Self-optimizing touch pad sensor circuit
Keyboard verification system
Electronic watch with touch-sensitive keys
Touch pad and display tube circuitry
Program controlled capacitive keyboard variable threshold sensing system Patent #: 4305135
ApplicationNo. 06/362290 filed on 03/26/1982
US Classes:341/24, With error prevention means (e.g., debounce, antichatter)341/33, Capacitive actuation361/287Mechanically variable
ExaminersPrimary: Groody, James J.
Attorney, Agent or Firm
International ClassesH03K 17/94 (20060101)
H03K 17/96 (20060101)
Foreign Application Priority Data1981-04-03 FR
AbstractApparatus for suppressing interference in a capacitive keyboard. Unconditioned operating signals from receiving lines are passed into a subtractor, which establishes the difference between the signal present on a reference line in the keyboard and supplies, at the output, a conditioned operating signal which is free from any unwanted electromagnetic component which may have entered the structure. In addition, in order to determine which of several keys is supplying the highest signal, operating signals corresponding to particular receiving lines are scanned in sequence to determine which has the highest amplitude. As the operating signal corresponding to each successive key is scanned, its voltage is compared with a previously-stored voltage for an earlier-scanned key. If a higher voltage is detected, the voltage and key address are stored in place of the previously-stored values.