PATENT DOCUMENT

Publication Number: US-8289115-B2
Application Number: US-201113037271-A
Country: US
Kind Code: B2

Title: Sensor fusion

Abstract:
Accurate and reliable techniques for determining a current status of an accessory device in relation to an electronic device are described.

Claims:
1. A method of continuously monitoring by a tablet device pivotally attached to a cover, a pivot angle of the cover in relation to the tablet device, the cover comprising a magnet, the tablet device comprising a processor coupled to which is a display having a top protective layer, a magnetic sensor configured to detect a magnetic field from the magnet through the top protective layer, and an inertial system configured to determine a spatial orientation of the tablet with respect to an inertial reference frame, in a closed configuration the pivot angle is 0 radians and the magnetic sensor is substantially co-planar with the magnet and separated by a first distance R 0  and detects a first magnetic field value propagating through the top protective layer from the magnet, and in an open configuration, the pivot angle is it radians and the magnetic sensor is substantially coplanar with the sensor and separated by a second distance R 1 , and detects a second magnetic field value propagating from the magnet, the second distance R 1  being greater than first distance R 0 , the method comprising: sensing a current magnetic field value from the magnet by the magnetic sensor; determining a relative magnetic field value by comparing the current magnetic field value to the first and second magnetic field values; determining a current spatial orientation of the tablet device with respect to the inertial reference frame by the inertial system; adjusting the relative magnetic field value in accordance with the current spatial orientation; and providing a current pivot angle in accordance with the adjusted relative magnetic field value. 
     
     
       2. The method as recited in  claim 1 , wherein the magnetic sensor is a magnetometer. 
     
     
       3. The method as recited in  claim 2 , the cover further comprising a first magnetic attachment unit. 
     
     
       4. The method as recited in  claim 3 , the tablet device further comprising a second magnetic attachment unit, the first and second magnetic attachment units configured to generate a mutual magnetic attachment force of sufficient strength to pivotally attach the tablet device and the cover. 
     
     
       5. The method as recited in  claim 4 , wherein the magnetometer detects a magnetic offset value in accordance with the mutual magnetic attachment force. 
     
     
       6. The method as recited in  claim 5 , wherein the processor determines that the cover and the tablet device are magnetically attached to each other when the processor receives an indication that the magnetometer has detected the magnetic offset value. 
     
     
       7. The method as recited in  claim 2 , wherein the magnetometer is a compass. 
     
     
       8. The method as recited in  claim 7 , further comprising compensating for a moving cover magnetic offset at the compass induced by the magnet as the cover moves. 
     
     
       9. The method as recited in  claim 8 , wherein the compensating for the moving cover magnetic offset comprises: determining a horizontal component of an external magnetic field; and using the horizontal component to estimate a maximum change in a magnetic compass heading induced by the relative change in position of the cover in relation to the tablet device. 
     
     
       10. The method as recited in  claim 1 , wherein the inertial system is an accelerometer coupled to the processor. 
     
     
       11. The method as recited in  claim 1 , wherein the inertial system is a gyroscope coupled to the processor. 
     
     
       12. The method as recited in  claim 1 , wherein the inertial system comprises an accelerometer and a gyroscope each coupled to the processor.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This U.S. patent application claims priority under 35 U.S.C. 119(e) to (i) U.S. Provisional Patent Application No. 61/384,179, filed Sep. 17, 2010 and entitled “Apparatus and Method for Magnetic Attachment” by Lauder et al., and (ii) U.S. Provisional Patent Application No. 61/438,220, filed Jan. 31, 2011 and entitled “Magnetic Attachment Unit and Methods of Use” by Lauder et al., each of which are incorporated by reference in their entirety for all purposes. This application is also related to U.S. patent application Ser. No. 12/971,411, filed Dec. 17, 2010 and entitled “Foldable Accessory Device” by Lauder et. al. also incorporated by reference in its entirety for all purposes. 
    
