Electrical switch and method of generating an electrical switch output signal

[0002] This application is based upon a provisional application filed on May 7, 1999 with a Ser. No. 60/133,002, and is hereby incorporated by reference.

[0003] The present invention relates to electric switches, and more particularly pertains to an improved piezoelectric switch incorporating a unique system of discerning between deliberate touch activation and various other false trigger possibilities which can provide information concerning the duration of the activating contact.

[0004] Mechanical activated switches provide switch control capabilities,but are affected by environmental factors such as extreme temperature variations and moisture and are subject to degradation due to wear, which can limit such switch's life and effectiveness. Non-mechanical, electrical switches, like piezoelectric switches, avoid the life limiting wear characteristics inherent to mechanical switches, but are subject to false activation.

[0005] The present invention provides an improved electrical switch which possesses the ability to detect the occurrence of when an object such as a human finger applies pressure to the switch and the ability to monitor the duration of the presence of such object in contact with the switch. The present invention, therefore, can provide a relatively accurate, controlled means of discerning between intentional switch actuation and anomalies which might cause unintentional activation as well as provide an accurate measure of the duration of the switch activation contact.

[0006] The present invention is broad enough to contemplate an electrical switch which monitors two separate conditions. The preferred embodiment, described in detail subsequent, monitors actuation pressure applied to the switch and capacitive change in the switch's case caused by contact with a conductive object, such as a human finger. By requiring these separate conditions precedent, the switch avoids actuation by pressure placed upon the switch inadvertently, such as by incidental contact or by sound waves or atmospheric variations, and avoids actuation by only conductive contact with the switch, such as by contact with inadvertent liquid spills, humidity, or rain.

[0007] The present invention contemplates an electrical switch and a method of generating an electrical switch output signal. The electric switch senses both pressure placed upon the switch's surface and the contact of the object exerting the pressure on the switch. When both conditions exist, the switch is activated. The electrical switch may employ a piezoelectric element to recognize the application of pressure, a capacitive sensing circuit to recognize the presence of an object applying the pressure, and a microcontroller circuit to control output switch circuity upon satisfaction of both conditions precedent. The electrical switch can be configured to provide a continuous output signal for the duration that the switch is pressed after the conditions are satisfied or to switch between open and closed states each time the conditions are satisfied

[0008] While the above are important features of the invention, there are, of course additional features of the invention that will be described hereinafter and which will form the subject matter of the claims appended hereto. In this respect, before explaining at least one preferred embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also it is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting. As such, those skilled in the art will appreciate that the conception, upon which the disclosure is based, may readily be utilized as a basis for the designing of other structures, methods, or systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention.

[0009] The foregoing features of the present invention will be more readily understood by reference to the following detailed description taken with the accompanying drawings, in which:

[0010] FIG. 1 is a longitudinal cross-sectional, schematic view of an electrical switch according to one embodiment of the present invention;

[0011] FIG. 2 is a schematic diagram of the circuitry of the embodiment of the present invention shown in FIG. 1;

[0012] FIG. 3 is a flow diagram of the operation of the embodiment of the present invention shown in FIG. 1 and 2;

[0013] FIG. 4 is a logic flow diagram of the operation of another embodiment of the present invention.

[0014] The present invention will be described with reference to the accompanying drawings wherein like reference numerals refer to the same item.

[0015] There is shown in FIG. 1 an electrical switch according to one embodiment of the present invention. The switch includes a substantially cylindrical, conductive case 10 possessing a closed distal end cap 12 and a series of threads about the external peripheral surface to permit installation of the switch in a correspondingly threaded aperture in a wall, plate, or other mounting structure. Thus, the switch may be adapted for a wide range of applications in a wide variety of mounting structures. While the preferred embodiment is depicted as a threaded cylindrical conductive case, the present invention contemplates cases of various shapes and sizes as well as a variety of installation means other than those depicted in FIG. 1.

