Patent Publication Number: US-2022237140-A1

Title: Transmission control architecture between sensing device and host device

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 63/142,967, filed on Jan. 28, 2021. The content of the application is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to signal transmission, and more particularly, to a transmission control architecture that relies on a single signal transmission interface to transmit signals of multiple transmission protocols between a master device and a sensing device. 
     2. Description of the Prior Art 
     Nowadays, digital microphones, such as digital micro-electromechanical systems (MEMS) microphones, usually rely on pulse-density modulation (PDM) interfaces to transmit audio signals. The PDM interface typically has a 1-bit data channel and a clock channel for serial transmission. However, the PDM interface does not have a control channel, and cannot be used to interchange digital microphone-related control parameters. In view of this, as long as a digital microphone is shipped, its acoustic and electrical characteristics, such as sampling rate, sensitivity, acoustic overload point (AOP), or filter settings cannot be changed. In order to adjust settings of the digital microphone, it is necessary to use a transmission protocol with in-band control mechanism, such as MIPI SoundWire or HD-Audio interface, or increase signal pins. However, these approaches inevitably increase system cost and circuit complexity. 
     SUMMARY OF THE INVENTION 
     With this in mind, it is one object of the present invention to provide approaches of integrating data and control interfaces, which uses provided signal transmission interfaces for transmitting sensed information and control information in a time division multiplexing manner, thereby to configure a sensing device and read its sensed information,. As such, setting/characteristic adjustment of the sensing device can be realized. Since the present invention effectively integrates different signal transmission interfaces, it will not cause a significant increase in cost. 
     According to one embodiment, a sensing device is provided. The sensing device comprises: a sensed information transmitting circuit, a control information slave circuit and a mode switching circuit. The sensed information transmitting circuit is configured to convert sensed information into a transmission signal compliant with a signal format of a first transmission protocol. The control information slave circuit is configured to convert a received signal received from a signal transmission interface into control information according to a second transmission protocol, thereby to configure the sensing device. The mode switching circuit is coupled to the sensed information transmitting circuit and the control information slave circuit, and configured to activate one of the sensed information transmitting circuit and the control information slave circuit based on one of a signal on a clock channel of the signal transmission interface, a signal on a data channel of the signal transmission interface or a signal on a power rail of the sensing device, thereby to transmit or receive signals through the signal transmission interface. 
     According to one embodiment, a master device is provided. The master device comprises: a sensed information receiving circuit, a control information master circuit and a mode switching circuit. The sensed information receiving circuit is configured to convert signal received from a signal transmission interface into sensed information according to a first transmission protocol. The control information master circuit is configured to convert control information into a transmission signal compliant with a signal format of a second transmission protocol. The mode switching circuit is coupled to the sensed information receiving circuit and the control information master circuit, and configured to adjust a signal on a clock channel of the signal transmission interface, a signal on a data channel of the signal transmission interface or a signal on a power rail of the master device according to an operation mode of the master device, thereby to control one of the sensed information receiving circuit and the control information master circuit to use the signal transmission interface for receiving or transmitting signals. 
     According to one embodiment a sensing system is provided. The sensing system comprises a master device and at least one sensing device. The master device comprises: a sensed information receiving circuit, a control information master circuit and a mode switching circuit. The sensed information receiving circuit is configured to convert signal received from a signal transmission interface into sensed information according to a first transmission protocol. The control information master circuit is configured to convert control information into a transmission signal compliant with a signal format of a second transmission protocol. The mode switching circuit is coupled to the sensed information receiving circuit and the control information master circuit, and configured to adjust a signal on a clock channel of the signal transmission interface, a signal on a data channel of the signal transmission interface or a signal on a power rail of the master device according to an operation mode of the master device, thereby to control one of the sensed information receiving circuit and the control information master circuit to use the signal transmission interface for receiving or transmitting signals. The sensing device comprises: a sensed information transmitting circuit, a control information slave circuit and a mode switching circuit. The sensed information transmitting circuit is configured to convert sensed information into a transmission signal compliant with a signal format of the first transmission protocol. The control information slave circuit is configured to convert a received signal received from a signal transmission interface into control information according to the second transmission protocol, thereby to configure the sensing device. The mode switching circuit is coupled to the sensed information transmitting circuit and the control information slave circuit, and configured to activate one of the sensed information transmitting circuit and the control information slave circuit based on one of a signal on a clock channel of the signal transmission interface, a signal on a data channel of the signal transmission interface or a signal on a power rail of the sensing device, thereby to transmit or receive signals through the signal transmission interface. 