    
     FIELD OF THE DESCRIBED EMBODIMENTS 
     The described embodiments generally relate to portable electronic devices. More particularly, the present embodiments describe use of multiple sensors in combination to confirm a status of an accessory device in relation to an electronic device. 
     DESCRIPTION OF THE RELATED ART 
     Recent advances in portable computing includes the introduction of hand held electronic devices and computing platforms along the lines of the iPad™ tablet manufactured by Apple Inc. of Cupertino, Calif. These handheld computing devices can be configured such that a substantial portion of the electronic device takes the form of a display used for presenting visual content leaving little available space for an attachment mechanism that can be used for attaching an accessory device. 
     When the accessory device takes the form of a cover, the handheld computing device can be operable in modes consistent with the presence of the cover. For example, when the handheld computing device has a display, the presence of the cover can render the display unviewable. In order to save power, the unviewable display can be rendered temporarily inoperable until the cover is moved or otherwise repositioned to expose the display. 
     Therefore, accurate and reliable techniques for determining a current status of an accessory device in relation to an electronic device to which it is connected are desired. 
     SUMMARY OF THE DESCRIBED EMBODIMENTS 
     This paper describes various embodiments that relate to a system, method, and apparatus for releasably attaching an accessory to an electronic device. 
     A consumer electronic product includes at least an electronic device. In the described embodiment, the electronic device includes at least a processor and a first sensor in communication with the processor arranged to detect a first type stimulus. The first sensor responds to the first type stimulus by providing a first signal to the processor indicating a first status of an accessory device in relation to the electronic device. The electronic device also includes at least a second sensor in communication with the processor arranged to detect a second type stimulus. The second sensor responds to the second type stimulus by providing a second signal to the processor indicating a second status of the accessory device in relation to the electronic device. In the described embodiment, when the processor receives the first signal from the first sensor, the processor compares the first status indicated by the first signal and the second status indicated by the second signal and when the processor determines that the indications of the first and second status are the same, the processor accepts the first signal, otherwise, the processor ignores the first signal. 
     In one aspect of the described embodiment, the accessory device is a protective cover having a flap incorporating a magnetic element and the first sensor is a Hall Effect (HFX) sensor. The protective cover is pivotally attached to the electronic device such that in a closed configuration the magnetic element in the flap provides a first stimulus in the form of a saturating magnetic field that is detected by the HFX sensor only when the flap is in a closed configuration with respect to the electronic device. The second sensor is any of at least an ambient light sensor, a camera, a magnetometer, a multi-touch sensitive surface, an RFID device, and a second Hall Effect sensor. 
     In another embodiment, a consumer electronic product includes at least an electronic device and an accessory unit. In the described embodiment, the electronic product includes a processor, a Hall Effect sensor (HFX) in communication with the processor arranged to detect a saturating magnetic field and in response to the detected saturating magnetic field, provide a signal to the processor where the processor uses the signal to alter an operating state of the electronic device. The electronic device also includes a second sensor separate and distinct from the HFX sensor. The accessory unit includes a body portion pivotally attachable to the electronic device having at least a magnetic element. When the accessory unit is in a closed configuration, an inner surface of the body portion is placed in proximity to the protective top layer such that the magnetic element presents the saturating magnetic field to the HFX sensor. When the processor receives the signal from the HFX sensor indicating the presence of the saturating magnetic field, the processor queries the second sensor to corroborate the signal received from the HFX sensor is consistent with the cover being in the closed configuration, the processor accepts the signal from the HFX sensor, otherwise the processor ignores the signal from the HFX sensor. 
     In yet another embodiment, in a consumer electronic product that includes an electronic device, a method performed by a processor in the electronic device is described. The method can be carried out by performing at least the following operations: detecting a first type stimulus at a first sensor in communication with the processor, receiving a first signal from the first sensor at the processor, the first signal indicating a first status of an accessory device in relation to the electronic device, detecting a second type stimulus at a second sensor in communication with the processor, receiving a second signal from the second sensor at the processor, the second signal indicating a second status of the accessory device in relation to the electronic device, comparing the indication of the first status and the indication of the second status by the processor, and accepting the first signal by the processor only when the comparing determines that the indications of that the first and second status are the same. 
     In another embodiment, non-transitory computer readable medium for storing program code executable by a processor for detecting a state of a protective cover in relation to an electronic device having a processor and at least a first sensor and a second sensor is described. The computer readable medium includes at least computer code for receiving a signal from the first sensor indicating that the protective cover is in a closed configuration with respect to the electronic device, computer code for querying the second sensor, computer code for receiving information from the second sensor, and computer code for ignoring the signal from the first sensor when the information from the second sensor does not corroborate the signal from the first sensor; otherwise, accepting the signal from the first sensor. 
     In one aspect of the described embodiment, the protective cover includes a flap incorporating a magnetic element and the first sensor is a Hall Effect sensor. The protective cover is pivotally attached to the electronic device such that in a closed configuration the magnetic element in the flap provides a first stimulus in the form of a saturating magnetic field that is detected by the HFX sensor only when the flap is in a closed configuration with respect to the electronic device. The second sensor is any of at least an ambient light sensor, a camera, a magnetometer, a multi-touch sensitive surface, an RFID device, and a second Hall Effect sensor. 
     Other aspects and advantages of the invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the described embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be readily understood by the following detailed description in conjunction with the accompanying drawings, wherein like reference numerals designate like structural elements, and in which: 
         FIG. 1  shows a top perspective view of an electronic device in accordance with the described embodiments. 
         FIG. 2A  shows a first perspective view of the electronic device in the form of a tablet device and the accessory device in the form of a protective cover. 
         FIG. 2B  shows a second perspective view of the electronic device in the form of a tablet device and the accessory device in the form of a protective cover. 
         FIG. 3A  shows a closed configuration of the cooperating system formed by the tablet device and protective cover shown in  FIGS. 2A and 2B . 
         FIG. 3B  shows an open configuration of the cooperating system shown in  FIG. 3A . 
         FIG. 4  shows a top view of an embodiment of a segmented cover assembly. 
         FIGS. 5A and 5B  illustrate representative magnetic interaction between and onboard compass and magnetic elements in a flap as part of an accessory unit. 
         FIGS. 6A and 6B  graphically illustrate various magnetic offsets that can be detected by onboard compass. 
         FIG. 7  shows a flowchart detailing process for confirming an indication from a Hall Effect sensor of the state of protective cover in relation to an electronic device. 
         FIG. 8  shows a flowchart detailing process for using an ambient light sensor (ALS) in combination with a Hall Effect sensor to corroborate a state of a protective cover with regards to an electronic device. 
         FIG. 9  shows a flowchart detailing process for using a camera in combination with a Hall Effect sensor to corroborate a state of a protective cover with regards to an electronic device. 
         FIG. 10  shows a flowchart detailing process for using a magnetometer in the form of a compass in combination with a Hall Effect sensor to corroborate a state of a protective cover with regards to an electronic device. 
         FIG. 11  shows a flowchart detailing process for using a multi-touch (MT) sensitive surface in combination with a Hall Effect sensor to corroborate a state of a protective cover with regards to an electronic device. 
         FIG. 12  shows a flowchart detailing process for using a RFID device in combination with a Hall Effect sensor to corroborate a state of a protective cover with regards to an electronic device. 
         FIG. 13  shows a flowchart detailing process for determining a state of a protective cover in relation to an electronic device using a dynamic model of a magnetic field to corroborate a state of a protective cover with regards to an electronic device. 
         FIG. 14  is a block diagram of an arrangement of functional modules utilized by a portable media device. 
         FIG. 15  is a block diagram of an electronic device suitable for use with the described embodiments. 
     
    
    
