the high working efficiency of hardware module and the collaborative working mode of hardware and software to make up for the low efficiency of multi-touch function.The main contents of this thesis are as follows:(1)Study the working principle and overall architecture of the multi-touch system,determine the prototype of the capacitive sensor and analyze the working principle of the capacitive sensor and its supporting front-end scanning circuit.(2)Based on Verilog HDL,the design and simulation of the hardware module used to control the front-end scanning circuit to complete capacitance data scanning in the capacitive sensor were carried out,and the timing and function analysis of the simulation results were carried out;By writing software to realize software and hardware communication function,reasonable arrangement of control time sequence to make software and hardware work synchronously.(3)Based on the CORTEX M1 softcore processor,the design work of capacitor data processing flow is completed.OTSU algorithm is used to reduce the amount of computation of data processing flow to further improve the system speed.Finally,the refresh rate of the touch control system reached 178 Hz,the accuracy of the signal point,the output coordinate jitter radius and linear error were controlled within 2mm,the output coordinate jitter radius was controlled within 4mm,and the miscontact recognition rate was more than 90%,which met the performance requirements of the current touch control system industry.(4)Build a hardware prototype test platform through FPGA,capacitive sensor and its front-end scanning circuit,and complete the prototype verification of the multitouch control system based on capacitive sensor.