     These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a schematic diagram of a master device and a sensing device according to one embodiment of the present invention. 
         FIG. 2  illustrates a detailed structure diagram of a mode detecting circuit according to one embodiment of the present invention. 
         FIG. 3  illustrates a signal timing diagram according to one embodiment of the present invention. 
         FIG. 4  illustrates a diagram of hysteresis control according to one embodiment of the present invention. 
         FIG. 5  illustrates a detailed structure diagram showing a master device controlling and accessing multiple sensing devices according to one embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present embodiments. It will be apparent, however, to one having ordinary skill in the art that the specific detail need not be employed to practice the present embodiments. In other instances, well-known structures, materials or steps have not been presented or described in detail in order to avoid obscuring the present embodiments. 
     Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment or example is included in at least one embodiment of the present embodiments. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures or characteristics may be combined in any suitable combinations and/or sub-combinations in one or more embodiments. 
     Please refer to  FIG. 1 , which illustrates a mater device and a sensing device with a signal transmission interface according to one embodiment of the present invention. A master device  100  can communicate with one or more sensing devices  200  through a signal transmission system of the present invention, so as to implement setting adjustment and sensed data reading of the one or more sensing devices  200 . In some embodiments, a signal transmission interface  300  comprises at least a first channel  310  and a second channel  320 . The first channel  310  can be utilized to transmit a clock signal, while the second channel  320  can be utilized to transmit data signals. However, this is not a limitation of the present invention. 
     The master device  100  includes a sensed information receiving circuit  110 , a control information master circuit  120 , and a mode switching circuit  130 . Based on a first transmission protocol, the sensed information receiving circuit  110  is utilized to convert signals received from the second channel  320  into specific sensed information (e.g. audio information, vibration information, pressure information, optical information or temperature information) in accordance the clock signal on the first channel  310 . In one embodiment, the first transmission protocol may be a transmission protocol based on pulse density modulation (PDM). Based on a second transmission protocol, the control information master circuit  120  is configured to send control information to the sensing device  200  through at least one of the first channel  310  and the second channel  320 . The second transmission protocol may be a synchronous transmission protocol or an asynchronous transmission protocol. For example, the synchronous transmission protocol could be I 2 C or serial peripheral interface (SPI) protocol, while the asynchronous transmission protocol could be universal asynchronous receiver/transmitter (UART) protocol or 1-wire protocol. If the second transmission protocol is a synchronous transmission protocol, the control information master circuit  120  transmits the clock signal through the first channel  310 , and transmits the control information through at least the second channel  320  (depending on the requirements of the transmission protocol, multiple non-clock channels may be needed for communication). If the second transmission protocol is an asynchronous transmission protocol, the control information master circuit  120  can send the control information through one of the first channel  310  or the second channel  320  (e.g., the 1-wire or UART single-ended transmission protocol), or both (e.g., UART differential transmission protocol). According to requirements of the master device  100 , the mode switching circuit  130  can switch the sensed information receiving circuit  110  or the control information master circuit  120  to use the first channel  310  and the second channel  320 . According to various embodiments of the present invention, the mode switching circuit  130  is operable to notify the sensing device  200  in advance by changing frequencies of signals on the first channel  310 , characteristics of signals on the second channel  320 , or voltage levels of signals on a power rail  400 . When the mater device  100  enters a setting adjustment mode, the control information master circuit  120  uses the signal transmission interface  300  to transmit control information. When the master device  100  enters a sensed information reading mode, the sensed information receiving circuit  110  uses the signal transmission interface  300  to receive the sensed information. In one embodiment, when the control information master circuit  120  prepares to transmit the control information to the sensing device  200  through the signal transmission interface  300 , the mode switching circuit  130  may transmit a signal whose frequency lower than a threshold through the first channel  310 , or increase a voltage level on the power rail  400 . In this way, the sensing device  200  can determine that the transmission signal on the signal transmission interface  300  is the control information, and accordingly request a corresponding circuit module to handle the signal on the channel. On the other hand, when the sensed information receiving circuit  110  prepares to receive the sensed information through the signal transmission interface  300 , the mode switching circuit  130  may transmit a signal whose frequency higher