     DETAILED DESCRIPTION OF SELECTED EMBODIMENTS 
     Reference will now be made in detail to representative embodiments illustrated in the accompanying drawings. It should be understood that the following descriptions are not intended to limit the embodiments to one preferred embodiment. To the contrary, it is intended to cover alternatives, modifications, and equivalents as can be included within the spirit and scope of the described embodiments as defined by the appended claims. 
     The following description relates in general to a mechanism that can be used to confirm a status of an accessory device in relation to an associated host device having operating states consistent with the accessory device status. More specifically, when the accessory device is a protective cover having a size and shape in accordance with the electronic device, the protective cover can have a hinge portion and flap pivotally attached to the hinge portion. The flap can rotate about the hinge portion in one direction to bring the flap in substantial contact with the electronic device in a closed configuration. Conversely, the flap can pivot about the hinge assembly in the other direction to expose the electronic device in an open configuration. In one embodiment, the electronic device can operate in a closed cover mode when the protective cover is detected to be in the closed configuration and an open cover mode when the cover is detected to be in the open configuration. The protective cover can provide protection to certain aspects (such as a display) of the electronic device while enhancing the overall look and feel of the electronic device. The protective cover can include at least a hinge portion. The hinge portion can be magnetically attached to the electronic device using a magnetic attachment feature. The hinge portion can be pivotally connected to a flap that can be placed upon a portion of the electronic device to be protected. The protective cover can include electronic circuits or other elements (passive or active) that can cooperate with electronic elements in the electronic device. As part of that cooperation, signals can be passed between the protective cover and the electronic device that can, for example, be used to modify operations of the electronic device, operations of electronic circuits or elements of the protective cover, and so forth. 
     The electronic device can include a magnetometer circuit that can be used to detect the directional magnitude of an external magnetic field. In this regard, the magnetometer can function as a compass arranged to indicate a directional bearing and magnitude of an external magnetic field. In this way, the directional heading of the electronic device in relation to the external magnetic field can be deduced. For example, when the external magnetic field is essentially the Earth&#39;s magnetic field, the onboard compass can provide an indication of the directional bearing of the electronic device in relation to the magnetic pole of the Earth. In one embodiment, the protective cover includes a flap having magnetic elements. The magnetic elements can include magnetic elements used for magnetic attachment and magnetic elements used to trigger a Hall Effect (HFX) sensor in the electronic device. In this situation, the onboard compass can be used to detect the presence of the flap based upon the effect of the magnetic elements on the onboard compass. 
     For example, the onboard compass can detect that the flap is magnetically attached to the electronic device based upon a first static magnetic deviation, also referred to as a hard magnetic offset. The first static magnetic deviation can be based upon the presence of magnetic elements included in the flap of the protective cover used to trigger the HFX sensor as well as magnetic elements used to magnetically attach the flap and the electronic device. In another embodiment, the compass can detect a dynamic magnetic displacement in accordance with movement of the magnetic elements in the flap as the flap rotates about the pivot axis of the hinge assembly. The dynamic magnetic displacement can be used to determine if the flap is in motion relative to the onboard compass. In one embodiment, the relative displacement of the flap and the electronic device can be deduced from data received in real time from an accelerometer and gyroscope. The data from the accelerometer and gyroscope can be related to the spatial orientation of the electronic device. The spatial orientation data and magnetic readings from the onboard compass can be used to determine if the magnetic elements in the flap are moving in relation to the electronic device providing an indication that the flap is rotating about the pivot line of the hinge assembly. 
     In one embodiment, the electronic device can have a touch sensitive surface that can react to a plurality of conductive elements incorporated into the protective cover near an inner layer of the protective cover. The plurality of conductive elements can be grounded when the protective cover is magnetically attached to the electronic device. In one embodiment, the conductive elements can be arranged in a pre-determined and therefore recognizable pattern. In this way, when an inner layer of the protective cover includes elements capable of interacting with the touch sensitive surface, the elements can be arranged in a pre-determined pattern in order to assist the electronic device in detecting the current position of the protective cover. For example, in one embodiment, the touch sensitive surface can be capacitive in nature in which case the embedded elements in the protective cover can be formed of conductive material such as metal along the lines of aluminum. The conductive elements can be grounded in order to increase a capacitive signal to noise ratio of the signal generated by the interaction between capacitive touch sensitive surface and the capacitive embedded elements. 
     The magnetic elements in the flap portion can interact with a magnetically sensitive circuit incorporated into the electronic device. The magnetically sensitive circuit can in one embodiment take the form of the HFX sensor that can detect the presence of an extrinsic magnetic field provided by the magnetic element in the protective cover. It should be noted, however, that in order to trigger the HFX sensor, the detected magnetic field must saturate the HFX sensor. In this way, the likelihood that the HFX sensor provides a false indication that the protective cover is enclosing the electronic device is greatly reduced. For example, the relatively weak magnetic field strength associated with the Earth&#39;s magnetic field is insufficient to saturate the HFX sensor thereby triggering a false indication of the protective cover status. 
     When the HFX sensor is exposed to a saturating magnetic field (i.e., one of sufficient magnetic strength to saturate the HFX sensor), the HFX sensor can respond to the saturating magnetic field by generating a binary (i.e., ON/OFF) signal. One of the advantages of using the HFX sensor (in addition to reducing the likelihood of a false cover status indication) is that the amount of power required to operate the HFX sensor is relatively small and therefore does not present an undue power drain on the electronic device. In any case, when the HFX sensor is exposed to the saturating magnetic field, the HFX sensor can issue a signal. The signal can be received by a processing unit and used to alter an operating state of the electronic device. It should be noted, however, that any appropriate sensing device in addition to or in place of the HFX sensor can be used to detect the status of the protective cover in relation to the electronic device. For example, a magnetometer (a form of which can be used as a compass) can be used in lieu of the HFX sensor. In contrast to the HFX sensor, the magnetometer is substantially more sensitive to an extrinsic magnetic field and will respond accordingly by providing a more continuous (analog) signal representative of the extrinsic magnetic field requiring a greater amount of power. Accordingly, dynamic magnetic activity can be detected by the magnetometer (indicative of, for example, relative motions of the magnetometer and a magnetic source) by periodically sampling the signal from the magnetometer. The sampled data can be used, for example, to provide a relative position of the magnetic elements in the protective cover in relation to the magnetometer in the electronic device. 
     Accordingly, the protective cover can include a magnetic element such as a permanent magnet having a magnetic field that can cause the HFX sensor to generate the signal. The magnetic element can be positioned on the protective cover in a location that triggers the HFX sensor to generate the signal when the cover is placed on or in proximity to a surface of the electronic device. The signal can indicate that the protective cover is in a predetermined position relative to the electronic device that can result in a change in an operating state of the electronic device. For example, with the portion of the protective cover having the magnetic element in proximity to the HFX sensor, the magnetic field from the magnetic element can cause the HFX sensor to generate a signal. The signal can, in turn, be used to alter the operating state to one consistent with a portion of the electronic device being covered. For example, when the electronic device includes a display, the protective cover can be used to cover the display and therefore render it unviewable and therefore the display can be disabled. On the other hand, when the portion of the protective cover having the magnetic element is removed to the point where the HFX sensor no longer responds to the magnetic field of the magnetic element, then the HFX sensor can generate another signal. The other signal can result in the electronic device entering another, different, operating state consistent with at least a portion of the display being uncovered and viewable and therefore enabled for displaying visual content. 
     However, the HFX sensor can be triggered by any magnetic field strong enough to saturate the HFX sensor thereby potentially providing a false indication of the presence of the protective cover. Therefore in order to avoid such false indications, when the HFX sensor is triggered, additional sensors can be queried in order to confirm that indication provided by the HFX sensor that the protective cover is in the closed configuration. In one embodiment, a triggering event at the HFX sensor indicating that the cover is in the closed configuration can also cause the electronic device to query at least another sensor in order to confirm the closed configuration indicated by the HFX sensor. 
     In one embodiment, an ambient light sensor (ALS) can be queried by the electronic device. The ALS can include a photosensitive circuit (such as a photodiode) that can respond to varying levels of incident light, typically in the form of ambient light. In one embodiment, the ALS can detect ambient light. The ALS can, however, be configured to respond to the detection of the ambient light in many ways. For example, the ALS can respond by providing a signal whenever the photosensitive circuit within the ALS detects an amount (i.e., intensity) of ambient light greater than a pre-defined amount of ambient light. In other words, the threshold amount of ambient light can be a defined threshold level. For example, a threshold amount of “x” lumens can represent an amount of ambient light consistent with the protective cover being in a closed configuration where the value “x” takes into account light leaking in from around the edges of the protective cover. Of course, the threshold amount of ambient light can be set to any amount deemed appropriate. For example, in some cases where the electronic device is in bright environment such as daylight, the amount of light leakage can be much higher than would be expected in darker conditions. Therefore, the amount of light leaking around the edges of the protective cover can be substantially greater and therefore, the threshold amount of light consistent with the protective cover being in the closed configuration can increased to take this fact into account. 
