GB1599660A - Code generating devices - Google Patents

Description

(54) CODE GENERATING DEVICES (71) We, THE MARCONI COMPANY LIMITED, a British Company, of Marconi House, New Street, Chelmsford, Essex CM 1 IPL, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to code generating devices and is specifically concerned with such devices which generate a digital code, when subjected to pressure. One known example of such a device is a push-button switch in combination with a code generating circuit. For some applications many such devices may be required.For example, in a keyboard used to enter data into a processing system, a large number of individual pushbutton switches are required which, when pressed, generate a particular code which can be used to instruct a processor accordingly.

The present invention seeks to provide such a code generating device which is relatively simple in construction and which is inherently reliable.

According to this invention, a code generating device includes a plurality of layers of piezo-electric material positioned one above the other; means for applying pressure to all layers. the device being arranged to generate a multi-bit digitally coded signal when said pressure is applied, and wherein said signal comprises a number of bits equal to the number of said layers with each bit being associated with a respective one of said layers.

Preferably, the piezo-electric material is polarised polyvinylidene fluoride (PVF2).

In a preferred embodiment, all layers are poled with a like polarity.

In such an embodiment, a code can be generated by taking the electrical signals from selected ones of the layers and applying them in parallel to a data highway having at least as many individual data paths as there are piezo-electric layers. A plurality of code generating devices can be provided, all of which can be coupled onto a common data highway. The application of pressure to a layer of PVF2 produces a voltage pulse having a particular polarity, and a pulse of similar shape but inverted polarity is produced when the pressure is removed. For some applications, it may be preferred to generate pulses having only a single polarity and, in this case, appropriately poled diodes can be connected to the signal outputs of each code generating device to remove the positive or negative pulse, as required.Alternatively, however, both the positive and negative pulses could be used to form two codes which follow each other in time, one code being the inverse of the other and being used to provide verification of the code generated.

It is possible to generate a code sequence by providing polarity inversion of selected layers of the piezo-electric material so that when pressure is applied to the self-encoding key, a coded pattern of positive and negative pulses is obtained, followed by a verification code consisting of an inverted sequence of pulses when the pressure is removed.

The invention is further described, by way of example, with reference to the drawings accompanying the Provisional specification in which, Figure 1 illustrates a single layer of a piezo-electric material which is provided with appropriate electrode areas on its two major faces, Figure 2 illustrates the nature of the pulses generated by a piezo-electric layer when it is subject to pressure and release, and Figure 3 illustrates diagrammatically a system having a number of code generating devices in accordance with the present invention.

Referring to Figure 1, there is shown therein a rectangular portion of an electrically polarised PVF2 film 1 having an electrode 2 on its upper surface and an electrode 3 on its lower surface. Such a film is typically very thin and may be between 6 ym to 25 /lm thick. As is known, PVF2, when suitably polarised, provides a voltage output when subjected to pressure, the nature of the output signal is shown in Figure 2 and it will be seen that when pressure is applied, a positive pulse having a rapid rise time and an exponential decay is produced and this is followed by a negative pulse of similar, but inverted, profile when the pressure is released. Whether a positive pulse is followed by a negative pulse, or vice-versa, will depend on the polarity of the polarisation of the PVF2 film 1.

Figure 3 shows a number of code generating devices 4, 5, 6, one of which, device 4, is shown in greater detail. Device 4 consists of a push-button 7 in contact with an elastomer pad 8 which transfers pressure evenly to a number of films 9 of PVF2. Each film of PVF2 is provided with a pair of electrodes 10 and 11 on its opposite major faces, and each film is separate from neighbouring layers by a thin insulating layer 12. The electrodes 10 are connected together and to a reference point 13 which, in this case, is shown as earth. The electrodes 11 are passed to a data highway 14 via a selector 15. At the selector 15, selected ones of the leads connected to electrodes 11 are interrupted so that no signal from these leads reaches the data highway 14.When pressure is applied to the pushbutton 7, each film of PVF2 generates a positive pulse, assuming that each layer is poled in a similar and appropriate manner, and these pulses are applied to individual data paths 16, 17, 19, 20 and 22, but no signal is applied to paths 18 and 21, since the corresponding lines are interrupted in selector 15. Accordingly. the code 1101101 appears on the data highway 14. Similar selfencoding keys are provided at 5 and 6 and the connections in the corresponding selectors 23 and 24 are chosen so that each key generates a unique code, which is passed onto the common highway 14. It will be appreciated that the inverse complementary code is generated when pressure is removed from the push-button 7.If it is not desired to allow negative pulses onto the data highway 14, appropriately poled diodes can be connected to each of the electrodes 11 so as to provide a short circuit to earth for a negative signal.