than the threshold through the first channel  310 , or reduce the voltage level on the power rail  400 , allowing the sensing device  200  to request a corresponding circuit module to transmit the sensed information. Please note that the approach described above is only a possible implementation of the present invention, which is suitable when a basic clock of the first transmission protocol (e.g., PDM) is higher in frequency than that of the second transmission protocol (e.g., I 2 C). In other embodiments, if the basic clock of the first transmission protocol is lower in frequency than that of the second transmission protocol, the approach for notifying the sensing device  200  of operation mode switching may be conversely. For example, before transmitting the control information, the mode switching circuit  130  may transmit a signal whose frequency higher than the threshold through the first channel  310 , or reduce the voltage level of the signal on the power rail  400 , allowing the sensing device  200  to determine the transmission signal on the interface  300  is the control information. Conversely, before receiving the sensed information, the mode switching circuit  130  may transmit a signal whose frequency lower than the threshold through the first channel  310 , or increase a voltage level on the power rail  400 , such that the sensing device  200  can request a corresponding circuit module to transmit the sensed information. In other words, in embodiments of the present invention, it is possible to reflect whether the master device  100  is in the setting adjustment mode or the sensed information reading mode through relationship between the frequency on the first channel  310  and the frequency threshold, or relationship between the voltage level on the power rail  400  and the voltage threshold. 
     In other embodiments of the present invention, the signal characteristics on the second channel  320  may be also used by the master device  100  to notify the sensing device  200  of mode switching. For example, the mode switching circuit  130  may transmit a signal with a specific pattern within a specific time interval, to the sensing device  200  through the second channel  320 , thereby informing the sensing device  200  of the operation mode which the master device  100  is currently operated in. Accordingly, the sensing device  200  can respond properly. For example, the master device  100  and the sensing device  200  may pre-set or decide a protocol on encoding rules and signal patterns. When the sensing device  200  decodes a packet from the master device  100 , and content of the decoded packet corresponds to a predetermined simple signal content or a series of cadence signal content (for example, but not limited to, the signal content is directed to continuous “up”, “up”, “down”, “down”, “left”, “right”, “left”, “right”, “B” and “A” (in form before being converted into binary), or a specific signal pattern such as 11011100), the sensing device  200  can determine that the transmission signal on the signal transmission interface  300  is control information, thereby to request a corresponding circuit module to handle the signal on the second channel  320 . 
     The sensing device  200  includes a sensed information transmitting circuit  210 , a control information slave circuit  220 , and a mode switching circuit  230 . According to the first transmission protocol, the sensed information transmitting circuit  210  is configured to convert a sensed signal generated by a sensing module  240  into a data signal on the second channel  320  based on a clock signal on the first channel  310 , and the converted data signal can be transmitted to the master device  100 . In one embodiment, the sensing module  240  (if the sensing device  200  is a digital microphone) may include (but is not limited to) an electroacoustic transducer, an analog-to-digital converter and a signal processing circuit. In another embodiment, the sensing module  240  (if the sensing device  200  is a temperature sensing device) may include (but is not limited to) a thermoelectric transducer, an analog-to-digital converter and a signal processing circuit. In addition, in various embodiments of the present invention, the sensing module  240  can also be a vibration sensor, a pressure sensor or an optical sensor. Furthermore, based on the second transmission protocol, the control information slave circuit  220  is configured to convert the signal received from at least one of the first channel  310  or the second channel  320  into control information, so as to conduct the setting adjustment of the sensing module  240  or other circuit elements in the sensing device  200 . Specifically, setting parameters used by one or more components in the sensing module  240  or in the sensing device  200  can be adjusted in accordance with the control information. In one embodiment, these setting parameters may include (but are not limited to): sampling rate, sensitivity, gain control, acoustic overload point (AOP), or filter settings. Furthermore, the mode switching circuit  230  includes a mode detecting circuit  232  and a mode control circuit  234 . The mode detecting circuit  232  can determine whether the current operating mode of the master device  100  is the setting adjustment mode or the sensed information reading mode according to the frequency of the signal on the first channel  310  or the voltage level of the signal on the power rail  400 . The mode control circuit  234  controls the sensed information transmitting circuit  210  and the control information slave circuit  220  according to the determination result of the mode detecting circuit  232 , thereby to allow the sensed information transmitting circuit  210  or the control information slave circuit  220 , to transmit or receive signals through the signal transmission interface  300 . 
