GB2080536A

GB2080536A - Touch Switch Device

Info

Publication number: GB2080536A
Application number: GB8022654A
Authority: GB
Original assignee: FAFF PETER
Current assignee: FAFF PETER
Priority date: 1980-07-10
Filing date: 1980-07-10
Publication date: 1982-02-03

Abstract

A sensor unit, for a touch switch, is operable by simple contacting of a conductive element (2) by the hand for modification of the state of a control circuit by capacitative effect. A touch plate structure has first and second elements (3), (4), for placing for example at one face of a panel such as a door or window, and a third element (2) for placing at the opposite face of the panel. Touching of the third element (2) with the hand effectively earths it and causes a change of state of a switching means connected to the second element (4), as a result of change of A.C. signal transmitted from the first (3) to the third element (2), and from the third (2) to the second element (4). In a preferred embodiment, the A.C. signal is at about 15 KHz and means are included for amplifying the signal received by the second element (4) such that high sensitivity is available to permit the third element (2) to be spaced from the first and second elements (3), (4) by a relatively wide dielectric gap. <IMAGE>

Description

SPECIFICATION A Touch Switch Device This invention relates to a touch switch device operable by simple contacting of a conductive element by the hand for modification of the state of a control circuit by a capacitative effect, as distinct from relative movement of electrical contacts.

It is known to provide such a touch switch in which the separation (gap) of the members forming the elements of the capacity unit is relatively small, say of the order of 2 or 3 millimetres.

It is a first object of the invention to provide an improved construction of touch switch control circuit in which the separation of the capacity unit members may be greatly enlarged, to the extent that the respective members may be utilised under conditions of relative spacing not hitherto envisaged and such that those members may be situated at opposite faces of structural parts of buildings such as doors, windows and especially double-glazing.

It is a second object of the invention to provide a new construction of door touch switch useful for example for the operation of an electrical function such as a door chime.

A third object of the invention is to provide an improved door chime assembly which does not require the positioning of any item through the thickness of the door, and which is thus particularly adapted for use on glass doors and especially double-glazed doors.

A fourth object of the invention is to provide in conjunction with a door touch switch, an improved sensor unit adapted to control a random tone generator.

According to the present invention a sensor unit for a touch switch comprises, in combination (i) a touch plate structure having two elements separated by dielectric from a third element, (ii) an oscillator for feeding a signal to a first of the two elements of the touch plate structure, and (iii) a sensor unit having a capacitance normally kept charged by the rectified amplified A.C. signal transferred from the third to the second of the two elements of the touch plate structure, and a circuit adapted to change its state upon discharge of the capacitance, the sensitivity of the sensor unit being made such that the first and second elements may be spaced from the third element by a gap of the order of up to, say, three centimetres.With such an arrangement the oscillator, which may operate for example at about 1 5 KHz. produces a signal which passes from the first element of the touch plate to the third element, and again from the third element to the second element, on the assumption that the third element is not effectively earthed. The rectified signal keeps the capacitance charged. If the third element is touched by the hand, the mass of the body is such that the third element becomes momentarily effectively earthed, and passage of signal to the second element falls largely or entirely, with the result that the capacitance is no longer kept charged and the following circuit changes its state to provide a switching signal.

In a preferred form, there is provided a circuit arrangement to ensure that only a single switching signal will be produced at each time of touching of the touch plate, rather than a train of switching signals, e.g. so that only a single operation of a door chime will occur at each time of touching the touch plate.

The output signal of the sensor unit may conveniently be a single negative-going pulse which may be arranged to actuate a relay for operation of a 'conventional bell or chime, or may be fed to a random tone generator, or other circuit as fully set out in the drawings referred to herein.

In order that the nature of the invention may be readily ascertained, an embodiment of door "chime" incorporating the various aspects of the invention is hereinafter particularly described with reference to the figures of the accompanying drawings, wherein: Figure 1 is a section through part of a pane of glass, forming part of a door or window, on which is mounted a touch switch for operation of a chime or the like (not shown); Figure 2 is an elevation of that face of the sensor unit of the touch switch which is presented tuwards the glass; Figure 3 is a circuit diagram tQ show the oscillator, touch plate and sensor unit, and Figure 4 is a circuit diagram to show a random tone generatoradapted to be actuated by the output from the sensor unit.

