WO1986001953A1

WO1986001953A1 - Switch

Info

Publication number: WO1986001953A1
Application number: PCT/GB1985/000434
Authority: WO
Inventors: Michael John Nobbs; Raymond Arthur Cummins
Original assignee: Michael John Nobbs; Raymond Arthur Cummins
Priority date: 1984-09-22
Filing date: 1985-09-20
Publication date: 1986-03-27
Also published as: GB8706278D0; GB2190488A; EP0227677A1; GB8424023D0

Abstract

A switch for operation by a finger F at a side of a glass plate (106) remote from the switch has an infra red emitting diode (104) and a phototransistor (107), which are mounted close to each other and the glass plate. A moulding (109) prevents transmission directly from the diode to the phototransistor whereby circuitry provided can detect presence of the finger according to whether the finger reflects transmission from the diode to the phototransistor or not. In one embodiment, the circuitry includes means (115) for sampling and holding the received signal, means (117) for amplifying it by a certain percentage and means (116) for comparing the held amplified signal with the non-amplified signal.

Description

SWITCH

Background of the Invention

The present invention relates to an electric switch. Touch switches exist. These operate for instance by a finger making contact with surface contacts in the switch or by a finger changing capacity of a switch electrode to earth on the finger being touched on the switch. Such switches do not operate when a plate of glass is interposed between the operating finger and the switch.

The object of this invention is to provide a switch which can be mounted on one side of a plate of glass and which can be operated by a finger or the like, being aligned on the other side of the glass with the switch. The Invention

According to the invention there -is provided a switch for operation by an object at a side of a transparent plate separate from the switch comprising:- an optical transmitter arranged for transmission of light through the transparent plate; an optical receiver arranged to receive light reflected back through the transparent plate from the object for operating the switch; means for mounting the optical transmitter and the optical receiver in close proximity with each other and with the transparent ^'plate; means for preventing optical transmission without reflection from the transmitter to the receiver; and circuitry for detecting reception by the receiver of optical transmission from the transmitter which has been reflected by the object.

In one embodiment, the transmitter is arranged so that no optical transmission can reach the receiver except via reflection from the object. Normally the receiver will be protected with a shield between itself and the transmitter. Such a shield may take the form of a sleeve for example of plastics or rubber material - preferably black in colour. Alternatively, the shield may be a moulding which additionally positively aligns the receiver with respect to the transparent plate.

It is conceivable that the shield may be dispensed with and protection against direct transmission from the trans¬ mitter to the receiver be provided by arranging the receiver in intimate contact with the transparent plate whereby light reflected from the object traverses no substantial air gap after leaving the last air/plate interface prior to reaching the receiver, such an air gap if present permitting reflection from the transmitter off the plate directly to the receiver.

It is conceivable that the transmitter also may be in intimate contact with the plate, but it is preferably spaced from the plate to avoid leakage of light direct, without any reflection, to the detecting head of the receiver.

Preferably the shield is provided and the receiver is in intimate contact with the transparent plate. Both the transmitter and the receiver may be accommodated in the shield.

Preferably the transmitter has a central axis arranged substantially normal to the transparent plate.

The transmitter and receiver may be mounted in a switch body which incorporates an integral transparent plate distinct from tKe transparent plate separating the switch on one side from the operating object on the other side. In this case, the receiver will normally touch the integral plate and the integral plate is arranged to be held in intimate contact with the separating plate with no air gap therebetween. Alternatively where no integral plate is provided the receiver may be arranged to touch the separating plate. The separating plate will normally be a glass plate such as a shop window glass, in which case the switch will be supplied separately from the separating plate, either with or without an integral plate. However it is conceivable that the switch may be supplied ready assembled to the separating plate.

The integral plate, where provided, may be of glass. Alternatively it, and possibly the separating plate, may be of transparent plastics material. The latter, especially in the case of the integral plate may be of flexible material to improve the intimacy of the contact with the receiver and the separating plate. As an alternative to the components touching, air gap filling mediums such as transparent adhesives may be provided to provide the intimate, air gapless, contact between the components.

The switch body may be secured by adhesive means, such as double sided tape, to the barrier plate. Again the switch body may be resilient to enhance the intimate contact. Alternatively or additionally the receiver may be resilient-, ly mounted in the body.

