WO2007110486A1 - Machine readable code and devices for reading the same - Google Patents

Abstract

The invention relates to two-dimensional machine readable codes (3), to devices for reading such codes, and to systems for creating such codes. In one embodiment, the machine readable code (3) comprises an array of electrically conductive code elements (9) that are electrically connected to each other. The machine readable codes are preferably formed by printing them onto a substrate (5) using conductive ink.

Description

MACHINE READABLE CODE AND DEVICES FOR READING THE SAME

The present invention relates to conductive machine readable codes, to devices that can read such codes using a capacitive sensing transducer and to systems for making such codes.

It is known to provide fingerprint sensors on computer devices, such as computers, telephones, personal digital assistants. The main purpose of providing the fingerprint sensor is to restrict access to the computer device so that only certain users can use the computer device. Various different sensing techniques are used for sensing the fingerprint. These include infrared-based sensors, optical-based sensors and capacitive-based sensors.

It is also known to provide such computer devices with sensing transducers for reading machine readable codes to facilitate the entry of data into such computer devices. For example, it is known to provide 2D sensing transducers for reading 2D codes and for generating a corresponding digital tag value for the 2D code. The computer device can use this 2D code tag value for inventory purposes or for any form of data input. Again, different sensing technologies have been proposed for sensing the machine readable code, including optical, capacitive, inductive etc.

According to one aspect, the present invention provides a computer device having a sensor that can be used for both fingerprint sensing and for code reading.

In order to facilitate the reading of the machine readable code, the code elements are preferably connected together using, for example, a conductive grid.

According to another aspect, the invention provides a novel electrode arrangement for a capacitive sensor comprising a drive electrode arranged over the sensing area and a plurality of sensor electrodes arrayed within but isolated from the drive electrode. These and other features and aspects of the present invention will become apparent from the following detailed description of embodiments which are given by way of example only and which are described with reference to the accompanying figures in which:

Figure 1 is a schematic diagram illustrating a mobile telephone having a capacitive sensing transducer for sensing conductive machine readable codes and for sensing characteristic features of fingerprints;

Figure 2 is a block diagram illustrating the main components of the mobile telephone shown in Figure 1 ;

Figure 3 is a schematic diagram illustrating the principle of operation of the capacitive sensing transducer used in this embodiment to sense conductive code elements of a machine readable code;

Figure 4 is a schematic block diagram illustrating the main components of the capacitive sensing transducer shown in Figure 1 ;

Figure 5 is a flow chart illustrating the processing steps performed by the code reader module to recover the code value represented by the 2D barcode whilst avoiding the conductive grid;

Figure 6a schematically illustrates the 2D array of sensor values obtained from the capacitive sensing transducer when reading the 2D barcode shown in Figure 1 ;

Figure 6b schematically illustrates a part of the scanned barcode data illustrating the resolution of the sensor data obtained relative to the resolution of the code elements of the 2D barcode;

Figure 7 is a block diagram illustrating a printing process used to generate a newspaper carrying the machine readable code shown in Figure 1 ;

Figure 8a is a schematic block diagram illustrating an alternative arrangement for connecting code elements of a machine readable code; Figure 8b illustrates a further alternative arrangement for connecting the code elements of a machine readable code;

Figure 9 illustrates a further alternative way in which the conductive code elements of a machine readable code may be connected together;

Figure 10 illustrates a further way in which the conductive code elements of a machine readable code may be connected together;

Figure 1 1 illustrates a further way in which the conductive code elements of a machine readable code may be connected together;

Figure 12a illustrates an alternative arrangement of sensor electrodes and drive electrode for sensing the presence of code elements of a machine readable code;

Figure 12b illustrates the way in which the arrangement of the sensor electrodes and the drive electrode shown in Figure 10a operate to sense the conductive code elements; and

Figure 13 illustrates a further alternative arrangement of the drive electrode and sensor electrodes that may be used for reading machine readable codes.

OVERVIEW

Figure 1 is a schematic diagram illustrating the components of a system 1 that allows users to obtain further information relating to, for example, a newspaper article by reading a two dimensional (2D) code 3 that is hidden under the printed surface of the newspaper 5. In this example, the 2D code 3 is hidden beneath a picture 7 of the newspaper article and is formed by a two-dimensional array of conductive code elements 9. The system 1 also includes a user's mobile (cellular) telephone 11 having a capacitive sensing transducer 13 which can read the 2D code 3 printed on the paper 5. In this embodiment, the sensing transducer 13 comprises a commonly available fingerprint sensor such as those provided by AuthenTec Inc., Melbourne, Florida, USA or Fingerprint Cards AB, Gothenburg, Sweden. As shown in the close-up view of the sensing transducer 13, the transducer 13 includes a sensing area 17 comprising a plurality of sensor electrodes 15 arranged in a two-dimensional array and a drive electrode 19 that surrounds the sensing area 17.

To read the 2D code 3, the user scans or swipes their mobile telephone 1 1 over the surface of the newspaper 5 until the sensing transducer 13 is swiped over the area of the newspaper 5 carrying the hidden 2D code 3. A visible symbol (not shown) may be printed on the surface of the newspaper 5 to indicate to the user that the hidden 2D code is present. The symbol might, for example, be provided next to the picture to indicate that the 2D code is under the picture.

When the code 3 is read, the information contained in the code is determined. The information obtained from the 2D code 3 may, for example, be the further information relating to the newspaper article, in which case it is output to the user on, for example, a display of the mobile telephone 1 1. In addition or alternatively, the information obtained from the 2D code 3 may include a link (URL) to further information or content stored on a remote server 20. In this case, the mobile telephone 11 uses the link to retrieve this further information or content from the remote server 20 via the Internet 21 and the mobile telephone network 23 and then outputs the retrieved information or content to the user.

In this embodiment, the mobile telephone 1 1 also includes a fingerprint sensing module that can use the same sensing transducer 13 for sensing the fingerprint of a user for authentication purposes. In this way, the same sensor 13 can be used to sense different things for different purposes. The mobile telephone 1 1 is arranged to automatically detect whether a fingerprint is being sensed or if a capacitive 2D code 3 is being sensed. This is possible, because fingers have different electrical characteristics to such conductive 2D codes and therefore, the signal levels from each will be different. Alternatively, this information may be input manually by the user via a keypad of the mobile telephone 1 1. A more detailed description will now be given of the 2D code 3 used in this embodiment and of the various components of the mobile telephone 1 1.

2D CODE

As is well known, 2D codes 3 such as the one shown in Figure 1 represent information by the presence or absence of code elements 9 within the 2D array of possible code element positions. In the Figures, the presence of a code element 9 is represented by a black square and the absence of a code element is represented by a white square. The way in which the information is represented and encoded within the 2D array is defined by an appropriate standard or by a proprietary encoding scheme. In this embodiment, the 2D code 3 that is used is based on a conventional "Data Matrix" type two- dimensional code, but modified so that all the conductive code elements 9 are electrically connected to the L-shaped frame 25 that borders the array of code elements 9. As those skilled in the art will appreciate, the L-shaped frame 25 is provided so that the reading device (i.e. the mobile telephone 11 ) can determine the relative orientation between the 2D code 3 and the capacitive sensing transducer 13 and hence where the 2D code 3 begins and where it ends.

