Classifications

• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03K—PULSE TECHNIQUE
  • H03K17/00—Electronic switching or gating, i.e. not by contact-making and –breaking
  • H03K17/94—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the way in which the control signals are generated
  • H03K17/941—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the way in which the control signals are generated using an optical detector
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03K—PULSE TECHNIQUE
  • H03K17/00—Electronic switching or gating, i.e. not by contact-making and –breaking
  • H03K17/94—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the way in which the control signals are generated
  • H03K17/96—Touch switches
  • H03K17/9627—Optical touch switches
  • H03K17/9629—Optical touch switches using a plurality of detectors, e.g. keyboard
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03K—PULSE TECHNIQUE
  • H03K17/00—Electronic switching or gating, i.e. not by contact-making and –breaking
  • H03K17/94—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the way in which the control signals are generated
  • H03K17/96—Touch switches
  • H03K17/9627—Optical touch switches
  • H03K17/9631—Optical touch switches using a light source as part of the switch
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03K—PULSE TECHNIQUE
  • H03K2217/00—Indexing scheme related to electronic switching or gating, i.e. not by contact-making or -breaking covered by H03K17/00
  • H03K2217/94—Indexing scheme related to electronic switching or gating, i.e. not by contact-making or -breaking covered by H03K17/00 characterised by the way in which the control signal is generated
  • H03K2217/9401—Calibration techniques
  • H03K2217/94026—Automatic threshold calibration; e.g. threshold automatically adapts to ambient conditions or follows variation of input

Definitions

• 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.
• 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.
• the transmitter is arranged so that no optical transmission can reach the receiver except via reflection from the object.
• a shield between itself and the transmitter.
• a shield may take the form of a sleeve for example of plastics or rubber material - preferably black in colour.
• the shield may be a moulding which additionally positively aligns the receiver with respect to the transparent plate.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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 may be of glass.
• 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.
• 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.
• the switch body incorporates a plurality of transmitters and corresponding receivers, arranged in respective channels, whereby the switch may be used as a keyboard.
• 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.
• 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.
• the transmitter has a central axis arranged at a shallow angle to a normal to the transparent plate.
• 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.
• 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.
• 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.
• 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.
• Figure 7 is a circuit diagram of a splitter circuit of the diagram of Figure 6.
• 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.
• 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.
• 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.
• the diodes 7 are all driven by a modulator 10 at a suitable frequency typically between 5 and 100 KHz.
• a modulator 10 typically between 5 and 100 KHz.
• 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.
• the corresponding comparator 15 will give an output, the components 11,12,13,14 & 15 being repeated for each key.
• one of the comparators gives an output, it is passed via an interface 16 to and controls a microcomputer (not shown) .
• the second embodiment 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.
• 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.
• FIG 4 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.
• 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.
• 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.
• 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
• 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.
• 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
• 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 may typically be 5 volts when quiescent. It is also passed on line 120 via a normally ON analogue switch
• 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.
• 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.
• 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 detects by subtracting the two ' signals or arranging the unwanted reflection signals to cancel out each other.
• the switches may be operated by objects other than fingers.

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• Electronic Switches (AREA)
• Switches Operated By Changes In Physical Conditions (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

ID=10567129

Family Applications (1)

Country Status (3)

Families Citing this family (14)

Family Cites Families (7)

• 1984
  • 1984-09-22 GB GB848424023A patent/GB8424023D0/en active Pending
• 1985
  • 1985-09-20 EP EP19850904837 patent/EP0227677A1/de not_active Withdrawn
  • 1985-09-20 WO PCT/GB1985/000434 patent/WO1986001953A1/en unknown
  • 1985-09-20 GB GB08706278A patent/GB2190488A/en not_active Withdrawn

Non-Patent Citations (1)

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