     In another embodiment, the threshold amount can be consistent with a differential change in ambient light detected by the photosensitive circuit in the ALS. For example, in those situations where electronic device is in a bright environment (such as outdoors in daylight), there can be substantial amount of light leakage when the protective cover is in fact closed. However, in order to reduce uncertainties related to just how much light leakage there really is, the ALS can be configured to provide a signal based upon a differential change in the amount of light detected by the photosensitive circuit within the ALS. For example, when the protective cover is open, the ALS can detect an amount of light represented by “y 1 ” lumens. However, when the protective cover is closed, the amount of light detected by the photosensitive circuit in the ALS can change from “y 1 ” to “y 2 ” lumens. Only in those situations where the difference in the amount of light detected (i.e., Δy=abs (y 1 −y 2 )) is greater than a predetermined value, will the ALS provide the appropriate signal indicating that the protective cover is in the closed configuration. The advantage to this approach lies in the fact that light leakage values are difficult to deduce and therefore by relying upon a well-defined change in detected ambient light a more accurate and robust indication of the status of the protective cover in relation to the electronic device can be forthcoming. 
     Therefore, by using the ALS, the electronic device can corroborate the indication of the status of the protective cover provided by the HFX sensor. In this way, if the ALS corroborates the indication from the HFX sensor by detecting an amount of ambient light consistent with the protective cover being in the closed configuration, the electronic device can accept the indication from the HFX sensor and alter the operating state of the electronic device accordingly. However, if the amount of ambient light is not consistent with the signal from the HFX sensor indicating that the protective cover is in the closed, configuration, the electronic device can query another sensor in order to obtain yet another data point to be used in evaluating the signal from the HFX sensor or more simply can ignore the indication from the HFX sensor altogether thereby presuming that the cover is not fully covering the electronic device and therefore the operating state of the electronic device will not be altered to one consistent with the electronic device being fully covered. If, however, the ALS detects an amount of light that corroborates the indication from the Hall Effect, then the electronic device can accept the indication from the HFX sensor that the protective cover is in the closed configuration and can thereby respond accordingly. 
     In another embodiment, a camera can be activated and based upon a type of image captured by the camera, can be used to corroborate the indication provided by the HFX sensor that the cover is closed. For example, when the cover is closed, the camera can capture an image that is essentially black (or very low luminance value). However, if the electronic device is located within dark environment such as a dark room, outdoors at night with little or no moonlight or other external light sources, and so on, what little external illumination there is (such as from the display) can provide sufficient illumination (on the end user&#39;s face for example) for the camera to capture an image. In one embodiment, the captured image can be characterized for an overall luminance value or luminance histogram which can be used to determine if the cover is fully closed or partially closed. For example, even with the cover fully closed, there may be some light leakage that can be captured by the camera resulting in a low luminance captured image. However, in another embodiment, the camera can be adjusted in such a way the unless there is sufficient light on the image capture device within the camera, there will be no image registered by the camera based upon, for example, a defined specification for light leakage. If, however, an image is captured by the camera, by evaluating the overall luminance value of the captured image (less than a threshold luminance value for example), the position of the protective cover can be estimated and used to corroborate (or not) the indication from the HFX sensor. 
     In another embodiment, a magnetometer in the form of an onboard compass can be used to detect the presence of a hard magnetic offset consistent with the magnetic element embedded in the protective cover in place at or near the HFX sensor. In this embodiment, the presence of the hard magnetic offset can be used to confirm the indication from the HFX sensor of the closed cover state. On the other hand, the absence of the hard magnetic offset can be used by the electronic device to decide that the indication from the HFX sensor is not accurate with regards to the state of the protective cover and can therefore be ignored, or other actions such as querying another sensor can be undertaken. 
     It should also be noted that magnetic materials included in the protective cover can affect the performance of the magnetometer such as the onboard compass. In particular, the basic operations of the onboard compass (embodied as instructions executable by a processor or other appropriate circuit) can be altered by the presence of the magnetic materials in the protective cover. In particular, the motion of the protective cover can be detected by the onboard compass as a change in magnetic field strength and direction that can result in an “error” since the onboard compass will experience a dynamic offset based upon the positional change in the protective cover. For example, when the cover is going from the open to closed configuration, the dynamic offset at the onboard compass can increase due to the fact that the magnetic elements within the protective cover are moving closer to the magnetometer and are therefore inducing a greater offset value in the readings of the onboard compass (of course, just the opposite occurs when the cover status changes from closed to open). 
     The maximum offset, or differential in compass heading, experienced by the onboard compass that can be induced by the change in position of the magnetic element in the protective cover is a function of the change in the magnitude of the magnetic field as seen by the magnetic sensor associated with the onboard compass when the position of the protective cover changes as well as the horizontal strength of the external magnetic field. In order to compensate for the offset induced by the motion of the protective cover (more specifically the magnetic elements in the protective cover), the onboard compass can utilize a model of the maximum change in magnetic field magnitude that the onboard compass can detect as a function of change in cover position. In this way, by using both the model of the maximum change in magnetic field magnitude as a function of cover position and a current estimate of the magnitude of the horizontal component of the external magnetic field, the electronic device can estimate a maximum change in compass heading likely to be induced by the relative change in position of the protective cover in relation to the electronic device. 
     Accordingly, an accelerometer and gyroscope incorporated within the electronic device can be used in conjunction with the compass to evaluate a dynamic magnetic signature of changes in detected external magnetic field. The accelerometer and gyroscope can provide, in real time, the spatial position and rotation of the electronic device and the compass can provide an indication, again in real time, of changes in external magnetic field. The readings from the accelerometer and gyroscope and the compass can be used together and compared to a model of the motion of the magnetic elements in relation to the electronic device and, in turn, be used to evaluate the likelihood that the cover is present and moving in relation to the electronic device (by way of the compass). 
     These and other embodiments are discussed below with reference to  FIGS. 1-15 . However, those skilled in the art will readily appreciate that the detailed description given herein with respect to these figures is for explanatory purposes only and should not be construed as limiting. For the remainder of this discussion, a first and second object each suitably configured to magnetically attach to each other in accordance with the described embodiments will be described. It should be noted, however, that any number and type of suitably configured objects can be magnetically attached to each other in a precise and repeatable manner. In particular, for simplicity and clarity, for the remainder of this discussion, the first object is presumed to take the form of an electronic device and in particular a handheld electronic device. 
     The electronic device can take many forms. For the remainder of this discussion, the electronic device is described in terms of a handheld portable computing device. Accordingly,  FIG. 1  shows a top perspective view of electronic device  10  in accordance with the described embodiments. Electronic device  10  can process data and more particularly media data such as audio, visual, images, etc. By way of example, electronic device  10  can generally correspond to a device that can perform as a smart phone, a music player, a game player, a visual player, a personal digital assistant (PDA), a tablet computer and the like. Electronic device  10  can also be hand held. With regards to being handheld, electronic device  10  can be held in one hand while being operated by the other hand (i.e., no reference surface such as a desktop is needed). Hence, electronic device  10  can be held in one hand while operational input commands can be provided by the other hand. The operational input commands can include operating a volume switch, a hold switch, or by providing inputs to a touch sensitive surface such as a touch sensitive display device or a touch pad. 
