A Music Keyboard with capacitive xy-finger position detection

capacitive music keyboard
	Audio DSP	This project shows my recent music keyboard using capacitive sensor pads. As an extension to the former version there is also an interpretation of the x-direction possible. This can be used to drive the vibrato channel or the static pitch of a key in a MIDI stream: PCB Hardware EAGLE Design Top and Bottom of the PCB design The pads are touched from the component side of the PCB (red) receiving two specially built signal patterns from the bottom side (blue). The amount of mixture in the receiving signal determines the detailed position of the finger at a normalised key position and thus the offset from the middle. Detailed noise analysis has to be performed to achieve this. FPGA Design FPGA-design of the circuit driver LFSRs are used to generate dedicated noise for both the capacitive key and the signal used as a reference for the internal comparator. The LFSRs produce different noise by different equations. Both some up together or alternatingly at the cathode which has a little BIAS. The ADC feeds the FPGA by I2C. Decimation and filtering is performed to prepare the signals for alter comparison. The final stage subtracts both signals from each other thus sorting out the information of pressure change for the subsequent processing module. See also the old pages for the version KB05 and KB99. The finger distubs the electrical field and changes the amplitude especially when it is close to the sensor pad and some pressure is applied. The position of the finger emphasises specific frequencies. The information of position is extracted from the phase information of these frequencies, by a gravity point analysis for both X and Y. FPGA-design of the circuit analyser FPGA Hardware Cyclone 2 Cyclone 2 - Development System A current Altera-FPGA is used to implement the full design. With the given resources 32 channels can be driven a the same time offering the chance to run 3.5 octaves of keys. For more information about the idea, see the former version The idea how to analyse small changes of a capacity is shown here: First Version / Invention