[0016] The closed distal end cap 12 of the case 10 is sufficiently pliant and elastic to bend slightly (to a deformity of approximately two or more microns) when the end cap 12 receives pressure input such as is generated by a person's finger. Standard human finger pressure is in the range of three to five Newtons. The distal end cap 12, therefore, is made of a material and is of a corresponding thickness which can be deflected two or more microns by ordinary human finger pressure. In the preferred embodiment described herein, the closed distal end cap 12 of the case 10 may be integrally formed with the case 10, but need not be. The case 10 may be fashioned of a conductive material such as aluminum, stainless steel, brass, or any other equivalent rigid, semirigid, or non-rigid conductive material. The cap 12 may be fashioned of a material which is either the same as or different from that forming the case 10. The preferred embodiment uses a cap 12 that can be deflected as described previously, however, the invention broadly contemplates other means of transmitting pressure information such as push buttons acting against a compression spring or similar means. A support frame 14 is mounted to the interior surface of the distal end cap 12 and holds a piezoelectric element 16 having a contact surface 22 in contact with the distal end cap 12, whereby pressure applied to the distal end cap 12 in the direction of arrow 17 shown in FIG. 1 is transmitted to the piezoelectric element 16. The support frame may be fashioned from any non-conductive material such as plastic, rubber or glass. When pressure is applied to the contact surface 22 of piezoelectric element 16, the element flexes, whereby surface charges are induced by the piezoelectric element's dielectric displacement, and an electrical field is built up within the piezoelectric element 16. Typical piezoelectric elements require being flexed less than two microns to generate such an electric field. Therefore, the pressure transmitted to flex the piezoelectric element need only be slight.

[0017] The electric field within the piezoelectric element 16 is transformed into electric voltage on the element's voltage transmission surface 24. This voltage is transmitted to piezo signal conditioning circuitry 18 by flexible leadless conductor pad 20. The preferred embodiment utilizes an anisotropic electrical conductive rubber. The invention, however, contemplates connecting the piezoelectric element 16 to the piezoelectric conditioning circuitry by any electrically conductive means. The transmitted voltage is received by piezo signal conditioning circuitry 18, which upon receipt of the transmitted voltage, generates a control signal, which signal is transmitted to the microcontroller circuitry 32. This signal indicates to the microcontroller that pressure is applied to the distal end cap 12 of the case 10.

[0018] Microcontroller circuitry 32 incorporates capacitive sensing circuitry which is electrically connected to the case 10 by enclosure contact clips 26. Contact by a human finger, hand, or other conductive object with the closed distal end cap 12 of the case 10 varies the base capacitance of the case 10 and generates a contact signal within the microcontroller circuitry 32 in a manner fully explained below. When the microcontroller circuitry 32 acknowledges the contact signal and receives the control signal from the piezo signal conditioning circuitry 18, the microcontroller circuitry 32 selectively instructs output switch circuitry 34 to provide either an active or an inactive current sink at interface terminal 28. The microcontroller circuitry 32 selection of active or inactive current sink is more fully explained below.

[0019] The microcontroller circuitry 32 and piezo signal conditioning circuitry 18 are both powered by power supply circuitry 30. The operation of the power supply circuitry 30 is more fully explained below.

[0020] FIG. 2 is a schematic diagram of the interface terminal 28, power supply circuitry microcontroller circuitry 32, piezo signal conditioning circuitry 18, and output switch circuitry 34. The interface terminal 28 possesses six interface pins. Power supply circuitry 30 is supplied external voltage, direct current or alternating current, through interface terminal 28 pin number two. Series diode 100 conducts only the positive component of the input waveform and the positive peak of the unregulated input voltage is then held by capacitor C1. Zener diode 102, biased by resistor 104, provides a stable reference voltage to the base of transistor Q106. Load current to power the microcontroller circuitry flows from C1 through the collector of transistor Q106, where the voltage is dropped to a steady five volts at the emitter of Q106. Capacitor C108 then provides high frequency decoupling for the microcontroller power supply.