Preferably the switch body incorporates a plurality of transmitters and corresponding receivers, arranged in respective channels, whereby the switch may be used as a keyboard. In this keyboard arrangement, the invention finds particular use in after hours enquiries applications. In such, with the switch mounted inside a shop front window a customer can make enquiries of a computer d^' splaying information via a visual display unit.

The provision of a plurality of channels enables compariso of the received signal from an individual channel with the average of the received signal from the outer channels to establish an "object present" signal. Lamps may be included in the keyboard to indicate which individual key has been operated.

In another embodiment, the receiver is arranged to receive a small amount of transmission from the transmitter via reflection from the separating plate (or the integral plate though this will not normally be provided in this embodiment) . This small permanently reflected signal allows the establishment of a reference against which the presently received signal can be compared. The reference is not dependent upon another channel, whereby this embodiment can be in the form of a single channel switch.

Preferably the transmitter has a central axis arranged at a shallow angle to a normal to the transparent plate.

Preferably the circuitry for the or each channel has means for sampling, and storing the received signal and means for comparing the sampled and stored signal with the presently received signal and for giving an output indicative of an object being present at the channel's transmitter and receiver when the comparator detects a difference between the sampled and stored signal and the presently received signal.

Preferably the comparing means comprises means for amplifying the sampled signal by a certain percentage and a comparator for comparing the presently received signal with the amplified signal and giving an object present signal when the presently received signal exceeds the sampled signal.

Conveniently, the sampling and storing means includes a capacitor connected to the input of the amplifying means for preventing the signal at this input from changing rapidly; and the sampling and storing means includes a switch for isolating the capacitor from the received signal when the object present signal is present from the comparator. The Drawings

To help understanding of the invention two specific embodiments thereof will now be described by way of example and with reference to the accompanying drawings, in which:-

Figure 1 is a front view of a switch of the invention in a keyboard arrangement;

Figure 2 is a scrap cross-sectional view on the line II-II in Figure 1; Figure 3 is a block diagram of a circuit detecting operation of the switch of Figure 1;

Figure 4 is a front view of another switch of the invention in a keyboard arrangement; Figure 5 is a scrap cross-sectional view similar to Figure 2 of the switch of Figure 4;

Figure 6 is a block diagram of a circuit detecting operation of the switch of Figure 4; and

Figure 7 is a circuit diagram of a splitter circuit of the diagram of Figure 6. First Embodiment

Referring first to Figure 1, the switch or keyboard has a box 1 with a plurality of front apertures 2 defining the individual keys, both as to their position and their function in that they are shaped as arrows to indicate cursor move¬ ments when the keyboard is connected to a micro-computer. The box 1 has end brackets 3 carrying double sided tape adhesive 4 for securing the keyboard to a separating plate 5 of shop front glass,^' with integral plates 6, see Figure 2, of individual key switches in intimate contact with the separating plate 5.

At each aperture 2 for each individual key switch, the integral plate 6 curves out through the aperture for intimate contact with the separating plate 5. An infra red emitting diode 7 is positioned slightly spaced -from the inside surface of the integral plate 6, with its central axis 7' normal to the integral plate 6 and the separating plate 5. Adjacent each diode 7 at each aperture 2 and in intimate contact with the inside surface of the integral plate 6 is a phototransistor 8 which is particularly sensitive to infra red light. Preferably the diode emits infra red light having a 940nm wavelength. However other wavelengths, even as far as the visible spectrum may be used. Each diode 7 and phototransistor 8 is mounted on a printed circuit board PCB and housed in a moulded plastics shield 9, shielding the phototransistor 8 from^' receiving light from the diode 7 other than by reflection from a finger F.

Referring now to Figure 3, the diodes 7 are all driven by a modulator 10 at a suitable frequency typically between 5 and 100 KHz. When the finger F or other object is present in the region of an individual aperture at the outside, see Figure 2 , of the separating plate 5, light from the individual diode 7 is reflected back from the finger to the individual phototransistor 8. Its output level then increases. It will have already been giving a background level output, from ambient light which may cause a DC output and a mains frequency, 50 Hz, output from for instance shop lighting. The output is passed via a DC block 11 and an amplifier 12 to a band pass filter 13, which passes only the components of the output from the phototransistor 8 resulting from light transmitted to it from the modulated diode 7 via the finger. The passed output signal is rectified in a rectifier 14 and fed to one input of a comparator 15. The other input of the comparator 15 receives the mean rectified signal from all the individual switches and hence corres¬ ponds substantially with the output in the absence of the finger from the phototransistors in the modulation frequency band. In the absence of the finger F, the two signals at the comparator will be substantially equal, and the comparator will give no input. When the finger is present at any key the corresponding comparator 15 will give an output, the components 11,12,13,14 & 15 being repeated for each key. When one of the comparators gives an output, it is passed via an interface 16 to and controls a microcomputer (not shown) .

