Patent Publication Number: US-2017351349-A1

Title: Fluid pressure force sensor interface

Description:
BACKGROUND 
     Electronic devices may accept user input dependent on the application of a force by the user to the electronic device or to an associated peripheral device. For example, a stylus peripheral for use with a tablet computer or smart phone may sense the force applied to the tip of the stylus and switch from a hover mode to an ink mode when the force applied by a user satisfies a minimum force condition. The stylus may sense increasing force and transmit a signal indicating the received force level to an electronic device accordingly. Peripherals that accept user input dependent on force often experience distortions from changes in environmental conditions, such as temperature, pressure, etc. These distortions may lead to user input inaccuracies and diminished user experience. 
     SUMMARY 
     The described technology includes a fluid force sensor interface between a pressure sensor, such as a barometric pressure sensor disposed inside a sensor housing with an aperture, and a container with an interior cavity exposed to the ambient environmental fluid pressure. The interior cavity of the container may equalize with the pressure of the ambient fluid environment, and may cooperate with the aperture on the sensor housing to create at least a partial fluid seal. A force member may transmit an applied outside force to deform the container, and the interior cavity therein, to reduce the volume of the interior cavity and thus increase pressure inside the interior cavity. The fluid force sensor may measure the applied force by sensing an increase in pressure inside the interior cavity. After the outside applied force has been removed, the pressure inside the interior cavity may equalize with the ambient fluid pressure. The sensor may operate at a wide range of ambient fluid pressures without recalibration because the applied force measurement may depend on a change in fluid pressure inside the interior cavity, and not on the absolute value of the fluid pressure measurement. 
     This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. 
     Other implementations are also described and recited herein. 
    
    
     
       BRIEF DESCRIPTIONS OF THE DRAWINGS 
         FIG. 1  illustrates an example barometric pressure force sensor in a stylus peripheral in a hover mode. 
         FIG. 2  illustrates an example barometric pressure force sensor in a stylus peripheral in an ink mode. 
         FIG. 3  is a plot of fluid pressure inside an interior cavity against barometric sensor output. 
         FIG. 4  illustrates an example container with an interior cavity configured to cooperate with the aperture on a barometric sensor housing. 
         FIG. 5  illustrates another example container with an interior cavity configured to cooperate with the aperture on a barometric sensor housing. 
         FIG. 6  illustrates another example container with an interior cavity configured to cooperate with the aperture on a barometric sensor housing with an applied force. 
         FIG. 7  illustrates another example container with an interior cavity configured to cooperate with the aperture on a barometric sensor housing without an applied force. 
         FIG. 8  illustrates another example container with an interior cavity configured to cooperate with the aperture on a barometric sensor housing with an applied force. 
         FIG. 9  illustrates another example container with an interior cavity configured to cooperate with the aperture on a barometric sensor housing without an applied force. 
         FIG. 10  illustrates another example container with an interior cavity configured to cooperate with the aperture on a barometric sensor housing with an applied force. 
         FIG. 11  is a plot of fluid pressure inside the interior cavity of a container against time. 
         FIG. 12  illustrates another example container with an interior cavity configured to cooperate with the aperture on a barometric sensor housing without an applied force. 
         FIG. 13  illustrates another example container with an interior cavity configured to cooperate with the aperture on a barometric sensor housing with an applied force. 
         FIG. 14  illustrates example operations for sensing an applied force. 
         FIG. 15  illustrates an example system that may be useful in implementing the described technology. 
     
    
    
     DETAILED DESCRIPTIONS 
     A fluid pressure force sensor interface includes a fluid pressure sensor, such as a barometric pressure sensor disposed inside a sensor housing with an aperture, and a container with an interior cavity exposed to the ambient environmental fluid pressure. The fluid force sensor may be used in a hand-held stylus designed for use as a peripheral with electronic devices, including smart phones, tablets, watches, desktop computers, gaming devices, wearable devices, televisions, video conferencing systems, etc. The fluid pressure force sensor interface is equipped with a deformable container having an interior cavity and an opening in the interior cavity to the ambient fluid environment, which may include the ambient fluid pressure. The interior cavity is configured to cooperate with the port of a fluid sensor, such as a barometric sensor. When a user applies a force to an applicator of the fluid pressure force sensor, such as the tip of a stylus, a pressure member decreases the volume, and thus increases the pressure, inside the interior cavity. When the user applies no force to the applicator (or, in an implementation, a force below a minimum force condition), the pressure in the interior cavity of the deformable container may equalize with the ambient environmental fluid pressure through the exterior opening, and the port of the fluid sensor may also calibrate (or tare) to ambient environmental pressure through the exterior opening or via a gap between the container and the housing of the fluid pressure sensor. There is no need for an additional fluid pressure sensor to measure a reference ambient environmental pressure because both the inside of the interior cavity of the container and the environment of the fluid pressure sensor return to the same ambient fluid pressure when there is no force on the applicator regardless of changes in environmental pressure. 
     A stylus or pen may communicate user input to an electronic device. The stylus may be powered by a battery, which may be a rechargeable battery, a replaceable battery, or a disposable battery. The stylus may include, as explained in more detail below, capabilities to support one or more wired or wireless communications protocols. In one implementation, antennas may be disposed inside or outside the stylus to communicate with electronic devices according to a variety of communications protocols. The stylus may include features such as one or more physical buttons selectable by a user. In one implementation, they stylus may include a clip that may also function as a physical button, an antenna, or an information indicator such as, for example but without limitation, by including an LED light or display. In implementations, the stylus may include user feedback features such as haptic feedback, audio alerts through one or more audio speakers, vibration user feedback, etc. 
     The stylus may operate according to one or modes of operation. The stylus may determine an appropriate mode of operation based on environmental conditions that may be sensed according to one or more sensors on the stylus. In another implementation, the stylus may determine an appropriate mode of operation according to an internal metric, for example without limitation, if a predetermined amount of time has passed since the stylus has received an input from the user or data from a paired device. In yet another implementation, a mode of operation may be selected by the user, for example without limitation, by pushing a button or switch on the device or by causing a sensor on the device to receive an input. 
     One mode of operation may be a stand-by mode, such as a low power mode or sleep mode. The stylus may enter stand-by mode, for example, when the stylus has been idle for a predetermined amount of time. Stand-by mode may conserve battery power by cutting power to unneeded subsystems of the stylus. The stylus may be woken up from stand-by mode by the user in a variety of ways, such as pressing a button on the stylus housing or applying pressure to the tip. In another implementation, the stylus may be awakened from stand-by mode or powered on remotely, such as by connecting a cable or wirelessly via a Bluetooth™ connection, a Wi-Fi connection, NFC communications, activation of an on-board sensor such as an accelerometer, heat sensor, noise sensor, or temperature sensor. Another mode of operation of the stylus may be an active mode. In active mode, the various subsystems on-board the stylus may be powered up. For example, without limitation, a communications system may power up in active mode, and attempt to establish a connection with an electronic device. 
     The stylus may also include a hover mode. In hover mode, a user may control the position of a pen cursor or pointer by directing the tip of the stylus at the screen of the electronic device without making physical contact with the screen. The stylus may detect hover mode when there is no pressure applied to the tip, but the stylus is within a predetermined distance from the screen of the electronic device. 
