CL850 PROJECTION KEYBOARD Block Diagram MainBoard PROJECTION KEYBOARD Block Diagram details for FCC ID TCLCL850 made by CELLUON, INC. Document Includes Block Diagram MainBoard : SubBoard_SW Part.[PDF] Piano player with Virtual touch keyboard - Columbia University Piano player with Virtual touch keyboard. Page 16 diagram, and then the output of the shift register is processed by a low pass filter. And after the signal passing through the low-pass filter, we feed back the signal to the input of the shift register. In this process, the signal will decay gradually.