Abstract:
A versatile and mobile keyboard and a highly energy efficient keyboard scanning method are provided. The keyboard may be used with a variety of mobile devices such as PDAs, cellular phones, and tablet PCs, through various interfaces such as an IR, USB, or Bluetooth™ interface. In particular, an IR head assembly is provided that includes an IR head, a movable arm on which the IR head is mounted, and a connector for attaching to a docking structure. The docking structure may be attached to a keypad, which is electrically coupled to the IR head for transmitting keystroke data through the IR head. When a mobile device is docked on the docking structure, the arm in the IR assembly may be moved to an optimal distance from the IR port of the mobile device to ensure high communication performance between the keyboard and the mobile device. An energy efficient keyboard scanning method utilizes higher-valued pull-up resistors for energy conservation. The keyboard scanning method includes a charging step to charge stray capacitance associated with the keys. The keyboard scanning method can also be operated at a variable scanning frequency.

Description:
REFERENCE TO RELATED APPLICATIONS 
   This application is a continuation of U.S. application Ser. No. 11/282,281 filed Nov. 18, 2005, which is a divisional of U.S. application Ser. No. 10/277,462 filed Oct. 21, 2002, now U.S. Pat. No. 6,999,008, the contents of which are incorporated by reference herein for all purposes. 

   BACKGROUND OF THE INVENTION 
   1. Field of Invention 
   The present invention generally relates to keyboards for mobile devices. More particularly, the present invention relates to a universal mobile keyboard including an infrared interface and an energy-efficient keyboard scanning method. 
   2. Discussion of the Related Art 
   Personal digital assistants (PDAs) have become more popular and affordable with improved technology, allowing for enhanced display quality, color richness, contrast, processing speed, power efficiency, memory capacity, RF communication capability, and other desirable characteristics. Similar advances have also been made in other mobile devices, such as cellular phones, smart phones (PDA plus cellular handset), industrial data terminals, and tablet PCs. Thus, there is a growing need for an efficient and convenient universal device and method for data entry and for providing a user interface with these mobile devices. 
   Some mobile devices offer touch-sensitive LCD screens with built-in recognition software for data input by handwriting or “graffiti.” However, data input using graffiti is not convenient or efficient unless the user is properly trained in the method. Even then, data input using graffiti is not usually as fast as using a keyboard. 
   Some PDAs have built-in soft or virtual keyboards, or other input means, such as thumb-boards, silk-screen keyboards, and rubber keyboards. However, these input means are less efficient than small foldable keyboards that connect to the mobile device, such as a PDA, and offer the familiar desktop/notebook keyboard input style. 
   Such small foldable keyboards typically require a connector customized for each mobile device make or model. Usually a device-specific connector is used for both data exchange and for holding the mobile device in place. Such a connector often lacks stability. Also, when a user gets a new mobile device, the user would also need to purchase a new keyboard. Some keyboards provide changeable connector heads. However, these changeable connector heads achieve only limited flexibility, given the many connector types that are used among mobile devices. 
   Accordingly, wireless keyboards (e.g., infrared-based keyboards) are desired. However, typical infrared (IR)-based keyboards in the prior art suffer from several disadvantages. For example, a typical prior art IR keyboard uses a polished metal reflector to guide the IR beam from the keyboard to the IR port of a mobile device, which can be found at the top or at the side of the mobile device. Such a polished metal reflector is awkward to adjust and difficult to keep steady. Furthermore, to achieve the IR beam reflection, a stronger IR beam intensity than otherwise needed for data transmission is used. Thus, battery energy is inefficiently used, resulting in a shorter battery life or requiring a larger number of batteries (e.g., from 1 to 3 AAA batteries) or a higher battery capacity. In addition, a stronger than required IR beam intensity may also in some instances overwhelm or “blind” the IR receiver circuitry in a mobile device IR port, causing data error or a sluggish response. A reflector-based IR beam guidance scheme has limited flexibility in aligning to IR ports, as the IR port may be found in any of a variety of possible locations on a mobile device. 