     Another mode of the stylus may be an ink mode, also known as a draw mode or write mode. The stylus may operate in ink mode when a pressure is applied to the tip of the stylus sufficient to satisfy an ink condition. The ink condition may be, for example without limitation, a minimum force applied to the stylus tip. Ink mode may be used to select an area of the screen of the electronic device indicated by the position of the tip. In ink mode, the electronic device may interpret input as drawing on the screen, such as for drawing a figure or when writing text. The stylus may sense various weights of ink depending on the amount of pressure applied to the stylus tip. For example, a light touch may indicate a relatively finer line should be drawn on the device. As the user increases pressure on the stylus, the weight of the line may increase accordingly. The stylus may therefore detect a binary condition indicating whether the stylus should draw or hover, and also, in ink mode, detect a pressure to indicate the weight of a line to be drawn. In one implementation, the stylus may sense 4096 or more discrete weights depending on the amount of pressure applied to the stylus against the screen of the electronic device. 
     Barometric pressure sensors measure force needed to stop a liquid or gas from expanding. To provide a pressure reading, a pressure sensor may need to establish a reference pressure against which a sensed pressure may be measured. One way of establishing a reference pressure is to use the local atmospheric pressure, also known as a differential pressure sensor. A differential pressure sensor is vented to the atmosphere surrounding the sensor. When a port in the sensor is exposed to the atmosphere, the sensor may indicate a pressure of zero. When a pressure is applied to the port, the sensor may report a pressure value indicating the difference between the ambient pressure and the applied pressure. Another way of establishing a reference pressure is to use a sealed pressure sensor. A sealed pressure sensor may include a hermetically sealed container that remains at a fixed internal pressure regardless of changing ambient conditions. A sealed pressure sensor may include a reference barometric sensor in contact with the sealed container to provide a reference pressure. A sealed pressure sensor may include a port exposed to the ambient atmosphere to expose a second barometric sensor to the ambient fluid pressure, which may include the ambient air pressure. If the ambient pressure equals the pressure inside the sealed container, the sealed pressure sensor will report a pressure of zero. If the ambient pressure surrounding the sealed pressure sensor differs from the pressure inside the sealed container, then the sealed pressure sensor will report a value indicating the difference. 
     The type of barometric pressure sensor used in the present stylus is an absolute sensor. An absolute sensor may include a single port and single barometric pressure sensor that measures pressure relative to a vacuum. Absolute barometric pressure sensors are available with a large dynamic range, e.g., up to 24-bit of data after the output has been sent through an analog-to-digital converter (ADC). The high dynamic range of the sensors may afford a wider range of pressure measurements than is likely to be needed for the environmental conditions in which the sensor is expected to operate. In other words, the range of expected measurements for the real-world environmental conditions experienced by the sensor may fit into a smaller output space such as 16- or 12-bits of data, thus relaxing the mechanical tolerances needed to construct the device because it is possible for the sensor to still sense all encountered environmental pressures even if there is some “drift” due to less stringent mechanical tolerances within the 24-bit range. 
     The force sensor disclosed herein may employ an absolute barometric sensor with a configurable output. Configuring output includes without limitation adjusting the gain on the sensor and/or adjusting the range of pressures the sensor is configured to report. Configuring the output of the sensor permits several modes of operation that may not be available with other types of sensors. It may be desired for the sensor to have a large resolution response for part of an applied force window, but a relatively lower resolution response for another part of an applied force window. For example, if the force on the stylus tip is expected to range from 0-350 g, the output of the sensor could be configured to provide a high resolution response in the window 0 g-100 g, and a lower resolution response in the window 100-350 g because it is likely that most users will operate the stylus in the 0-100 g range the majority of the time, and the users may desire a finer response in that range. If the stylus detects an applied force is in the 0-100 g range, it may dynamically configure the output of the sensor to provide a larger response resolution by using a relatively larger portion of the range of the sensor. If the stylus detects an applied force above 100 g, it may dynamically configure the sensor to include forces up to 350 g (or above) to continue detecting applied force, but with less precision than in the lower range. In one implementation, the output of the sensor in the stylus may be so configured as to meet a logarithmic response curve specification. When the stylus is in a hover mode, a high resolution response may be desired for pressures near the ambient fluid pressure to detect a force needed to switch the stylus to an ink mode. In hover mode, the output of the sensor may be configured to provide such a large resolution response until an applied force has been detected that is deemed sufficient satisfy an ink condition, for example over a range of 0-5 g. 
     The stylus is capable of passively compensating for a wide range of ambient fluid pressure without calibration because the stylus relies on the high dynamic range of the sensor to sense changes in pressure (referred to herein as ΔP) when a force is applied to the tip no matter where the ΔP occurs within the sensor&#39;s range. The stylus may calibrate the sensor to a zero level when the sensor when the stylus wakes up from a sleep mode or under a variety of other conditions, as explained below. The calibration operation may zero (or “tare”) the sensor to the ambient fluid pressure because the sensor is exposed to the ambient fluid pressure when there is no force applied to the tip. Once the stylus has been zeroed to the ambient pressure, any measured increase in pressure can be attributed to a force on the tip, regardless of the actual reading reported by the sensor. In other words, the stylus may rely only on a sensed ΔP to measure an applied force without regard to where in the sensor&#39;s range the ΔP occurs. 
     Use of a configurable absolute barometric sensor with a high dynamic range also provides power savings to the stylus by avoiding or reducing on-board processing. In one implementation, the barometric sensor includes an analog front end with a serial output that may transmit readings to the stylus or to an associated electronic device via direct memory access (DMA). Using DMA, it is possible for the associated electronic device to receive a transmission from the sensor without using, or even waking up, an on-board processor on the stylus to process the sensor output, as may be necessary with a digital sensor output, such as a 12-bit digital output. 
       FIG. 1  illustrates an example stylus  100  in a hover mode. The stylus  100  includes a stylus body  102 . In an implementation, the stylus body  102  may be formed of a material suitable for enclosing the components described herein. The stylus body  102  may be formed from, for example without limitation, plastic, rubber, metal, carbon fiber, etc., and/or any combinations thereof. In an implementation, the stylus  100  may include one or more physical buttons  104  selectable by a user. Selection of one of the physical buttons  104  may cause a user input to be transmitted to the stylus  100 . For example, without limitation, selection of a physical button  104  may select an application program executing on an electronic device with which the stylus communicates according to a wired or wireless communication protocol. Physical buttons  104  may wake the pen from standby mode and/or activate menus and/or other user interface designs on an application executing on an electronic device. In another implementation, physical buttons  104  may select or “click” an element on a graphical user interface on the electronic device via a cursor. In other implementations, the stylus  100  may include a cap button  106 . The cap button  106  may be a physical button selectable by the user, and may perform any of the aforementioned functions mentioned with respect to buttons  104 . The stylus  100  may include one or more friction areas for facilitating the user&#39;s grip and manipulation, such as, for example, a rubber friction area or textured area to increase friction with a user&#39;s hand and/or fingers. In an implementation, the stylus  100  includes a tip  110 . The tip  110  may be positioned at the distal end of the stylus  100  on the opposite end of the stylus from the physical button  106 . 