[0021] Piezo signal circuitry 18 comprises piezoelectric element 16 in parallel with load resistor 136 and spike arrest zener diode 110. Output voltage derived from bending the piezoelectric element 16 turns on transistor 112 dropping input potential to the microcontroller circuitry 32 from its normally high state (VDD) to low (gnd/RTN), thereby indicating pressure applied to distal closed end 12 of the case 10.

[0022] Microprocessor 114 generates an oscillating output waveform at microprocessor 114 pin number five which is received by microprocessor 114 pin number seven through resistor 116. When the switch is untouched, capacitor 118 leaves the output waveform unaffected. When contact is made with the switch such as human contact, the capacitance of the case 10 increases. The increased capacitance appears in series with capacitor 118 through enclosure contact clips 26. The combined capacitance phase shifts the oscillating output waveform as the waveform is received at microprocessor 114 pin number seven. The microprocessor 114 is internally programmed to recognize this phase shift as contact with the closed distal end cap 12 of the case 10. The microprocessor 114 can be programmed to recognize any range of capacitive change to increase or decrease the actuation contact requirement for a corresponding range of switch sensitivity. While the preferred embodiment utilizes capacitive sensing circuitry to sense contact with the case, the invention broadly contemplates other presence sensing devices which may not require contact with the case. Such presence sensing devices may include photovoltaic cells in which an object interferes with the light detection of the cell, magnetic or electromagnetic field detection circuitry which can sense a change in magnetic or electromagnetic fields induced by proximate objects, temperature sensing means which senses change in temperature due to proximate objects, or any other similar presence sensing devices.

[0023] When microprocessor 114 receives a low signal from piezo signal conditioning circuitry 18 and recognizes contact with the closed distal end cap 12 of the case 10, the microprocessor 114 produces two output signals at microprocessor 114 pins four and five, one constant and the other a pulse of five hundred millisecond duration. The five hundred millisecond signal can be used for a variety of purposes, for example, to create an audible signal which indicates switch actuation. As the invention is not limited to these particular output signals, the microprocessor can be programmed to generate a variety of other outputs signals of varying duration or to output waveforms in response to recognition of the two conditions precedent. The output signals are transmitted to identical circuits within output switch circuitry 34. While the preferred embodiment utilizes a microprocessor, the invention contemplates other determining means such as linear logic circuitry or discrete circuitry.

[0024] The preferred embodiment utilizes output switch circuitry to provide current-sink outputs which are transmitted through the interface terminals to external electronic equipment. The invention is broad enough, however, to contemplate a switch providing actual electrical continuity between two or more electrical nodes, or the output of waveforms or various signals responsive to satisfaction of the two predetermined conditions precedent. To provide current-sink switch capability, transmitted output signals from the microprocessor 114 are received at the gates of transistors 120 and 122 across resistors 124 and 126 respectively. High transmitted output signals turns off transistors 120 and 122 which, in turn, turns off transistors 128, 130, 132, and 134. When transistors 128, 130, 132, and 134 are off, electrical discontinuity exists between interface terminal 28 output pin numbers one and three and ground/RTN. This “inactive current-sink” state is recognized by external circuitry to be the electrical equivalent of an “open” circuit. Low transmitted output signals turns on transistors 120 and 122 which in turn turns on transistors 128, 130, 132, and 134. With transistors 128, 130, 132, and 134 on, electrical continuity exists between interface terminal 28 output pin number 6 and ground/RTN, and between interface terminal 28 output pin number 4 and ground/RTN, allowing AC or DC current to flow through each circuit. This “active current-sink” state is recognized by external circuitry to be the electrical equivalent of a “closed” circuit.