In a variant of the above circuit, individual modulation frequencies can be employed for each key. This enables the keys to be placed closer together since stray light from one key will not operate the adjacent key's detection circuitry.- Second Embodiment

The second embodiment, described with reference to Figures 4 to 7, employs circuitry for detecting the presence of a finger at the switch which is self-contained - not requiring signals from other channels for establishing the "finger absent" or quiescent level at- a comparator. Accordingly this embodiment may be configured as a simple ON-OFF switch though a plurality of channels are provided in the switch of Figure 4. For establishing the quiescent signal with which a signal obtained in the presence of a finger is compared, light reflected from a transmitting/ light emitting diode to a receiving phototransistor in the absence of a finger is utilized, facilitating simplification of the arrangement of these components. Referring now to Figure 4, this shows the arrangement in a box 101 of four switch apertures 102, controlling up, right, down and left cursor movements in a preferred "joy¬ stick" configuration. Additionally, a further single switch aperture 103 is provided. The box may be mounted by means similar to those described for the box 1. At each aperture 102,103, in the front panel 105 of the box 101 an infra red emitting diode 104 is arranged with a central axis 104' at a shallow angle of between 10° and 30°, preferably between 15° and 25°, to a normal to the front plate whereby radiation from the diode 104 is reflected from a separating plate 106, to which the box 101 is secured, back towards a phototransistor 107 along a path P in the presence or absence of a finger F. The diode 104 is housed in a bore 108 of a moulded mount 109 to prevent non-reflected trans- mission to the phototransistor 107. The latter is of the type having a sensitive area in a flat side surface and is supported on a seat 110 in the mount 109. In the presence of the finger F considerably more radiation than that taking the path P arrives at the phototransistor 107 after reflection from the finger F, thereby causing the signal obtained from the phototransistor to be increased.

Referring now to Figure 6 this signal passes through an amplifier 111, a DC block 112, a band- pass filter 113 and a rectifier 114 in a manner similar to that of Figure 3. The 5 output of the rectifier 114 is passed to a splitter circuit

115 which passes the presently occurring signal straight on to a comparator 116. The splitter circuit also passes the signal immediately preceding a marked increase in the signal from rectifier 114 as in the presence of the finger F to an 0 amplifier 117 which adds 10% to the signal and feeds the other input of the comparator 116. Thus the comparator 116 gives a "finger present" signal to a driver circuit 118 for a computer (not shown) when the radiation following the path P increases by more than 10%. This is a significant

•_j_5 advantage since deviations of less than 10% over a number of seconds, as can be caused during system switch on or deviations of more than 10% but occurring over long periods of time as the characteristics of the diode 104 and the phototransistor 107 change over their life,are not detected.

20 The splitter circuit 115 will be described in more detail with reference to Figure 7. The output signal from the rectifier 114 is passed on line 119 to the comparator

116 and may typically be 5 volts when quiescent. It is also passed on line 120 via a normally ON analogue switch

25 121 through a resistor 122 to the amplifier 117 whose feed back resistor 12^'3 is of such value that the amplifier gives an output signal on line 124 of 110% of its input signal. This 110% signal, typically 5.5 volts is passed to the comparator 116. Whilst the signal on line 119 remains

30 below the signal on line 124, the comparator provides no

"finger present" signal on its output line 125 to the driver . circuit 118.

In the presence of a finger at the switch aperture for . the channel concerned, the signal on line 119 increases .

35 rapidly, typically to 7 volts. However the line 126 connecting the resistor 122 to the amplifier 117 is connected to a capacitor 127 whose other terminal is earthed in a "sample and hold" circuit. Thus the voltage on the line 126 can change only relatively slowly and in practice much more slowly than the signal on line 119 changes. Thus when a finger is placed at the switch aperture, the comparator 116 in comparing the newly increased signal on line 119 with the previous quiescent signal plus 10% changes condition to give a "finger present" signal on line 125. This is passed via line 128 to the analogue switch 121 which switches off.

