Abstract:
A protective circuit for an apparatus includes an accelerometer having an output and a microcontroller coupled to the output of the accelerometer. The protective circuit also includes a switch for controlling the apparatus coupled to an output of the microcontroller and a load coupled to the switch. A power source is coupled to the load and the switch. In operation the microcontroller is cable of sending a signal to the switch to turn of power to the load when a dangerous condition as detected from the accelerometer data has occurred.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a continuation of U.S. application Ser. No. 12/331,364, filed Dec. 9, 2008, now abandoned, the disclosure of which is incorporated by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The invention relates, in general, to a protection circuit that is capable of disabling an apparatus after sensing a predetermined condition. More particularly, the protection circuit may be used in appliances that are capable of generating a dangerous condition. 
       BACKGROUND 
       [0003]    Consumer appliances can be dangerous when left unattended. For example, the heat generated by an electric iron that is left on and unattended can damage the surface on which it is resting or potentially cause a fire. Other consumer appliances such as curling irons, soldering irons, electric heaters, and the like may also be dangerous if left on in an unattended state, exceedingly more so if oriented in certain positions, e.g., arranged on a heating surface for an electric iron. Accordingly, in the related art, different types of protection circuits have been developed to address these problems. These circuits disable or turn off the appliance if it is not being used and/or is sitting in a potentially hazardous position. 
         [0004]    Typical related art methods use a mechanically operated switch driven by gravity or some other acceleration. One type of switch includes a metal ball that is free to roll on a track and comes to rest on a set of electrical contacts at certain angles or under certain accelerations. This type of switch is problematic as it can lose its reliability over time. For example, the mechanical aspects of the switch may corrode over time. In addition, the number of potentially dangerous conditions for which these switches provide useful prevention is narrow due to the mechanical limitations of the switch. The mechanical switch design typically requires a large angle of rotation for the metal ball to move and make contact with the electrical contacts. 
         [0005]    Another related method is taught by U.S. Pat. No. 4,203,101, incorporated by reference, which discloses an electric iron having a sensor in the handle that is sensitive to the pressure of an operator&#39;s hand. These types of sensors are also limited in their applicability as a user may not want the apparatus to turn off even if the sensor is not triggered. 
       SUMMARY OF THE INVENTION 
       [0006]    Accordingly, the invention is directed to a protective circuit for an apparatus that substantially obviates one or more of the problems due to limitations and disadvantages of the related art. 
         [0007]    An advantage of the invention is to provide a low cost, accurate protective circuit for use in a wide variety of apparatuses. 
         [0008]    Another advantage of the invention is to provide a protective circuit that is capable of turning off an apparatus if left in an unattended state for a predetermined period of time or if left in a hazardous orientation also for a predetermined period of time. 
         [0009]    Additional features and advantages of the invention will be set forth in the description which follows and in part will be apparent from the description or may be learned by practice of the invention. The features of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. 
         [0010]    To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described, the invention is directed towards a protective circuit for an apparatus including an accelerometer having an output and a microcontroller coupled to the output of the accelerometer. The protective circuit also includes a switch for controlling the apparatus coupled to an output of the microcontroller and a load coupled to the switch. A power source is coupled to the load and the switch. In operation the microcontroller is capable of sending a signal to the switch to turn off power to the load when a dangerous condition has occurred. 
         [0011]    In another aspect of the invention, a protective circuit for an appliance includes a two-axis micro electro-mechanical systems (MEMS) accelerometer having a first axis in a y-direction and a second axis in an x-direction. The protective circuit also includes a microcontroller coupled to an output of the two-axis MEMS accelerometer and a switch to turn on or off the small appliance coupled to an output of the microcontroller. The microcontroller is configured to turn off the switch when the appliance is in a predetermined orientation for a predetermined period of time. The protective circuit also includes a load coupled to the switch and a power source coupled to the load and the switch. 