[0025] While the preferred embodiment described in FIGS. 1 and 2 and explained above show an electric switch case 10 within which all circuitry is self contained, the invention should not be so limited. Variations of the invention are possible whereby all or some of the elements and circuitry described are electrically interconnected but separate from the body of the switch. Such variations would allow for installation in locations where a self contained switch may be impractical.

[0026] FIGS. 3 and 4 shows the microprocessor's operational flow for two embodiments of the electrical switch. In FIG. 3, interface terminal 26 output pins one and three begin in a default “open” or “inactive current-sink” state. When the case 10 is touched as described above, the microprocessor 114 senses a change in the case's 10 capacitance as described previously and initializes a two second timer. If within the two second period, the piezo signal conditioning circuitry 18 is activated by pressure as previously described, the microprocessor 114 sets interface terminal 28 output pin one to the “closed” or “active current-sink” state and interface terminal 28 output pin three to the “closed” or “active current-sink”state for five hundred milliseconds and then resets interface terminal 28 output pin three to the “open” or “inactive current-sink” state. The microprocessor 114 then initializes a ten millisecond timer. If within ten milliseconds, the case's 10 capacitance returns to its initial value due to removal of contact with the case 10, the terminal 28 output pin remains in the “closed” or “active current-sink” state until the ten millisecond time period is over. If the case's 10 capacitance indicates touch contact has returned prior to the end of the ten millisecond period, the terminal 28 output pin one remains in the “closed” or “active current-sink” state, and the microprocessor 114 reinitializes the ten millisecond timer, thereby monitoring the switch every ten milliseconds until the case 10 is released. In this way, the ten millisecond timer allows inadvertent removal of touch contact with case 10 without resetting terminal 28 output pin one to an “open” or “inactive current-sink” state. This is a method of providing a switch “debounce”. If the case's 10 capacitance remains at its initial value at the end of the ten millisecond period, indicating that contact with the case 10 has been removed, the microprocessor 114 resets terminal 28 output pin one to an “open” or “inactive current-sink” state. This embodiment therefore, provides current-sink output for the duration that the electrical switch's closed distal end cap 12 of the case 10 is pressed. Again, the invention is not limited to the particular timer durational increments mentioned above (two seconds and five-hundred milliseconds). Other timer increments can easily be programmed into the microprocessor 114 to alter the inventions sensitivity and speed.

[0027] An alternative embodiment shown in FIG. 4 utilizes the microprocessor 114 to alternate setting interface terminal 28 pin 1 to the “open” and “closed” states upon satisfaction of the two conditions precedent described in detail above. The default state is, therefore, unimportant. When the case 10 is touched as described above, the microprocessor 114 initializes a two second timer. If within the two seconds the piezo conditioning circuitry 18 sends a pressure signal as described above, the microprocessor 114 sets interface terminal 28 pin 3 to the “closed” or “active current-sink” state for five hundred milliseconds and then resets interface terminal 28 pin 3 to the “open” or “inactive current-sink” state. At the same time, the microprocessor senses whether interface terminal 28 pin 1 is in the “closed” or “open” state and sets the output to the opposite state. In this embodiment, therefore, the electrical switch's output current-sink will toggle between active and inactive with each individual contact with the closed distal end cap 12 of the case 110. The invention is not limited to the two second timer duration mentioned above. Other timer increments can easily be programmed into the microprocessor 114 to alter the inventions sensitivity and speed.

[0028] While the above are important features of the invention, there are, of course additional features of the invention that will form the subject matter of the claims appended hereto. In this respect, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the previous description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also it is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting. As such, those skilled in the art will appreciate that the conception, upon which the disclosure is based, may readily be utilized as a basis for the designing of other structures, methods, or systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention.

[0029] The invention is illustrated with respect to specific embodiments thereof. Though numerous characteristics and advantages are set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only. Changes may be made in detail, especially in matters of materials, shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed. Various modifications and additions may be made and will be apparent to those skilled in the art. Accordingly, the invention should not be limited by the foregoing description in any manner, but rather should be defined only by the following claims.