Thereafter the capacitor 127 maintains its charge and the voltage on line 126 continues at its quiescent value, whereby the comparator continues to compare the line 119 signal with the previous quiescent + 10% signal. Once the finger is removed, the signal on line 119 drops below the signal on line 124 and the signal on line 125 reverts so that the switch 121 is switched off to return the splitter circuit to the original condition.

A further analogue switch 129 is provided in line 128. It is initially off until its capacitor 130 is charged up. This allows the capacitor 127 to charge up on initial switching on of the circuitry otherwise the signal on line 124 would never reach its value greater than the signal on line 119 and the comparator would permanently provide a "finger present" signal.

The invention is not intended to be restricted to the above described embodiments. For instance in the first embodiment where reflection from the transmitter to the receiver other than from the finger is troublesome, two receivers may be provided, one arranged to receive only the unwanted reflections and the other to receive both the wanted and unwanted reflections. The circuitry then detects by subtracting the two^' signals or arranging the unwanted reflection signals to cancel out each other. Of course the switches may be operated by objects other than fingers.

Claims

1. A switch for operation by an object at a side of a transparent plate separate from the switch comprising:- an optical transmitter (7,104) arranged for transmission of light through the transparent plate; an optical receiver (8,107) arranged to receive light reflected back through the transparent plate from the object for operating the switch; means (1,101) for mounting the optical transmitter and the optical receiver in close proximity with each- other and with the transparent plate; means (9,109) for preventing optical transmission without reflection from the transmitter to the receiver; ^and circuitry for detecting reception by the receiver of optical transmission from the transmitter which has been reflected by the object.

2. A switch as claimed in claim 1, wherein the transmitter and the receiver are arranged for optical transmission from the transmitter to be partially reflected by the transparent plate to the receiver, the transmitter having a central axis arranged at a shallow angle to a normal to the transparent plate.

3. A switch as claimed in claim 1 wherein the trans¬ mitter is arranged for negligible optical transmission from the transmitter to reach the receiver via reflection from transparent plate, the transmitter having a central axis arranged substantially normal to the transparent plate.

4. A switch as claimed in claim 3, wherein the receiver is arranged to contact the transparent plate.

5. A switch as claimed in claim 3, including an integral transparent plate, the central axis of the trans¬ mitter being arranged substantially normal to the integral plate.

6. A switch as claimed in claim 5, wherein the receiver is arranged to contact the integral plate.

7. A switch as claimed in any preceding claim, wherein the transparent plate is provided permanently mounted to the mounting means.

8. A switch as claimed in any preceding claim, wherein the circuitry includes a printed circuit board and the optical transmission preventing means comprises a moulding mounted on the printed circuit board and accommodating, the transmitter and the receiver.

9. A switch as claimed in any one of claims 1 to 7, optical transmission preventing means comprising a sleeve on the transmitter.

10. A switch as claimed in any preceding claim, including a plurality of transmitters and receivers arranged in a plurality of channels each having one transmitter and one receiver, the circuitry including means for averaging the signal received in the channels and, in each channel, means for comparing the signal received in the channel in question with the average of the signals received and for giving an output indicative of an object being present at the channel's transmitter and receiver when the comparator detects that the channel's received signal differs from the average of the received signals.

11. A switch as claimed in any one of claims 1 to 9, including a single or a plurality of channels each having one transmitter and one receiver, the circuitry for the or each channel having means for sampling and storing the received signal and means for comparing the sampled and stored signal with the presently received signal and for giving an output indicative of an object being present at the channel's transmitter and receiver when the comparator detects a difference between the sampled and stored signal and the presently received signal.

12. A switch as claimed in claim 11, wherein the comparing means comprises means for amplifying the sampled signal by a certain percentage and a comparator for comparing the presently received signal with the amplified signal and giving an object present signal when the presently received signal exceeds the sampled signal.

13. A switch as claimed in claim 12, wherein the sampling and storing means includes a capacitor connected to the input of the amplifying means for preventing the signal at this input from changing rapidly.

14. A switch as claimed in claim 13, wherein the sampling and storing means includes a switch for isolating the capacitor from the received signal when the object present signal is present from the comparator.

15. A switch as claimed in any one of claims 10 to 14, including in the or each channel:- means for modulating the transmitter; means for removing any DC component of the. received signal; and a band pass filter for filtering from the received signal any AC components of a frequency substantially different from the AC modulation frequency.