         [0012]    In yet another aspect of the invention, a method of controlling an apparatus with a protective circuit of the invention includes performing a periodic interrupt on a microcontroller. In a next step, values are read from a MEMS accelerometer, wherein the values include a first gravitational measurement in a first direction and a second gravitational measurement in a second direction being substantially perpendicular to the first direction. In a subsequent step, the first and second gravitational values are compared with a previous first and second gravitational value and a no motion counter is incremented when the first and second gravitational values are within a first predetermined range of a previously read first and second gravitational values. In addition, the no motion counter is reset to zero when the first and second gravitational values are within a second predetermined range of the previous first and second gravitational values when comparing the no motion counter to a predetermined first maximum no motion count. Moreover, the first and second gravitational values are compared with predetermined first and second gravitational values when the no motion counter is greater than the maximum no motion counter. A signal is sent to turn off load to an apparatus when the no motion counter is above the first predetermined maximum no motion count the first and second gravitational values are within a predetermined tolerance of the predetermined first and second gravitational values. Moreover, a return command is sent to the microcontroller when the first and second gravitational values are not within a predetermined tolerance of the predetermined first and second gravitational values. 
         [0013]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    The accompanying drawings are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. 
           [0015]    In the drawings: 
           [0016]      FIG. 1  illustrates a block diagram of a protective circuit in accordance with an embodiment of the invention; 
           [0017]      FIGS. 2A and 2B  illustrate an electric iron implementing a protective circuit in accordance with another embodiment of the invention; 
           [0018]      FIG. 3A  illustrates a theoretical output of a two-axis MEMS accelerometer in an electric iron positioned stationary upright on its heel; 
           [0019]      FIG. 3B  illustrates a theoretical output of a two-axis MEMS accelerometer in an electric iron when moving the iron in a front to back motion primarily along an axis parallel to the face of the iron and substantially parallel to a line running from toe to heel of the iron; 
           [0020]      FIG. 3C  illustrates a theoretical output of a two-axis MEMS accelerometer in an electric iron when moving the iron in a side to side motion primarily along the axis substantially parallel to the face of the iron and substantially perpendicular to a line running from toe to heel of the apparatus; 
           [0021]      FIG. 3D  illustrates a theoretical output of a two-axis MEMS accelerometer in an electric iron positioned stationary on its heating surface; 
           [0022]      FIG. 3E  illustrates a theoretical output of a two-axis MEMS accelerometer in an electric iron positioned stationary laying on its side having the heating surface of the iron apparatus substantially perpendicular to the axis of gravity; and 
           [0023]      FIG. 4  is a flowchart illustrating functionality of a microcontroller according to another embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0024]    The invention relates, in general, to a protection circuit that is capable of disabling an apparatus after sensing a predetermined condition. More particularly, the protection circuit may be used in appliances that are dangerous if left unattended especially if oriented in certain positions. 
         [0025]    One embodiment of the invention is directed towards a protective circuit for an apparatus. The apparatus may be any apparatus capable of implementing the protective circuit. For example, the apparatus may be an electric iron, soldering iron, hair dryer, electric heater and the like. The protective circuit includes an accelerometer having an output and a microcontroller coupled to the output of the accelerometer. A switch to control a power source is coupled to an output of the microcontroller and a load of the apparatus. The switch is capable of being activated by a signal output from the microcontroller. When utilizing an alternating current (AC) power source the switch may be a triac. Alternatively, when utilizing a direct current (DC) power source the switch may be a field effect transistor (FET). Of course, other switches as known in the art may also be utilized. 
         [0026]    In a preferred embodiment, the microcontroller is configured to output a control signal to turn off the switch when it receives output values from the accelerometer that are substantially equal to predetermined values after a predetermined time period. The predetermined values correspond to a potentially dangerous orientation of the apparatus. The predetermined time period is chosen based on the hazard of leaving an apparatus in a potentially dangerous orientation for a period of time. For example, the predetermined time period for an apparatus left unattended on its heating surface may be less than that for the apparatus left unattended on its heel, e.g., 5 minutes and 10 minutes, respectively. 