Although only seven layers of PVF2 material are shown in the code generating device 4, a great many more layers could be provided if desired, since each layer is very thin. In this way, long and complex codes can be generated. It will be appreciated that the operation of the devices requires no external power supply.

WHAT WE CLAIM IS: 1. A code generating device including a plurality of layers of piezo-electric material positioned one above the other; means for applying pressure to all layers, the device being arranged to generate a multi-bit digitally coded signal when said pressure is applied, and wherein said signal comprises a number of bits equal to the number of said layers with each bit being associated with a respective one of said layers.

2. A device as claimed in claim I and wherein the piezo-electric material is polarised polyvinylidene fluoride (PVF2).

3. A device as claimed in claim 1 or 2 and wherein all layers are poled with a like polarity.

4. A device as claimed in any of the above claims and wherein appropriately poled diodes are connected to the signal outputs to remove either the positive or negative component of a signal generated when pressure is applied to the device.

5. A device as claimed in claim 3 or 4 and wherein a code is generated by taking the electrical signals from selected ones of the layers and applying them in parallel to a data highway having at least as many individual data paths as there are piezo-electric layers.

6. A data distribution arrangement including a data highway having a plurality of individual data paths; a plurality of code generating devices, each device being as claimed in any one of claims 1 to 4, and which are coupled to said data highway; and wherein respective digits of each signal are applied to predetermined ones of the individual data paths.

7. A code generating device substantially as illustrated in and described with reference to the drawings accompanying the Provisional specification.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (7)

**WARNING** start of CLMS field may overlap end of DESC **. exponential decay is produced and this is followed by a negative pulse of similar, but inverted, profile when the pressure is released. Whether a positive pulse is followed by a negative pulse, or vice-versa, will depend on the polarity of the polarisation of the PVF2 film 1. Figure 3 shows a number of code generating devices 4, 5, 6, one of which, device 4, is shown in greater detail. Device 4 consists of a push-button 7 in contact with an elastomer pad 8 which transfers pressure evenly to a number of films 9 of PVF2. Each film of PVF2 is provided with a pair of electrodes 10 and 11 on its opposite major faces, and each film is separate from neighbouring layers by a thin insulating layer 12. The electrodes 10 are connected together and to a reference point 13 which, in this case, is shown as earth. The electrodes 11 are passed to a data highway 14 via a selector 15. At the selector 15, selected ones of the leads connected to electrodes 11 are interrupted so that no signal from these leads reaches the data highway 14.When pressure is applied to the pushbutton 7, each film of PVF2 generates a positive pulse, assuming that each layer is poled in a similar and appropriate manner, and these pulses are applied to individual data paths 16, 17, 19, 20 and 22, but no signal is applied to paths 18 and 21, since the corresponding lines are interrupted in selector 15. Accordingly. the code 1101101 appears on the data highway 14. Similar selfencoding keys are provided at 5 and 6 and the connections in the corresponding selectors 23 and 24 are chosen so that each key generates a unique code, which is passed onto the common highway 14. It will be appreciated that the inverse complementary code is generated when pressure is removed from the push-button 7.If it is not desired to allow negative pulses onto the data highway 14, appropriately poled diodes can be connected to each of the electrodes 11 so as to provide a short circuit to earth for a negative signal. Although only seven layers of PVF2 material are shown in the code generating device 4, a great many more layers could be provided if desired, since each layer is very thin. In this way, long and complex codes can be generated. It will be appreciated that the operation of the devices requires no external power supply. WHAT WE CLAIM IS:

1. A code generating device including a plurality of layers of piezo-electric material positioned one above the other; means for applying pressure to all layers, the device being arranged to generate a multi-bit digitally coded signal when said pressure is applied, and wherein said signal comprises a number of bits equal to the number of said layers with each bit being associated with a respective one of said layers.

2. A device as claimed in claim I and wherein the piezo-electric material is polarised polyvinylidene fluoride (PVF2).

3. A device as claimed in claim 1 or 2 and wherein all layers are poled with a like polarity.

4. A device as claimed in any of the above claims and wherein appropriately poled diodes are connected to the signal outputs to remove either the positive or negative component of a signal generated when pressure is applied to the device.

5. A device as claimed in claim 3 or 4 and wherein a code is generated by taking the electrical signals from selected ones of the layers and applying them in parallel to a data highway having at least as many individual data paths as there are piezo-electric layers.

6. A data distribution arrangement including a data highway having a plurality of individual data paths; a plurality of code generating devices, each device being as claimed in any one of claims 1 to 4, and which are coupled to said data highway; and wherein respective digits of each signal are applied to predetermined ones of the individual data paths.

7. A code generating device substantially as illustrated in and described with reference to the drawings accompanying the Provisional specification.