公开(公告)号：CA1147868A

公开(公告)日：1983-06-07

申请号：CA352829

申请日：1980-05-27

Applicant: IBM

Inventor： DAHL JEROME P ,  EPLEY PHILLIP R ,  FOX JON E

IPC: G06F3/02 ,  G06F3/023 ,  H03K17/96 ,  H03K17/98 ,  H03M11/20

Abstract: PROGRAM CONTROLLED CAPACITIVE KEYBOARD SENSING SYSTEM An improved sensing apparatus for detecting impedance changes in a variable impedance matrix keyboard is described. A microprocessor is utilized to control the basic key intersections scanning and for accurately calibrating and adjusting the sensing threshold of the sense amplifier prior to testing each key intersection so that the effects of stray impedance and varying voltage levels may be compensated for.