Patent GB-1219074-A (GB)
Title: Keyboard encoder
Inventor: GABOR WILLIAM DIXON
IPC: H03K17/972
Filed: 1966-10-14
Abstract: 1,219,074. Touch operated switches. SANDERS ASSOCIATES Inc. 5 Jan., 1968 [14 Oct., 1966], No. 46048/66. Heading H3B. [Also in Division G4] Actuation of a key (or the presence of an operator's finger) produces a coded output from a set of sensing elements associated with the key (position). Capacitive embodiments.-The capacitance associated with a group of plates 24-32, Fig. 3, symmetrically located with respect to a key 12 is varied by a conductive ring 20 which approaches the plates on actuation of the key. Plates 24-32 which represent a corresponding binary 1 bit in all the key sets are connected in a double tubed oscillator circuit for that bit, Fig. 7 (not shown), the remaining plates representing binary O being earthed. The bit oscillators may have different operating frequencies. Whenever a key is actuated, the capacitance in the oscillator circuits corresponding to the 1 bits for that key is increased to cause oscillation, and the coded signal is obtained by detecting the oscillator outputs. The code signal may be entered in a register for a C.R.T. display. The movable key 12 and ring 20 may be dispensed with, the required capacitance change being caused by proximity of an operator's finger, Fig. 9 (not shown). Inductive embodiments.-Each key may carry a ferrite or conductive ring (similar to ring 20 in Fig. 3) to increase the inductance or act as a shortened turn to decrease the inductance of a set of conductive turns located similarly to the plates 24-32 in Fig. 3, Figs. 10-12 (not shown). The inductors may be connected in oscillator circuits similar to Fig. 7 (not shown). In another embodiment, each key, when actuated, moves a permanent magnet towards a set of saturable transformer cores, there being a core for each 1 bit of the associated code, thereby saturating the cores and decreasing the coupling between their primary and secondary windings. The transformers 230, Fig. 14, representing corresponding bits may be connected in series as shown, whereby pulses from source 242 only reach detectors 244 for the O bits of the code corresponding to an actuated key. Alternatively depression of a button can reverse the phase of the pulse train. In the preferred embodiment, Fig. 15, each key has a single transformer core 302 with appropriate 1 bit secondary windings, the cores being normally saturated by permanent magnets 303 in the non-actuated position of the keys. A directly coded output is obtained on leads 308. A further secondary winding 314 common to all cores, carries a signal the magnitude of which is indicative of the number of keys pressed, the signal induced in each secondary winding rising linearly with key depression. Preferably, the windings are single turn windings, but when more than one turn is required on each core, the windings may be threaded completely through adjacent rows of cores several times to produce the required number of turns. Space bar.-An elongated (or equivalent) sensor arrangement allows for detection of space bar depression at one end. Circuit, Fig. 18.-As a button is depressed, the signal on sense line 314 (Fig. 15) increases and eventually overcomes the threshold bias of an amplifier 351 to set a trigger 344. The output pulse, differentiated at 355a, resets an error trigger 356 and differentiated at 355b triggers a monostable circuit 360 to gate the signals on the data lines into register 340. An amplifier 361 is set to a lower (termination) threshold than amplifier 351 and causes a train of reset pulses to be applied to trigger 344 after the actuated button has been released. The reset output pulse from trigger 344 sets a trigger 342 to produce a data present signal for a data processor 376. After data transfer, the acknowledge signal resets trigger 342 followed by register 340, trigger 342 preventing setting of trigger 344 again until transfer has been acknowledged. The data lines are coupled to register 340 through threshold circuits which reduce the possibility of erroneous recording if two keys are depressed " simultaneously " since the register gating signal for the first key is.normally over before the second key signals exceed the threshold. Threshold amplifier 394 detects excessively large signals on sense line 314 when more than one button is depressed and sets trigger 356 to inhibit NOR gate 357 and thus the production of the data present signal by trigger 342 is prevented. When a repeat key 379 is depressed simultaneously with a character key, threshold amplifier 381 sets trigger 382 and when monostable circuit 360 returns to its stable state after loading register 340, trigger 342 is set to produce the data present signal and trigger 344 is reset. With the character key held down, resetting of trigger 342 by the acknowledge signal allows trigger 344 to be set by amplifier 351 and the character is repeatedly transmitted to data processor 376 until either the character key or the repeat key is released.