     According to one embodiment of the present invention, hysteresis control technique is utilized for mode switching, so as to ensure that the sensing device  200  receives the control information transmitted by the master device  100 . For further understandings, please refer to the schematic diagram shown in  FIG. 2  in conjunction with a signal timing diagram shown  FIG. 3 . First, as shown in  FIG. 2 , the mode detecting circuit  232  of the sensing device  200  further comprises a static state detecting unit  2321  and a frequency detecting unit  2322 . As shown in  FIG. 3 , before the master device  100  enters the setting adjustment mode or the sensed information reading mode, the mode switching circuit  130  is required to transmit a direct current (DC) signal through the first channel  310 , where the DC signal may have logic high level or logic low level. Once the static state detecting unit  2321  detects that the signal on the first channel  310  remains direct current for a period of time (state A), it determines that the master device  100  enters the setting adjustment mode (state B), and thus the mode control circuit  234  is instructed to perform mode switching. Accordingly, the sensing device  200  enters the setting adjustment mode, allowing the control information slave circuit  220  to be activated (state C). After that, the control information master circuit  120  transmits the control information in a signal format compliant with the second transmission protocol through the first channel  310  and the second channel  320  (state D). After the control information master circuit  120  completes the transmission of the control information, the mode switching circuit  130  will again transmit the DC signal through the first channel  310  (state E). At this time, the frequency detecting unit  2322  does not detect that the frequency reaches the predetermined threshold, which leads to a hysteresis effect. Thus, it is determined that the master device  100  is still in the setting adjustment mode (state F). Accordingly, the mode control circuit  234  stays in the setting adjustment mode, which allows the control information slave circuit  220  to remain activated (state G). After that, when the master device  100  intends to start reading the sensed information, the mode control circuit  234  will instruct the sensed information receiving circuit  110  to send a clock signal compliant with the first transmission protocol through the first channel  310  (state H). The frequency detecting unit  2322  will detect that the frequency of the signal on the first channel  310  is greater than a frequency threshold TH (e.g., 400 KHz), thereby determining that the master device  100  has switched to the sensed information reading mode (State I), and further allow the mode control circuit  234  to activate the sensed information transmitting circuit  210  (State J). Then, the sensed information transmitting circuit  210  transmits the sensed information generated by the sensing module  240  to the master device  100  through the second channel  320  in a signal format compliant with the second transmission protocol (state K). However, under the sensed information reading mode, if the frequency detecting unit  2322  detects that the frequency of the signal on the first channel  310  is lower than the frequency threshold value TH (state L, state M), since the static state detecting unit  2321  does not detect the signal on the first channel  310  is direct current, the mode switching circuit  230  will not immediately allow the mode control circuit  234  to activate the control information slave circuit  220  to enter the setting adjustment mode, nor will it end the sensed information reading mode. Instead, before determining that the master device  100  enters the setting adjustment mode, it is necessary to wait until the static state detecting unit  2321  detects that the signal on the first channel  310  remains direct current, the mode control circuit  234  then activates the control information slave circuit  220 . The details of the above mode switching can also be understood from a diagram shown in  FIG. 4 . As shown in figure, under the setting adjustment mode, the frequency needs to exceed the threshold TH before switching to the sensed information reading mode. However, once the frequency is lower than the threshold value TH, the sensed information reading mode is not switched to immediately. Instead, the sensed information reading mode will be switched to only when the frequency is zero (i.e., direct current). 