In this embodiment, the code elements 9 are connected together and to the L-shaped frame 25 by using a conductive grid 27 superimposed over the code elements 9 which extends from the L-shaped frame 25 in both the horizontal and vertical directions. This modification to the standard 2D code structure allows the 2D code 3 to be read by many types of conventional fingerprint sensors. In particular, many existing fingerprint sensors rely on the user's finger touching the drive electrode 19 surrounding the sensing area 17 to provide a current path through the user's finger between the drive electrode 19 and the sensor electrodes 15. Therefore, with the modified 2D code 3 used in this embodiment, the drive electrode 19 can couple directly with the L-shaped frame 25 and since each code element 9 is electrically connected to the L-shaped frame 25, a current path is provided from those sensor electrodes 15 that are adjacent the code elements 9 to the drive electrode 19 via the conductive grid 27 and the L-shaped frame 25. Without the conductive grid 27, the code elements that are isolated from the other code elements and the frame 25 will not be sensed by the sensor electrodes 15 and therefore, the sensing transducer 13 will not be able to read the 2D code 3 accurately.

In this embodiment, the 2D code 3 has dimensions of 1 cm x 1 cm and the code elements 9 have dimensions 0.2mm x 0.2mm. This means that in this embodiment, the 2D code 3 can represent about 2.4kbits of data. As mentioned above, the way in which this data is represented in the geometrically distributed array of code elements 9 is defined by the standard code type used (in this case by the Data Matrix standard).

In this embodiment, the 2D code 3 is printed onto the newspaper 5 using conductive ink in an initial print run and then the text and pictures of the newspaper article are printed in a second print run, so that they obscure or hide the 2D code 3. In this way, the 2D code 3 does not take up any additional space on the newspaper 5. The conductive ink used to print the code elements should be formed from ink having a sheet resistance less than 100 kOhms/square so that the sensing transducer can clearly distinguish between the positions in the 2D code 3 having conductive ink and the positions in the 2D code 3 without conductive ink.

MOBILE TELEPHONE

Figure 2 is a block diagram illustrating in more detail the main components of the user's mobile telephone 1 1. As shown, the mobile telephone 1 1 includes a transceiver circuit 31 and an antenna 33 for transmitting signals to and for receiving signals from the mobile telephone network 23. The mobile telephone 1 1 also includes a loudspeaker 35 and a microphone 37 which are both connected to the transceiver circuit 31 so that the user can make and receive telephone calls in the usual way.

As shown in Figure 2, the mobile telephone 11 also includes a processor 41 which controls the operation of the mobile telephone 11 under control of various software modules stored within memory 43. In this embodiment, the memory 43 includes a fingerprint sensing module 45, a code reader module 47, a web browser 49 and a working memory area 51. The processor 41 is connected to the transceiver circuit 31 which allows the web browser 49 to transmit information to and receive information from the remote server 20 via the telephone network 23 and the Internet 21.

Figure 2 also shows the capacitive sensing transducer 13 which forms part of the mobile telephone 11 and which is used to read the capacitive 2D codes 3 or the user's fingerprint. In this embodiment, the capacitive sensing transducer 13 is normally powered down to save battery power. Therefore, in this embodiment, when the user wishes to scan a fingerprint or a 2D code 3, they must press an appropriate button on a keypad 53 to cause the processor 41 to power-up the sensing transducer 13. The signals obtained from the sensing transducer 13 are then passed to the processor 41 which stores the data in the working memory 51. In response, the processor 41 initiates the fingerprint sensing module 45 if a fingerprint is being scanned or the code reader module 47 if a capacitive 2D code 3 is being scanned. The appropriate module then processes the sensor values stored in the working memory area 51.

In particular, when a fingerprint is being scanned, the fingerprint sensing module 45 processes the sensor data values stored within the working memory area 51 to identify the characteristic features of the fingerprint which it compares with stored fingerprint data for the user (obtained in a prior registration process) for authentication purposes. When a capacitive 2D code 3 is being scanned, the code reader module 47 processes the sensor data values stored within the working memory area 51 to recover the information defined within the 2D code 3. As discussed above, depending on the content of this information, the code reader module 47 may output the information to the user via the display 55. If, however, the information in the 2D code 3 includes a URL, then the code reader module 47 passes the URL to the web browser 49 which uses the URL to retrieve the information associated therewith from the remote server 20 via the transceiver circuit 31 , the mobile telephone network 23 and the Internet 21. The information returned is then output to the user via, for example, the display 55. CAPACITIVE SENSING TRANSDUCER - PRINCIPLE OF OPERATION

Figure 3 is a schematic diagram illustrating the way in which the capacitive sensing transducer 13 used in this embodiment detects the code elements 9 of the conductive 2D code 3. (As will be apparent to those skilled in the art, other types of capacitive sensing transducer 13 may operate under different principles.) As illustrated in Figure 3, the drive electrode 19 is connected to an AC source 61 and is capacitively coupled (represented by capacitor C) to the conductive 2D code 3 via the conductive L-shaped frame 25 that partially surrounds the 2D code 3. In this embodiment the drive electrode 19 is capacitively coupled to the frame 25 as a layer of conventional (non- conductive) printing ink is provided over the 2D code 3. In alternative embodiments where there is no overlying non-conductive layer, drive electrode 19 may be galvanically coupled to the frame 25. As discussed above, all of the code elements 9 of the 2D code 3 are connected to the frame 25 via the conductive grid 27. As a result, the drive signal generated by the drive electrode 19 will couple to each of the code elements 9 via the frame 25.

As shown in Figure 3, the drive signal generated by the source 61 is connected between the drive electrode 19 and a grounded reference electrode 63 located under the array of sensor electrodes 15. As a result, an electric field 65 will be generated between the code elements 9 of the 2D code 3 and the reference electrode 63. In this embodiment, the frequency of the AC signal applied to the drive electrode 19 is approximately 100 kHz which means that the wavelength of the electric field 65 is much larger than all dimensions of the code elements 9 and of the sensor area 17 of the transducer 13. As a result, the field 65 generated between the code elements 9 and the reference electrode 63 will be purely electric with no magnetic component and no electromagnetic effects. Consequently, the electric field 65 can be treated as a quasi-static electric field whose field strength varies with the geometric distribution of the code elements 9. Thus, the array of sensor electrodes 15 placed in the electric field 65 will acquire voltages that represent the spatial variation of the electric field 65 from which the spatial distribution of the code elements 9 of the 2D code 3 can be determined and hence the information contained within the 2D code 3. In this embodiment, the sensor electrodes 15 are square having a size of approximately 50 microns by 50 microns and have a pitch also of about 50 microns, so the sensor electrodes 15 are very close to each other relative to their dimensions. As discussed above, the sensing transducer 13 is intended to be swiped across the 2D code 3 to be read. Therefore, as shown in Figure 1 , the sensing area 17 is elongate with the longer edge being slightly larger than the width of the 2D code 3 to be read. In this embodiment, the sensing area 17 has dimensions 12 mm x 2 mm and includes approximately 9600 sensor electrodes 15. Although it would be possible to detect and read the 2D code 3 using a single column of sensor electrodes 15, in this embodiment, several columns of sensor electrodes 15 are provided within the sensing area 17 along the swipe direction, which allows the code reader to determine the speed at which the sensing transducer 13 is swiped over the 2D code 3.