   Therefore, what is needed is a keyboard for a mobile device that is operable with a large number of mobile devices. In particular, a keyboard with an IR interface is needed that is operable with and adjustable for a variety of possible IR port locations found on various mobile devices. Additionally, a keyboard scanning method is needed that is highly energy efficient to increase battery life and improve keyboard portability. 
   SUMMARY 
   The present invention provides a universal keyboard that includes multiple interfaces for operability with a variety of mobile devices, such as PDAs, smart telephones, and cellular telephones. Furthermore, a highly energy-efficient method for scanning a keyboard is provided. 
   According to one embodiment of the present invention, a universal keyboard includes an IR head capable of transmitting data, an arm operably coupled to the IR head, a docking structure, a connector operably coupled to a base of the arm and the docking structure to allow the arm movement within a plane, and a keyboard device operably coupled to the docking structure and the IR head, such that data entered on the keyboard can be transmitted by the IR head to a mobile device placed on the docking structure. 
   According to another embodiment of the present invention, a universal keyboard selectably operates an IR interface, a USB interface, or a Bluetooth™ interface to transmit data input on the keyboard over the selected IR interface, the USB interface, or the Bluetooth™ interface. 
   According to another embodiment of the present invention, a method for a low-power operation of a keyboard provides a micro-controller having output pins and input pins, wherein each key of the universal keyboard is coupled to both a designated output pin and a designated input pin, providing each input pin a pull-up resistor operably coupled to a voltage source. The pull-up resistor has a value between about 1 mega-ohm and about 100 mega-ohms to decrease power consumption. To operate this universal keyboard, a selected output pin is placed at a first voltage level, for example ground voltage level, and each input pin is then sensed to determine if a selected one of the keys associated with the selected output pin and one of the input pins is depressed. If the key is depressed, the output pin corresponding to the selected key is driven to a second voltage level, for example power source voltage level, to recharge the stray capacitance associated with the output pin and the selected input pin. After recharging, the output pin is put in high-impedance state and depends on the pull-up resister to maintain the voltage level. 
   The present invention allows for great flexibility in transmitting data to an IR port located at any of many positions on a mobile device while also providing a highly energy efficient keyboard scanning method. 
   According to another aspect of the present invention, a method is provided whereby the software driver for operating the keyboard is downloaded from a storage medium in the keyboard to a mobile device, according to the make and model of the program device, without having to place the mobile device in a cradle or a docking device attached to a desktop computer or a notebook computer. 
   These and other features and advantages of the present invention will be more readily apparent from the detailed description of the embodiments set forth below taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
       FIGS. 1A-1D  show different views of an unfolded universal keyboard in accordance with an embodiment of the present invention. 
       FIGS. 2A-2D  show different views of an unfolded universal keyboard with an example of a docked PDA in accordance with an embodiment of the present invention. 
       FIG. 3  shows an unfolded universal keyboard with an example of a docked cellular telephone in accordance with an embodiment of the present invention. 
       FIG. 4  shows an unfolded universal keyboard operably coupled to an example of a docked tablet PC in accordance with an embodiment of the present invention. 
       FIGS. 5A-5B  show an unfolded universal keyboard in accordance with another embodiment of the present invention. 
       FIGS. 6A-6B  show the outer surface of the folded universal keyboard of  FIGS. 5A-5B  in accordance with an embodiment of the present invention. 
       FIG. 6C  shows a docking structure, IR head, arm structure, and connector of the universal keyboard of  FIGS. 5A-5B  in accordance with an embodiment of the present invention. 
       FIGS. 7A-7C  show different views of the outer surface of a folded universal keyboard, IR head, arm, and connector in accordance with another embodiment of the present invention. 
       FIG. 8  shows an example of a foldable keyboard with a locking mechanism in accordance with an embodiment of the present invention. 
       FIGS. 9A-9C  show a central hinge of a universal keyboard in accordance with an embodiment of the present invention. 
       FIGS. 10A-10B  show a central hinge of a universal keyboard in accordance with another embodiment of the present invention. 
       FIG. 11  shows an example a mouse or cursor selector in accordance with an embodiment of the present invention. 
       FIGS. 12A-12B  show different views of a folded universal keyboard with a top cover in accordance with an embodiment of the present invention. 