     Electronic device  10  can include housing  12 . In some embodiments, housing  12  can take the form of a single piece housing formed of any number of materials such as plastic or non-magnetic metal which can be forged, molded, or otherwise formed into a desired shape. In those cases where electronic device  10  has a metal housing and incorporates radio frequency (RF) based functionality, a portion of housing  12  can include radio transparent materials such as ceramic, or plastic. Housing  12  can be configured to enclose a number of internal components. For example, housing  12  can enclose and support various structural and electrical components (including integrated circuit chips) to provide computing operations for electronic device  10 . The integrated circuits can take the form of chips, chip sets, or modules any of which can be surface mounted to a printed circuit board, or PCB, or other support structure. For example, a main logic board (MLB) can have integrated circuits mounted thereon that can include at least a microprocessor, semi-conductor memory (such as FLASH), and various support circuits and so on. Housing  12  can include opening  14  for placing internal components and as necessary can be sized to accommodate display assembly for presenting visual content, the display assembly being covered and protected by cover layer  16 . In some cases, the display assembly can be touch sensitive allowing tactile inputs that can be used to provide control signals to electronic device  10 . In some cases, the display assembly may be a large prominent display area that covers a majority of the real estate on the front of the electronic device. 
     Electronic device  10  can include a magnetic attachment system that can be used to magnetically attach electronic device  10  to at least one other suitably configured object. The magnetic attachment system can include a number of magnetic attachment features distributed within and in some cases connected to housing  12 . For example, the magnetic attachment system can include first magnetic attachment feature  18  and second magnetic attachment feature  20  located on different sides of electronic device  10 . In particular, first magnetic attachment feature  18  can be located in proximity to side wall  12   a  of housing  12 . Second magnetic attachment feature  20  can be located within opening  14  near side wall  12   b  of housing  12 . In those embodiments where electronic device  10  includes a display with cover glass substantially filling opening  14 , second attachment feature  20  can be placed beneath the cover layer. 
     The placement of first magnetic attachment feature  18  at side wall  12   a  can facilitate the use of magnetic attachment feature  18  to magnetically attach electronic device  10  to another suitably configured object such as another electronic device or an accessory device. Accordingly, without loss of generality, first magnetic attachment feature  18  will henceforth be referred to as device attachment feature  18 . The placement of second magnetic attachment feature  20 , on the other hand, can facilitate the use of second magnetic attachment feature  20  to secure aspects of another device attached to electronic device  10  by way of device attachment feature  18 . In this way, the overall attachment between the other device and electronic device  10  can be more secure than attaching through first attachment feature  18  alone. Accordingly, and again without loss of generality, second attachment feature  20  will henceforth be referred to as securing attachment feature  20 . Securing attachment feature  20  can include one or more of magnetic elements  22 . When a plurality of magnetic elements is used, the arrangement of the plurality of magnetic elements can be widely varied and can magnetically interact with a cooperating feature on another device. In one embodiment, the plurality of magnetic elements associated with securing feature  20  can assist in securing at least a portion of another device otherwise attached to electronic device  10  by way of device attachment feature  18 . Electronic device  10  can also include Hall Effect sensor  24  and magnetometer circuit  26  in the form of onboard compass  26 . 
     The remainder of this discussion will describe particular embodiments of devices that can use the magnetic attachment system. In particular,  FIG. 2A  and  FIG. 2B  show electronic device  100  presented in terms of tablet device  100  and accessory device  200  is shown as protective cover  200  each in perspective top views. These elements may generally correspond to any of those previously mentioned. In particular,  FIGS. 2A and 2B  shows two perspective views of tablet device  100  and protective cover  200  in the open configuration. For example,  FIG. 2A  shows device attachment feature  108  included in tablet device  100  and its relationship to tablet device  100 .  FIG. 2B , on the other hand, is the view presented in  FIG. 2A  rotated about 180° to provide a second view of attachment feature  202  and its relationship with protective cover  200 . 
     Tablet device  100  can take the form of a tablet computing device such as the iPad™ manufactured by Apple Inc. of Cupertino, Calif. Referring now to  FIG. 2A , tablet device  100  can include housing  102  that can enclose and support device attachment feature  108 . In order to not interfere with the magnetic field generated by device attachment feature  108 , at least that portion of housing  102  nearest device attachment feature  108  can be formed of any number of non-magnetic materials such as plastic or non-magnetic metal such as aluminum. Housing  102  can also enclose and support internally various structural and electrical components (including integrated circuit chips and other circuitry) to provide computing operations for tablet device  100 . Housing  102  can include opening  104  for placing internal components and can be sized to accommodate a display assembly or system suitable for providing a user with at least visual content as for example via a display. In some cases, the display assembly can include touch sensitive capabilities providing the user with the ability to provide tactile inputs to tablet device  100  using touch inputs. The display assembly can be formed of a number of layers including a topmost layer taking the form of transparent cover glass  106  formed of polycarbonate or other appropriate plastic or highly polished glass. Using highly polished glass, cover glass  106  can substantially fill opening  104 . 
     Although not shown, the display assembly underlying cover glass  106  can be used to display images using any suitable display technology, such as LCD, LED, OLED, electronic or e-inks, and so on. The display assembly can be placed and secured within the cavity using a variety of mechanisms. In one embodiment, the display assembly is snapped into the cavity. It can be placed flush with the adjacent portion of the housing. In this way, the display can present visual content that can include visual, still images, as well as icons such as graphical user interface (GUI) that can provide information the user (e.g., text, objects, graphics) as well as receive user provided inputs. In some cases, displayed icons can be moved by a user to a more convenient location on the display. 
     In some embodiments, a display mask can be applied to, or incorporated within or under cover glass  106 . The display mask can be used to accent an unmasked portion of the display used to present visual content and can be used to make less obvious device attachment feature  108  and securing attachment feature  20 . Tablet device  100  can include various ports that can be used to pass information between tablet device  100  and the external environment. In particular, data port  109  can facilitate the transfer of data and power whereas speakers  110  can be used to output audio content. Home button  112  can be used to provide an input signal that can be used by a processor included in tablet device  100 . The processor can use the signal from home button  112  to alter the operating state of tablet device  100 . For example, home button  112  can be used to reset a currently active page presented by the display assembly. Tablet device  100  can also include camera assembly  114  arranged to capture an image or images. Tablet device  100  can also include ambient light sensor  116  (ALS) used to detect a level of ambient light. In one embodiment ALS  116  can be used to set a brightness level of the display assembly. For example, in a darker environment with little ambient light, the readings from ALS  116  can cause a processor in tablet device  100  to dim the display assembly. In a brighter environment, the display assembly can be made brighter. Tablet device can further include compass  118  used to detect external magnetic fields that can help in the determination of a position of tablet device  100 . Tablet device  100  can also include Hall Effect sensor  120  that can be used to detect the presence of a magnetic element in when cover  200  is placed on top of tablet device  100  in a closed configuration. An accelerometer and gyroscope (not shown) can determine any dynamic changes in the position and orientation of tablet device  100  in real time. 
     Protective cover  200  can have a look and feel that complements that of the tablet device  100  adding to overall look and feel of tablet device  100 . Protective cover  200  is shown in  FIGS. 2A and 2B  attached to tablet device  100  in an open configuration in which cover glass  106  is fully viewable. Protective cover  200  can include flap  202 . In one embodiment, flap  202  can have a size and shape in accordance with cover glass  106 . Flap  202  can be pivotally connected to accessory attachment feature  204  by way of hinge assembly  206  each shown in  FIG. 2B . In this way, flap  202  can rotate about pivot line  211 . The magnetic attachment force between attachment feature  204  and device attachment feature  108  can maintain protective cover  200  and tablet device  100  in a proper orientation and placement vis-a-vis flap  202  and cover glass  106 . By proper orientation it is meant that protective cover  200  can only properly attach to tablet device  100  having flap  202  and cover glass  106  aligned in a mating engagement. The mating arrangement between cover glass  106  and flap  202  is such that flap  202  covers substantially all of cover glass  106  when flap  202  is placed in contact with cover glass  106  as shown in  FIG. 3A . 
     Flap  202  can be pivotally connected to hinge assembly  206  that, in turn, can be connected to attachment feature  204 . Hinge assembly  206  can, in turn, be coupled to electronic device  100  by way of accessory attachment feature  204 . In this way, the flap  202  can be used as a protective cover to protect aspects of electronic device  100  such as a display cover  106 . Flap  202  can be formed of various materials such as plastic, cloth, and so forth. Flap  202  can be segmented in such a way that a segment of the flap can be lifted to expose a corresponding portion of the display. Flap  202  can also include a functional element that can cooperate with a corresponding functional element in electronic device  100 . In this way, manipulating flap  202  can result in an alteration in the operation of electronic device  100 . 
     Flap  202  can include magnetic material. For example, magnetic elements  207  can be used to magnetically attach to corresponding magnetic attachment feature  20  whereas magnetic element  209  can be used to activate Hall Effect sensor  120  when flap  202  is in position above cover glass  106 . In this way, Hall Effect sensor  120  can respond by generating a signal that can, in turn, be used to alter an operating state of electronic device  100 . Since the cover can be easily attached directly to the housing of the tablet device without fasteners, the flap  202  can essentially conform to the shape of electronic device  100 . In this way, the cover  200  will not detract or otherwise obscure the look and feel of electronic device  100 . Flap  202  can also include capacitive elements  208  arranged in a defined pattern. Capacitive elements  208  can be used to activate a multi-touch (MT) sensitive layer incorporated in display assembly. When flap  202  is placed upon cover glass  106 , the MT sensitive layer can respond to the presence of capacitive elements  208  by generating a touch pattern consistent with the defined pattern. In this way, the signal from Hall Effect sensor  120  indicating the presence of flap  202  in the closed configuration can be corroborated. When corroborated, tablet device  100  can accept the indication from Hall Effect sensor  120  that flap  202  is in the closed configuration and react accordingly. 