As discussed above, the 2D code 3 has dimensions of 1 cm x 1 cm and the code elements 9 have dimensions 0.2mm x 0.2mm. With the size of the sensor electrodes 15 used in this embodiment, it would be possible to reduce the size of the code elements 9 and hence increase the amount of data that can be stored in the 2D code 3. However, as the size of the code elements 9 is reduced, the more unreliable the sensing becomes as fewer measurements will be obtained from each code element 9.

CAPACITIVE SENSING TRANSDUCER - COMPONENT STRUCTURE

Figure 4 is a schematic block diagram illustrating the main components of the capacitive sensing transducer 13 used in this embodiment. As shown, the transducer 13 includes the array of sensor electrodes 15 and the drive electrode 19. The drive electrode 19 is connected to a drive amplifier 71 which amplifies a drive signal generated by a drive signal generator 73. In this embodiment, the drive signal generator 73 only generates the drive signal when instructed to do so by the processor 41. Figure 4 also shows that, in this embodiment, each of the sensor electrodes 15 is connected to a respective high impedance amplifier 75 which amplifies the signal from that sensor electrode 15. High impedance amplifiers 75 are required as the sensor electrodes 15 have characteristic impedances in the Teraohm range.

As discussed above, in this embodiment, the source 61 (i.e. the drive signal generator 73) generates an AC drive signal. Therefore, the electric field 65 generated by the code elements 9 will also be an AC electric field at the drive frequency. Consequently, the output from each high impedance amplifier 75 will also be an AC signal at the drive frequency whose peak amplitude depends on the presence or absence of a code element 9 adjacent the corresponding sensor electrode 15. As shown in Figure 4, the outputs from the high impedance amplifiers 75 are demodulated and filtered by a respective demodulation and filtering circuit 77 to obtain a DC voltage level that depends upon the peak amplitude of the AC signal output by the corresponding amplifier 75. The output from each demodulation and filtering circuit 77 is then input to a respective sample and hold circuit 79 which samples the voltage level when triggered to do so by the processor 41.

As discussed above, in this embodiment, the dimensions of the sensing area 17 are such that to read the 2D code 3, the capacitive sensing transducer 13 has to be scanned across the 2D code 3 (or the 2D code 3 has to be scanned across the sensing transducer 13). Therefore, in this embodiment, the processor 41 causes the sample and hold circuits 79 to sample the output from the demodulation and filtering circuit 77 at a sampling rate that ensures that sufficient samples are obtained to allow the detection of the code pattern for some maximum speed at which the sensing transducer 13 is likely to be scanned across the 2D code 3.

As shown in Figure 4, the voltage levels held by the sample and hold circuits 79 are digitised by an analogue to digital converter 81 and then stored in the working memory area 51 for processing by the code reader module 47 or the fingerprint sensing module 45. The way in which the fingerprint sensing module 45 processes the digitised voltage levels to determine the characteristics of the fingerprint will be well known to those skilled in the art and will not, therefore, be described in further detail here. However, the way in which the code reader module 47 processes the digitised voltage levels to determine the 2D code value is different from the conventional techniques that are used, as the code reader module 47 must take into account the presence of the grid 27 to ensure that it does not affect the determined 2D code value. The way in which the code reader module 47 processes the digitised voltage levels in this embodiment, to determine the 2D code value will now be described.

CODE READER MODULE

Figure 5 is a flow chart illustrating the processing steps performed by the code reader module 47 to determine the 2D code value defined by the scanned 2D barcode 3. As the digitised voltage levels obtained from the capacitive sensing transducer 13 effectively represent a two-dimensional image of the scanned 2D barcode 3, the processing techniques that are used to determine the 2D code value are based on established image processing techniques used to obtain code values obtained from scanned optical barcodes.

The processing starts at step s1 , where the code reader module 47 processes the array of voltage levels stored in the working memory 51 to remove the overlapping portions caused by the scanning of the transducer over the 2D barcode 3 and to normalise for the speed of the scan. The techniques employed in this step are the same as those employed in conventional optical barcode scanning systems and will not, therefore, be described in further detail here. Figure 6a schematically illustrates the form of the resulting "image" 84 of the 2D barcode 3 that is obtained. In the following description, the 2D array of voltage levels obtained from the capacitive sensing transducer will be referred to as image data and individual voltage levels in the 2D array will be referred to as "pixels", although it should be appreciated that the 2D array of voltage levels will not normally be displayed on a display at any stage.

At step s3, this "image data" (i.e. the array of voltage levels obtained from the scan) is binarised. This is achieved by identifying the maximum and minimum voltage levels obtained from the capacitive sensing transducer 13 and setting a threshold to be the average value between them. Each voltage level in the array is then compared with this threshold and set to a value of zero if it is less than the threshold or one if it is greater than the threshold.

At this stage, the binarised image data will include image data of the scanned 2D barcode 3 together with image data of the background. Therefore, in step s5, the code reader module 47 processes the binarised image data to identify the region of interest (ROI) which contains the 2D barcode 3. This is achieved by starting with a rectangle in the centre of the image 84 and then increasing the size of this rectangle in all directions until the rectangle does not intersect with the 2D barcode 3 and is fully located within the background. In this embodiment, at each step that the rectangle is increased, it is increased by eight pixels in all directions. Once the rectangle is fully within the background, the size of the rectangle is reduced in all four directions one pixel at a time, in order to find a more precise rectangle that contains the 2D barcode.

As those skilled in the art will appreciate, as a result of the scanning process, the edges of the 2D barcode 3 in the image data are unlikely to be parallel with the horizontal and vertical lines of the containing rectangle that has been identified. Therefore, the directions of these horizontal and vertical lines of the containing rectangle are corrected in the following way.

Firstly, each line of the containing rectangle is divided into two equal segments. The code reader module 47 then identifies for each segment of each line, the pixel in the image 84 of the 2D barcode that is closest to that segment so that two pixels are identified for each line. The positions of these two pixels for each line then define a respective corresponding line of a containing four sided polygon which contains the pixels of the 2D barcode. The four sided polygon is then corrected back into a containing rectangle by, for example, linearly extrapolating the pixel values of the four sided polygon as necessary to fill in the gaps between the four sided polygon and the final corrected containing rectangle.