         [0027]    The accelerometer may include any axis accelerometer, e.g., a four-axis accelerometer, three-axis accelerometer, two-axis accelerometer, and one-axis accelerometer. In a preferred embodiment, a two-axis accelerometer is utilized in the apparatus. The accelerometer may include any axis MEMS accelerometer as known in the art. In a preferred embodiment, a two-axis MEMS accelerometer is used having an orientation axes generally at right angles to each other. The MEMS accelerometer operates in-plane and is designed to be sensitive only to a direction in the plane of the die. Accelerometers may be either digital or analog. In a preferred embodiment, the accelerometers are digital accelerometers. When utilizing an analog accelerometer the device may be using an internal analog to digital (A/D) converter in the microcontroller. An additional axis may be added, e.g., adding an additional out-of-plane axis, thereby forming a 3-axis accelerometer. 
         [0028]    MEMS accelerometers are available in a wide variety of measuring ranges, reaching up to thousands of Gs. The designer optimizes the apparatus by compromising between sensitivity and the maximal acceleration that can be measured. Some example MEMS accelerometers include STMicroelectronics LIS302DL MEMS motion sensor, the data sheet of which is incorporated by reference for all purposes as if fully set forth herein; STMicroelectronics LIS202DL MEMS motion sensor, the data sheet of which is hereby incorporated by reference for all purposes as if fully set forth herein; STMicroelectronics LIS331DL MEMS motion sensor, the data sheet of which is hereby incorporated by reference for all purposes as if fully set forth herein; STMicroelectronics LIS244AL MEMS motion sensor, the data sheet of which is hereby incorporated by reference for all purposes as if fully set forth herein; and STMicroelectronics LIS244ALH MEMS motion sensor, the data sheet of which is hereby incorporated by reference for all purposes as if fully set forth herein. Of course other accelerometers as known in the art may also be used, such as, laser accelerometers and the like. 
         [0029]    The microcontroller may be any conventional microcontroller. For example, the microcontroller may include 8 bit architecture, 16 bit architecture or higher architectures. In a preferred embodiment, a low cost microcontroller is utilized, such as, STMicroelectronics 8-bit ST7LITE39 microcontroller; the data sheet for ST7LITE39 is hereby incorporated by reference as if fully set forth herein. 
         [0030]    Reference will now be made in detail to other embodiments of the invention, examples of which are illustrated in the accompanying drawings. 
         [0031]      FIG. 1  illustrates a block diagram of a protection circuit in an apparatus according to one aspect of the invention. Referring to  FIG. 1 , the protection circuit is generally depicted as reference number  100 . The protection circuit includes a two-axis MEMS accelerometer  102  coupled to a microcontroller  104 . Output signals  106  from the MEMS accelerometer  102  are input into the microcontroller  104 . The output signals  106  are described with more specificity in  FIGS. 3A-3E  below. Switches  112  provide inputs to microcontroller  104  that may be used to turn the appliance on or off or to select various settings. The microcontroller  104  has an output signal  114  coupled to a switch  116 . 
         [0032]    The output signal  114  controls the state of the switch  116 , e.g., on or off. The switch  116  is coupled to a load  118  and power source  120 . In a preferred embodiment the power source is an alternating current (AC) power source and the switch  116  is a Triac. However, in an alternative embodiment the power source may be a direct current (DC) power source and switch  116  may be a field effect transistor (FET). The microcontroller  104  can act to turn the device off if the appliance is in an unsafe orientation and/or left unattended for a predetermined period of time. 
         [0033]      FIG. 2A  illustrates a side view of an electric iron implementing a protective circuit in accordance with another embodiment of the invention.  FIG. 2B  illustrates a face view of an electric iron implementing a protective circuit in accordance with another embodiment of the invention. Referring to  FIGS. 2A and 2B , the electric iron apparatus is generally depicted as reference number  200  and includes a protective circuit  100  to turn off the iron  200  after a predetermined condition for a predetermined amount of time. The protective circuit includes a two-axis MEMS accelerometer as shown in  FIG. 1 . The two-axis accelerometer is oriented in the apparatus  200  such that the first axis of measurement  202  is in the y-direction and is substantially parallel to a heating surface of the iron. The second axis of measurement  206  is in the x-direction and is oriented substantially parallel to the heating surface of the iron and is also oriented to be substantially perpendicular to the first axis of measurement  202 . 
