Patent Publication Number: US-2006012944-A1

Title: Mechanically operable electrical device

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a mechanically operable electrical device.  
      2. Description of the Related Art  
      Electrical switches comprising of a pair of electrodes which are brought into contact to complete a circuit are well known. A potential problem with some such switches is that repetitive use causes mechanical wear of the electrodes and consequent failure.  
      In addition, code reading devices are known such that when a coded card to be read is inserted, conductive patches of the card electrically connect selected electrodes of the device to complete electrical circuits. However, due to abrasion by the connecting electrodes, the conductive patches may become worn and lead to incorrect reading of the code.  
     BRIEF SUMMARY OF THE INVENTION  
      According to a first aspect of the present invention, there is provided a mechanically operable electrical device, comprising a transmitter electrode, a receiver electrode and a moveable conductive element, wherein: said device is configured such that said conductive element is moveable to a first position remote from said electrodes such that said transmitter electrode is capacitance coupled to said receiver electrode; and said conductive element is moveable to a second position closer to said electrodes such that said capacitance coupling is reduced.  
      According to a second aspect of the present invention, there is provided code reading apparatus, and a coded object having one or more conductive regions at defined locations to define a code, wherein said device comprises: a plurality of capacitor devices each having a transmitter electrode and a capacitance coupled receiver electrode; a signal generating device configured to supply a signal of a predetermined type to each said transmitter electrode; and a signal analysing means for analysing a received signal received by said receiving electrodes, wherein said code reading device is configured to receive said one or more conductive regions of said coded object such that the capacitance coupling between the electrodes of one or more corresponding capacitor devices is modified, whereby the signal received at one or more corresponding receiving electrodes is modified.  
      According to a third aspect of the present invention there is provide a document interpreting system comprising location detection means under which may be placed one or more documents and for detecting the location of pointing means directed at an area of a topmost document of the one or more documents, speech storage means for storing speech relating to different areas of said one or more documents, and speech reproduction means for reproducing speech stored in said speech storage means corresponding to the area of said topmost document to which said pointing means is directed, wherein said pointing means comprises electronic pointing means coupled to said document interpreting system and adapted in use to be directed at any arbitrary area of said topmost document, said location detecting means being arranged to detect electronically the location of said arbitrary area for causing speech stored in said speech storage means corresponding to the arbitrary area of said topmost document to which said pointing means is directed to be reproduced, wherein said location detecting means comprises a transparent or translucent membrane through which the electronic pointing means is directed at the arbitrary area of said topmost document.  
      Such a system enables, for example, a user to point to any part of a document which is being read and to obtain a spoken version of any text e.g. words, phrases, sentences, etc in the vicinity of a pointer or a spoken description of any picture in said area. It would also be possible for the spoken version or description to be in a foreign language thereby assisting foreign language learning. It is to be noted that the document being read may be in its original form and does not require any additional matter, e.g. bar codes for its interpretation.  
      An exemplary embodiment of the invention will now be described With reference being made to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       FIG. 1  shows an electrical appliance  101  embodying the present invention;  
       FIG. 2  shows an exploded perspective view of components of the linear array of button switches  101 ;  
       FIGS. 3A and 3B  show a front and rear view of the PCB  206  respectively;  
       FIGS. 4A and 4B  illustrates the operation of the button switch  102 ;  
       FIG. 5  shows a diagram of a circuit used to determine the status of the button switches  102  to  105 ;  
       FIG. 6  shows signals which illustrate the operation of the circuit of  FIG. 5 ;  
       FIG. 7  shows an exploded perspective view of components of the rotary switching device  106 ;  
       FIGS. 8A and 8B  show front and rear views respectively of the PCB  704 ;  
       FIG. 9  show an alternative rotary switching device  900 ;  
       FIG. 10  shows an electronic apparatus  1001  and a card  1002  used with the apparatus  1001 ;  
       FIG. 11  shows the code reader  1008  and the card  1002  of  FIG. 10 ;  
       FIGS. 12 and 13  show the facing surfaces of the printed circuit boards  1120  and  1121  respectively;  
       FIGS. 14A and 14B  show cross-sectional views of capacitor devices of card reader  1008  which illustrate their operation;  
       FIG. 15  shows a diagram of the electronic circuitry  1501  of card reader  1008 ; and  
       FIG. 16  shows an alternative card reading arrangement for the toy  1001 .  
       FIG. 17  shows a diagrammatic representation of a document interpretation system in accordance with the present invention;  
       FIG. 18  depicts in greater detail the appearance of a topmost card shown in  FIG. 17  which is useful in explaining the operation of the system of  FIG. 17 ;  
       FIG. 19  shows a block schematic diagram of the document interpretation system of  FIG. 17 ; and  
       FIG. 20  is a flow diagram relating to the document interpretation system of  FIGS. 17 and 19 . 
    
    
     WRITTEN DESCRIPTION OF THE BEST MODE FOR CARRYING OUT THE INVENTION  
       FIG. 1 .  
      An electrical appliance  101  embodying the present invention is shown in  FIG. 1 . The appliance  100  has a linear array  101  of four manually operable push button switches  102 ,  103 ,  104  and  105  which allow a user to select functions of the appliance. In addition, the appliance  101  has a rotary switching device  106  which may be manually rotated to one of five positions to allow a further optional selection to be made.  
     