At this stage, the code reader module 47 knows the overall size of the scanned barcode 3, but it does not know the number of code elements 9 in each dimension of the barcode and hence the size of the code elements 9 within the image data. However, the code reader module 47 estimates, in step s7, the size of the code elements 9 using the known characteristics of the type of 2D barcode 3 that is being used. As mentioned above, in this embodiment, the 2D barcode 3 that is used is a Data Matrix barcode. Such Data Matrix barcodes come in a limited range of sizes (in terms of the number of code elements in each dimension). Some examples of Data Matrix barcode sizes are: (26,26), (32,32), (16,48), (48,48) etc. Additionally, the black and white cells of a Data Matrix barcode have the same size and are square. Therefore, given this information, the code reader module 47 can determine in advance (or can be preprogrammed with) the possible sizes (in terms of the number of pixels in the image data) that the code elements 9 can have.

For example, for the image 84 of the scanned barcode 3 shown in Figure 6, if the distance between opposite segments of the corrected containing rectangle is 195 pixels in the illustrated horizontal direction and 185 pixels in the illustrated vertical direction, then the code reader module 47 can determine that the overall shape of the 2D barcode is square and can therefore exclude the possible barcode sizes which are rectangular (e.g. (16,48)). Therefore, if the maximum number of code elements is (48,48), then this means that the minimum code element size will correspond to a region of four pixels by three pixels in the image data of the scanned barcode. Similarly, if the minimum size of the barcode is (26,26), then this means that the maximum code element size will correspond to a region of seven pixels by seven pixels in the image data. The code reader module 47 then processes the image data obtained from the scanned barcode to identify the sizes (in terms of the number of pixels in both dimensions) of both white and black regions in the image data. The code reader module 47 then selects the minimum obtained size that corresponds to a real Data Matrix size and which was obtained for both black and white regions.

As those skilled in the art will appreciate, during this processing step, the code reader module 47 is processing the image data which contains the conductive grid 27. However, since the grid is only in black and since the grid lines are too thin compared to the white gaps between them, their dimension will be eliminated from possible code element sizes. Further, in white areas of the barcode 3, the distance between the grid lines can provide useful information relating to the actual size of the white code elements.

Therefore, at the end of step s7, the code reader module 47 knows the size of the 2D barcode (in terms of the number of code elements positions in each dimension) that has been scanned. Thus, for the barcode illustrated in Figure 6a, the code reader module 47 knows that the barcode is of size (32,32). Consequently, given that the size of the region of interest (ROI) is 195 pixels by 185 pixels, this means that each code element 9 has a size of approximately 6 pixels in the horizontal direction (N_x) and 5 pixels in the vertical direction (N_y), as illustrated in Figure 6b which shows part of the 2D barcode 3 and the regions 86 of pixels that represent the code elements 9.

At this stage, it is not known in which orientation the 2D barcode 3 was in when it was scanned by the capacitive sensing transducer 13. Therefore, in step s9, the code reader module 47 processes the image data 84 corresponding to the 2D barcode 3 to identify where the L-shaped frame 25 is located in the image data. Again, the code reader module 47 does this using known characteristics of the Data Matrix barcode 3. In particular, in all Data Matrix barcodes, the sides opposite the L-shaped frame 25 are formed from alternating patterns of black and white code elements. Therefore, in this embodiment, the code reader module 47 processes the image data 84 at the edges of the 2D barcode to identify which edges have more transitions from black to white and therefore which edges contain the L-shaped frame 25.

More specifically, for the vertical edges, the code reader module 47 counts the number of transitions from black to white on N_x vertical lines of pixels from the left border of the region of interest towards the right, where N_x is the number of pixels in the vertical direction corresponding to one code element (as calculated in step s7). For the example barcode illustrated in Figure 6, N_x is 6 pixels. The code reader module 47 then stores the maximum number of transitions thus determined as M|_Θft. The code reader module 47 then counts the number of transitions from black to white on N_x vertical lines of pixels from the right-hand border of the region of interest towards the left. The code reader module 47 then stores the maximum number of transitions that are determined as M_rlght. The code reader module 47 then determines if M|_Θft is greater than M_rιght. If it is, then the alternating pattern of black and white code elements is on the left-hand side of the image 84 and the vertical part of the L-shaped frame 25 is on the right-hand side. Otherwise the alternating pattern is on the right and the vertical portion of the L-shape frame 25 is on the left. The same procedure is then repeated for the horizontal direction to identify on which side of the image data 84 the horizontal portion of the L- shaped frame 25 is located.

At the next processing stage (step s1 1 ), the code reader module 47 determines a scanning grid (i.e. horizontal and vertical lines of grid points) along which the image data 84 will be sub-sampled, in order to recover the barcode tag value for the scanned 2D barcode 3 whilst avoiding the conductive grid 27. This processing starts by computing an origin for the scanning grid. This is set to be at (INT[N_x/2],INT[N_y/2]), where INT[] is the integer part of the expression within the brackets. For the example image data 84 shown in Figure 6a, with N_x equal to 6 and N_y equal to 5, the origin is set at the pixel (3,2) within the region of interest. The scanning grid positions are then calculated at (INT[N_x/2+i(Sχ)],INT[N_y/2+j(Sγ)]), for i,j = 0,1...31 and where S_x and S_y are the horizontal and vertical distances between code elements as calculated from the width of the region of interest divided by the number of code elements in the respective dimensions. In the example shown in Figure 6a, S_x = 195/32 = 6.09375 and S_y equals 185/32 = 5.78125. Figure 6b illustrates the locations of the grid points thus calculated by the circular dots, some of which have been referenced 87.

As those skilled in the art will appreciate, the equidistant scanning grid computed above may result in some of the grid points 87 lying on the conductive grid 27. Therefore, for each row and column of grid points 87, the code reader module 47 considers the rows and columns of pixel values containing these grid points 87 and moves the rows and columns of grid points 87 to ensure that they do not fall on the conductive grid 27. The way in which the code reader module 47 performs this processing will now be explained for a single row of the grid points 87.

As will be apparent to those skilled in the art from the above discussion, each row of code elements 9 within the 2D barcode 3 will be represented by N_y lines of pixels within the image data. One of more of those lines of pixels may contain the conductive grid 27 and cannot, therefore, be used. Additionally, the lines of pixels at the edges of each row of code elements 9 will be unreliable and therefore should not considered. Therefore, in this embodiment, the code reader module 47 calculates, for the centre N_y-1 lines of pixels that correspond to a row of code elements, the number of white pixels in each line. The row of grid points 87 for that row of code elements is then moved so that the grid points are placed on the line of pixels having the largest number of white pixels (as the conductive grid 27 is black).

The code reader module 47 performs the same processing for each row of grid points 87 and for each column of grid points 87 (as in this embodiment the conductive grid 27 includes both horizontal and vertical lines). Once the final positions of all the grid points 87 have been determined, the code reader module 47 samples, at step s13, the image data at the determined grid point locations to recover the bit pattern of the 2D barcode 3. This bit pattern is then checked to find the encoded message, exploiting the error correcting mechanisms embedded into the Data Matrix code specifications. The processing then ends.