       FIG. 13  shows an example of an inside surface of a top cover that is capable of holding various cards and memory devices. 
       FIG. 14  shows an example of an IR, USB, or Bluetooth™ interface selector in accordance with an embodiment of the present invention. 
       FIG. 15  shows an example of a universal keyboard circuit diagram in accordance with an embodiment of the present invention. 
       FIG. 16  shows an adaptor for a USB interface, according to one embodiment of the present invention. 
       FIG. 17  shows an adaptor for a Bluetooth™ interface, according to one embodiment of the present invention. 
       FIG. 18  shows circuit  1800  suitable for implementing switching between battery power (IR interface) and a serial or USB interface. 
   

   Use of the same reference symbols in different figures indicates similar or identical items. It is further noted that the drawings may not be drawn to scale. 
   DETAILED DESCRIPTION 
   The present invention provides a universal keyboard that can be used with any of a variety of mobile devices, such as PDAs, cellular/smart phones, and tablet PCs. The present invention also provides a universal and highly energy efficient keyboard. 
     FIGS. 1A-1D  illustrate an unfolded universal keyboard  100 , in accordance with one embodiment of the present invention. As shown in  FIGS. 1A-1D , an infra-red (IR) head assembly  101  is mounted on a docking structure  108 , which is attached to keypad  116 . Top cover  112  may also optionally be included with universal keyboard  100 . 
   In one embodiment, IR head assembly  101  includes IR head  102 , which is mounted on an arm  104  that is rotatable about an axis perpendicular to a plane of docking structure  108 , and connector  106 . IR head  102  includes an IR light emitting diode (LED). In one embodiment, the LED is biased to conduct an electrical current that provides an IR beam intensity calculated to achieve a high IR signal-to-noise ratio and a small IR data error rate, based upon an estimation of the minimum and maximum distances between IR head  102  and an IR port of a mobile device that can be mounted on the docking structure  108 . In one implementation, the minimum and maximum IR beam distances are determined to be about 0.3 cm and about 3 cm, respectively. In that implementation, using a commercially available IR LED Vishay TSMF1000, the electrical current supplied to the IR LED may range between about 2 mA to about 10 mA. 
   IR head  102  may be mounted on arm  104  by a hinge  103  or other suitable mechanism in order to enable IR head  102  to be positioned at any of a range of angles relative to arm  104  ( FIGS. 1C and 1D ). Arm  104  is mounted on docking structure  108  by connector  106  (e.g., a ball bearing) that allows arm  104  to rotate around an axis perpendicular to a plane of docking structure  108 . The location of connector  106  and the length of arm  104  are selected to allow IR head  102  to be positioned for line-of-sight communication with an IR port of any of a large number of mobile devices that can be mounted on docking structure  108 , regardless of their IR port locations. To ensure a consistent electrical current to IR head  102  regardless of the position of rotatable arm  104  and to maintain a relatively thin structure, a circular multi-hub copper contact structure is included in connector  106 . In one example, arm  104  has a length of about 8 cm. In addition, in one implementation, one or more batteries that are housed in arm  104  power IR head  102 . 
   In one embodiment, docking structure  108  includes spring-loaded movable device holders  110  for securely holding in place a mobile device (e.g., a PDA, a smart phone, or a tablet PC) oriented in one of many possible orientations, such as shown in  FIGS. 2A-2D ,  3 , and  4 .  FIGS. 2A-2B  show a PDA  202  securely docked in a “portrait” position on docking structure  108  and  FIGS. 2C-2D  show a PDA  202  securely docked in a “landscape” position on docking structure  108 .  FIG. 3  shows a cellular phone  302  securely docked on docking structure  108  and  FIG. 4  shows a tablet PC  402  securely docked on docking structure  108 . 