         [0034]      FIG. 3A  illustrates a theoretical output of a two-axis MEMS accelerometer in an electric iron positioned stationary upright on the iron&#39;s heel. Referring to  FIG. 3A , a graph includes a y-axis measuring the average acceleration produced by gravity at the Earth&#39;s surface (g) and an x-axis measuring time (ms). The graph represents a theoretical output of a two-axis MEMS accelerometer positioned as described with reference to  FIG. 2 . By way of example, if the iron is at rest on its heel with its heating surface  204  perpendicular to the gravitational field, an output  302  of the first axis of measurement  202  is shown at about 1 G. Moreover, an output  304  of the second axis of measurement  206  is shown at about 0 G. 
         [0035]      FIG. 3B  illustrates a theoretical output of a two-axis MEMS accelerometer in an electric iron when moving the iron in a front to back motion primarily along an axis parallel to the face of the iron and substantially parallel to a line running from toe to heel of the iron.  FIG. 3C  illustrates a theoretical output of a two-axis MEMS accelerometer in an electric iron when moving the iron in a side to side motion primarily along the axis substantially parallel to the face of the iron and substantially perpendicular to a line running from toe to heel of the apparatus. 
         [0036]    Referring now to  FIG. 3B , the graph represents the theoretical output of a two-axis MEMS accelerometer. Accelerations of the two-axis MEMS accelerometer are theoretically measured as the iron is moved in a back and forth motion. As shown, an output  306  of the second axis of measurement  206  is shown at about 0 G. The output  308  measuring the gravitational field on the first axis of measurement  202  corresponds to movement of the iron. As shown, as the iron theoretically moves back and forth so does the output signal  308  while the output signal  306  remains relatively static. 
         [0037]    Referring now to  FIG. 3C , the graph represents the theoretical output of a two-axis MEMS accelerometer. Accelerations of the two-axis accelerometer are theoretically measured as the iron is moved in a side to side motion. As shown, an output  310  measuring the gravitational field on the first axis of measurement  202  is shown at about 0 G. The output  312  measuring the gravitational field on the second axis of measurement  206  corresponds to movement of the iron. As shown, as the iron theoretically moves side to side so does the output signal  312  while the output signal  310  remains relatively static. 
         [0038]      FIG. 3D  illustrates a theoretical output of a two-axis MEMS accelerometer in an electric iron positioned stationary on its heating surface. Referring now to  FIG. 3D , the graph represents the theoretical output of a two-axis MEMS accelerometer. Accelerations of the two-axis accelerometer are theoretically measured as the iron is laying stationary on its heating surface. As shown, an output  314  measuring the gravitational field on the first axis of measurement  202  is shown at about 0 G. The output  316  measuring the gravitational field on the second axis of measurement  206  is also at about 0 G. 
         [0039]      FIG. 3E  illustrates a theoretical output of a two-axis MEMS accelerometer in an electric iron positioned stationary laying on its side having the heating surface of the iron apparatus substantially perpendicular to the axis of gravity. The graph represents the theoretical output of a two-axis MEMS accelerometer. An output  318  measuring the gravitational field on the first axis of measurement  202  is shown at about 0 G. Also, an output  320  measuring the gravitational field on the second axis of measurement  206  has a value of about 1 G. 
         [0040]      FIG. 4  is a flowchart illustrating functionality of a microcontroller according to another embodiment of the invention. 