Referring to Figure 1, a pane of glass 1 has mounted on a first face a touch plate element 2 which constitutes the "third" elemenfreferred to herein and is intended for contact with the hand by the user. The element may conveniently be a sheet of aluminium foil which is self-adhesive to the glass. On the other face of the glass 1 there are secured two smaller elements 3 and 4 which constitute the "first" and "second" elements referred to herein. These comprise two foil areas on one side of a double sided printed circuit board (5) and are connected to the other side by thruboard connections.

Referring to Figure 2, it will be seen that the elements 3 and 4 are rectangular, and noted that the shape and area of the element 2 is such as to cover the combined elements 3 and 4.

The whole of the sensor circuit (see Fig. 3) is provided in the form of an encapsulated circuit represented by item 6 secured to the outer face of the mounting board 5. Leads 7 are taken from the circuit 6 for current supply, output signal etc. Due to the relatively high sensitivity of the device, the external element may be separated from the elements 3, 4 by the comparatively thick glass pane 1, or even by two panes of glass with an intervening airgap as found in double glazing. A control is also provided to vary the sensitivity of the circuit. There is accordingly no need to drill holes in the glass pane or panes for wiring, and the external touch plate element 2 may be simply a sheet of self-adhesive aluminium foil stuck onto the outer face of the glass, and is thus cheap, waterproof, and vandal proof.

Referring now to Figure 4 there is shown, by way of example, a circuit diagram of a random tone generator which would preferably be situated at some convenient location isolated from the door or window pane but connected by flexible leads to the sensor unit. The negativegoing single pulse output signal of the sensor unit is fed in at the bottom left of this figure, and a loud-speaker unit at the top right of this figure provides the tone output for a predetermined short period at each time of actuation of the touch plate.

Claims

1. A sensor unit, for a touch switch, comprising in combination: (i) a touch plate structure having first and second elements separated by dielectric from a third element, (ii) means for feeding an A.C. signal to said first element of the touch plate structure, for transfer from the first element through the dielectric material to the third element, and for transfer from the third elernent through the dielectric material to the second element so long as the third element is not effectively earther, and (iii) a switching means connected to the second element and responsive to change of signal amplitude received by the second element, to produce a switching signal.

2. A sensor unit, as claimed in claim 1, wherein the means for feeding an A.C. signal is an oscillator operative at about 1 50 KHz.

3. A sensor unit, as claimed in either of claims 1 and 2, wherein the switching means comprises means for amplifying the signal received by the second element, means for rectifying the output of the amplifying means, a capacitance connected to the rectifying means and normally kept in charged state by the rectified output, and a circuit connected to the capacitor and adapted to change its stage upon discharge of the capacitance.

4. A sensor unit, as claimed in any one of the preceding claims, wherein the switching means includes circuit means adapted to ensure that only a single switching signal is produced at each time of change of signal amplitude received by the second element.

5. A sensor unit, as claimed in any one of the a preceding claims, wherein the switchlng signal is a negative-going pulse.

6. A sensor unit, as claimed in any one of the preceding claims, including a control for varying sensitivity.

7. A sensor unit as claimed in any one of the preceding claims wherein the first and second elements are conductive areas on one face of a double-sided printed circuit board, the other face having the remainder of the electronic circuitry of the sensor unit encapsulated thereon.

8. In combination, a sensor unit as claimed in any one of claims 1 to 7 and a relay connected to the switching means and adapted to operate an audible warning device.

9. In combination, a sensor unit as claimed in any one of claims 1 to 7 and a random tone generator connected to the switching means and adapted to feed an audio transducer.

10. A sensor unit, for a touch switch, substantially as described herein with reference to the accompanying drawings.

11. A touch switch including a sensor unit substantially as described herein with reference to the accompanying drawings.