       FIG. 2 
     
      An exploded perspective view of components of the linear array of button switches  101  is shown in  FIG. 2 . Each of the four switches  102  to  105  in the array comprises of a button portion,  202 ,  203 ,  204  and  205  respectively. The button portions are configured to be depressed by finger pressure, and they are subject to spring mechanisms (not shown) which return them to their original positions after being pressed and released. The buttons may also be subject to a mechanism which maintains their position after depression, until they are re-pressed. Such mechanisms are known in the art.  
      The button portions  202  to  204  are manufactured from an electrically insulating material such as a plastics material. An electrically grounded (earthed) conductive element, made from a rectangular piece of metal, is rigidly attached to the rear side of each button portion. Thus, for example, conductive portion  201  is rigidly attached to the rear surface of button portion  202 .  
      The linear array  101  of button switches also contains a printed circuit board (PCB)  206 , which defines a capacitor device  212 ,  213 ,  214 , and  215  for each of the button switches  102  to  105  respectively.  
      When the button portions are not depressed, the conductive portion  201  is located remotely from the corresponding capacitor device  212 . For example, it may be positioned ten millimetres away. Upon depression of the button portion, the conductive element  201  is relocated to a position relatively near to the capacitor device  212 , for example two millimetres away. The consequential electrical effects on said capacitor device are detected as will be described below.  
      The conductive element  201  is never brought into contact with electrodes of the capacitor device  212 . To ensure this contact does not take place, the conductive element and/or the electrodes of the capacitor device are covered with an insulating layer, for example, a plastic layer or coating. Alternatively, the movement of the button portion may be mechanically limited to ensure the conductive element cannot make contact upon the PCB.  
      In an alternative embodiment, the PCB  206  is replaced with a plastic membrane supporting conductive material, such as a conductive ink, defining the capacitance devices and the corresponding tracks providing electrical connections to said devices.  
      It should be understood that although switch array  101  has been described by way of example to have four button switches, other switch arrays embodying the present invention may be produced with more or less than four such switches. Thus, in the simplest case, the switch array comprises a single button switch.  
     
       FIGS. 3A and 3B 
     
      A front and rear view of the PCB  206  is provided by  FIGS. 3A and 3B  respectively.  
      The capacitor devices  212  to  215  each comprise of a transmitter electrode  302 ,  303 ,  304  and  305  respectively and a receiver electrode  312 ,  313 ,  314 ,  315  respectively. Each transmitter electrode takes the form of an open circular element which is concentric with a smaller circular element defining the corresponding receiver electrode. Tracks  322  to  325  on the front surface of the PCB provide individual electrical connection to corresponding transmitter electrodes  302  to  305  respectively. The receiving electrodes  312  to  315  are connected to a common track  301  on the rear of the PCB  206  via plated through holes in the PCB. One end of the track  301  terminates in a region  350  of the PCB which supports electronic circuitry for processing signals received by the receiving electrodes.  
      Hatched areas  351  and  352  on the front and rear of the PCB are electrically grounded. In additions conductive circular arcs  332  to  335  are arranged concentrically around the capacitor devices  212  to  215  respectively on the front surface of the PCB, and conductive circular arcs  342  to  345  are arranged concentrically around the receiving electrodes  312  to  315  respectively on the rear surface of the PCB. The arcs  342  to  345  and  332  to  335  are also electrically grounded.  
      The close proximity of the electrically grounded elements  342  to  345  and  332  to  335  ensures that spurious signals received at the receiving electrodes caused by external radiation are kept to within tolerable limits.  
       FIGS. 4A and 4B  The operation of the button switch  102  is illustrated in  FIGS. 4A and 4B .  
      The button switch  102  is shown in the non-pressed configuration in  FIG. 4A . Consequently, the gap between conductive element  201  and the capacitor device  212  is large compared to the relatively small gap of  FIG. 4B  where the switch is shown depressed.  
      During operation of the appliance  101 , a series of square electrical pulses are applied to the transmitter electrode  302  and the resulting signal received at receiving electrode  312  is analysed to determine whether the button switch  102  is depressed or not.  
      When the moveable conductive element  201  is remote from the device  212 , as shown in  FIG. 4A , the close proximity of the transmitter electrode  302  and the receiver electrode  312  provides sufficient capacitance coupling between said electrodes to allow the signal received at the receiver electrode to be detected. In contrast, when the moveable conductive element  201  is close to the device  212 , as shown in  FIG. 4B , the closeness of said conductive element reduces the capacitance coupling between the transmitter and receiver electrodes such that the received signal is significantly reduced in amplitude.  
      Example lines of electrical flux  401  and  402 , established during the application of the square pulse to the transmitter electrode  302 , are illustrated in  FIG. 4A and 4B  respectively. The flux lines  401  illustrate how an electric field is generated between the transmitter electrode  302  and receiver electrode  312 , when the button switch is not depressed. Whereas, when it is depressed, the close proximity of the conductive element  201  modifies the electric field such that the flux  402  between the transmitter electrode  302  and the conductive element  201  is increased and that between the transmitter electrode and receiving electrode  312  is correspondingly decreased.  
     
       FIG. 5 
     
      A diagram of a circuit used to determine the status of the button switches  102  to  105  is shown in  FIG. 5 . Each of the transmitter electrodes  302  to  305  is connected to a respective low impedance output port OP 1 , OP 2 , OP 3  and OP 4  of a micro-controller  501 . The micro-controller operates under instructions received from read only memory (ROM)  502 . The ROM  502  and the controller  501  may be part of a single application specific integrated circuit (ASIC). The micro-controller is also in communication with an additional memory device, in the form of an EPROM (erasable programmable read only memory)  503 , which may be a plug-in device allowing the operation of the micro-controller to be modified.  
      The receiving electrodes  312  to  315  of the capacitor devices  212  to  215  are all connected together to the input of analysing electronic circuitry  504 . The circuitry  504  comprises of an amplifier  505 , a bandpass filter  506  configured to filter the output of said amplifier, and a comparator  507 , which takes the output of said filter as its input. The output from the comparator is connected to an input port, IP 1 , of the micro-controller  501 .  
      The micro-controller  501  also has four output ports connected to drive circuitry  508  which generates drive signals in response to the output signals received from the micro-controller. The drive signals may energise actuators, heaters, lights etc. (not shown) in accordance with the type and function of the appliance  101 .  
     