         [0041]    Referring to  FIG. 4 , a flowchart depicts functionality of a microcontroller in accordance with an embodiment of the invention. The flowchart is generally depicted as reference number  400 . The flowchart  400  is a graphical illustration of the functionality of the microcontroller. Step  402  provides a periodic interrupt to execute functionality of the microcontroller as depicted in the flowchart  400 . The periodic interrupt can be configured to occur in accordance with the characteristics of the microcontroller as would be known to one of ordinary skill in the art. For example, depending on the architecture of the microcontroller, i.e., 8 bit, 16 bit, a suitable time for the periodic cycle may be chosen. In one embodiment, the periodic interrupt is set to 30 ms. In step  404  output values of the accelerometer are read. This reading may include multiple readings and averaging the average values to filter noise as known in the art. Moreover, the reading may also include debounce logic as known in the art. These additional techniques (averaging, filter, debounce logic) are instituted to remove unwanted noise; of course other conventional techniques may also be utilized. 
         [0042]    Step  406  compares the read values with previously read values to determine if they are approximately equal. In one embodiment, a tolerance ranging from about 5 percent to about 10 percent or higher is utilized in order to eliminate noise. Other tolerancences may be used to maximize the accuracy of the comparison, thereby eliminating noise. If the values are substantially equal then step  408  is performed. If the values are not substantially equal then step  410  is performed. In a two-axis MEMS accelerometer the values include a gravitational measurement in an x-direction and a gravitational measurement in a y-direction. In a three-axis MEMS accelerometer the values would also include a gravitational measurement in a z-direction. 
         [0043]    In step  408 , the previously read values and the currently read values are not substantially equal, thereby indicating the apparatus has been moved or is in some form of motion as compared to the time the previously read values were read. In this step, the no motion counter is reset indicating there has been motion of the apparatus. In step  410 , the previously read values and the currently read values are substantially equal. In this step, the no motion counter is incremented thereby indicating there has been no motion of the apparatus from the time the previously read values were read. 
         [0044]    Next in step  412 , the no motion counter is compared to a predetermined maximum count (max 1). If the no motion counter is greater than max 1 then step  414  is executed. If the no motion counter is less than or equal to max 1 then a return  416  is executed. In step  414 , an orientation of the apparatus is determined by comparing predetermined orientation values with measured values of step  404 . In this embodiment, the predetermined orientation values correspond to an orientation shown in  FIG. 3D . That is, an orientation where the apparatus is resting on a heating surface. This may also be referred to as a predetermined condition. As shown with reference to  FIG. 3D , a first output of a two-axis MEMS accelerometer measuring the gravitational field on the first axis of measurement  202  has a value of about 0 G. A second output measuring the gravitational field on the second axis of measurement  206  has a value of about 0 G. In this comparison step  414 , the values of step  404  are compared to determine if they are approximately equal to the predetermined condition representing a predetermined orientation. If the values  404  are approximately equal to the values of the predetermined values then step  418  is executed. If the values are not approximately equal to predetermined values then step  416  is executed. It is noted that an error tolerance may be used to account for noise, for example, a tolerance ranging from about 1 percent to 5 percent or higher. In step  418 , the microcontroller sends an off signal to turn off a switch thereby disabling power to a load on the apparatus. By way of example and referring to  FIG. 1 , an off signal  114  is sent to switch  116  to turn off power supply  120  to the load  118 . 
         [0045]    Of course any predetermined value may be utilized as a comparison value. These predetermined values correspond to orientations of the apparatus. Some example values from a two-axis MEMS accelerometer are shown in  FIGS. 3A-3E . Also, more than one predetermined value may be utilized in the flowchart  400  by adding additional logic blocks as shown in steps  420  and  422 . That is, optionally these blocks may be added to monitor additional predetermined conditions in the same flow diagram  400 . In one embodiment, this is accomplished as shown in  FIG. 4 . More specifically, when the comparison step  414  is not satisfied, step  420  is executed rather than proceeding to the return step  416 . In step  420 , the no motion counter is compared to a second predetermined maximum (max 2). If the no motion counter is greater than max 2 then step  422  is executed. In this comparison step  422 , the values of step  404  are compared to determine if they are approximately equal to a second predetermined condition representing a second predetermined orientation and having a second predetermined value. If the values of step  404  are approximately equal to the second predetermined values then step  418  is executed. If the values of step  404  are not approximately equal to the second predetermined values then step  416  is executed. 
         [0046]    It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.