   As noted above, a prior art connector-based keyboard uses the connector to hold the mobile device in place, often resulting in an unstable configuration. By contrast, holders  110  are designed and positioned to secure onto docking structure  108  any of a large number of mobile devices of various lengths, widths, and thicknesses. Grooves into which holders  110  may be folded or retracted are provided on one surface of docking structure  108  ( FIG. 1B ). Holders  110  are designed to be flush with the surface of docking structure  108 , when folded or retracted into the grooves. Holders  110  need to be placed and/or shaped only as shown in  FIGS. 1A-1D . Holders  110  may be placed in various positions and formed into various shapes with corresponding grooves to securely hold a mobile device.  FIGS. 5A-5B  illustrate examples of other spring-loaded holders  510  that may be used in accordance with the present invention. 
   In one embodiment as further shown in  FIGS. 1A-1D , docking structure  108  includes a recessed area  111  on an inside surface of docking structure  108  at which connector  106  connects to IR head assembly  101 . Recessed area  111  allows the arm structure of IR head assembly  101  to freely move through a large range of angles when a mobile device is docked, and provides the universal keyboard a thin profile when docking structure  108  is in the folded position for storage. 
   Alternatively, IR head assembly  101  may be mounted on an outer surface of docking structure  108  to enable more holders or holder structures to be provided on the inside surface of docking structure  108 , such that a greater number of mobile devices of various shapes and sizes can be held by docking structure  108  in a variety of positions (e.g., in portrait or landscape positions). 
   FIGS.  5 A and  6 A- 6 B show an IR head assembly  501  that is provided on an outer surface of docking structure  508 , with a recessed area into which IR head assembly  501  can be secured when the IR keyboard  500  is in the folded, or storage position. In that configuration, the properly secured IR head assembly  501  is substantially flush with the outer surface of docking structure  508 . 
     FIGS. 7A-7C  show IR keyboard  700 , according to another embodiment of the present invention, in which IR head assembly  701  is mounted by a spring-loaded mechanism to an outer surface of docking structure  708 . IR head assembly  701  may be placed within a recessed area of the outer surface of docking structure  708  in the storage or folded position ( FIG. 7A ). IR head assembly  701  can be lifted up from the recessed area ( FIG. 7B ), and be allowed to move freely along a circular arc that is parallel to the surface of docking structure  708  ( FIG. 7C ) and centered about an axis perpendicular to docking structure  708 . 
   Referring back to  FIG. 1C , docking structure  108  may also include stand  120  which is attached to the outer surface of docking structure  108 . Stand  120  may be slotted into any one of several grooves  122  provided on the inner surface of top cover  112 , such that docking structure  108  can be supported at various inclined angles relative to the surface of top cover  112 . Alternatively, stand  120  may be made free-standing at one of various inclined angles on the flat surface on which IR keyboard  100  is unfolded.  FIG. 6C  shows IR keyboard  500  having stand  510  supporting an outer surface of docking structure  508  at various inclined angles relative to the surface on which keyboard  100  is placed. Alternatively, referring back to  FIG. 1C , stand  120  may be attached to top cover  112  and may be coupled into any one of several grooves formed into an outer surface of docking structure  108 . 
   Docking structure  108  may also include battery compartment  109  to hold one or more batteries used for providing power to IR head  102 . Of course, battery compartment  109  need not be placed in docking structure  108  but may also be placed in keypad  116  instead.  FIG. 5B  shows batteries  530  being placed in battery compartment  109  provided at the upper left hand corner of keypad  116 . 
   As shown in  FIGS. 1A-1D , in one embodiment, keypad  116  includes foldable sections  116   a  and  116   b  joined by a central hinge or coupler  118 . Alternatively, as shown in  FIG. 8 , keypad  116  includes latch  802  that, when moved to an “open” position, locks keypad sections  116   a  and  116   b  in a spread-flat position to allow a steady surface to facilitate touch typing. 