     In hover mode, there is no pressure applied to the tip  110  of the stylus  100  (or the pressure is below a minimum ink condition pressure), such as by contact with a screen  112  of an associated electronic device  114 . In  FIG. 1 , components housed inside stylus body  102  are shown in greater detail in bubble  108 . Other components in addition to those shown in bubble  108  may be present inside stylus body  102 , including without limitation inside stylus body  102  at the distal end near the tip in the area depicted by bubble  108 . In an implementation, a tip  110  extends beyond the distal end of the stylus body  102 , and is mechanically coupled to a tip holder shaft  116 . The tip holder shaft  116  may be vertically disposed inside stylus housing  102 . The tip holder shaft  116  and tip  110  may be slidably coupled to the interior of stylus housing  102 . When a user applies pressure to tip  110 , such as, for example, by pressing the stylus  100  onto the surface of an electronic device, the tip  110  and tip holder shaft  112  may slide in concert inside stylus body  102 . 
     In one implementation, the tip holder shaft  112  may be operatively coupled to a force assembly  118 . The force assembly may exert a force on the tip holder  116  and the other components coupled thereto to ensure the tip  110  does not move until a minimum force has been applied. The force assembly  118  may include a spring that may be pre-loaded to a desired amount according to a number of methods. The spring may be pre-loaded using pre-load spacers added to one or both ends of spring, or by using threaded pre-load assemblies, etc. Increasing the amount of pre-loading on the spring in the force assembly  118  will increase the force that must be applied to tip holder  112  via tip  110  to move the spring from a pre-loaded position. In one implementation, the pre-load is greater than the weight of the tip  110 , the tip holder shaft  116 , and any other components slidably connected to the interior of stylus housing  102 , such that the tip  110  will remain in a fully extended position when the user holds the stylus  100  in any orientation, such as a vertical orientation. In this implementation, the tip  110  will remain fully extended when the user applies force to the tip  110 , such as when the user wishes to provide input to an electronic device by writing on the surface  112  of the device  114  with the stylus  100 , until such time that the user applies more force to the tip  110  than the amount of pre-loading on spring  114 . When the user applies more force to the tip  110  than the amount of pre-loading on spring  114 , the tip holder shaft  112  will begin to compress spring  114 . The spring  114  will continue to compress as force on the tip increases until the spring reaches a maximum compression. In another implementation, the force assembly  118  may include a rubber dome to hold the tip holder  116  and associated components in a fully extended position until the user applies a sufficient force to collapse the rubber dome and compress the force assembly  118 . In yet another implementation, the force assembly  118  includes a mechanical switch that may be configured to compress in a variety of ways (e.g., with an operating point, pressure point, reset point, tactile point, etc.) when the user applies a force to tip  110 . 
     In an implementation, the stylus  100  includes a container  122 . The container  122  may be formed in a variety of shapes suitable to permit an interior cavity  124  having a volume and an opening in the interior cavity  126  to the ambient fluid pressure. The opening in the interior cavity  126  allows the fluid pressure inside the interior cavity  124  to equalize with the ambient fluid pressure when the stylus  100  is in a hover mode, as in  FIG. 1 . The container  122  may be formed of a deformable material such that the container  122 , and the interior cavity  124 , may at least partially collapse to a reduced volume when an outside force is applied. In an implementation, the container  122  may be formed of a material that resists deforming until a minimum force has been applied. 
     In another implementation, the container  122  includes a cap section  128 . In one implementation, the cap section  128  is in the shape of a dome. The cap section  128  may be formed of a different material than the remainder of container  122 , such that an applied force will tend to collapse the cap section  128  more readily than the remainder of container  122 . The collapse of cap section  128  may be designed to facilitate a reduction in volume in interior cavity  124  when an outside force is applied to the container  122 . 
     The stylus  100  may include a force member  120 . In an implementation, the force member  120  may be operatively coupled to the force assembly  118  and to at least a portion of container  122 . The force member  120  may be formed according to a variety of shapes suitable to transmit a force applied by a user to container  122  via tip  110 , tip holder  116 , and force assembly  118 , which may be all slidably connected to the inside of stylus body  102 . In one implementation, the force member  120  has a flared end in contact with container  122  to distribute an applied force over a greater surface area of the container  122 . In another implementation, the force member  120  may include a rounded tip to concentrate the force applied by the user in a relatively smaller region of container  122 . The force member  120  may itself be deformable, and may compress between force assembly  118  and container  122  when a user applies a force to tip  110 . 
     In an implementation, a barometric sensor is disposed inside a sensor housing  130  and is in fluid communication with the ambient fluid pressure through an aperture  132  in the sensor housing  130 . A surface of the sensor housing may be separated from the container  132  by an air gap  134 . The surface of the sensor housing  130  may be smooth to facilitate a seal between the sensor housing and the container  122  when the container slidably cooperates with the sensor housing. In some implementations, the seal is not a complete seal, and some fluid continues to leak out from the interior cavity to the environment when the container slidably cooperates with the sensor housing. The aperture  132  in the sensor housing may be sized to be smaller than the size of the opening  126  in the interior cavity  124 . In one implementation, the aperture  132  in the sensor housing may be substantially smaller than the opening  126  in the interior cavity to facilitate a more substantially complete seal around the sensor aperture when the container  122  cooperates with the surface of the sensor housing. 
     Inside the sensor housing  130 , there may be various components including a circuit board, a temperature sensor, one or more strain gauges, electronic components such as a bridge rectifier, etc. The components inside the sensor housing  130  may be communicatively connected to a controller and other components inside the stylus body  102  for transmitting readings from the barometric pressure sensor, the strain gauges, the temperature sensor, etc. The sensor housing may be disposed on the end of a central shaft  134 . The central shaft  134  may be fixably attached to the inside of stylus body  102 , such that the sensor housing remains stationary when an outside force has been applied by the user via the tip  110  and other components connected thereto. 
       FIG. 2  illustrates an example stylus  200  in an ink mode. The stylus  200  includes a stylus body  202 . In an implementation, the stylus body  202  may be formed of a material suitable for enclosing the components described herein. The stylus body  202  may be formed from, for example without limitation, plastic, rubber, metal, carbon fiber, etc., and/or any combinations thereof. In an implementation, the stylus  200  may include one or more physical buttons  204  selectable by a user. Selection of one of the physical buttons  204  may cause a user input to be transmitted to the stylus  200 . For example, without limitation, selection of a physical button  204  may select an application program executing on an electronic device with which the stylus communicates according to a wired or wireless communication protocol. Physical buttons  204  may wake the pen from standby mode and/or activate menus and/or other user interface designs on an application executing on an electronic device. In another implementation, physical buttons  204  may select or “click” an element on a graphical user interface on the electronic device via a cursor. In other implementations, the stylus  200  may include a cap button  206 . The cap button  206  may be a physical button selectable by the user, and may perform any of the aforementioned functions mentioned with respect to buttons  204 . The stylus  200  may include one or more friction areas for facilitating the user&#39;s grip and manipulation, such as, for example, a rubber friction area or textured area to increase friction with a user&#39;s hand and/or fingers. In an implementation, the stylus  200  includes a tip  210 . The tip  210  may be positioned at the distal end of the stylus  200  on the opposite end of the stylus from the physical button  206 . 