2D CODE PRINTING

As discussed above, in this embodiment, the 2D code 3 is formed from conductive ink that is printed onto the newspaper 5. Figure 7 illustrates the printing process used in this embodiment to print the modified 2D codes and the newspaper article onto the paper. In this embodiment the printing process is controlled using conventional programmable computer processors that are programmed with appropriate computer implementable instructions. As shown, the system includes a code print data processor 85 that receives the print data 87 defining the conventional 2D code to be printed as well as modification data 89 that defines how the 2D code is to be modified so that the code elements 9 of the 2D code are connected together and to the frame 25. As discussed above, this is achieved in this embodiment using the conductive grid 27. Therefore, in this embodiment the modification data defines the size, position and structure of the grid 27 relative to the code elements 9 and the frame 25. The code data processor 85 operates to modify the conventional print data 87 for the 2D code to be printed in accordance with the modification data 89 to generate modified 2D code print data 91 that defines the position and shape of all the code elements 9 to be printed as well as the position and shape of the frame 25 and the grid 27 to be printed. As shown in Figure 7, this modified 2D code print data 91 is passed to a first print engine 93 that prints the modified 2D code onto the paper in a single printing process, using conductive ink 94 from a reservoir 95.

As shown, the paper with the printed 2D code is then passed to a second print engine 97 which prints the newspaper article on the paper using printing inks 98 from a reservoir 99 in accordance with article print data 101 obtained from an article print data processor 103. The print engines 93 and 97 can use a variety of different printing techniques, such as inkjet printing, laser printing, offset printing, gravure printing or flexography.

The printing system used in this embodiment offers the advantage that the print data used to print the conductive grid 27 is combined with the print data for the conventional 2D code before being printed out. As a result, both structures are printed out together and consequently it is not necessary to pass the paper through the printing engine 93 twice or to provide two printing engines for the modified code - one for printing the conventional code and one for printing the grid structure 27. This also avoids errors in the structure of the resulting 2D code because of any misalignment between the code elements 9 and the grid 27 that might result if the code elements 9 are printed separately from the grid 27.

ALTERNATIVE 2D CODE STRUCTURES

In the above embodiment, the code elements 9 of the 2D code 3 were connected together using a grid 27 formed from horizontal and vertical conductive lines which connect to the L-shaped frame 25 that borders the code elements 9 of Data Matrix codes. As those skilled in the art will appreciate, it is not essential to provide both horizontal and vertical conducting lines to connect the code elements 9 together. The connecting lines may be provided in any direction or in only one direction, such as horizontally from the vertical limb of the L-shaped frame 25. In the above embodiment, separate connecting lines connected the individual code elements 9 to an L-shaped frame 25 of the 2D code 3. In an alternative embodiment, the 2D code 3 may be modified so that the code elements 9 are enclosed within a solid frame, as illustrated in Figures 8a and 8b. As shown, in these two examples, horizontal bars 11 1 connect the code elements 9 to a frame 1 13 that completely surrounds the array of code elements 9. In this embodiment, the frame 1 13 is asymmetrical such that the part of the frame 1 13 that previously formed the L-shaped frame is made thicker than the other part. This allows the code reading module 47 to be able to determine the relative orientation between the 2D code 3 and the capacitive sensing transducer 13 and hence where the 2D code begins and where it ends. As those skilled in the art will appreciate, the use of a frame 1 13 which completely surrounds the code elements can also be used in an embodiment that uses a grid structure that includes connecting lines in both the horizontal and vertical directions.

As those skilled in the art will appreciate, there are various other ways in which the code elements 9 can be connected together. Figure 9 schematically illustrates the way in which code elements 9 can be connected together by keeping their positions fixed relative to their neighbouring code elements 9 and by enlarging the area of each of the code elements 9 so that immediately adjacent code elements overlap each other. Any code elements that remain isolated from the other code elements (such as code element 9- 1 ) are then connected to its neighbouring code elements by appropriate bridges 1 15. Figure 10 illustrates a modified version of the 2D code shown in Figure 9, in which the L-shaped frame is replaced by a frame 1 13 that completely surrounds the code elements 9 thus, in this case, rendering the bridges 1 15 unnecessary. Of course, if there are any isolated elements located away from the frame 113, then such elements would still require bridges 1 15 to connect them to the other code elements 9.

In the above embodiments, the code elements 9 of the 2D codes were connected together using appropriate connecting lines. Figure 1 1 illustrates a way to avoid the use of such connecting lines so that the printed code looks exactly the same as the conventional code. In particular, in this embodiment, the printed code elements 9 are formed on top of a layer 121 of conducting material so that current can pass through the code elements 9, into the layer 121 and towards, for example, the L-shaped frame 25 to which the drive electrode 19 couples. With this arrangement, the conductive layer 121 will usually be printed first on the substrate 123 (e.g. paper) using conductive ink. The 2D array of code elements 9 is then printed on top of the conductive layer 121 and then a final layer 125 of ink is printed over the 2D code 3 so that it is hidden from view. In the example of the first embodiment, the top layer 125 will form the image of the newspaper picture 7 which hides the 2D code 3.

In order that there is a "contrast" between the positions in the 2D code 3 where there are code elements 9 and positions in the 2D code 3 where there are no code elements 9, the admittance (opposite of impedance) of the code elements 9 in the direction perpendicular to the substrate is much higher than the corresponding admittance of the positions in the 2D code 3 where there is no conductive ink. In addition, the contrast is dependent on the particular fingerprint sensor used and its parameter values, such as the frequency of the signal generator 61. As a result of this difference in admittance, sensor electrodes 15_IJ+i disposed above a conductive code element 9 will experience a different impedance than sensor electrodes 15_U that are disposed above positions where there is no code element. Therefore, the signal levels output from the array of sensor electrodes 15 will still vary with the spatial distribution of the code elements 9 and hence with the code value of the 2D code.

As those skilled in the art will appreciate, one of the advantages of the code structure shown in Figure 1 1 is that the print data that defines the geometrical pattern of the code elements 9 to be printed will be identical to that used when printing similar 2D codes for optical detection.

ALTERNATIVE SENSING TRANSDUCERS

In the embodiments described above, a separate drive electrode 19 was provided around the outside of the sensor electrodes 15. Further, the 2D codes 3 to be read by the sensing transducer 13 had a frame surrounding at least part of the 2D code elements 9 for coupling with the drive electrode 19. The individual code elements 9 of the 2D code 3 were also connected to this frame via an appropriate electrical connection. An alternative form of sensing transducer 13 will now be described which avoids the need to have such an electrical connection between the code elements 9 and the frame 25. In this alternative sensing transducer 13, the drive electrode and the sensor electrodes are arranged so that each of the individual code elements 9 forming the 2D code 3 is directly coupled to the drive electrode.