     FIGS. 9A-9C  and  10 A- 10 B illustrate two central hinge mechanisms that can be used to couple two keypad sections and allow them to fold and unfold properly, in accordance with two embodiments of the present invention. According to one embodiment, shown in  FIGS. 9A-9C , keypad section  902   a  and  902   b  each include plates  904  provided on opposite sides of the keypad section and connected by rod  908 , thus forming a hinge about which plates  904  can rotate. Plates  904  of keypad sections  902   a  and  902   b  on each side of the keypad sections are connected by central face plate  906 . Plates  904  are each provided teeth-like structures. Central face plate  906  keeps keypad sections  902   a  and  902   b  properly aligned by ensuring the teeth on plates  904  on keypad sections  902   a  and  902   b  properly mesh during folding or unfolding keypad  902 . Central face plate  906  is kept centered at all times during folding or unfolding (i.e., does not slide to either side of center line A), thus allowing for precisely positioned opening and closing of keypad sections  902   a  and  902   b .  FIG. 9A  shows a side view of a completely folded keyboard device. Keypad sections  902   a  and  902   b  are aligned such that plates  904  are properly meshed when folding or unfolding the keypad sections, as shown in  FIG. 9B .  FIG. 9C  shows a completely unfolded keyboard device. 
     FIGS. 10A-10B  illustrate another hinge mechanism that may be used in accordance with another embodiment of the present invention.  FIG. 10A  shows a top view of keypad sections  1002   a  and  1002   b  coupled by a hinge mechanism. Keypad sections  1002   a  and  1002   b  each include a pair of arms, designated  1004   a  for keypad section  1002   a  and designated  1004   b  for keypad section  1002   b . For each keypad section, the arms are located on opposite side of the keypad section. Between the arms in each pair of arms (i.e., each of arms  1004   a  and  1004   b ) is provided a cylindrical through-hole for receiving a pin (designated pin  1006 , as shown by dashed lines in  FIG. 10A ) that runs the length of the through-hole. When the keyboard is unfolded, keypad sections  1002   a  and  1002   b  each rotate around the pins  1006 , while coupler  1008 , shown by a side view in  FIG. 10B , couples pins  1006  to keep the keypad sections  1002   a  and  1002   b  properly aligned during folding and unfolding. Of course, various other variations of hinge mechanisms, such as a single rod with meshed arms, may also be used within the scope of the present invention. 
   According to another embodiment of the present invention,  FIG. 11  illustrates keypad  1116  on which are provided mouse and cursor controls  1102 . A toggle switch or button is provided to activate alternatively keypad  1116  for cursor and mouse functions. 
   In one embodiment, the keyboard driver software, including software drivers needed for controlling the mouse or cursor functions are loaded into a mobile device from a compact disk through a desktop or notebook computer. Alternatively, the keyboard driver software can be pre-loaded by the manufacturer of a mobile device. According to one embodiment of the present invention, the driver software can be provided in one or more removal storage devices (e.g., a flash memory card) that can be plugged into a card reader installed on the universal keyboard. In that embodiment, when the universal keyboard first communicates with a mobile device over a wireless, USB or another serial interface, the universal keyboard queries the make and model of the mobile device and downloads from the removable storage device into the mobile device the appropriate software drivers to control the universal keyboard, including the mouse and cursor functions. Using this arrangement, it is not necessary to download the keyboard software from a desktop or notebook computer to the mobile device, using a docking station or cradle of the mobile device. 
   As further shown in  FIGS. 1A-1D , top cover  112  may be included with universal keyboard  100  to provide a protective top surface and covering to the folded keyboard. In one embodiment, as shown in  FIGS. 12A-12B , top cover  1212  folds over docking structure  1208 , folded keypad  1216 , and central hinge  1218 . As discussed above, the IR head assembly can be mounted to either the inner surface or outer surface of the docking structure, and the top cover may be designed to accommodate either configuration. 
     FIG. 13  illustrates inner surface  1300  of top cover  1212 , with accommodation of various accessories, according to one embodiment of the present invention. As described above, inner surface of top cover  1212  may include grooves  1322  for holding a stand in place. Furthermore, the inner surface of top cover  1212  may include recesses for accessories, such as memory cards, compact flash (CF) cards, secure digital (SD) cards, multi-media cards (MMC), memory sticks, and PCMCIA (PC) cards. 
