turning now to the drawings , there is shown a membrane switch ( i . e ., a switch in which a flexible layer is flexed in order to produce a signal output ) in which the signal output is produced by a large change in capacitance . the device may perhaps be most understandably explained by an initial description of how it is made . there is shown in fig3 a a bottom plan view of top layer 10 . it comprises 5 - mil thick transparent polyester layer 10 , on the bottom surface of which has been vacuum deposited thereon through a suitable mask a multiplicity of round pads 12 and conductors 14 , of copper , 1500 angstrom units thick . fig3 b is a bottom view of said top layer 10 showing positioned over the surfaces , including the pads and connectors , illustrated in fig3 a , a layer 16 of insulating epoxy ( one mil thick ), ultraviolet curable and capable ( like the other elements of the switch ) of withstanding elevated temperature and humidity ( e . g ., 85 ° c . and 85 % r . h . ), screened through a mask prior to curing , and including a multiplicity of zones 18 in which , corresponding with the locations of pads 12 , the epoxy is laid down , not in an uninterrupted layer as throughout most of the device , but in sets of grid lines 20 . the layer of epoxy is also relieved at three areas 21 , corresponding with the location of contact areas 22 ( shown in fig3 a ). fig3 c is a plan view of bottom layer 24 , also of five mil thickness transparent polyester film , on which has been deposited , through a mask , a 1 / 2 - mil thick layer 26 of pressure - sensitive acrylic adhesive , interrupted by generally circular zones 28 corresponding to the locations of conducting pad zones 22 on the top layer 10 . fig3 d is a plan view of the bottom layer 24 following the next step in the manufacturing process , namely , the assembly of the three elongated strips 30 , which are held in place by adhesive layer 26 , and are formed from 1 / 4 - mil polyester on each outer surface of which is vacuum deposited by rf sputtering layers 1000 angstrom units in thickness of aluminum . fig3 e is a plan view of bottom layer 24 after the next stop in manufacture of the device . in this step there is deposited through a mask , over the area indicated in dots , a layer 31 of acrylic pressure - sensitive adhesive one mil in thickness . as shown in the drawings , this step leaves uncoated areas 32 corresponding to the contact areas 22 in top element 10 and areas 34 corresponding to the pads 12 of element 10 . the step just described leaves extending freely the tips 36 of strips 30 . these tips are then folded up around edges 38 of adhesive layer 31 , as illustrated in fig3 f , as well as in fig2 . dots 40 of a silver filled conductive epoxy ( amicon 3050 , sold by amicon corporation of lexington , mass .) are then deposited along the fold line of the strips 30 , to supplement conductivity through the outer aluminum layers of strips 30 and make contact with pads 22 . the steps thus far described are carried out on the top and bottom elements ( to be assembled into the switch ) separately , and while each is part of a web of greater width than the final width dimension of the switch . in the top element , portions to define the tail 42 are cut out before the upper and lower portions are assembled . also before assembly , a cut is made to define edge 46 of the lower portion as well as a window of which the edge 46 is one of the four sides to permit movement therethrough for soldering of tail 42 . they are then assembled , and held together by adhesive layer 31 . next they pass over a roller which causes tail 42 to extend in a direction facilitating adding thereto , over the conductor areas 44 , by standard solder wave techniques , one mil thick layer of 50 % indium - 50 % tin alloy . ( this approach permits use of a very short integral tail , with consequent savings of expensive polyester ; as long a tail as desired may then be attached through an alloy seal with a similar alloy on the tail extended ; the seal can be simply effected by a pressure - heat step -- 50 psi at 125 ° centigrade for half a second ). the construction at the tail - extender joint is shown in fig5 in which is seen switch top layer 10 bearing conductive tracks 80 and insulating layer 16 , extending over switch bottom layer 24 . tail extender 82 initially carries copper track 84 protected with epoxy layer 86 and an indium - tin layer over the tracks at their ends to enable making the seal . the indium - tin layer 88 is created by fusion pursuant to pressure of the indium - tin layer carried by tail 42 and the indium - tin layer carried by extender 82 . adhesive strips 90 and 92 cooperate to aid in maintenance of the seal . a suitable detection circuit is disclosed in fig4 . a single switch shown as indicated at 50 corresponds to one of the 12 switching areas shown in the preferred embodiment . clock 52 sends out square wave pulses at a frequency of 2 khz through inverter 54 and resistance 56 into one side of switch 50 and simply through resistance 58 into the other . so long as the switch 50 is not actuated , so that both air capacitor 60 and polyester capacitor 62 are in the circuit , current flows through inverter 64 and transmission gate 66 are insufficient to transmit signals past rc networks 68 and 70 . when the air capacitor 60 is taken out of the circuit by pressing the appropriate area , signals do pass rc networks 68 and 70 , providing output signals at transmission gates 72 and 74 , the former providing information , in the preferred embodiment , of the x position of the switch pressed , and transmisson gate 74 providing similar information as to the y position . in operation , a pad 12 is pushed downwardly by flexing flexible layer 10 , which carries it , until pad 12 engages a strip 30 . ( the amount of force required to do this may be regulated partially by the spacing of epoxy grid lines 20 ; the more closely spaced are the grid bars 20 , the more difficult is it to push down layer 10 and pad 12 between them to engage strip 30 .) this in effect eliminates one of two capacitors in series ( the air capacitor 60 ), leaving the polyester capacitor , causing the capacitance of the circuit through this contact made to increase enormously . in the preferred embodiment just described the capacitance increases from 30 picofarads to 10 nanofarads -- i . e ., over three hundred times . other embodiments within the invention will occur to those skilled in the art . for example only , i mention a few . for the polyester layer producing the large capacitance could be substituted , for example , a deposited layer of tantalum pentoxide , which has a dielectric constant many times that of polyester . instead of insulating epoxy , a diecut polyester spacer could be used . conductor areas could be made by printing or etching . the polyester capacitor strip could be folded on itself to produce increased capacitance . instead of being constructed in the x - y matrix disclosed the device could be a common ground one , with a separate lead coming off each conductive pad ; here the other lead to all the pads might desirably be a single layer capacitor spacer ( as opposed to the three strips shown in the embodiment described ). the entire device could be made transparent , so that it might be mounted on the face of a crt . the substrate of the device could be made rigid . in another embodiment , the capacitor spacing layer is a single sheet substantially the size of the overall device and located in it below a layer carrying on it a plurality of x - row pads and beneath it a layer of y - column pads , with spacers between the central layer and each of the other two . the detection circuit disclosed herein is the invention of james p . walber . the grid system described herein is the joint invention of dr . brian e . aufderheide and the undersigned . nor was the conception , broadly , of a tail extender , mine .