Figure 12a schematically illustrates the form of the drive electrode 131 and the two-dimensional array of sensor electrodes 133 used in this embodiment. As shown, in this embodiment, the sensor electrodes 133 are arranged in four rows with the positions of the sensor electrodes 133 in each row being staggered relative to the positions of the sensor electrodes 133 in the other rows. As those skilled in the art will appreciate, by staggering the rows of sensor electrodes 133 in this way, it is still possible to obtain an accurate picture of the geometrical arrangement of the code elements 9 even when the code elements 9 have a similar size to the size of the sensor electrodes 133. The lines 135 shown in Figure 12a indicate different directions of swiping the sensor relative to the 2D code. As can be seen, the layout of the sensor electrodes 133 serves to minimise the redundant readings from them, assuming of course that the sensing transducer 13 is swiped along a straight line.

As can be seen from Figure 12a, in this embodiment, the drive electrode 131 is formed from a substantially planar uniform layer of conductor which extends over the entire sensing area 17 where the sensor electrodes 133 are located. With this arrangement, there will be a direct coupling between the drive electrode 131 and each of the individual code elements 9 of the 2D code 3 and each code element 9 will provide the return current path between the adjacent sensor electrode 133 and the drive electrode 131 (as shown in Figure 12b).

Various manufacturing techniques can be used to manufacture the drive electrode 131 and the array of sensor electrodes 133 shown in Figure 12a. For example, a continuous layer of conductor may be provided on an insulating base and then a ring 137 surrounding each sensor electrode 133 may be etched away, thereby insulating each sensor electrode 133 from the drive electrode 131. This technique would be particularly suitable where the electrodes are made using printed circuit boards. Other manufacturing techniques could of course be used. For example, the electrodes may be formed as conductive layers on a silicon substrate, which are formed through different deposition techniques.

In the above embodiment, the drive electrode 131 was formed as a substantially planar layer of conductor. In an alternative embodiment, the drive electrode may be formed from a plurality of connected ring portions which surround the individual sensor electrodes 133. Such an arrangement is illustrated in Figure 13. As the ring portions 139 are connected together, the drive electrode 141 shown in Figure 13 only needs a single connection point (not shown) to the excitation source 61. If the individual ring portions 139 are electrically disconnected from each other then separate connections would have to be provided to each drive electrode. As those skilled in the art will appreciate, this is not preferred as it increases the complexity of the wiring arrangement for connecting the source 61 to the drive electrodes.

OTHER MODIFICATIONS AND ALTERNATIVES

In the first embodiment described above, in steps s11 and s13 described with reference to Figure 5, the code reader module determined appropriate sampling points for sampling the scanned image data 84. During this processing, the code reader module considered the rows and columns of pixel values containing the grid points and moved the rows and columns to ensure that they do not fall on the conductive grid 27. In an alternative embodiment, instead of moving the rows and columns of grid points, the code reader module 47 may be arranged to define an area surrounding each grid point. The code reader module 47 can then determine the value associated with the current grid point by determining whether or not there are any white pixels in the area associated with the grid point. If there are, then the code reader module decides that the corresponding bit value is zero otherwise it is one. The area surrounding each grid point is set to be slightly smaller than the area corresponding to each code element (for example an area corresponding to N_x-I pixels in the horizontal direction and Nγ-1 pixels in the vertical direction).

As those skilled in the art will appreciate, if a conductive grid is used that only has horizontal or vertical lines, the processing by the code reader module (in order to avoid sampling the conductive grid) is made easier as it only has to avoid the conductive grid in one dimension. This means that in the modification discussed above, instead of considering an area surrounding each grid point, the code reader module only has to consider the values of the pixels in the line which extends through the grid point at right angles to the direction of the conductive grid.

In the first embodiment, the capacitive sensing transducer 13 included a drive electrode 19 that was provided around the periphery of the sensing area 17. Further, in the first embodiment, the sensing transducer 13 was arranged so that it had to be swiped across the fingerprint or the 2D code to be sensed.

As those skilled in the art will appreciate, the surface area of the 2D array of sensor electrodes 15 may be made considerably larger so that it corresponds at least to the surface area of the 2D code 3 to be read. In this way, it is not necessary to swipe the sensing transducer 13 across the 2D code or across the fingerprint to be able to read the same. The use of such an "area" transducer will reduce the complexity of the detection software modules that are used to detect the 2D code and the characteristics of the fingerprint, but will require a larger and more expensive sensing area 17. It will also require the position of the 2D code 3 to be known so that the sensing transducer 13 can be placed over the 2D code 3.

In the first embodiment described above, a separate electrical connection was provided from each sensor electrode to a corresponding high impedance amplifier. As those skilled in the art will appreciate, it is not essential to have a separate processing channel (comprising the high impedance amplifier, demodulator and filter circuit and sample and hold circuit) for each sensor electrode. Instead, the signals from the different sensor electrodes may be multiplexed through a smaller number, or even a single processing channel. In the above embodiments, the 2D code was based on a Data Matrix type code in which the code elements 9 are arranged in a two-dimensional Cartesian array and bordered by an L-shaped frame 25. As those skilled in the art will appreciate, it is possible to apply the invention to other types of 2D codes, such as to conventional 2D barcodes, Maxicodes, Code one type codes, QR codes, Aztec codes etc. or to 2D codes in which the positions of the code elements are defined in polar coordinates.

In the above embodiment, a user's mobile telephone included a capacitive sensing transducer which could be used for both fingerprint sensing and 2D code reading. As those skilled in the art will appreciate, the above-described capacitive sensing transducer and the above-described fingerprint sensing and code reader modules may be provided in any type of computer device, such as a personal (laptop) computer, a portable digital assistant, etc.

In the above embodiments, the fingerprint sensing module and the code reader module operated substantially independently of each other. However, in some applications, these two modules may cooperate. For example, if the 2D code decoded by the code reader module 47 identifies a product code and a web address of a remote server from which more information may be obtained about the product, the fingerprint sensing module can provide valuable user ID information which will help the remote server target the information for that particular user. For example, if the remote server knows the identity of the user who has scanned the 2D code and it has a user profile for that user, it can target the information that is returned to the user's mobile telephone. In some cases the user identity may be determined from the mobile telephone number of the user's mobile telephone. However, where several users share the same mobile telephone, this is not possible. Consequently, the fingerprint sensing module 45 may be used to identify the current user, which information can then be sent to the remote server together with the product code corresponding to the scanned 2D code.

In the above embodiment, the information obtained from the 2D code was further information relating to the newspaper article and/or a link (URL) to further information or content stored on a remote server. As those skilled in the art will appreciate, in addition or alternatively, the information obtained from the 2D code may include an instruction to start a software module stored within the memory of the mobile telephone. Additionally, the software module can be configured to operate in a particular mode depending on the information obtained from the 2D code.