     In an ink mode, a user applies pressure to the tip  210  of the stylus  200 , such as by contact with a screen  212  of an associated electronic device  214 . Components housed inside stylus body  202  are shown in greater detail in bubble  208  as arranged when the stylus  200  is in an ink mode. Other components in addition to those shown in bubble  208  may be present inside stylus body  202 , including without limitation inside stylus body  202  at the distal end near the tip in the area depicted by bubble  208 . In an implementation, a tip  210  extends beyond the distal end of the stylus body  202 , and is mechanically coupled to a tip holder shaft  216 . The tip holder shaft  216  may be vertically disposed inside stylus housing  202 . The tip holder shaft  216  and tip  210  may be slidably coupled to the interior of stylus housing  202 . When a user applies pressure to tip  210 , the tip  210  and tip holder shaft  212  may slide in concert inside stylus body  202 . 
     In one implementation, the tip holder shaft  212  may be operatively coupled to a force assembly  218 . The force assembly may exert a force on the tip holder  216  and the other components coupled thereto to ensure the tip  210  does not move until a minimum force has been applied. The force assembly  218  may include a spring that may be pre-loaded to a desired amount according to a number of methods. The spring may be pre-loaded using pre-load spacers added to one or both ends of spring, or by using threaded pre-load assemblies, etc. Increasing the amount of pre-loading on the spring in the force assembly  218  will increase the force that must be applied to tip holder  212  via tip  210  to move the spring from a pre-loaded position. In one implementation, the pre-load is greater than the weight of the tip  210 , the tip holder shaft  216 , and any other components slidably connected to the interior of stylus housing  202 , such that the tip  210  will remain in a fully extended position when the user holds the stylus  200  in any orientation, such as a vertical orientation. In this implementation, the tip  210  will remain fully extended when the user applies force to the tip  210 , such as when the user wishes to provide input to an electronic device by writing on the surface  212  of the device  214  with the stylus  200 , until such time that the user applies more force to the tip  210  than the amount of pre-loading on spring  214 . When the user applies more force to the tip  210  than the amount of pre-loading on spring  214 , the tip holder shaft  212  will begin to compress spring  214 . The spring  214  will continue to compress as force on the tip increases until the spring reaches a maximum compression. In another implementation, the force assembly  218  may include a rubber dome to hold the tip holder  216  and associated components in a fully extended position until the user applies a sufficient force to collapse the rubber dome and compress the force assembly  218 . In yet another implementation, the force assembly  218  includes a mechanical switch that may be configured to compress in a variety of ways (e.g., with an operating point, pressure point, reset point, tactile point, etc.) when the user applies a force to tip  210 . 
     In an implementation, the stylus  200  includes a container  222 . The container  222  may be formed in a variety of shapes suitable to permit an interior cavity  224  having a volume and an opening in the interior cavity  226  to the ambient fluid pressure. The opening in the interior cavity  226  allows the fluid pressure inside the interior cavity  224  to equalize with the ambient fluid pressure when the stylus  200  is in a hover mode, as in  FIG. 1 . The container  222  may be formed of a deformable material such that the container  222 , and the interior cavity  224 , may at least partially collapse when an outside force is applied. In an implementation, the container  222  may be formed of a material that resists deforming until a minimum force has been applied. 
     In another implementation, the container  222  includes a cap section  228 . In one implementation, the cap section  228  is in the shape of a dome. The cap section  228  may be formed of a different material than the remainder of container  222 , such that an applied force will tend to collapse the cap section  228  more readily than the remainder of container  222 . The collapse of cap section  228  may be designed to facilitate a reduction in volume in interior cavity  224  when an outside force is applied to the container  222 . 
     The stylus  200  may include a force member  220 . In an implementation, the force member  220  may be operatively coupled to the force assembly  218  and to at least a portion of container  222 . The force member  220  may be formed according to a variety of shapes suitable to transmit a force applied by a user to container  222  via tip  210 , tip holder  216 , and force assembly  218 , which are all slidably connected to the inside of stylus body  202 . In one implementation, the force member  220  has a flared end in contact with container  222  to distribute an applied force over a greater surface area of the container  222 . In another implementation, the force member  220  may include a rounded tip to concentrate the force applied by the user in a relatively smaller region of container  222 . The force member  220  may itself be deformable, and may compress between force assembly  218  and container  222  when a user applies a force to tip  210 . 
     In an implementation, a barometric sensor is disposed inside a sensor housing  230  and is in fluid communication with the ambient fluid pressure through an aperture  232  in the sensor housing  230 . A surface of the sensor housing may be separated from the container  232  by an air gap  234 . The surface of the sensor housing  230  may be smooth to facilitate a seal between the sensor housing and the container  222  when the container cooperates with the sensor housing. The aperture  232  in the sensor housing may be sized to be smaller than the size of the opening  226  in the interior cavity  224 . In one implementation, the aperture  232  in the sensor housing may be substantially smaller than the opening  226  in the interior cavity to facilitate a complete seal around the sensor aperture when the container  222  cooperates with the surface of the sensor housing. 
     Inside the sensor housing  230 , there may be various components including a circuit board, a temperature sensor, one or more strain gauges, etc. The components inside the sensor housing  230  may be communicatively connected to a controller inside the stylus body  202  for transmitting readings from the barometric pressure sensor, the strain gauges, the temperature sensor, etc. The sensor housing may be disposed on the end of a central shaft  234 . The central shaft  234  may be fixably attached to the inside of stylus body  202 , such that the sensor housing remains stationary when an outside force has been applied by the user via the tip  210  and other components connected thereto. 
     When a user applies a force to tip  210 , force member  220  and container  222  may slidably move towards sensor housing  230 , such that the opening  226  of the interior cavity  224  cooperates with the aperture  232  and compresses the container  222  to reduce volume of the interior cavity  224  and increase fluid pressure therein. 
       FIG. 3  is a plot of pressure inside the interior cavity of the container as measured by the barometric pressure sensor. The x-axis in the plot represents actual pressure inside the interior cavity and the y-axis in the plot represents the value reported by the sensor. The scale of the y-axis has been converted to a 12-bit scale, such as by an analog-to-digital converter. 
     In an embodiment, the barometric sensor has a substantially linear response to increasing pressure. As the sensor has a high dynamic range of sensor outputs, the output may be adjusted to cover all expected pressure values expected to be encountered by the device. In one implementation, the barometric pressure sensor output is configured to sense a range of pressures starting at greater than one atmosphere of pressure (i.e., below sea level) up to 0.1 atmospheres of pressure, which is likely lower than the environmental pressure encountered on a pressurized airplane or in a geographic area of high elevation. The output of the sensor may be further configured to account for increased pressure inside the interior cavity of the container. In one implementation, the output of the sensor is further adjusted to account for up to 400 g of force on the tip of the stylus. The increased pressure inside the interior cavity corresponding to 400 g of force on the tip of the stylus is dependent upon the shape and volume chosen for the interior cavity. 
