IL43873A - Touch actuated electronic switch - Google Patents

Abstract

1462777 Touch responsive switching systems MAGIC DOT Inc 3 Dec 1973 [12 Jan 1973] 55874/73 Heading G1N In a touch operated switch the touch plate 12 is connected to one input 26 of a differential amplifier 78 to both inputs 24, 26 of which are also supplied an alternating common mode voltage from source 22 and the output of which is coupled to an integrator 16. The amplifier 78 is provided with a capacitor 82 to provide a shunt at the alternating frequency of the common mode voltage for the amplifier output. Initially when touch plate 12 is not touched the amplifier 78 is balanced and the circuit is arranged so that the voltage at 140 is at the supply voltage. Transistor 168 of amplifier 165 is biased off and there is no voltage across integrating capacitor 16. Amplifier 18 including Darlington pair 184, 186 is non-conducting and there is a high impedance across terminals 204, 84. When the touch plate is touched by an operator current flows from source 22 to earth through the capacitance of the operator's body resulting in amplifier 78 being unbalanced. When the output of amplifier 78 changes state 140 is at earth potential so that transistor 168 is turned on and capacitor 16 charged. Amplifier 18 becomes conducting and the impedance across terminals 204, 84 changes to a low value. The lead 30 to the touch plate is twisted in a pair with conductor 28 to obtain a better noise suppression. By appropriate modification of the circuit the potentials at 140 may be opposite to those described above. In a modification, Fig. 2 (not shown) the touch plate 12 is connected to terminal 24 and a capacitor of value equivalent to that of an operator is coupled between input terminal 26 and ground. In this arrangement the differential amplifier is unbalanced normally but becomes balanced when the operator touches the touch plate. [GB1462777A]

Claims (1)

1. CLAIMS 1. A touch actuated electronic switch, comprising in combination: differential amplifier means including first signal input means and second signal input means for receiving providing an e ectrical connection between the: integrating means and the input means of the additional amplifier means. : 4. The touc actuated electronic switch of any of Claims 1*3 wherein the means for providing an electrical connection between the receiving means and the differentlal amplifier includes impedance means connected to the first signal inpu means and impedance means connected to the second Signal input 5. The touch actuated electronic switch of any of ^ Claims 1-4 wherein the means for providing an electrical connection between the touch surface and an input to the differential amplifier means comprises a twisted pair of wires with one wire connected to one signal input means of the differential amplifier means and the second wire connected to the remaining signal input means of the differential amplifier means for better providing noise immunity between the touch surface and the differential amplifier means. ^ 6. ' / A' single touch actuated electronic switch, comprising combinationί different al sensing means including first signal input means and second signal input means for receiving differential signals and including signal output means for providing an output signal related to the input signals receive a touch surface; means for providing an electrical connection between the touch surface and an input means to the differentia sensing means; means for receiving an alternating frequency voltage; means for provlding_an electrical^connection between t receiving means and the differential sensing means to provide a substantially equal common mode alternating frequency voltage to the input means of the sensing means. 7. The touch actuated electronic switch of claim 6, including integrating means and means for providing an electri connection between the output means of the differential sensing means and the Integrating means, 8. The touch actuated electronic switch of Claims 6 or 7, f m e ei me 43873/2 ^ 10. The touch actuated electronic switch of any of Claims 6-9, wherein the means for providing an electrical connection between th touch sur ace and an input to the differential amplifier means comprises a twisted pair of wires with one wire connected to one signal input means of the differential amplifier means and the second wire connected to the remaining signal input means of the differential amplifier means for better providing noise immunity between the touch surface and th differential amplifier.means. 11. The touch actuated electronic switch of any of Claims 6-?10 , wherein the means for providing an electrical connection between the receiving means and the differential amplifier means includes impedance means connected to the first signal input means and impedance means connected to the second signal input means. 12. The touch actuated electronic switch of any of Claims 6-11, wherei the means for providing an electrical connection between the touch surface and in input to the differential sensing means comprises a twisted pair of wires with one wire connected to one signal input means of the means for providing an electrical connection between the integrating means and the input mean of the additional amplifier means. 43873/2 wh n t e ns 43873/2 28. The touch actuated electronic switch of Claim 27 ',. wherei the impedance for causing the diff rential sensing means to assume a preferred output state in the absenc of input signals comprises a capacitor connected to a signal input means of the sensing means· For the Applicants PARTNERS SC:CB