       FIG. 5  further illustrates detailed architecture regarding a master device controlling and accessing multiple sensing devices according to one embodiment of the present invention. As shown in the figure, the master device  100  controls and accesses the sensing devices  200 _ 1 - 200 _ 3  through the first channel  310 , the second channel  320 , and the third channel  330 . Please note that, in this embodiment, the number of sensing devices that the master device  100  is simultaneously accessible to is not a limitation of the present invention. The master device  100  typically includes a master circuit  150 , one or more sensed information receiving circuits  110 _ 1 - 110 _ 3 , control information master circuits  120 _ 1 - 120 _ 3 , multiplexers  161 - 169 , and logic control circuits  171 - 173 . In this embodiment, the control information master circuits  120 _ 1 - 120 _ 3  are substantially I 2 C master circuits, which control the sensing devices  200 _ 1 - 200 _ 3  according to the I 2 C transmission protocol. In this way, multiplexers  161 - 162 ,  164 - 165  and  167 - 168  (where the multiplexers  161 ,  164  and  167  are labeled with “ON” or “OFF” to reflect their enablement), logic control circuits  171 - 173  and resistors  181 - 186  are configured to meet requirements of the I 2 C transmission protocol, which implements signal pulling-up or down on transmission channels (since I 2 C master circuit relies on an open-drain architecture). Accordingly, in other embodiments of the present invention, if the control information master circuits  120 _ 1 - 120 _ 3  are not I 2 C master circuits, the above-mentioned circuit components may be omitted. 
     The master circuit  150  can control the master device  100  to be switched between two operating modes: the setting adjustment mode or the sensed information reading mode. By controlling multiplexer  163 , the master circuit  105  is operable to determine the clock signals (labeled as “CLK” or “CLK_Data” in the figure) either generated by the sensed information receiving circuit  110 _ 1  or by the control information master circuit  120 _ 1  to be transmitted to the clock channel  310  (i.e., the above-mentioned first channel  310 ) through the clock pad  191 . In the setting adjustment mode, the multiplexer  163  allows the clock signal generated by the control information master circuit  120 _ 1  to be transmitted to the clock channel  310  and received by the sensing devices  200 _ 1 - 200 _ 3 . Meanwhile, the signals (labeled as “Data_O” in the figure) generated by the control information master circuits  120 _ 2  and/or  120 _ 3  can be transmitted to the data channels  320  and  330  through the data pads  192  and  193 , where these data signals carrying specific control information, such as device ID and control parameters. Once the mode detecting circuits  232 _ 1 - 232 _ 3  in the sensing devices  200 _ 1 - 200 _ 3  detects that the signal on the clock channel  310  is direct current, the sensing devices  200 _ 1 - 200 _ 3  switch to the setting adjustment mode, activating the control information slave circuits (i.e., the I 2 C slave circuit)  220 _ 1 - 220 _ 3 . These circuits can receive the signals from the data channels  320  and  330 . In addition, the sensing devices  200 _ 1 - 200 _ 3  selectively adjust the setting parameters according to the device ID carried by the signals. Through the switching of the multiplexers  166  and  169 , the master circuit  150  allows the control information master circuit  120 _ 2  and/or  120 _ 3  to receive the signals (labeled as “Data”, and received as “Data_I” by the control information master circuit  120 _ 2  and  120 _ 3 ) from the data channels  320  and  330  via the data pads  192  and  193 , such as, receiving parameter setting reports feedback by the sensing devices  200 _ 1 - 200 _ 3 . 