In the above embodiment, the 2D conductive code was formed from conductive ink and hidden under a visible image printed on a newspaper. As those skilled in the art will appreciate, transparent conductive material can be used, in which case, the 2D code may alternatively be formed on top of the text or picture of the newspaper article. Alternatively still, different colours of conductive inks could be used to form the conductive code. In this case, the 2D code can be hidden from the user's view by blending the code into the surrounding text or image. As those skilled in the art will appreciate, by hiding or merging the 2D code into the text or image, the code does not require any extra space on the printed medium.

In the above embodiment, the 2D code was printed on a newspaper and provided additional information relevant to an overlying newspaper article. As those skilled in the art will appreciate, the use of such codes can be used in a number of different applications. For example, various labels used on products typically require the provision of a visible machine readable code which can be optically scanned to identify the product. With the type of capacitive code described in the present application, such codes can be hidden within the label thus providing more space for advertising material on the label.

In the above embodiments, the sensing transducer was arranged to provide a drive signal to the code elements via a drive electrode. However, as those skilled in the art will appreciate, other types of sensing systems may be used. For example, instead of coupling the code elements to the drive electrode, the code elements may be coupled to a ground electrode of the sensing transducer. In this case, the sensing electrodes may each be arranged to sense a change in the local impedance or capacitance in its vicinity, which will vary depending on whether or not there is a grounded code element in its vicinity. In another example, each sensing pixel includes two adjacent sensor plates that form a capacitor. The dielectric of the capacitor then varies depending on whether or not the plates are adjacent a code element. Therefore, by connecting this capacitor to an appropriate detection circuit, the sensor can detect the presence or absence of the code elements by detecting the variation of the capacitance of the capacitor. Additionally, in the above embodiments it is not essential to use an AC drive signal, a DC drive signal may be used instead.

In the first embodiment described above, a DC voltage level was obtained from each sensor electrode, which voltage level varied depending on whether or not there was a code element adjacent the sensor electrode. As those skilled in the art will appreciate, this voltage level will also vary depending on the conductivity of the code elements. Therefore, in an alternative embodiment, instead of using 2D codes in which the presence or absence of a code element represents a binary one or a binary zero, the conductivity in the different code elements may also be varied thereby allowing more data to be stored per code element. For example, if four levels of conductivity are defined, two bits of information will be stored at each code element site within the 2D codes. Such an arrangement would therefore double the amount of information stored within the 2D code.

In the above embodiments, the sensor electrodes were square or circular. As those skilled in the art will appreciate, the sensor electrodes may be arranged to have any convenient shape. For example, in other embodiments, the sensor electrodes may be hexagonal in shape.

In the first embodiment described above, an array of sensor electrodes was provided with a drive electrode mounted around the outside of the array. As those skilled in the art will appreciate, the sensor could also work by making the drive electrode the sensor electrode and by making the sensor electrodes individual drive electrodes. In this case, the individual drive electrodes could be driven sequentially, with the output from the sensor electrode being processed through a single processing channel to provide the corresponding voltage level. Alternatively, the drive electrodes may be driven simultaneously with a respective drive signal at a respective different drive frequency. In this case, the signals obtained from the common sensor electrode would have to be frequency analysed to obtain the relevant voltage levels for each frequency and hence the signal levels associated with each drive electrode. The way in which such frequency analysis can be carried out will be apparent to those skilled in the art and will not be described further here.

In the above embodiments, the conductive codes were formed by printing conductive ink onto paper. As those skilled in the art will appreciate, different conductive print material could be used other than conductive ink. For example, conductive toner could be used instead. Similarly, the codes can be printed onto other print substrates, such as cardboard, plastic, textiles, glass etc. Such substrates are preferably substantially non-conductive, like paper. However, conductive substrates could be used. As those skilled in the art will appreciate, where such a conductive substrate is used, all the conductive code elements will be connected to each other automatically as soon as they are formed on the substrate.

Further, as those skilled in the art will appreciate, it is not essential to form the 2D codes on the substrate by printing them using conductive material. Alternatively, the 2D code may be formed using appropriate conductive material that is glued to or attached in some way to the appropriate substrate. In such a case, the code elements may be individually attached to the substrate or a layer of conductive material may be attached to the substrate and then portions of it etched or milled away to define the 2D code.

In the above embodiment, the 2D code is hidden from view under a picture of a newspaper article. As those skilled in the art will appreciate, the user may have to scan their mobile telephone over the entire image before the user's mobile telephone finds and decodes the 2D code. In order to mitigate this problem, the 2D code may be printed in several locations and in several different orientations on the printed medium.

In the above embodiments, the capacitive sensing transducer was formed integrally within the housing of the mobile telephone 1 1. As those skilled in the art will appreciate, the capacitive sensing transducer 13 may be provided in a separate housing and connected to the appropriate computer device via an appropriate wired or wireless link. As discussed above, in the first embodiment, the user's mobile telephone included various software modules, including the code reader module and the fingerprint sensing module. These software modules may be preinstalled in the mobile telephone or they may be installed by the user after purchasing the telephone. The software may be provided on a recording medium, such as a CD ROM or the like. Alternatively, the software may be downloaded on a carrier signal from a remote computer. The software may be provided in any convenient format, such as in a compiled executable format or in microprocessor language. Alternatively, the functionality of these software modules may be provided by dedicated hardware circuits.

As those skilled in the art will appreciate, the various embodiments and modifications described above are given by way of example only. Various other embodiments and modifications will be apparent to those skilled in the art.

Claims

CLAIMS:

1. A machine readable conductive array comprising: a plurality of conductive code elements geometrically distributed in a two-dimensional array in accordance with an associated code value; and conductive means connecting the plurality of conductive code elements together.

2. The array of claim 1 , wherein said conductive means connecting the plurality of conductive code elements together comprises a conductive grid arranged over the two-dimensional array of conductive code elements.

3. The array of claim 2, wherein conductive portions of said grid are connected in common to a conductive frame portion which borders at least part of said two-dimensional array of conductive code elements.

4. The array of claim 3, wherein said conductive portions of the grid extend in straight lines across the array of code elements.

5. The array of claim 4, wherein said conductive portions of the grid extend across the array in both dimensions of the array.

6. The array of claim 1 , wherein said conductive means connecting the plurality of conductive code elements together comprises a layer of conductive material.

7. The array of claim 6, wherein said conductive code elements have a first conductivity and wherein said layer of conductive material has a second conductivity which is different from said first conductivity.

8. The array of claim 1 , wherein the code elements are sized so that immediately adjacent code elements in the array overlap with each other and wherein said conductive means connecting the plurality of conductive code elements together comprises the overlapping portions of said conductive code elements.

9. The array of any preceding claim formed on a substantially non-conductive substrate.

10. The array of claim 9, wherein said substrate is made of at least one of: paper, cardboard, board, plastic, textile, glass.

1 1. The array of claim 9 or 10, wherein said conductive code elements are formed from print material printed onto the substrate.