   As shown in  FIGS. 1A-1C , curved arrows A-C indicate the manner in which universal keyboard  100  is folded and unfolded, in accordance with an embodiment of the present invention. To fold universal keyboard  100 , section  116   a  first folds over section  116   b , as illustrated by arrow A in  FIG. 1A . Then, docking structure  108  and top cover  112  may fold over folded key pad section  116   a , as shown by arrows B and C. In order to open or unfold universal keyboard  100 , docking structure  108  is first unfolded in the manner indicated by arrow A in  FIG. 1B . Then, keypad  116   a  is unfolded away from keypad section  116   a  in the manner indicated by arrow B in  FIG. 1B . Docking structure  108  may then be pulled away from top cover  112  and set at an inclined angle, as shown by arrow C in  FIG. 1C . In other embodiments, docking structure  108  and top cover  112  may be coupled so that docking structure  108  and top cover  112  open and close together, automatically moving with one motion by the user. 
   According to another embodiment of the present invention, the universal keyboard includes not only an IR interface but a universal serial bus (USB) interface and a Bluetooth™ interface. As shown in  FIG. 14 , a universal keyboard may include interface switch  1402  that controls which interface is active. Interface switch  1402  may be set by a user, or by a sensor sensing whether the universal keyboard is coupled to communicate over the USB or Bluetooth™ interface. Driver software for each mobile device type, brand, and model are loaded into the corresponding mobile device to allow the mobile device to communicate with the universal keyboard. 
   A USB interface applies well to any tablet PC ( FIG. 4 ) or other products equipped with a host-USB port. In one embodiment, the universal keyboard of the present invention has a built-in USB port for connecting an intelligent USB cable to host-USB equipped products. 
   Alternatively, the universal keyboard may provide simply 4-pin connector into which a USB adaptor, a Bluetooth™ adaptor, or another adaptor to another industry standard interface may be provided.  FIGS. 16 and 17  show respectively an adaptor for a USB interface and an adaptor for a Bluetooth™ interface. As shown in  FIG. 16 , adaptor  1600  includes serial port connector  1601  for coupling into a corresponding serial port on universal keyboard  100 . Serial port  1601  includes power pin  1601   a , input pin  1601   b , output pin  1601   c  and ground pin  1601   d . In USB adaptor  1600 , the power and ground signals are provided as corresponding power and ground signals in USB connector  1602 . USB adaptor chip  1603  (e.g., microcontroller integrated circuit MC68HC908JB8) can be programmed to translate between the signals in input pin  1601   b  and output pin  1601   c  and the corresponding signals in a USB Human Interface Device (HID). Similarly, as shown in  FIG. 17 , Bluetooth™ adaptor integrated circuit (e.g., the BlueCore™ integrated circuit from CSR Limited, Cambridge UK)  1702  translates between the signals in input pin  1601   b  and output pin  1601   c  and corresponding signals under the Bluetooth™ standard. In  FIG. 17 , power is provided by a battery in adaptor  1700 , and signals over the Bluetooth™ interface is transmitted and received through antenna  1703 . 
   Unlike PDAs or smart or cellular phones, no driver software is required to operate a tablet PC using a USB interface. Once a cable (e.g., a USB cable) is inserted into the universal keyboard&#39;s port (e.g., serial port  1601  described above), a circuitry in the universal keyboard of the present invention automatically senses the inserted cable and turns off electrical current to the IR head, and switches to a serial mode or a USB mode, depending on whether the inserted cable is a serial cable or a USB cable. Under the serial mode or the USB mode, the universal keyboard takes power from the host system (e.g., tablet PC).  FIG. 18  shows circuit  1800  suitable for implementing switching between battery power (IR interface) and a serial or USB interface. As shown in  FIG. 18 , a sensor sensing whether or not a cable is inserted into serial port  1601  controls switch  1802  between a “door open” (i.e., cable inserted, serial or USB port mode) and a “door closed (i.e., no cable inserted, IR interface mode). When switch  1802  is in a “door open” position, power to microcontroller  1804  (i.e., the controller for universal keyboard  100 ) is provided by power pin  1601   d  from the external device. When switch  1802  is in the “door closed” position, power to microcontroller  1804  is provided by internal battery  1803 . 