     On the other hand, under the sensed information reading mode, the multiplexer  163  allows the clock signal generated by the sensed information receiving circuit  110 _ 1  to be transmitted to the clock channel  310  through the clock pad  191 . Accordingly, the clock signal is received by the sensing devices  200 _ 1 - 200 _ 3 . The mode detecting circuits  232 _ 1 - 232 _ 3  in the sensing devices  200 _ 1 - 200 _ 3  can detect that the frequency of the signal on the clock channel  310  is greater than the threshold TH, thereby to switch to the sensed information reading mode. As such, the sensed information transmitting circuits  210 _ 1 - 210 _ 3  are activated. The sensed information transmitting circuits  210 _ 1 - 210 _ 3  report the sensed information generated by the sensing devices  200 _ 1 - 200 _ 3  to the master device  100  through the data channels  320  and  330 . Meanwhile, through the switching of the multiplexers  166  and  169 , the sensed information receiving circuits  110 _ 2  and/or  110 _ 3  can receive signals (labeled as “Data”, and received as “Data_I” by sensed information receiving circuits  110 _ 2  and  110 _ 3 ) from the data channels  320  and  330  through the data pads  192  and  193 , thereby acquiring the sensed information reported by the sensing device  200 _ 1 - 200 _ 3 . Please note that, in this embodiment, the master device  100  may include the sensed information receiving circuits  110 _ 1 - 110 _ 3  and the control information master circuits  120 _ 1 - 120 _ 3 . However, in other embodiments, a part of the sensed information receiving circuits or the control information master circuits can be integrated into a single one circuit. For example, the control information master circuits  120 _ 1 - 120 _ 3  can be integrated into one circuit, while the sensed information receiving circuits  110 _ 1 - 110 _ 3  can be integrated into two circuits. 
     Furthermore, although in the above embodiments, the mode detecting circuit  232  and the mode control circuit  234  in the sensing device  200  perform mode detection and switching based on the frequency of the signal on the clock channel  310 . However, in other embodiments of the present invention, the mode detecting circuit  232  and the mode control circuit  234  in the sensing device  200  can also perform mode detecting and switching based on the voltage level of the signal on the power rail  400 . For example, the mode switching circuit  130  in the master device  100  can increase the voltage level of the signal on the power rail  400  to 2.7V when the master circuit  150  intends to transmit the control information, or reduce the voltage level of the signal on the power rail  400  to 1.8V when the master circuit  150  intends to receive the sensed information. Accordingly, the mode detecting circuit  232  and the mode control circuit  234  in the sensing device  200  can determine when to activate the sensed information transmitting circuit  210  or the control information slave circuit  220  according to the voltage level of the signal on the power rail  400 . 
     In summary, the present invention provides a signal transmission architecture that integrates sensed information transmission/control information transmission, which allows single signal transmission interface to support signals of multiple different transmission protocols. For example, it can support the PDM-based transmission protocol that is used to transmit sensed information, and the I 2 C protocol, SPI protocol, UART protocol, or 1-wire protocol that is used to transmit control information. Therefore, the present invention can control the sensing device and read the sensed information without significantly increasing hardware cost and circuit complexity, so as to realize setting/characteristic adjustment of the sensing device. 
     Embodiments in accordance with the present embodiments can be implemented as an apparatus, method, or computer program product. Accordingly, the present embodiments may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware aspects that can all generally be referred to herein as a “module” or “system.” Furthermore, the present embodiments may take the form of a computer program product embodied in any tangible medium of expression having computer-usable program code embodied in the medium. In terms of hardware, the present invention can be accomplished by applying any of the following technologies or related combinations: an individual operation logic with logic gates capable of performing logic functions according to data signals, and an application specific integrated circuit (ASIC), a programmable gate array (PGA) or a field programmable gate array (FPGA) with a suitable combinational logic. 
     The flowchart and block diagrams in the flow diagrams illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments of the present embodiments. In this regard, each block in the flowchart or block diagrams may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical function(s). It is also noted that each block of the block diagrams and/or flowchart illustrations, and combinations of blocks in the block diagrams and/or flowchart illustrations, can be implemented by special purpose hardware-based systems that perform the specified functions or acts, or combinations of special purpose hardware and computer instructions. These computer program instructions can be stored in a computer-readable medium that directs a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable medium produce an article of manufacture including instruction means which implement the function/act specified in the flowchart and/or block diagram block or blocks. 
     Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.