       FIG. 6 
     
      Signals illustrating the operation of the circuit of  FIG. 5  are shown in  FIG. 6 .  
      As illustrated by graphs  601  to  604 , the controller  501  sequentially outputs, to the transmitter electrodes  302  to  305 , a square pulse  611  via output port OP 1 , a square pulse  612  via output port OP 2 , a square pulse  613  via output port OP 3 , and then a square pulse  614  via output port OP 4 . The sequence is then repeatedly repeated.  
      An example signal received at the receiving electrodes is shown in graph  605  after amplification and filtering by amplifier  505  and filter  506 . The square pulse applied to a transmitter electrode causes charge flow to and from the corresponding receiver electrode. Thus each square pulse generates a positive going pulse  615  to  618  and a negative going pulse  625  to  628  respectively at a receiver electrode.  
      The filtered signal received at the comparator  507  is compared with a threshold voltage. When the filtered signal is above the threshold voltage a high voltage is supplied to the micro-controller input, and when the filtered signal is below the threshold voltage a low (zero) voltage supplied to the micro-controller input. The graph  606  therefore illustrates the signal received at the input IP 1  from the comparator output.  
      In the present example, it has been assumed that only button switch  104  has been depressed. Consequently, positive going pulse  617  is below the threshold voltage while the other similar pulses  615 ,  616  and  618  are above it. In response, the comparator outputs square pulses  635 ,  636  and  638  while the comparator input is above the threshold voltage. It may be noted that, due to the finite rise time of the pulses  615 ,  616  and  618 , there is a delay between leading edge of the square pulses  611 ,  612  and  614  and the corresponding leading edge of the square pulses  635 ,  636  and  638 .  
      Following the output of a square pulse to one of the transmitter electrodes  302  to  305 , the micro-controller monitors the signal level at the input port IP 1  for a subsequent predefined period to determine whether the corresponding switch is depressed. For example, following the output of pulse  611  to switch  102 , the pulse  635  received at input port IP 1 , indicates to the micro-controller that the button switch  102  is not depressed. Whereas, following the output of pulse  613  the voltage on input port IP 1  remains low in the subsequent period and thus the micro-controller determines that the button switch  104  is depressed.  
     
       FIG. 7 
     
      An exploded perspective view of components of the rotary switching device  106  is shown in  FIG. 7 . A circular disc  701  is rigidly attached to the manually operable part of the rotary switching device such that it is rotatable about its central axis. The disc  701  has a base made from an insulating material with an electrically grounded conductive region  702  on one of its sides. The disc may thus be made in the manner of a printed circuit board. The conductive region  702  has a circular portion  703  located off-centre so that as the disc is rotated the portion  703  rotates about the disc&#39;s axis.  
      The side supporting the conductive region  702  is parallel to and closely spaced from a printed circuit board (PCB)  704  such that they share a common central axis. The PCB  704  contains five capacitor devices  711 ,  712 ,  713 ,  714  and  715 , and it is rigidly mounted within the appliance  101 . Consequently, as the disc  701  is rotated it rotates with respect to the PCB  704 , and the conductive portion  703  may be located over each of the five capacitor devices in turn. Preferably, the rotary switching device  106  contains a ratchet mechanism (not shown) so that, when the rotary switching device is rotated and released, the conductive portion  703  is brought to rest directly over a capacitor device.  
     
       FIG. 8 
     
      The PCB  704  is shown in greater detail in the front and rear views of  FIGS. 8A and 8B  respectively. Each of the five capacitor devices  711  to  715  have a similar structure to the capacitor devices on PCB  206 . Thus, capacitor device  711  has a small circular receiver electrode  812  surrounded by a transmitter electrode  802 . The transmitter electrode  802  is itself surrounded by an electrically grounded ground electrode  832 . The receiver electrodes of each capacitor device are all connected to a single track  801  via plated through holes in the PCB  704  and tracks  808  on its rear surface.  
      The rear surface of the PCB  704  has arc shaped ground electrodes  842 ,  843 ,  844 ,  845  and  846 , which are concentric with the capacitor devices  711  to  715  respectively.  
      As shown in  FIG. 8A , the transmitter electrodes such as electrode  802  form the greater part of a circle but a gap in the circle allows for an extended portion  809  of the ground electrodes, such as electrode  832 , to extend inwards towards the transmitter electrodes, such as  812 . The extended portion of the ground electrodes has a form and position which corresponds to a section of the tracks  808  on the rear side and thus provides additional shielding for the receiver electrodes.  
      The effect of the conductive region  703  (shown in  FIG. 7 ) on the capacitor devices  711  to  715  is the same as that of the conductive element  201  on capacitor device  212 . Thus, for example, when the conductive region  703  is rotated to a position which is remote from the capacitor device  71   1 , the capacitance coupling between the transmitter electrode  802  and the receiver electrode  812  is relatively high and allows a signal applied to the transmitter electrode to be received at the receiver electrode, and, when the conductive region is rotated to a position which is adjacent to said capacitor device, the capacitance coupling is reduced thereby reducing the amplitude of the received signal.  
      The rotary switching device  106  is incorporated into a similar circuit to that shown in  FIG. 5 , whereby a manual selection, made by rotating the conductive region  703  over a particular one of the capacitor devices  711  to  715 , is received.  
      In an alternative embodiment, a linear switch array, similar to that shown in  FIG. 2 , and a rotary switching device, similar to that shown in  FIG. 7 , share a single PCB. Thus the features of PBC  206  and PCB  704  are produced on a single PCB. Advantageously, the receiving electrodes of the switch array and the rotary switching device are connected together. Consequently, the same analysing electronic circuitry and micro-controller may be used to determine selections made at the switch array and the rotary switching device.  
     