     In one embodiment, flap  202  can include RFID device  210  that can be used to identify protective cover  200 . In particular, when protective cover  200  is in the closed configuration, flap  202  can be in contact with cover glass  106  thereby allowing a RFID sensor within tablet device  100  to “read” RFID device  210 . In this way not only can the indication from Hall Effect sensor  120  be corroborated, but an identification of protective cover  200  can also be performed. 
       FIGS. 3A and 3B  show protective cover  200  and tablet device  100  magnetically attached to each other.  FIG. 3A  shows a closed configuration in which cover glass  106  is fully covered by and in contact with flap  202 . Protective cover  200  can pivot about hinge assembly  206  from the closed configuration of  FIG. 3A  to an open configuration of  FIG. 3B . In the closed configuration, inner layer of flap  202  can come in direct contact with cover glass  106 . In this way, capacitive elements  208  can be detected by MT circuit disposed within the display assembly beneath cover glass  106 . Moreover, the MT circuit can detect a pattern, or signature, corresponding to the pattern of capacitive elements  208 . In this way, the detection of the pattern can corroborate the indication from Hall Effect sensor  120  that flap  202  is in contact with cover glass  106 . If the pattern is not detected, then tablet device  100  can ignore the indication from Hall Effect sensor  120  (or possibly use another sensor, such as ALS  116  as a further check). 
     In order to transition from the closed to the open configuration, releasing force F release  can be applied to flap  202 . Releasing force F release  can overcome the magnetic attractive force between attachment feature  207  in flap  202  and attachment feature  110  in tablet device  100 . Hence, protective cover  200  can be secured to tablet device  100  until releasing force F release  is applied to flap  202 . In this way, flap  202  can be used to protect cover glass  106 . For example, protective cover  200  can be magnetically attached to tablet device  100 . Flap  202  can then be placed upon and magnetically secured to cover glass  106  by the magnetic interaction between magnetic attachment feature  20  and  207 . Flap  202  can be detached from cover glass  106  by the application of releasing force F release  directly to flap  202 . Releasing force F release  can overcome the magnetic attraction between magnetic attachment features  20  and  207 . Hence, flap  202  can then move away from cover glass  106  unhindered. 
       FIG. 4  shows a top view of a specific embodiment of protective cover  200  in the form of segmented cover  300 . Segmented cover  300  can include body  302 . Body  302  can have a size and shape in accordance with tablet device  100 . Body  302  can be formed from a single piece of foldable or pliable material. Body  302  can also be divided into segments separated from each other by a folding region. In this way, the segments can be folded with respect to each other at the folding regions. In one embodiment, body  302  can be formed layers of material attached to one another forming a laminate structure. Each layer can take the form of a single piece of material that can have a size and shape in conformance with body  302 . Each layer can also have a size and shape that correspond to only a portion of body  302 . For example, a layer of rigid or semi-rigid material about the same size and shape of a segment can be attached to or otherwise associated with the segment. 
     In another example, a layer of rigid or semi-rigid material having a size and shape in accordance with body  302  can be used to provide segmented cover  300  as a whole with a resilient foundation. It should be noted that the layers can each be formed of materials having desired properties. For example, a layer of segmented cover  300  that comes in contact with delicate surfaces such as glass can be formed of a soft material that will not mar or otherwise damage the delicate surface. In another embodiment, a material such as micro-fiber can be used that can passively clean the delicate surface. On the other hand, a layer that is exposed to the external environment can be formed of a more rugged and durable material such as plastic or leather. In yet another embodiment, capacitive elements  208  can be incorporated within the laminate structure of cover assembly  300 . 
     In a specific embodiment, segmented body  302  can be partitioned into a number of segments  304 - 310  interspersed with thinner, foldable portions  312 . Each of the segments  304 - 310  can include one or more inserts disposed therein. By way of example, the segments can include a pocket region where the inserts are placed or alternatively the inserts may be embedded within the segments (e.g., insert molding). If pockets used, the pocket region can have a size and shape to accommodate corresponding inserts. The inserts can have various shapes but are most typically shaped to conform to the overall look of segmented body  302  (e.g., rectangular). The inserts can be used to provide structural support for segmented body  302 . That is, the inserts can provide stiffness to the cover assembly. In some cases, the inserts may be referred to as stiffeners. As such, the cover assembly is relatively stiff except along the foldable regions that are thinner and do not include the inserts (e.g., allows folding) making segmented cover  300  more robust and easier to handle. In one embodiment segments  304 ,  306 , and  310  can be related to segment  308  in size in the proportion of about 0.72 to 1 meaning that segments  304 ,  306  and  310  are sized in width to be about 72% of the width of segment  308 . In this way, a triangle having appropriate angles can be formed (i.e., about 75° for display stand and about 11° for keyboard stand discussed below). 
     Segments  306 ,  308 , and  310  can include inserts  314 ,  316 , and  318 , respectively (shown in dotted lines form). Inserts  314 - 318  can be formed of rigid or semi-rigid material adding resiliency to body  302 . Examples of materials that can be used include plastics, fiber glass, carbon fiber composites, metals, and the like. Segment  304  can include insert  320  also formed of resilient material such as plastic but also arranged to accommodate magnetic elements  322  some of which can interact with magnetic elements in table device  1100  and more specifically attachment feature  110 . Inserts  314 - 318  can also incorporate capacitive elements  208  that can be sensed by a MT sensitive portion of the display of tablet device  100 . 
     Due to the ability of segmented body  302  to fold and more particularly the various segments to fold with respect to each other, most of magnetic elements  322  can be used to magnetically interact with magnetically active insert  324  embedded in insert  318 . By magnetically binding both active insert  324  and magnetic elements  322  various support structures can be formed some of which can be triangular in shape. The triangular support structures can aid in the use of tablet device  1100 . For example, one triangular support structure can be used to support tablet device  1100  in such a way that visual content can be presented at a desirable viewing angle of about 75° from horizontal. However, in order be able to appropriately fold segmented cover  300 , segment  308  can be sized to be somewhat larger than segments  304 ,  306  and  310  (which are generally the same size). In this way, the segments can form a triangle having two equal sides and a longer third side, the triangle having an interior angle of about 75°. 
     Cover assembly  300  can pivotally attach to accessory attachment feature  202  by way of a hinge assembly. The hinge assembly can provide one or more pivots to allow the cover to fold over on the device while the cover assembly is attached to the device through the magnets. In the illustrated embodiment, the hinge assembly can include first hinge portion (also referred to as first end lug)  328  and a second hinge portion (or second end lug)  330  disposed opposite the first end lug. First end lug  328  can be rigidly connected to second end lug  330  by way of connecting rod  332  (shown in dotted line form) incorporated into a tube portion of segmented body  302 . The longitudinal axis of connecting rod  332  can act as pivot line  1333  about which the segmented body can pivot relative to the hinge assembly. Connecting rod  332  can be formed of metal or plastic strong enough to rigidly support cover assembly  300  as well as any objects, such as tablet device  1100 , magnetically attached to magnetic attachment feature  202 . 
     In order to prevent metal on metal contact, first end lug  328  and second end lug  330  can each have protective layers  336  and  338 , respectively, attached thereto. Protective layers (also referred to as bumpers)  336  and  338  can prevent direct contact between first end lug  328  and second end lug  330  with housing  102 . This is particularly important when end lugs  328 ,  330  and housing  102  are formed of metal. The presence of bumpers  336  and  338  can prevent metal to metal contact between the end lugs and housing  102  thereby eliminating the chance of substantial wear and tear at the point of contact that can degrade the overall look and feel of tablet device  1100 . 
     First end lug  328  and second end lug  330  can be magnetically connected to the electronic device by way of hinge span  340  that is configured to pivot with respect to the end lugs. The pivoting can be accomplished using hinge posts  342  (a portion of which can be exposed). Hinge posts  342  can rotatably secure hinge span  340  to both first end lug  328  and second end lug  330 . Hinge span  304  can include magnetic elements. The magnetic elements can be arranged to magnetically attach hinge span  340  to a magnetic attachment feature having a matching arrangement of magnetic elements in the electronic device. In order to fix the magnetic elements in place within hinge span  340 , hinge posts  342  can be used to secure magnetic elements located at both ends of hinge span  340  reducing the likelihood that the magnetic elements in hinge span  340  will move about having the potential for disrupting the magnetic attachment between hinge span  340  and the magnetic attachment feature in the electronic device. 
       FIGS. 5A and 5B  illustrate representative magnetic interaction between onboard compass  118  and magnetic elements  207  and  209  in flap  202 . For the remainder of this discussion, for sake of clarity, magnetic elements  207  and  209  are presumed as a combined magnetic element ME located distance r from onboard compass  118 . In the open configuration, distance r is a fixed distance R open , whereas in the closed configuration distance r is a fixed distance R closed . Accordingly, onboard compass  118  can detect magnetic flux density M emanating from combined magnetic element ME according to Eq. (1):
 