     The plot in  FIG. 3  illustrates the reliance of the force sensing of the device on the ΔP measured by the sensor rather than on any particular pressure value. For example, in one implementation, the stylus tares (or “zeroes”) the sensor when the stylus wakes from a sleep mode into an active mode. If the user is operating the stylus in a geographical area of high elevation, the pressure point at which the sensor tares may be represented by P 1 . At point P 1 , the sensor may report a reading of S 1 . If the user applies a force to the tip of the stylus, the fluid pressure in the interior cavity will increase to P 2  while the container cooperates with the sensor housing. The value reported by the sensor will accordingly climb to S 2 . The difference between the sensor outputs S 1  and S 2  may be represented by ΔY, which may be interpreted by the stylus as the ink state value for the force applied by the user. In one implementation, the ink state value may correspond to the thickness of a line the user wishes to draw on an associated electronic device. The ink state value, or ΔY, depends only on the difference between sensor readings S 1  and S 2 , and is independent of the actual sensor readings themselves. 
     In another example, the user of the stylus leaves the geographic area of high elevation, and travels to sea level. When the user awakens the stylus from a sleep mode near sea level, the stylus tares (or “zeroes”) the sensor to a pressure represented by P 3 , which corresponds to a sensor reading of S 3 . If the user now applies a force to the tip of the stylus, the pressure inside the interior cavity may rise to P 4  because the force will reduce the volume in the interior cavity, and the sensor will report a corresponding value of S 4 . As in the prior example, the difference in sensor values may be represented by ΔY′, which may be interpreted by the stylus as the ink state value for the force applied by the user. As before, the ink state value, or ΔY′, depends only on the difference between sensor readings S 3  and S 4 , and is independent of the actual sensor readings themselves. In this manner, the force sensor may passively “slide” up and down the linear response curve as environmental pressure conditions change without the need to calibration of the device. 
       FIG. 4  illustrates an example container  408  with an interior cavity  410  configured to cooperate with the aperture  404  on a barometric sensor housing  402 . The container  408  may include a top section  416  that is more easily deformable than the remainder of container  408  to facilitate reduction in volume of the interior cavity  410  when a force is applied to the top section  416 . The body of container  408  may be substantially more rigid than top section  416  to maintain a more complete fluid seal between the bottom surface  412  of the container  408  and the top surface of the sensor housing  402  with which the container  408  may cooperate. 
     The container  408  is slidably coupled to the inside of the stylus body. A force applied to the device slides the container  408  towards the sensor housing  402  until the container contacts the sensor housing  402  and the interior cavity cooperates with the aperture  404  on the barometric sensor housing  402 . In an implementation, the top section  416  and/or the body of container  408  are rigid enough not to deform under a force when sliding against the inside of the stylus body, and only begin to deform after the container  408  has stopped moving against the sensor housing  402 . Once the container  408  begins to deform, the volume of interior cavity  410  will decrease and fluid pressure inside interior cavity  410  will increase because the fluid able to escape from the interior cavity  410  will be minimized. One way of minimizing escaping fluid is raised annular port  406  in sensor housing  402 . The raised annular port  406  may be sized smaller than the opening  414  in interior cavity  410  to permit the raised annular port  406  to fit inside the opening  414 . In another embodiment, a skirt section extends from container  408  and interfaces with the sensor housing  402  to guide the container so that the opening  414  does not misalign with the raised aperture  406  and/or assists with creating a seal between the interior cavity  410  and the ambient fluid pressure. Another way to minimize escaping fluid is to provide a smooth surface on the top of the sensor housing  402  to interface with the bottom surface  412  of container  408 . Bottom surface  412  of container  408  may include a friction grip, rubber, or other material for decreasing sliding movement against the top of the sensor housing  402 . In another implementation, the bottom surface  412  of container  408  and/or the top of sensor housing  402  include a microcellular urethane (e.g., Poron). 
     When the applied force is removed from the tip of the stylus, the container  408  may slide back up, such that there is an air gap again between the opening  414  and the sensor housing  402 . When the container  408  raises back up, the fluid pressure in the interior cavity  410  will equalize with the ambient fluid pressure. The container may be raised up by a force assembly including a pre-loaded spring, a rubber dome, and/or a mechanical switch. In another implementation, the container  408  is raised back up by springs disposed between the sensor housing  402  and the container  408 . In yet another implementation, the container  408  is raised back up by wings disposed on the bottom surface  412  of container  408  that collapse when the container  408  presses on the top surface of sensor housing  402  but expand to push against the container when the applied force is removed. 
       FIG. 5  is another implementation of a container  508  with an interior cavity  510  including an opening  514  from the interior cavity  510  to the ambient fluid pressure. The container  508  is disposed above a sensor housing  502  containing a sensor aperture  504  and two grooves  506  to receive the bottom portion of container  508  when the opening  514  cooperates with the sensor aperture  504 . When the container  508  is in a raised position, there is a fluid gap between the opening  514  and the surface of the sensor housing  502 . In this position, the fluid pressure inside the interior cavity  510  equalizes with the ambient fluid pressure. 
     The container  508  may have a top section  512  in a flat shape. The flat shape of top section  512  and a relatively wider body section of container  508  may provide a greater increase of fluid pressure in the interior cavity  510  for a fixed applied force because the flat shape allows for a greater reduction in volume inside the interior cavity  510  than a more rounded cap section would. The shape of cap section  512  and the rest of container  508  may be chosen in this manner to tune the response of the barometric sensor for a given mechanical movement of the force member pressing on the container  508 . 
       FIG. 6  illustrates another example container  608  with an interior cavity  610  configured to cooperate with the aperture  604  on a barometric sensor housing  602  when a force is applied by force member  614 . In an implementation, the sensor housing  602  includes a groove  606  to receive the bottom portion of the container  608 . In an implementation, the groove  606  is a circular groove that surrounds the aperture  604  to permit an improved fluid seal between the interior cavity  610  and the surface of the sensor housing  602 . Since the seal is dependent on force applied by the force member  614 , a harder force will tend to produce a better fluid seal. 
     When the applied force is removed from the tip of the stylus, the container  608  may slide back up, such that there is an air gap again between the opening  614  and the sensor housing  602 . When the container  608  raises back up, the fluid pressure in the interior cavity  610  will equalize with the ambient fluid pressure. The container may be raised up by a force assembly including a pre-loaded spring, a rubber dome, and/or a mechanical switch. In another implementation, the container  608  is raised back up by springs disposed between the sensor housing  602  and the container  608 . In yet another implementation, the container  608  is raised back up by wings disposed on the bottom surface  612  of container  608  that collapse when the container  608  presses on the top surface of sensor housing  602  but expand to push against the container when the applied force is removed. 
       FIG. 7  is another implementation of a container  704  with an interior cavity  706  including a fluidly permeable section  710  between the interior cavity  706  to the ambient fluid pressure. The container  704  is disposed above a sensor housing  702  containing a sensor on the surface of the housing (not shown). The container  704  does not have raised and lowered positions, but rather always sits in contact with the sensor housing  702 , regardless of whether a force member applies a force to the top section  708 . In an implementation, the fluidly permeable section  710  may be formed of open-cell foam. In the absence of a force applied to the top section  708 , the fluid pressure in the interior cavity  706  will tend to equalize with the ambient fluid pressure via the fluidly permeable section  710 . The rate at which the interior cavity  706  equalizes with the ambient fluid pressure may be chosen by selecting a material for the fluidly permeable section  710  with greater or lesser fluid permeability. In an implementation, the fluidly permeable section  710  may be located at the bottom of container  704 , near the surface of sensor housing  702 . In another implementation, the fluidly permeable section may be located elsewhere on container  704 , such as near the top section  708  or at any other location on container  704 . 