       FIG. 9 
     
      An alternative rotary switching device  900  is shown in  FIG. 9 . The device  900  uses the same PCB  704  as device  106 . However, the rotatable disc  701  is replaced with an insulating board or sheet  901  which has a fixed location close to, and parallel to, the PCB  704 . For example, in this embodiment the PCB  704  and insulating sheet  901  are separated by 1 mm. The sheet  901  is made from a plastics material but in alternative embodiments is made from paper or card. The sheet  901  has five circular regions  902 ,  903 ,  904 ,  905 ,  906  on its side facing away from the PCB  704 , that are coated with a conducting material. The conductive material may be a conductive ink, such as a carbon ink, a silver ink or transparent conductive ink, or a conductive paint etc. The positions of the conductive regions  902  to  906  correspond to those of the five capacitor devices  711  to  715 , so that they overlay said capacitor devices.  
      In common with device  106 , device  900  has a rotatable handle  907  allowing manual selection by its rotation. A sprung electrically grounded electrode  908  is rigidly attached to the handle  907 . The ground electrode  908  has smooth connecting portion  909  which presses against the sheet  901  and which may be brought into contact with any one of the five conducting regions  902  to  906  by rotation of the handle  907 .  
      During operation, the capacitance coupling between the transmitter electrodes and receiver electrodes of each of the capacitor devices  711  to  715  may be reduced by rotating the ground electrode  908  to a position where it electrically grounds the corresponding conductive region  902  to  906  respectively.  
     
       FIG. 10 
     
      An electronic apparatus  1001  and a card  1002  used with the apparatus  1001  is shown in  FIG. 10 . In this instance, the electronic apparatus  1001  is an educational toy for a child.  
      To use the toy  1001  a card such as the card  1002  is inserted into a slot  1003  in said toy. When it is fully inserted, an image  1009  on the card is viewable through a transparent window  1010  in the upper face of the toy. The toy  1001  is provided with an internal spring loaded arm (not shown) which maintains the position of the card within the slot  1003  while it is being used.  
      After pressing an “ON” button  1004  a child is able to interact with the toy by indicating selected regions of the card  1002  using a stylus  1005 . This is achieved by receiving signals at an electrical receiver located in the stylus tip  1006  that are transmitted by a matrix of linear electrodes within the toy  1001 . Devices having such position detection means are known in the art.  
      The card  1002  is one of many cards which may be used in co-operation with the toy  1001 . Therefore, in order to operate correctly, the identity of the card  1002  must be provided to the toy  1001 . For this reason, the card  1002  has an identifying code  1007  arranged along an end portion of the card, and the toy  1001  has code reader  1008 . The code reader  1008  receives the end portion of an inserted card and identifies it from the identifying code  1007 .  
      The toy  1001  and card  1002  provide an example of the present invention. However, it should be understood that other portable objects supporting code defined by conductive elements may be used with code reading apparatus operating in accordance with the present invention. For example, the code reading apparatus may form part of a security device, such as a door lock, requiring the insertion of a card having a particular code in order to be activated.  
     
       FIG. 11 
     
      The code reader  1008  and the card  1002  of  FIG. 10  are shown in  FIG. 11 . The identifying code  1007  comprises of a series of conductive pads linearly arranged adjacent the edge  1101  of the card  1002 . Cards, such as card  1002 , have eight regions  1111  to  1118  inclusive, reserved for the possible application of a conductive pad. One or more of the conductive pads are applied to the card as conductive ink, or paint, during their production. Preferably, the card is subsequently laminated or coated with an insulating protective layer of, for example, a plastics material. (The protective layer  1400  is shown in  FIGS. 14A and 14B ). Thus the ink is protected from abrasion during use.  
      The cards, such as card  1002 , are individually identifiable by the presence or absence of conductive ink in each of the reserved regions  1111  to  1118 . For example, the pattern of the conductive pads may be considered to define a binary code number which identifies the card. For example, card  1002  has a conductive pad at regions  1111 ,  1113 ,  1116 ,  1117  and  1118  while regions  1112 ,  1114  and  1115  are devoid of conductive material. Thus, the conductive pads on card  1002  define the binary number 10100111, or 167 in base ten. In this way, using eight reserved regions and at least one conductive pad on each card, two hundred and fifty-five different cards may be identified. Alternatively, the cards may have different images on each of their faces so that they may be used either way up. In this case, each face of the card is identified by the identifying code  1007 . For example, if card  1002  were turned up side down and edge  1101  inserted into card reader  1008 , it would present the binary number 11100101 (two hundred and twenty-nine in base ten) to the card reader. i.e. the reverse of binary number 10100111. Thus, the two faces of the card are individually represented by a single identifying code.  
      The card reader  1008  comprises of two printed circuit boards  1120  and  1121  spaced apart by spacers  1122 . The gap between the PCB  1120  and the PCB  1121  is sufficiently wide to provide a loose fit for the end portion of cards, such as card  1002 . Typically, the gap is between two millimetres to five millimetres wide, and preferably it is two millimetres to three millimetres wide. The upper surface  1123  of PCB  1120  is conductive and electrically grounded to provide shielding for receiver electrodes located on it lower surface.  
      Transmitter electrodes are located on the upper surface of the PCB  1121 , and in combination with the receiver electrodes they define eight capacitor devices. Each capacitor device is positioned to receive one of the reserved regions  1111  to  1118  when a card is inserted. The reduction of conductance coupling in one of said capacitor devices, caused by the presence of a conductive pad, allows the card reader  1008  to determine its presence.  
     