 M ( r )= B   ME   /r   2   Eq. (1)
 
     where:
         B ME  is magnetic flux density of combined magnetic element ME (Tesla); and   r is distance between combined magnetic element ME and onboard compass  118 .       

     Accordingly, in the open configuration, onboard compass  118  can detect a magnetic flux density according to Eq. (2):
 
 M   open   =B   ME   /R   open   2   Eq. (2).
 
Whereas, in the closed configuration, onboard compass  118  can detect a magnetic flux density according to Eq. (3):
 
 M   closed   =B   ME   /R   closed   2   Eq. (3).
 
However, since distance r between combined magnetic element ME and onboard compass  118  varies with pivot angle Θ, a change in magnetic flux density M detected by onboard compass  118  can provide an estimation of the movement of flap  202  about pivot line  211 . In this way, by modeling the motion of flap  202  about pivot line  211 , motion of flap  202  can be deduced by evaluating the change of the magnetic flux density M of combined magnetic element ME detected by compass  118  according to Eq. (4):
 
 M (Θ)= B   ME   /r (Θ) 2   Eq. (4)
 
where: 0≦Θ≦π.
 
     Since tablet device  100  cannot detect the pivoting angle Θ directly, an indirect determination can be obtained using an accelerometer and gyroscope (not shown) included in tablet device  100 . The accelerometer and gyroscope can provide a spatial orientation of tablet device  100  and onboard compass  118  can detect an overall magnetic flux density (including magnetic offsets shown in  FIGS. 6A and 6B ) that can be compared to the dynamic model to deduce if flap  202  is rotating about pivot line  211 . 
       FIGS. 6A and 6B  graphically illustrate various magnetic offsets that can be detected by onboard compass  118 . For example, magnetic elements in magnetic attachment feature  204  can create magnetic offset M 1 . Magnetic offset M 1  can provide an indication that protective cover  200  is magnetically attached to tablet device  100 . For example, if onboard compass  118  detects a change in magnetic flux density along the lines of magnetic offset M 1 , then onboard compass  118  can provide a corresponding signal to a processor in tablet device  100 . The processor can use the signal to deduce that protective cover  200  has been magnetically attached to tablet device  100 . 
       FIG. 7  shows a flowchart detailing process  700  for confirming an indication from a Hall Effect sensor of the state of protective cover in relation to an electronic device. Process  700  can begin at  702  by detecting a first type stimulus at a first sensor in an electronic device. At  704 , receiving a first signal in accordance with the detecting the first signal indicating a first status of an accessory device in relation to the electronic device. At  706 , detecting a second type stimulus at a second sensor in the electronic device. At  708 , receiving a second signal in accordance with the detecting, the second signal indicating a second status of the accessory device in relation to the electronic device. At  710 , if the first and second status is the same, then the first signal is accepted at  712  and process  700  ends. Otherwise, at  714  a determination is made if a signal from another sensor is to be received. If it is determined that another signal from another sensor is to be received, than control is passed to  706 , otherwise, the first signal is ignored at  716  and process  700  ends. 
       FIG. 8  shows a flowchart detailing process  800  as one embodiment of step  702  of process  700  where the first sensor is a Hall Effect (HFX) sensor. More specifically, process  800  begins at  802  by receiving the indication from the HFX sensor that the state of the cover is closed. At  804 , an ambient light sensor is activated. At  806 , a determination is made if the ALS has detected an amount of ambient light greater than a threshold value of ambient light. If the amount of detected ambient light is greater than the threshold value, then the indication from the HFX sensor that the cover is closed is not corroborated and the indication from the HFX sensor that the cover is closed is ignored at  808 , otherwise, the electronic device accepts the indication from the HFX sensor at  810 . 
       FIG. 9  shows a flowchart detailing process  900  as one embodiment of step  702  of process  700  where the first sensor is a Hall Effect (HFX) sensor. More specifically, process  900  begins at  902  by receiving the indication from the HFX sensor that the state of the cover is closed. At  904 , a camera is activated and at  906  a determination is made whether or not an image has been captured by the camera. If at  906  it is determined that the camera has not captured an image, then the indication from the HFX sensor that the cover is closed is accepted at  908 . On the other hand, if at  906  it is determined that the camera has captured an image, then the indication from the HFX sensor that the cover state is closed is not corroborated and the indication from the HFX sensor is ignored by the electronic device at  910 . 
       FIG. 10  shows a flowchart detailing process  1000  as one embodiment of step  702  of process  700  where the first sensor is a Hall Effect (HFX) sensor. More specifically, process  1000  begins at  1002  by receiving the indication from the HFX sensor that the state of the cover is closed. At  1004 , a magnetic field is detected at the compass and at  1006  a determination is made whether or not the detected magnetic field is consistent with a hard magnetic offset resulting from the presence of magnetic elements in the cover. If at  1006  it is determined that the there is no hard offset detected, then the indication from the HFX sensor that the cover is closed is not corroborated and the electronic device ignores the indication from the HFX sensor at  1008 . On the other hand, if at  1006  it is determined that the hard offset is detected, then the indication from the HFX sensor that the cover state is closed is corroborated and the indication from the HFX sensor is accepted by the electronic device at  1010 . 
       FIG. 11  shows a flowchart detailing process  1100  as one embodiment of step  702  of process  700  where the first sensor is a Hall Effect (HFX) sensor. More specifically, process  1100  begins at  1102  by receiving the indication from the HFX sensor that the state of the cover is closed. At  1104 , a MT event is detected at a MT sensitive surface. At  1106 , a determination is made if the MT event matches an MT signature consistent with the cover state being closed. If the MT signature is determined to be consistent with the cover state being closed, then at  1108 , the electronic device accepts the indication from the HFX sensor. On the other hand, if the MT event does not match the MT signature, then the electronic device ignores the indication from the HFX sensor at  1110  and process  1100  ends. 
       FIG. 12  shows a flowchart detailing process  1200  as one embodiment of step  702  of process  700  where the first sensor is a Hall Effect (HFX) sensor. More specifically, process  1200  begins at  1202  by receiving the indication from the HFX sensor that the state of the cover is closed. At  1204 , an RFID signature is detected. At  1206 , a determination is made if the RFID signature matches an RFID signature consistent with the cover. If the RFID signature is determined to be consistent with the cover, then at  1208 , the electronic device accepts the indication from the HFX sensor. On the other hand, if the RFID signature is not consistent with the cover, then the electronic device ignores the indication from the HFX sensor at  1210  and process  1200  ends. 
