| 摘要 |
In a contact free keyboard with a matrix (11) of key transformers (11') associated to a transformer (12) for the compensation of all transformers, said transformer is arranged so that when a key is actuated a phase skip occurs in the secondary signal with respect to the primary signal. The multiplication of the primary signal and the secondary signal will be effected in a multiplier (18). The direct component, being in the output signal resulting from the multiplication, changes its polarity during the phase skip. This component will be transformed into a logical signal in a hysterisis circuit (20). The alternating component will be eliminated by a low pass filter (19). A microprocessor (27) controls the explorations (13, 14) of the matrix and gives the addresses of the keys known as being activated, for example in the ASCII code. |