       FIGS. 12 and 13 
     
      The facing surfaces of the printed circuit boards  1120  and  1121  are shown in  FIGS. 12 and 13  respectively. PCB  1120  has eight circular receiver electrodes  1201  to  1208  inclusive, which are linearly aligned and equally spaced. The PCB also supports signal analysing circuitry within a region  1210 , and all the receiving electrodes  1201  to  1208  are connected to said circuitry by a single conductive track  1209 . A grounded electrode  1211  (shown hatched) surrounds the receiving electrodes  1201  to  1208  and the conductive track  1209 , to provide further shielding for the receiving electrodes from electromagnetic noise.  
      As shown in  FIG. 13 , the upper surface of PCB  1121  has eight square shaped transmitter electrodes  1301  to  1308  inclusive. The eight transmitter electrodes are positioned such that they face the receiver electrodes  1201  to  1208  when the card reader  1123  is assembled. The transmitter electrodes are connected to terminals  1309  by plated through holes in their centres and conductive tracks on the reverse side of the PCB  1121  (illustrated by dashed lines  1310 ). A ground electrode  1311  surrounds the transmitter electrodes to provide further screening from electromagnetic noise.  
     
       FIG. 14A and 14B 
     
      The operation of capacitor devices of card reader  1008  is illustrated in the cross-sectional views of  FIGS. 14A and 14B .  FIG. 14A  shows the capacitor device defined by transmitting electrode  1302  and receiving electrode  1202  while reading card  1002 . In operation, a square pulse is applied to the transmitter electrode  1302  via a conductive track  1310 . In the absence of a conductive pad, the capacitance coupling between said electrodes remains relatively high, and consequently a relatively high signal is received at receiving electrode  1202 .  
       FIG. 14B  shows the capacitor device defined by transmitting electrode  1303  and receiving electrode  1203  while reading the same card,  1002 . In this instance, a conductive pad  1401  is present between said electrodes and, consequently, the capacitance coupling between them is reduced to a relatively low value. Therefore, when a square pulse is applied to the transmitter electrode  1303 , the presence of the conductive pad  1401  causes a relatively low signal to be received at receiving electrode  1203 .  
      Thus, by supplying a square pulse to each of the transmitting electrodes  1301  to  1308  in turn, and monitoring the amplitude of the pulse received at receiving electrodes, it is possible to determine the identifying code on the currently inserted card.  
     
       FIG. 15 
     
      A diagram of the electronic circuitry  1501  of card reader  1008  is shown in  FIG. 15 . Many of the components of circuit  1500  are the same as those of  FIG. 5  and operate in a similar manner. Thus, circuit  1500  has a micro-controller  1501 , in communication with a ROM  1502  and an EPROM  1503 . The EPROM  1503  may be configured to be replaceable, so that a particular EPROM which is designed for use with a particular set of cards may be used.  
      The micro-controller  1501  also receives digital signals from analysing electronic circuitry  1504 , itself comprising an amplifier  1505 , a bandpass filter  1506  configured to filter the output of said amplifier, and a comparator  1507 .  
      Eight output ports of the micro-controller  1501  are each connected to one of the transmitter electrodes  1301  to  1308 . The receiving electrode  1201  to  1208  are all connected to a single input of amplifier  1505 .  
      A ninth output port of micro-controller  1501  is connected to amplifier  1510  which provides signals to an audio speaker  1511 . Thus, in response to the identification of a card, signals relating to the card are supplied to the amplifier  1501  in accordance with data stored in EPROM  1503 .  
      The operation of the circuit  1500  is essentially the same as the circuit of  FIG. 5 . Thus, the micro-controller  1501  supplies a square pulse to each transmitter electrode  1301  to  1308  in turn, and in a following period, it monitors the signal received from comparator  1507 . Signals received by receiving electrodes are amplified by amplifier  1505  before being filtered by bandpass filter  1506 . The comparator  1507  determines whether the signal goes above a threshold value, and if so then a high output is supplied to microprocessor  1501 . Consequently, the micro-controller is able to determine the presence or absence of a conductive pad in each of the regions  1111  to  1118  of a card, and thus determine the identity of said card.  
     
       FIG. 16 
     
      An alternative card reading arrangement for the toy  1001  is illustrated by  FIG. 16 . A PCB  1601  has essentially the same structure as PCB  1120  except that it contains ten receiving electrodes, instead of eight. However, unlike the card reader  1008 , the corresponding transmitting electrodes  1603  are printed onto a flexible plastic membrane  1602 . As well as forming a part of the card reading arrangement, the plastic membrane supports the matrix of linear conductors which are used in co-operation with the stylus  1006  to provide an X-Y position sensing device.  
      Thus when a card is initially inserted, or the toy is first switched on, signals are supplied via the linear conductors to the transmitter electrodes to identify the card. Having identified the card the matrix is then used in the position sensing mode.  
      In a further alternative card reading arrangement for the toy  1001 , the PCB  1601  is replaced with an extended portion of plastic membrane  1602 . Receiving electrodes are printed onto the extended portion, and the membrane is folded such that each of the receiving electrodes is positioned opposite one of the transmitting electrodes  1603 . The membrane is folded such that a suitable gap is provided between the receiving electrodes and transmitting electrodes for receiving a card such as card  1002 . This alternative arrangement operates in the same manner as those of  FIG. 10 , or  FIG. 16 , but has the advantage of not requiring a PCB to provide the transmitting and receiving electrodes.  
      The receiving electrodes and transmitting electrodes are separated by a gap produced by the folding.  
     