       FIG. 13  shows a flowchart detailing process  1300 . More specifically, process  1300  begins at  1302  using an accelerometer and gyroscope in real time to detect a current spatial position and rotation of the electronic device. At  1304 , an extrinsic magnetic field is detected by a magnetometer (in the form of the compass). At  1306 , a resulting dynamic magnetic field is provided in real time based upon the accelerometer and gyroscope readings and the compass readings, the resulting magnetic field being a net magnetic field of all extrinsic magnetic fields measured at the compass. The net magnetic field is updated in real time based upon the current spatial position and rotation of the electronic device to provide a dynamic resulting magnetic that is compared at  1308  to a reference datum of the dynamic magnetic field consistent with no cover present. At  1310 , a deviation of the measured dynamic magnetic field and the reference datum is determined. If the deviation is less than a threshold deviation value, then the cover is not present and the electronic device ignores the indication from the HFX sensor at  1312 . On the other hand, if the deviation is greater than the threshold deviation value, then the cover is present and the electronic device accepts the indication from the HFX sensor at  1314 . 
       FIG. 14  is a block diagram of an electronic device  1450  suitable for use with the described embodiments. The electronic device  1450  illustrates circuitry of a representative computing device. The electronic device  1450  includes a processor  1452  that pertains to a microprocessor or controller for controlling the overall operation of the electronic device  1450 . The electronic device  1450  stores media data pertaining to media items in a file system  1454  and a cache  1456 . The file system  1454  is, typically, a storage disk or a plurality of disks. The file system  1454  typically provides high capacity storage capability for the electronic device  1450 . However, since the access time to the file system  1454  is relatively slow, the electronic device  1450  can also include a cache  1456 . The cache  1456  is, for example, Random-Access Memory (RAM) provided by semiconductor memory. The relative access time to the cache  1456  is substantially shorter than for the file system  1454 . However, the cache  1456  does not have the large storage capacity of the file system  1454 . Further, the file system  1454 , when active, consumes more power than does the cache  1456 . The power consumption is often a concern when the electronic device  1450  is a portable media device that is powered by a battery  1474 . The electronic device  1450  can also include a RAM  1470  and a Read-Only Memory (ROM)  1472 . The ROM  1472  can store programs, utilities or processes to be executed in a non-volatile manner. The RAM  1470  provides volatile data storage, such as for the cache  1456 . 
     The electronic device  1450  also includes a user input device  1458  that allows a user of the electronic device  1450  to interact with the electronic device  1450 . For example, the user input device  1458  can take a variety of forms, such as a button, keypad, dial, touch screen, audio input interface, visual/image capture input interface, input in the form of sensor data, etc. Still further, the electronic device  1450  includes a display  1460  (screen display) that can be controlled by the processor  1452  to display information to the user. A data bus  1466  can facilitate data transfer between at least the file system  1454 , the cache  1456 , the processor  1452 , and the CODEC  1463 . 
     In one embodiment, the electronic device  1450  serves to store a plurality of media items (e.g., songs, podcasts, etc.) in the file system  1454 . When a user desires to have the electronic device play a particular media item, a list of available media items is displayed on the display  1460 . Then, using the user input device  1458 , a user can select one of the available media items. The processor  1452 , upon receiving a selection of a particular media item, supplies the media data (e.g., audio file) for the particular media item to a coder/decoder (CODEC)  1463 . The CODEC  1463  then produces analog output signals for a speaker  1464 . The speaker  1464  can be a speaker internal to the electronic device  1450  or external to the electronic device  1450 . For example, headphones or earphones that connect to the electronic device  1450  would be considered an external speaker. 
     The electronic device  1450  also includes a network/bus interface  1461  that couples to a data link  1462 . The data link  1462  allows the electronic device  1450  to couple to a host computer or to accessory devices. The data link  1462  can be provided over a wired connection or a wireless connection. In the case of a wireless connection, the network/bus interface  1461  can include a wireless transceiver. The media items (media assets) can pertain to one or more different types of media content. In one embodiment, the media items are audio tracks (e.g., songs, audio books, and podcasts). In another embodiment, the media items are images (e.g., photos). However, in other embodiments, the media items can be any combination of audio, graphical or visual content. Sensor  1476  can take the form of circuitry for detecting any number of stimuli. For example, sensor  1476  can include a Hall Effect sensor responsive to external magnetic field, an audio sensor, a light sensor such as a photometer, and so on. 
     The various aspects, embodiments, implementations or features of the described embodiments can be used separately or in any combination. Various aspects of the described embodiments can be implemented by software, hardware or a combination of hardware and software. The described embodiments can also be embodied as computer readable code on a non-transitory computer readable medium. The computer readable medium is defined as any data storage device that can store data which can thereafter be read by a computer system. Examples of the computer readable medium include read-only memory, random-access memory, CD-ROMs, DVDs, magnetic tape, and optical data storage devices. The computer readable medium can also be distributed over network-coupled computer systems so that the computer readable code is stored and executed in a distributed fashion. 
     The foregoing description, for purposes of explanation, used specific nomenclature to provide a thorough understanding of the described embodiments. However, it will be apparent to one skilled in the art that the specific details are not required in order to practice the described embodiments. Thus, the foregoing descriptions of the specific embodiments described herein are presented for purposes of illustration and description. They are not target to be exhaustive or to limit the embodiments to the precise forms disclosed. It will be apparent to one of ordinary skill in the art that many modifications and variations are possible in view of the above teachings. 
     The advantages of the embodiments described are numerous. Different aspects, embodiments or implementations can yield one or more of the following advantages. Many features and advantages of the present embodiments are apparent from the written description and, thus, it is intended by the appended claims to cover all such features and advantages of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, the embodiments should not be limited to the exact construction and operation as illustrated and described. Hence, all suitable modifications and equivalents can be resorted to as falling within the scope of the invention.

Metadata:
Filing Date: 20110228
Publication Date: 20121016
Grant Date: 20121016
Priority Date: 20100917
Inventors: CRETELLA, JR. MICHAEL A.
DUGGINENI VENU MADHAV
ENG MICHAEL MAN-CHEUNG
HUANG RONALD KERYUAN
MOORE CHRISTOPHER
MULLENS CHRISTOPHER T.
Assignee: APPLE INC
CPC Classifications: [{"code": "G06F1/1626", "inventive": true, "first": true, "tree": "[]"}, {"code": "Y10T24/32", "inventive": false, "first": false, "tree": "[]"}, {"code": "Y10T24/32", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F9/00", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F2200/1634", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F2200/1633", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F1/1677", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F1/1626", "inventive": true, "first": false, "tree": "[]"}, {"code": "G05B15/02", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F2200/1633", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F2200/1634", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F1/1677", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 45818515