Contactless keyboard

Details Contactless keyboard Contactless keyboard

H - Electricity

03

M

340/177

H03M 11/00 (2006.01) H03K 17/972 (2006.01)

Patent

CA 1204840

In a contactless keyboard including d matrix (11) of key transformers (II') and including a compensation transformer (12) common to all transformers the latter is so designed that a phase shift of the secondary signal with respect to the primary signal occurs when a key is operated. In d multiplier (18) the primary and secondary signals are multiplied. The DC-component of the multiplier output signal having a change of sign at said phase shift is con- verted into a logic signal by a hysteresis circuit (20) whereas the AC- component is suppressed by a low pass filter (19). A microprocessor (27) controls the scanning (13, 14) of the matrix and delivers the addresses of the operated keys e.g. as an ASCII-code signal.

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