       FIG. 17 
     
      For effective learning, particularly of language, it is most helpful for a student to have the advantage of considerable attention, if not full time attention, of a teacher. For example, a young child will often learn to read by looking at a book containing pictures and corresponding words with an adult reading the words as the child follows the words and looks at the associated pictures. Thus the mind of the child is focusing on an image depicting something, is being given the spoken word and is seeing the written word. Furthermore, from the context the child is absorbing the word within the scope of a grammatical structure and is gathering the meaning, either from the pictures if relevant or with the aid of an explanation. At any stage the teacher can discuss with the child any word or its meaning or draw to the child&#39;s attention a similar word and provide explanations and definitions of grammar and meaning, i.e. syntax and semantics.  
      Similarly, when a child is beginning to read, the adult can monitor the reading and provide immediate feedback on a one-to-one basis to maximise the rate at which the child gains reading skills and remembers vocabulary. The interest and motivation of the child can be maintained at high levels.  
      However, apart from a domestic situation, the cost of such teaching techniques makes them prohibitive, yet there is a very substantial need for such additional support, particularly in the areas of adult illiteracy, foreign language teaching and remedial language teaching.  
      Furthermore, similar needs for feedback and flexible recapitulation of concepts, explanations and facts are needed in many of the areas of education including mathematics and other science subjects. The availability to a student, of a teacher who can be requested to repeat an explanation, elaborate on some point of commentary or deal with any other relevant question is an extremely valuable resource in many situations.  
      It is known to students with e.g tape recordings of an explanation. When such recordings are applied to the process of learning to read, a simple system is one in which a tape recording of a printed work is given to a student and then student has the opportunity of following the words, repeating segments of the tape recording and indeed recording his or her own attempts at reading the words and comparing with the tape recordings of the tutor. However, such a system is inflexible and hard to operate.  
      One published approach to the teaching of language is contained in PCT International Publication No. WO 83/02188 (MERIT BOND LIMITED) wherein printed text is provided with bar codes associated with at least some of the text, a manually controlled reading device being used to access the bar codes as the user may require, and an electronic processing means used to cause the apparatus to synthesise voice reproduction corresponding to the text with which the selected bar code is associated. Such a device has limitations in terms of functions fulfilled and in the special preparation required of the printed material, i.e. it can not be used with conventional books.  
      Another published approach, (PCT WO 87/06752) in the teaching of language is one in which sets of bar codes are arranged on respective lines corresponding to lines of printed text. Each bar code set, when accessed, causing a particular storage location from a message store to be accessed to be reproduced by a speech producer. The limitations of such a system are that a book can not be used in its original format, since bar codes have to be added or overprinted onto the original document at the expense of text. Further, the selection of the bar code set may lead to confusion and small children may have difficulty scanning a bar code.  
      Yet another published approach (PCT WO 90/15402) relates to a document interpreting system comprising location detecting means on which a plurality of documents to be interpreted may be stacked and for detecting through said documents the location of pointing means directed at an area of the topmost document of said stack, speech storage means for storing speech relating to different areas of said documents and speech reproduction means for reproducing speech stored in said speech storage means corresponding to the area of said topmost document to which said pointing means is directed. In the system disclosed, the pointing means takes the form of a user&#39;s finger.  
      Another published approach (EP 0 572 466) relates to a document interpreting system comprising location detecting means on which a book or other stack of documents may be placed and electronic pointing means coupled to said location detecting means and adapted in use to be directed at an arbitrary area of the topmost document of the stack of documents, said location detecting means being adapted to detect electronically through said stack the location of said arbitrary area to cause speech stored in a speech storage means associated with said arbitrary area to be reproduced.  
      A disadvantage with the document interpreting system of EP 0 572 466 is that if the stack of documents, for example the pages of a book, contain documents with metallic embossing or if the humidity of the stack of documents is high then there is considerable distortion in the location detection process leading to a shift in the detected position of the pointing means which can lead to speech associated with an incorrect arbitrary area being reproduced.  
      The present embodiment is directed to a document interpretation system which overcomes the above limitations and provides for a practical and useful device which eliminates the need for specially printed codes associated with the words and phrases of the written material an enables a wide variety of normal books to be used including those having metallic embossing or documents having high humidity.  
      The document interpreting system depicted in  FIG. 17  of the drawings is especially applicable for assisting learning of reading or pronunciation or understanding of words, phrases or sentences or interpretation of drawings, pictures, etc. It should be understood that the term “document” covers any printed matter or indeed any written or drawn matter, and in particular includes books.  
      The document interpretation system comprises a membrane  1701  which overlies a cartridge  1702  in which are located one or more cards  1703  in the form of a stack. The card to be read by the user (not shown) is placed as the topmost card  1704  where more than one card is present. The cartridge  1702  and membrane  1701  are shown as schematically in  FIG. 17 . In practise, the membrane  1701  may be housed in a frame formed as part of the upper surface of the cartridge  1702  of fixedly located on, or hinged to the upper surface of the cartridge  1702  by any suitable means. The important aspect is that the membrane  1701  is located in use, or may be brought into location for use, such that it overlies the card or cards  1703  stored in the cartridge  1702 .  