       FIG. 8  illustrates another example container  806  with an interior cavity  808  fixed atop a sensor housing  802  including an aperture  804 . When the applied force is removed from the tip of the stylus, the container  806  and top section  810  may deform to reduce the volume of interior cavity  808 . Although some fluid will escape through fluidly permeable section  812 , the resulting increase in fluid pressure inside the interior cavity  808  may still be measured by the barometric sensor via the aperture  804 . In one implementation, the leakage caused by fluidly permeable sections  812  may be accounted for when interpreting the measurement of the barometric sensor. For example, a fluidly permeable section  812  may permit the passage of fluid at a rate proportional to the difference in fluid pressure between the interior cavity  808  and the ambient fluid pressure. A controller on the stylus or an electronic device associated with the stylus may calculate this pressure loss, and adjust the estimated force accordingly. In one implementation, a contact force applied to container  806  by force member  814  will result in an initially increasing, then slowly decreasing fluid pressure inside interior cavity  808  as fluid seeps out through fluidly permeable sections  812 . The stylus and/or electronic device associated with the stylus may interpret the slowly decreasing fluid pressure inside interior cavity  808  as a constant force. 
     When the force member  814  retracts and no longer applies a force to cap section  810 , then the fluid pressure inside interior cavity  808  may equalize with the ambient fluid pressure. Since the barometric pressure sensor has a high dynamic range, the sensor may tare to the current fluid pressure when the force member  814  retracts, but before the fluid pressure inside interior cavity  808  has fully equalized with the ambient fluid pressure. In one implementation, the barometric pressure sensor tares at discrete time intervals after the force member  814  retracts to prepare to measure the ΔP of another application of force to the top section  810  that may come before the fluid pressure inside interior cavity  808  has fully equalized. Since the container  806  does not need to travel so that the interior cavity  808  cooperates with the aperture  804  in the sensor housing  802  when a force is applied via force member  814 , the container  806  may provide a lower activation point for sensing a force than a container that must close an air gap before the fluid pressure in the interior cavity rises. 
       FIG. 9  is another implementation of a container  906  with an interior cavity  908  including a fluid channel  912  between the interior cavity  908  and the ambient fluid pressure. The container  906  is disposed above a sensor housing  902  containing an aperture  904  for a barometric pressure sensor. The container  906  does not have raised and lowered positions, but rather always sits in contact with the sensor housing  902 , regardless of whether a force member applies a force to the top section  910 . In an implementation, the fluidly channel  912  may be an open channel. In the absence of a force applied to the top section  910 , the fluid pressure in the interior cavity  908  will tend to equalize with the ambient fluid pressure via the fluidly channel  912 . The rate at which the interior cavity  908  equalizes with the ambient fluid pressure may be chosen by selecting a width for fluid channel  912 . In an implementation, the fluidly channel  912  may be located at the bottom of container  906 , near the surface of sensor housing  902 . In another implementation, the fluidly permeable section may be located elsewhere on container  906 , such as near the cap section  910  or at any other location on container  906 . 
       FIG. 10  illustrates another example container  1006  with an interior cavity  1008  fixed atop a sensor housing  1002  including an aperture  1004 . When a force is applied to the tip of the stylus, force member  1012  may transmit the applied force to the container  1006  and cap section  1010 , which may deform to reduce the volume of interior cavity  1008 . Although some fluid will escape through fluid channel  1016 , the fluid channel  1016  may be configured to collapse under the force of force member  1012  to partially or completely seal the fluid channel  1016 , such that fluid leakage is reduced or eliminated. Even with some fluid leakage, the resulting increase in fluid pressure inside the interior cavity  1008  may still be measured by the barometric sensor via the aperture  1004 . In one implementation, the leakage caused by fluid channel  1016  may be accounted for when interpreting the measurement of the barometric sensor. 
     When the force member  1012  retracts and no longer applies a force to cap section  1010 , then the fluid pressure inside interior cavity  1008  may equalize with the ambient fluid pressure via fluid channel  1016 . Since the barometric pressure sensor has a high dynamic range, the sensor may calibrate to a zero level at the current ambient fluid pressure when the force member  1012  retracts, but before the fluid pressure inside interior cavity  1008  has fully equalized with the ambient fluid pressure. In one implementation, the barometric pressure sensor tares at discrete time intervals after the force member  1012  retracts to prepare to measure the ΔP of another application of force to the top section  1010  that may come before the fluid pressure inside interior cavity  1008  has fully equalized. Since the container  1006  does not need to travel so that the interior cavity  1008  cooperates with the aperture  1004  in the sensor housing  1002  when a force is applied via force member  1012 , the container  1006  may provide a lower activation point for sensing a force than a container that must close an air gap before the fluid pressure in the interior cavity rises. 
       FIG. 11  is a plot of fluid pressure inside the interior cavity of a container against time when a force has been applied by a force member. The x-axis of the plot represents time, and the y-axis of the plot represents pressure inside the interior cavity of a container relative to a tare level. In one implementation, the zero point on the y-axis represents the fluid pressure measured by a barometric sensor at power-up, before the user has applied a force to the tip of the stylus, e.g., the zero point represents the ambient fluid pressure. At the beginning of a first time interval, ΔT, the user begins to apply a force to the tip of the stylus, and a force member compresses the container, thus reducing the volume inside the interior cavity and accordingly increasing the fluid pressure inside the interior cavity until the fluid pressure reaches a local maximum for a total fluid pressure change designated by ΔP. The stylus may interpret ΔP as corresponding to a measured applied force. In one implementation, ΔP corresponds to an ink thickness transmitted to an electronic device associated with the stylus. 
     At the end of the time period represented by ΔT, the fluid pressure inside the interior cavity begins to return to the ambient fluid pressure level, i.e., the zero level on the plot. Before the fluid pressure in the interior cavity reaches the ambient fluid pressure, the user applies another force to the tip of the stylus at the beginning of time period ΔT′. This second application of force causes the fluid pressure inside the interior cavity to begin to rise again until the end of time period ΔT′ for a gain of ΔP′. In an implementation, the stylus does not measure applied force based on the actual value of P, but rather based on the values of ΔP and ΔP′. Near the end of the plot of  FIG. 11 , the fluid pressure inside the interior cavity returns to the level of the ambient fluid pressure. 
