Patent GB-1429682-A (GB)
Title: Pressure sensitive switch assembly
IPC: G06F3/0487
Filed: 1973-05-07
Abstract: 1429682 Selective signalling INTERNATIONAL BUSINESS MACHINES CORP 7 May 1973 [12 May 1972] 21626/73 Heading G4H [Also in Division H1] A pressure sensitive switch assembly, Fig. 5 (see Division H1) comprises a flexible overlay 1 which when depressed selectively closes switches formed by contacts 4a, 4b, connected in matrix formation, which provides signals and illuminates light sources (LED's) 13a, 13b, Fig. 9 (not shown). The assembly forms a panel, Figs. 4, 4a (not shown) for mounting in a host equipment, e.g. a computer. Circuits are described in the following for scanning the panel to sense which switches are closed, for controlling the indicating illumination and for output to the host equipment. Referring to Fig. 11, multivibrator 103 sends pulses to scan circuit 101 which sends pulses through R 11 , R 1n  to Fig. 12 and scans through RC 1 , RC n  the row conductors on film 39 (Fig. 5) which when a switch 4a, 4b, is closed completes a circuit through column conductors on film 43 (Fig. 5) to CC 1 , CC m , which sends pulses through C 11 , C 1m  to Fig. 12, also completes a circuit to 108 which (a) signals 103 to stop the scan and freeze the system, (b) gives an audible "beep" at 114, and (c) through anti-bounce 115 (in more detail in Fig. 11a, not shown) energizes one-shot 116 to send a 1 Ás. pulse through SC to Fig. 12. Referring to Fig. 12, the 1 Ás. pulse SC from Fig. 11 partially conditions ANDs 118, 119, 120. AND 118 conditions circuits 121 (panel on/off, associated with contact 74 on Fig. 4, not shown) which has a toggle effect (i.e. push-on, push-off) which in the on condition supplies enabling conditioning to AND 120 and "beep" on/off control, and which in the off condition disables AND 120 disabling contact sensing circuit 125 thereby rendering all switches on the control panel inoperative except contacts 74, 75 and stops the "beep". AND 119 conditions circuits 123 (panel power on/off, associated with contact 75), and AND 120 conditions circuits 125 (all panel contacts other than 74, 75). Lines R 11 -R 1n  and C 11 -C 1m  from Fig. 11 go to circuit 125 which senses when a switch 4a, 4b, is closed and is detailed in Figs. 13 and 15 (not shown). Fig. 13 is associated with one contact group (group 70, with 16 contacts, on Fig. 4) and Fig. 15 is associated with all the other contacts. Fig. 13 comprises OR circuits, AND circuits, latches and a one-shot giving a 10 second delay pulse, which encodes the switch closures from group 70 into a coded output B 0 , B 1 , B 2 , B 3 , which is fed via other latches and gates (Fig. 14, not shown) to panel indicators 13B (Fig. 4) and to the host/ panel interface 185, Fig. 12. Fig. 15 comprises AND, OR circuits to convert the switch closure into latching pushbutton, momentary pushbutton, rotary switches and other unspecified operations. In Fig. 16, the momentary pushbutton operation is effected by an AND circuit 225 supplied from row and column R 1x , C 1y , which is not timed and therefore the signal persists as long as the switch is closed. Pulse action is by a one-shot circuit 228 which receives a signal of indefinite duration from momentary circuit 225 and converts it into a timed pulse. A rotary switch operation is provided by circuit 235 in which the inputs from the rows and columns R 1x1 , C 1y1 , &c. comprising the rotary switch group are fed to latches L and to OR circuit 239 from which it goes to an AND gate 237 along with a timed pulse from clock circuit SCC, the output from gate 237 also going to latches L gating the latches in concert momentarily for the duration of SCC. Fig. 14 (not shown) converts the output B 0 -B 3  from Fig. 13, the output 284 from Fig. 15, conditioning 283 from the host control, by-pass input 299 from the host, and input 295 into signals from the host interface and also energize the appropriate LEDs 13a, 13b (Figs. 9, 9a, not shown) to give the corresponding illuminated panel display, by OR, AND and LATCH circuits. Thus the panel can be remotely controlled completely by the host as well as by the switches 4a, 4b closed by overlay 1.