GB1253337A - Improvements in neutralizing of unwanted signals by location of conductors on contiguous printed circuit boards - Google Patents

Abstract

1,253,337. Keyboard circuits. GENERAL ELECTRIC CO. 21 May, 1970 [4 June, 1969], No. 24542/70. Heading G4H. In a keyboard of the kind in which a gapped core 10, 12, 14, Fig. 2, is associated with each key, the gap of a core being closed by operating the corresponding key, a drive line 20 threading all the cores and sense lines 22, 24, 26 threading different combinations of cores so that, according to which key is pressed, a corresponding pattern of signals appears at the outputs when the drive line 20 is pulsed by generator 18, unwanted signals on the sense lines induced by running in proximity to the drive line are cancelled in the form of Fig. 2 by extensions 30, 32, 34 of the sense lines running in the opposite direction adjacent the drive line. The conductors are printed on a printed circuit board, apertures being provided to receive the gapped cores. In the form of Fig. 3, a separate conductor 40 is provided, adjacent the drive line 20, through which the sense lines are connected to earth. Tappings 42, 44, 46 and 48 are provided, the sense lines being connected to the terminal providing the appropriate neutralizing signal. In another form (Fig. 4, not shown) the drive and sense lines are provided on separate printed circuit boards adapted to be assembled in a pack. The drive line has a limb running in one direction threading all the cores and a limb running in the opposite direction to induce neutralizing currents in the sense lines. The sense lines have appropriate portions running adjacent the second limb of the drive line to pick up the necessary neutralizing signal.