       FIG. 12  is another implementation of a container  1206  with an interior cavity  1214  including a fluid channel  1216  between the interior cavity  1214  and the ambient fluid pressure. The container  1206  is disposed above a sensor housing  1202  containing an aperture  1204  for a barometric pressure sensor. The container  1206  does not have raised and lowered positions, but rather always sits in contact with the sensor housing  1202 . A force member  1208  forms a portion of the walls of container  1206 . In an implementation, the force member  1208  forms the top wall of the container  1206 , and is slidably insertable into the interior cavity  1214  according to rollers  1210  when a force is applied to the tip of the stylus. In the absence of a force applied to the force member  1208 , the fluid pressure in the interior cavity  1214  will tend to equalize with the ambient fluid pressure via the fluid channel  1216 . The rate at which the interior cavity  1214  equalizes with the ambient fluid pressure may be chosen by selecting a width for fluid channel  1216 . In an implementation, the fluid channel  1216  may be located at the bottom of container  1206 , near the surface of sensor housing  1202 . In another implementation, the fluid channel  1216  may be located elsewhere on container  1206 , such as near the force member  1208  or at any other location on container  1206 . 
       FIG. 13  illustrates another example container  1306  with an interior cavity  1314  fixed atop a sensor housing  1302  including an aperture  1304 . When a force is applied to the tip of the stylus, force member  1308  may slidably insert into, and reduce the volume of, interior cavity  1314 . Although some fluid will escape through fluid channel  1316 , the resulting increase in fluid pressure inside the interior cavity  1314  may still be measured by the barometric sensor via the aperture  1304 . In one implementation, the leakage caused by fluid channel  1316  may be accounted for when interpreting the measurement of the barometric sensor. 
     When the force member  1308  retracts from the interior cavity  1314 , then the fluid pressure inside interior cavity  1314  may equalize with the ambient fluid pressure via fluid channel  1316 . Since the barometric pressure sensor has a high dynamic range, the sensor may calibrate to a zero level at the current fluid pressure when the force member  1308  retracts, but before the fluid pressure inside interior cavity  1314  has fully equalized with the ambient fluid pressure. In one implementation, the barometric pressure sensor tares at discrete time intervals after the force member  1308  retracts to prepare to measure the ΔP of another application of force to force member  1308  that may come before the fluid pressure inside interior cavity  1314  has fully equalized. Since the container  1306  does not need to travel so that the interior cavity  1314  cooperates with the aperture  1304  in the sensor housing  1302  when a force is applied via force member  1308 , the configuration of container  1306  may provide a lower activation point for sensing a force than a container that must close an air gap before the fluid pressure in the interior cavity rises. 
       FIG. 14  illustrates example operations  1400  for sensing an applied force using a barometric sensor. Step  1402  is disposing a container with an interior cavity and an opening the interior cavity to the ambient fluid pressure in fluid communication with a barometric pressure sensor. The container may be slidably connected to the inside of a peripheral device, and in mechanical connection with a portion of the device, such as the tip of a stylus. When a user applies a force to the tip of the stylus, a force member in contact with a portion of the container may slide the container towards a sensor housing, such that the opening in the interior cavity cooperates with the aperture in the sensor housing. In an implementation, there is a force assembly between the tip of the stylus and the force member configured to compress until a minimum force has been applied before the force member will transmit the force to the container. The force assembly may include a pre-loaded spring, a rubber dome, and/or a mechanical switch. 
     Step  1404  of operations  1400  is establishing, by the barometric pressure sensor, a baseline pressure reading. In one implementation, the baseline pressure reading is of the ambient fluid pressure, such as, for example, when the stylus wakes up from a sleep mode, and before the user has applied a force to the tip. In another implementation, the baseline pressure reading is taken after a force has been applied to the tip, but before the fluid pressure in the interior cavity has returned to ambient fluid pressure. Taking the baseline pressure reading before the fluid pressure in the interior cavity has returned to an ambient fluid pressure may be advisable for the sensor to be able to measure an additional application of force to the tip of the stylus that may occur in the time period before the interior cavity returns to ambient fluid pressure. 
     The next step, step  1406 , is transmitting an applied force to the container that increases the fluid pressure inside the interior cavity. In one implementation, the applied force at least partially deforms the container to reduce the volume of the interior cavity located therein. In another implementation, a force member comprises at least partially a wall of the interior cavity, and the applied force slides the force member into the container, thus reducing the volume of the interior cavity and increasing fluid pressure therein. The last step is  1408 , measuring the change in fluid pressure in the interior cavity from the baseline pressure reading. The change in fluid pressure in the interior cavity from the baseline pressure reading may be referred to as ΔP, and may represent a measurement of the force applied to the tip of the stylus. 
       FIG. 15  illustrates an example system (labeled as a stylus  1500 ) that may be useful in implementing the described stylus. The stylus  1500  includes a processor  1502 , a memory  1504 , and other interfaces  1508  (e.g., a buttons, fingerprint scanner, etc.). The memory  1504  generally includes both volatile memory (e.g., RAM) and non-volatile memory (e.g., flash memory). An operating system  1510 , such as the Microsoft Windows® Phone operating system, resides in the memory  1504  and is executed by the processor  1502 , although it should be understood that other operating systems may be employed. 
     One or more application programs  1512  are loaded in the memory  1504  and executed on the operating system  1508  by the processor  1502 . The one or more application programs may include data and routines for executing the methods and stylus apparatus disclosed herein. For example, the applications  1512  may include routines and methods for controlling the barometric pressure sensor, communicating with an associated electronic device, processing data received from the barometric pressure sensor and any other sensors or devices disclosed herein. The stylus  1500  includes a power supply  1516 , which is powered by one or more batteries or other power sources and which provides power to other components of the stylus  1500 . The power supply  1516  may also be connected to an external power source that overrides or recharges the built-in batteries or other power sources. 
     The stylus  1500  includes one or more communication transceivers  1530  to provide network connectivity (e.g., mobile phone network, Wi-Fi®, BlueTooth®, etc.). The stylus  1500  also includes various other components, such as one or more accelerometers  1522 , a barometric pressure sensor  1524 , and additional storage  1528 . Other configurations may also be employed. 
     In an example implementation, a mobile operating system, various applications, and other modules and services may be embodied by instructions stored in memory  1504  and/or storage devices  1528  and processed by the processing unit  1502 . The instructions stored in memory  704  may include instructions for activating a power system in the stylus  1500 , instructions for measuring electrical characteristics of circuits in the stylus  1500 , instructions for measuring characteristics of environmental conditions surrounding the stylus  1500 , instructions for measuring pressure via a barometric pressure sensor  1524 , and/or for storing data relating to measurements. User preferences, service options, and other data may be stored in memory  1504  and/or storage devices  1528  as persistent datastores. 
     Stylus  1500  may include a variety of tangible computer-readable storage media and intangible computer-readable communication signals. Tangible computer-readable storage can be embodied by any available media that can be accessed by the stylus  1500  and includes both volatile and nonvolatile storage media, removable and non-removable storage media. Tangible computer-readable storage media excludes intangible communications signals and includes volatile and nonvolatile, removable and non-removable storage media implemented in any method or technology for storage of information such as computer readable instructions, data structures, program modules or other data. Tangible computer-readable storage media includes, but is not limited to, RAM, ROM, EEPROM, flash memory or other memory technology, CDROM, digital versatile disks (DVD) or other optical disk storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other tangible medium which can be used to store the desired information and which can be accessed by stylus  1500 . In contrast to tangible computer-readable storage media, intangible computer-readable communication signals may embody computer readable instructions, data structures, program modules or other data resident in a modulated data signal, such as a carrier wave or other signal transport mechanism. The term “modulated data signal” means a signal that has one or more of its characteristics set or changed in such a manner as to encode information in the signal. By way of example, and not limitation, intangible communication signals include wired media such as a wired network or direct-wired connection, and wireless media such as acoustic, RF, infrared and other wireless media. 