      The membrane  1701  is transparent or at least sufficiently translucent as to allow the user to determine the contents of the topmost card  1704  when viewing through the membrane  1701 . The membrane  1701  comprises a grid  1705  formed of conductive stands creating an X-Y pattern dividing the membrane  1701  into substantially squared shaped segments.  
      The membrane  1701  is formed from a pair of transparent films, one of which defines a set of parallel conductive strands in a first (X) direction, and the second film defining conductive strands in a second (Y) direction perpendicular to the first direction. The transparent films are Orgacon Conductive Transparent Films and the conductive strands are defined by screen printing of Strupas ink. The Orgacon films and Strupas ink are supplied by Agfa-Gevaert N.V., of Mortsel, Belgium.  
      The membrane  1701 , and specifically the grid  1705 , is electrically coupled to a printed circuit board (PCB)  1709 . The PCB  1709  has mounted thereto an Application Specific Integrated Circuit (ASIC)  1711 . The PCB  1709  is further provided with a power source in the form of a battery  1710  and a speaker  1712 . The PCB  1709  may be formed as part of the cartridge  1702 , as part of the frame housing the membrane  1701 , or as part of a separate unit.  
      The ASIC  1711  is provided with its own power source in the form of a battery  1708 . Alternatively, the ASIC  1711  may be powered directly from the PCB battery  1710 .  
      A pen or pointer  1706  is coupled to the PCB  1709  by means of a cable  1707 . The pointer  1706  is adapted to be pointed at an area of the membrane  1701  coincident with a arbitrary area of the topmost card  1704  viewed through the membrane  1701  so as to enable the co-ordinate location of the arbitrary area to be detected by the membrane  1701  and in turn determined by the ASIC  1711 .  
      The pointer  1706  is, for example, magnetically or capacitively coupled to the membrane  1701  in use. Importantly, since the relative positions of the membrane  1701  and the pointer  1706  are determined magnetically or capavitively rather than by pressure applied to the membrane  1701 , the document interpretation system finds particular application for use with young children who are apt to press randomly and unintentionally on the membrane  1701  whilst using the system. With a membrane activated by pressure such contacts would lead to a large number of false readings and hence confusion to the user.  
      The ASIC  1711  contains machine code and/or software programs and solid state circuitry to control operation of the pointer  1706 , membrane  1701  and speaker  1712 . In addition, the ASIC  1711  stores speech associated with areas of the cards  1703 .  
      In use, the output from the grid  1705  of the membrane  1701 , consisting of the co-ordinate details of an area of the card  1704  to which the pointer  1706  is directed, is fed to the ASIC  1711  on the PCB  1709 . The machine code and/or other software encoded in the ASIC  1711  resolves the co-ordinate details from the membrane  1701  and determines the speech stored in the ASIC  1711  which is associated with the area of the topmost card  1704  to which the pointer  1706  is directed.  
      It will be appreciated by those skilled in the art that the location of the card  1704  or other document to be read, relative to the membrane  1701 , may be established by, for instance, physical means such as the internal dimensions of the cartridge  1702  to ensure the card is placed in a known location relative to the overlying membrane  1701 . Alternatively, the card  1704  or other documents may be placed in the cartridge  1702  in any orientation and known features such as corners of the card  1704  may be registered by pointing at them through the membrane  1701  with the pointer  1706  in an initialising registration procedure. By this method the location of the words and pictures, etc. may be calculated by such known means as simple co-ordinate geometry routines.  
      In addition, it will be appreciated that the ASIC  1711  will need to determine which of the cards  1703  is the topmost card  1704 . This may be done, for example, by providing a unique identifier area on each card  103  to which the pointer  1706  is first directed. By arranging for each card  1703  in the stack to have its identifier area in a different position, the ASIC  1711  is able to determine the identity of the topmost card  1704 . Alternatively, a manual mechanism may be provided wherein the PCB  1709  is provided with an input terminal by which the user may enter an identifier, e.g and alpha-numeric character or characters, to identify the topmost card  1704 .  
      In use of the system thus far described, a user points the pointer  1706  at an area at the topmost card of the stack of cards  1703 , e.g some printed text or a picture. The grid  1705  of the membrane  1701  detects the presence of the pointer  1706  by means of the magnetic or capacitive changes in the grid  1705  of the membrane  1701  caused by the proximity of the pointer  1706 . The membrane  1701  outputs signals representing the co-ordinates of the designated area to the ASIC  1711 . The machine code or software program embedded in the ASIC  1711  processes the signals and resolves the corresponding co-ordinates and generates a signal instructing the speaker  1712  to output an audio signal corresponding to speech corresponding to the printed text pointed to on the card  1704  or alternatively corresponding to the picture pointed to on the card  1704 .  
      Optionally, the user of the system can access a button or switch either on, for example the stylus-to give a real voice reply of individual words when touched by the pointer  1706 . Alternatively, another button may be provided which when accessed causes reproduction of the whole sentence when the first or any word in that sentence is touched by the pointer  1706 . Another button may be provided which when accessed allows the user to receive prompts, such as a suggestion to look the syllables within the word selected or the system can be set up to sound out the word phoneme by phoneme. A further button may be provided which, when accessed by the user, will give an explanation of the word or picture which may be in terms of its definition, mode of usage or other commentary.  
      The system may also be used for teaching a second language, in which case, for example, a sentence can be reproduced in both languages in the correct idiom for each language using two different buttons, e.g on the cartridge  1702 . Each word can also be represented in each language, word for word, by the selection an appropriate button. Where complex multi-syllable foreign words are being taught, the word may be represented both in its normal presentation at normal dictation speed and also by a further selection at a slowed down speed enabling the student to dissect the pronunciation of the word, syllable by syllable.  
     
