H - Electricity – 04 – L
Patent
H - Electricity
04
L
340/181, 354/236
H04L 1/24 (2006.01)
Patent
CA 1154120
45 SL-01296 KEYBOARD VERIFICATION SYSTEM ABSTRACT OF THE DISCLOSURE A capacitive keyboard veritification system is disclosed wherein key movement is verified with a high degree of accuracy in a manner largely immune to ambient noise or other electronic or electromagnetic interference. A pulse signal, in the form of a train of pulses, is periodically applied across the capacitor associated with each key. The signal coupled through the capacitor is reconstructed only if it exceeds a predetermined reference level. A test, which depends on the previously verified key state, is made to determine the existing key state. The test for the active key state is conditioned on multiple true comparisons of a reconstructed signal with the originally applied signal throughout the duration of the test. The test for the inactive key state is conditioned on the absence of a reconstructed signal throughout the test. In both instances the newly indicated key state is compared with the state to which the key is assumed to have changed from its previously verified state. If the test fails, the key is considered to have remained in its previously verified state. Immunity to noise is enhanced by making the pulse signal a pseudo-random signal which is successively applied across the key-associated capacitors in a timing sequence out of synchronism with the generation of the pulse signal. The system disclosed avoids the requirements for massive shielding, for selective routing of conductors, or for the assignment of special, physical key locations in the electronic scanning sequence, while providing fully verified key actuation at reduced overall system cost.
348736
Miller Donald E.
Painter John P.
Company General Electric
Eckersley Raymond A.
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