     Some embodiments may comprise an article of manufacture. An article of manufacture may comprise a tangible storage medium to store logic. Examples of a storage medium may include one or more types of computer-readable storage media capable of storing electronic data, including volatile memory or non-volatile memory, removable or non-removable memory, erasable or non-erasable memory, writeable or re-writeable memory, and so forth. Examples of the logic may include various software elements, such as software components, programs, applications, computer programs, application programs, system programs, machine programs, operating system software, middleware, firmware, software modules, routines, subroutines, functions, methods, procedures, software interfaces, application program interfaces (API), instruction sets, computing code, computer code, code segments, computer code segments, words, values, symbols, or any combination thereof. In one embodiment, for example, an article of manufacture may store executable computer program instructions that, when executed by a computer, cause the computer to perform methods and/or operations in accordance with the described embodiments. The executable computer program instructions may include any suitable type of code, such as source code, compiled code, interpreted code, executable code, static code, dynamic code, and the like. The executable computer program instructions may be implemented according to a predefined computer language, manner or syntax, for instructing a computer to perform a certain function. The instructions may be implemented using any suitable high-level, low-level, object-oriented, visual, compiled and/or interpreted programming language. 
     The stylus may communicate with an electronic device according to a variety of methods. In one implementation, the stylus may contain a Bluetooth™ antenna and communicate with an electronic device according to the Bluetooth™ wireless protocol. In another implementation, the stylus may contain a Wi-Fi antenna and communicate, directly or indirectly, with an electronic device according to one or more Wi-Fi wireless protocols. In other implementations, the stylus may communicate with an electronic device according to a wired connection, for example without limitation a Universal Serial Bus (USB) connection. The stylus may utilize one of the aforementioned communications protocols, or similar communications protocols, to communicate a variety of data to an electronic device. In one implementation, the stylus may pair with an electronic device according to one of the communications protocols. Further, and as explained in more detail below, the stylus may communicate data to an electronic device including position data, mode of operation data, input data, etc. 
     The stylus may advantageously allow a memory for on board storage of user files received via a wired or wireless connection to the electronic device. The stylus may contain a processor configured to execute code stored on the memory such as operating system code or code downloaded to the stylus over a digital communications channel. The stylus may further advantageously contain a glass display to determine or display to the user any of the following: the power status of the battery, the current wireless signal strength, or other information relating to an electronic device configured to receive user input from the stylus. 
     An example apparatus includes a pressure member configured to transmit an applied force. A barometric pressure sensor having a sensor housing and an aperture is disposed in the sensor housing. A container having an interior cavity and an opening in the interior cavity is in fluid communication with ambient fluid pressure. The interior cavity is subject to a decrease in volume and an increase in fluid pressure by a force applied by the pressure member. The container is configured to cooperate with and form at least a partial fluid seal around the aperture in the sensor housing to communicate at least part of the increase in fluid pressure to the barometric pressure sensor. 
     Another example apparatus of any preceding apparatus includes an interior cavity that is in fluid communication with the ambient fluid pressure at least partially via open cell foam. 
     Another example apparatus of any preceding apparatus includes a fluid communication between the interior cavity with the ambient fluid pressure is at least partially restricted when the force applied by the pressure member satisfies a choke condition. 
     Another example apparatus of any preceding apparatus includes a pressure member forms a part of a wall of the interior cavity and reduces volume inside the interior cavity by moving into the interior cavity. 
     Another example apparatus of any preceding apparatus includes a container and the opening in the interior cavity slidably cooperate with the aperture in the sensor housing before the pressure member increases fluid pressure inside the interior cavity. 
     Another example apparatus of any preceding apparatus includes an aperture in the sensor housing includes a raised annular port, the raised annular port fitting at least partially inside the opening in the interior cavity when the container and the opening in the interior cavity slidably cooperate with the aperture in the sensor housing. 
     Another example apparatus of any preceding apparatus includes a force assembly configured to establish a minimum force to slideably move the container. 
     Another example apparatus of any preceding apparatus includes a force assembly includes at least one of: a pre-loaded spring, a rubber dome, and a mechanical switch. 
     Another example apparatus of any preceding apparatus includes an aperture in the sensor housing that includes a groove, the groove configured to cooperate with at least a portion of the bottom of the container when the container and the opening in the interior cavity slidably cooperate with the aperture in the sensor housing. 
     Another example apparatus of any preceding apparatus includes a container including a deformable cap section. 
     Another example apparatus of any preceding apparatus includes a deformable cap section in the shape of a dome. 
     Another example apparatus of any preceding apparatus includes a deformable cap section that is substantially flat. 
     Another example apparatus of any preceding apparatus includes a barometric pressure sensor that is an absolute pressure sensor. 
     An example method includes sensing an applied force including disposing a container with an interior cavity and an opening in the interior cavity to ambient fluid pressure in fluid communication with a barometric pressure sensor, establishing, by the barometric pressure sensor, a baseline pressure reading, transmitting an applied force to the container that increases the fluid pressure inside the interior cavity, and measuring, by the barometric pressure sensor, the change in fluid pressure in the interior cavity from the baseline pressure reading. 
     Another example method of any preceding method includes communicating the measured change in fluid pressure to an associated electronic device if the measured change in fluid pressure satisfies a minimum pressure condition. 
     Another example method of any preceding method includes identifying, by a computer processor, a device state depending on the measured change in fluid pressure. 
     Another example method of any preceding method includes the baseline pressure reading is a reading of the ambient fluid pressure. 
     An example stylus peripheral includes a stylus body, a tip slidably disposed at the distal end of the stylus body, a container having an interior cavity and an opening in the interior cavity to ambient fluid pressure, and a force assembly connected to the tip and slidably disposed inside the stylus body, the force assembly configured to transmit a force applied to the tip to the container to reduce the volume of the interior cavity. 
     Another example stylus peripheral of any preceding stylus peripheral includes a barometric pressure sensor in fluid communication with the interior cavity, and configured to sense a change in fluid pressure inside the interior cavity, and a communications assembly configured to communicate the sensed change in fluid pressure by the barometric pressure sensor in the interior cavity from the ambient fluid pressure to an associated electronic device. 
     Another example stylus peripheral of any preceding stylus peripheral includes a container cooperates with a housing of a barometric pressure sensor in fluid communication with the interior cavity to form at least a partial fluid seal. 
     The implementations described herein are implemented as logical steps in one or more computer systems. The logical operations may be implemented (1) as a sequence of processor-implemented steps executing in one or more computer systems and (2) as interconnected machine or circuit modules within one or more computer systems. The implementation is a matter of choice, dependent on the performance requirements of the computer system being utilized. Accordingly, the logical operations making up the implementations described herein are referred to variously as operations, steps, objects, or modules. Furthermore, it should be understood that logical operations may be performed in any order, unless explicitly claimed otherwise or a specific order is inherently necessitated by the claim language. The above specification, examples, and data, together with the attached appendices, provide a complete description of the structure and use of exemplary implementations.