       FIG. 18 
     
      Some examples of the use of the system described with reference to  FIG. 17  will now be described with reference to  FIG. 18  which depicts the topmost card  1704  of  FIG. 17  in greater detail.  
      Referring to  FIG. 18 , a rectangular area  1801  is reserved on cards  1703  for displaying a unique identifier. Thus card  1704  has a unique identifier  1802  within the area  1801 . Consequently, using pointer  1706  of  FIG. 17  to point to rectangular area  1802  identifies card  1704  to the document interpretation system of  FIG. 17 .  
      Using pointer  1706  to point to area  1803  would cause the sentence “K is for Katie kangaroo” to be reproduced. Pointing to area  1804  may cause the phrase “hello I am Katie kangaroo” to be reproduced.  
      Pointing in each of the areas  1805  to  1813  inclusive would cause the individual words “kangaroo”, “kitten”, “Kite”, “Orange”, “K”, “is”, “for”, “Katie” and “Kangaroo”, respectively, to be reproduced.  
      It should be appreciated that the rectangular areas referred to in  FIG. 18  are used by a way of example only and other shaped areas, such as a circular shaped areas may be used.  
     
       FIG. 19 
     
      In  FIG. 19  of the drawings, there is shown a block schematic diagram relating to the document interpretation system of  FIG. 17 . This comprises the membrane  1701  which affords and output  1908  to the PCB  1709 , which is itself connected to the pointer  17806  via the cable  1707  and to the speaker  1712 .  
      The PCB  1709  has mounted thereon the ASIC  1711  which typically comprises a microprocessor  1930  which operates under the control of a program stored in read only memory “ROM”  1931  and receives the signals representing the co-ordinate details via output  1908  from the membrane  1701 . A random access memory (RAM)  1932  is provided in which is stored the speech signals corresponding to the various areas of the documents being read, e.g the cards  1703 . The micro processor  1930  outputs the speech signals to the speaker  1712 , via an input/output (I/O) interface  1933  which causes the speech signals to be reproduced by the speaker  1712 .  
      It is envisaged that that random access memory  1932  may take the form of a removable RAM-card in which the various speech signals are stored corresponding to the different areas if the cards  1703 , thereby enabling a set of cards  1703  and associated RAM-card to be sold as a package.  
     
       FIG. 20 
     
      In  FIG. 20  of the drawings there is shown a flow diagram of a typical operating system of the arrangement depicted in  FIG. 19 . At step  2001 , the micro-processor  1930  monitors the membrane  1701  for new data. The new data is decoded at step  2002  to obtain the corresponding speech signal stored in the RAM  1932 . At step  2003 , the speech signal is output to the speaker  1712 , the output of which is monitored by the micro-processor  1930  via the I/O interface  1933 , at step  2004 , to determine the conclusion of the speech signals corresponding to the selected area. The system is then ready for re use.  
      It will be appreciated that new cards, or locally generated documents, e.g. flash cards and picture stories, may have their textual and pictorial co-ordinates recorded by means similar to that of  FIG. 17  with the system operating in a “writing” mode. In this mode the co-ordinates of individual words, pictures, phrases, etc. are read, via the pointer  1706 , from cards placed in the cartridge  1702  under the membrane  1701  by the program in the read only memory  1931  ( FIG. 19 ). These co-ordinates are then converted into the corresponding speech signals stored in the random access memory  1932  for subsequent use in the “reading” mode described above.  
      The document interpreting system which has been described is advantageous in that it enables normal printed or written documents to be “read” without special overprinting of bar codes, magnetic codes, etc. The system can also operate with documents containing metallic embossing or having pages with high humidity content. RAM-cards and sets of cards  1703  may also be sold as a package in respect to particular items for use by teachers, pupils, etc. on equipment in many different locations.  
      It should be appreciated that the document interpreting system which has been described has been given by a way of example only and various modifications may be made dependent upon any particular application. Although the pointer  1706  has been shown as connected to the PCB  1709  by means of a cable  1707 , it may be remotely connected to it using, for example, an infrared, radio or other link. Also, although the use of an ASIC  1711  in conjunction with a speaker has been described, other speech storage systems may be used, such as using tape or compact disk and associated player. Other output devices may also be used such as headphones.  
      Further, whilst the set of cards  1703  has been described as being stored in a cartridge  1702 , other means of locating the cards  1703  relative to the membrane  1701  may be utilised, for example, by clipping or otherwise temporarily fixing the card  1704  or cards  1703  to the underside of the membrane  1701 .  
      Further, a mechanism may be provided to enable the cards  1703  in the cartridge  1704  to be shuffled so as to change the identity of the topmost card  1704 . For example, an aperture may be provided in the cartridge  1702  to allow the stack of cards  1703  to be removed, manually shuffled and reinserted into the cartridge  1702 .  
      The system may also be used with documents other than individual cards  1703 . For example, the system may be used with complete books wherein the membrane  1701  is placed over each page of the book in turn. Advantageously, means may be provided, such as a book stand, for holding the book at rest with the membrane  1701  hinged thereto such that the membrane  1701  may be hinged upwards away from contact with the page of the book to allow for the pages to be turned. The membrane  1701  may then be hinged back down into contact with the subsequent page of the book.  
      Another form of document that may be used with the system is a scroll comprising an elongate document wound onto one or a pair of rollers. In use, the roller or rollers can be rotated so as to bring the required portion of the document into line with the membrane  1701 .  
      Further, while it is important that the membrane  1701  is transparent or at least translucent, the membrane  1701  may be manufactured to be flexible or inflexible. In particular, where the membrane  1701  is flexible, a separate strengthening member may be provided, for example, a frame to stiffen the membrane  1701 .