12. The array of claim 1 1 , wherein said print material comprises conductive ink or conductive toner.

13. The array of any preceding claim, wherein the code elements are formed in an array defined by Cartesian or polar coordinates.

14. In combination, a computer device and a machine readable conductive array according to any preceding claim, the computer device comprising: a capacitive sensing transducer being operable to capacitively couple to said machine readable conductive array and to generate signals that vary with the geometric distribution of said conductive code elements; and a code reader module operable to process the signals generated by said capacitive sensing transducer to determine the code value associated with said machine readable array.

15. The combination of claim 14, wherein the capacitive sensing transducer comprises: i) a plurality of electrodes arranged over a sensing area of the transducer; ii) drive circuitry operable to generate a drive signal and to apply the drive signal to a first subset of the plurality of electrodes; and iii) sensor circuitry operable to sense signals obtained from a second subset of the plurality of electrodes, and wherein the capacitive sensing transducer and said machine readable array are arranged so that when the machine readable array is placed over said capacitive sensing transducer and upon the application of said drive signal to said first subset of electrodes, said signals which vary with the geometrical distribution of said code elements are generated in the second subset of electrodes.

16. The combination of claim 15, wherein said first subset of electrodes comprises an electrode provided around a periphery of said sensing area of the transducer.

17. The combination of claim 16, wherein said electrode which is provided around the periphery of said sensing area is a drive electrode, wherein the machine readable conductive array comprises a conductive frame bordering at least a portion of said two-dimensional array of conductive code elements and to which the conductive code elements are connected; wherein said conductive frame and said drive electrode are arranged so that, in use, they are coupled to each other whereby a drive signal applied to said drive electrode is coupled to said conductive frame and hence to each of the code elements in said array, thereby causing said code elements to generate a two-dimensional geometrically varying electric field in the vicinity of said sensor electrodes; and wherein said second subset of electrodes are operable to sense said geometrically varying electric field and to generate therefrom signals that vary in dependence upon the geometrical variation of the electric field and hence with the geometrical distribution of the code elements in said array.

18. The combination of claim 15, 16 or 17, wherein said first subset of electrodes and said machine readable array are arranged so that, in use, they are capacitively or galvanically coupled to each other.

19. The combination of any of claims 14 to 18, wherein said capacitive sensing transducer is further operable, in use, to capacitively couple to a finger placed over the capacitive sensing transducer and to generate therefrom signals that vary with identifying characteristics of said finger, and wherein said computer device further comprises a fingerprint sensing module operable to process signals generated by said sensing transducer when a finger is placed over said capacitive sensing transducer to determine the identifying characteristics of said finger.

20. The combination of claim 19, wherein said computer device is further operable: to automatically detect if a finger or a machine readable array is placed over said capacitive sensing transducer; and to pass the signals generated by said capacitive sensing transducer either to said fingerprint sensing module or to said code reader module in dependence upon said detection result.

21. The combination of claim 19 or 20, wherein said capacitive sensing transducer is operable to sense said finger or said machine readable code when scanned across the finger or machine readable code.

22. A printing system comprising: a reservoir of conductive printing material; a print data processor operable: i) to receive print data defining a conventional machine readable code comprising a 2D array of code elements; ii) to receive modification data defining modifications to be made to said received print data so that, when printed, the code elements are connected together; and iii) to process the received print data in accordance with the received modification data to generate modified print data defining a modified machine readable code comprising a modified 2D array of code elements; and a printer operable to receive the modified print data defining the modified machine readable code and operable to print the modified machine readable code using the conductive printing material from said reservoir on a print substrate, whereby the printed code elements of the machine readable code are connected together.

23. A system according to claim 22, wherein said printing material comprises conductive ink.

24. A system according to claim 23, wherein said conductive ink includes ink of different colours.

25. A system according to claim 22, wherein said printing material comprises transparent conductive material.

26. A system according to any of claims 22 to 25, further comprising a second reservoir of printing material and a second printer operable to receive print data for text and/or images to be printed on said substrate and operable to print the text and/or images using the printing material from the second reservoir on the print substrate.

27. A system according to claim 26, wherein said second printer is operable to print said text and/or images on said print substrate after said first printer has printed said code elements on said print substrate.

28. A capacitive sensing transducer comprising: a first electrode; and a plurality of second electrodes arrayed over a sensing area of the transducer; wherein the first electrode is geometrically distributed over the sensing area to surround each second electrode.

29. A transducer according to claim 28, wherein said first electrode comprises a plurality of ring portions each of which surrounds a respective one of the second electrodes and which are connected together to form a common electrode.

30. A transducer according to claim 28, wherein the first electrode is formed as a continuous electrode in the spaces between the second electrodes.

31. A transducer according to any one of claims 28 to 30, wherein said first electrode is a drive electrode and said second electrodes are sensor electrodes and wherein said drive electrode is operable, when energised, to generate a drive electric field in the local vicinity of each sensor electrode.

32. A computer device comprising a capacitive sensing transducer according to any of claims 28 to 31 formed integrally therewith for sensing machine readable conductive codes.

33. The computer device of claim 32 selected from one of the following: a mobile telephone, a portable digital assistant and a laptop computer.

34. A method of manufacturing an article comprising the steps of: receiving data defining a machine readable code comprising a 2D array of code elements; forming the machine readable code on the article in accordance with the received data; and outputting the article comprising the formed machine readable code; wherein said forming step forms said machine readable code using a conductive material to form individual code elements of the machine readable code and using a conductive structure to connect the individual code elements of the machine readable code together.

35. The method of claim 34, wherein said forming step forms said code elements on the article by printing conductive material onto the article.

36. The method of claim 35, wherein said forming step forms said conductive structure by printing conductive material onto the article.

37. A data processing apparatus comprising: a memory operable to hold a two dimensional array of sensor data representing a machine readable code comprising a plurality of code elements geometrically distributed in a two dimensional array in accordance with an associated code value, and a grid connecting the code elements together; and a processor operable to process the two dimensional array of sensor data to recover the code value represented by the array of code elements whilst avoiding the grid connecting the code elements together.

38. An apparatus according to claim 37, wherein the resolution of said two dimensional array of sensor data is greater than the resolution of said two dimensional array of code elements and wherein said processor is operable to sub-sample the sensor data to recover the code value represented by the array of code elements whilst avoiding the grid connecting the code elements together.

39. An apparatus according to claim 38, wherein said processor is operable to define an equispaced grid of sampling points and is operable to consider the sensor data around each grid point to determine the value of the bit corresponding to that grid point.

40. An apparatus according to claim 38, wherein said processor is operable to consider the data within rows or columns of the sensor data to identify the rows or columns having the greatest variation in sensor data values and is operable to move the positions of sampling points in dependence upon the determined rows or columns having the greatest variation in sensor data values.

41. A computer executable instructions product comprising computer executable instructions for causing a programmable computer device to carry out the method of any of claims 34 to 36 or for configuring a programmable computer device as the printing system of any of claims 22 to 27 or as the data processing apparatus of any of claims 37 to 40.