GB1227669A - - Google Patents

Abstract

1,227,669. Typewriters &c. SIEMENS A.G. 9 June, 1969 [10 June, 1968], No. 29017/69. Heading B6F. [Also in Divisions G4 and H3] A key for a keyboard comprises a ferrite assembly 7 containing a signal coil 9 and a saturating excitation winding 8, a signal being induced in coil 9 when the magnetic circuit is broken by motion of iron disc 10 caused by actuation of knob 2. The motion of the knob is initially taken up by spring 4, then a flange 2a attached to the knob operates a trip 5 to accelerate weight 3 downwardly and displace the disc 10. A light spring 6 normally biases weight 3 away from the disc. In another embodiment, Fig. 2 (not shown), the attractive force between a permanent magnet (19) and a part of the key casing must be overcome before the weight is released to displace the disc. The pulse from each key is shaped, Fig. 3, by a series capacitor C1 and fed to an OR gate G1. The gate output is closed after one microsecond and reopened after seven microseconds to prevent mixed keying during all but the initial microsecond. If a second pulse occurs during the seven microsecond period it is indicated by a lamp SL. To avoid any pulse longer than seven microseconds, the pulse shaping capacitors C1 are discharged through a transistor Tr by diodes D2 within seven microseconds. A capacitor C2 at the output of gate G1 eliminates multiple switching by a single pulse. The excitation windings of the keys in Fig. 3 are series connected to minimize heating effects and loading of the signal coils.