   Alternatively, in one embodiment, to select the IR interface, the user places a switch in the “IR” position. In that position, the switch physically obstructs the USB port. Alternatively, when the switch is placed in the “USB” or “serial” port position, the USB serial port is activated. Such an interface switch prevents the IR port and the USB or serial port to be simultaneously activated. Prevention of simultaneous activation of the IR and USB ports is desirable because, when the IR port is selected, the battery in the keyboard is in the active discharging mode. At the same time, if the USB or serial port is also active, the power from the USB host system force-charges the keyboard battery, and hence causing a possible hazard. 
   The Bluetooth™ interface can be provided in any PDA, smart or cellular phone, tablet PC, or other mobile product equipped with Bluetooth™ capability, either embedded or externally attached through an adapter or memory card, in one example. When a Bluetooth™ module is plugged into the USB port of the universal keyboard, the keyboard circuitry automatically senses the Bluetooth™ module and turns off electrical current to the IR head and switches to the Bluetooth™ module, according with one embodiment of the present invention. 
   In accordance with another embodiment of the present invention, a method for low-power scanning a keyboard is provided utilizing an example of a keyboard circuit shown in  FIG. 15 . In one embodiment, micro-controller  1506  controls keypad  1516  of universal keyboard  1500  using input pins  1508  (usually 8) to micro-controller  1506  and output pins  1510  (usually 10 to 19) from micro-controller  1506 . Output pin  1512  from micro-controller  1506  is also connected to an infrared light emitting diode (IR LED)  1514 , which transmits data to a mobile device through IR radiation. According to the present invention, an appropriate low-power micro-controller (e.g., a 3-volt micro-controller) is chosen to control universal keyboard  1500 . 
   Keypad  1516  of universal keyboard  1500  includes keys  1504 , each of which is electrically connected to one of input pins  1508  and one of output pins  1510 . Thus, when a user depresses a key, one of the input pins is shorted to one of the output pins. For example, when a user depresses key  1504   a , input pin  1508   a  and output pin  1510   a  are shorted. This short circuit can be sensed by applying a known voltage briefly and successively on the output pins one at a time, and then sensing the voltage at each of the input pin successively while the voltage is being applied to the output pin. This process for detecting the depressed key is termed “keyboard scanning.” In the embodiment shown in  FIG. 15 , each of input pins  1508  is connected to a power supply  1518  through individual pull-up resistors  1502 . Thus, in the absence of an applied voltage on the output pins, input pins  1508  are pulled up to the power supply voltage level, or “high” level. In the prior art, such pull-up resistors are usually in the tens of kilo-ohms range, so that a few tenths milliampere of current flow through the pull-up resistor when a connected output pin is driven to a “low” level. In the prior art, the pull-up resistor value cannot be increased because stray capacitances in the wires that connect to the keys are of the order of hundreds of picofarads. A higher resistor value would result in an unacceptably large RC time constant. The RC time constant limits how quickly an input pin can return to the high level ready for detecting the next depressed key. 
   According to the present invention, the firmware of micro-controller  1506  “scans” the keyboard device of universal keyboard  1500  by first driving one of the output pins  1510  to the ground or “low” level, while leaving all other output pins  1510  in a high impedance state. When a short circuit is created due to a depressed key, the input pin corresponding to the depressed key is pulled to a low level by a low voltage on the output pin corresponding to that depressed key. 
   The firmware of prior art keyboards scan the keyboard at fixed time intervals (e.g., once every 10 to 40 milliseconds). Because of the low resistance in the pull-up resistors, each scan consumes a considerable amount of energy. The longer the scanning interval (i.e., the less frequent the keyboard is scanned), the less energy is used on the average. However, the scanning interval must be short enough to maintain responsiveness to the user&#39;s typing. Otherwise, the scanning mechanism may miss some of the keys depressed by a fast typist. 
   According to one embodiment of the present invention, rather than using a fixed scanning interval, an adaptive scanning interval is used. The scanning interval according to the present invention is determined by the frequency in which keys  1504  are depressed and released. When keys  1504  are depressed and released quickly, the firmware shortens its scanning interval so that it does not miss any user action. When the firmware senses that keys  1504  are depressed and released less frequently, it lengthens the scanning interval to conserve energy. 
   In accordance with another embodiment of the present invention, the value of pull-up resistors  1502  is increased above 100 kilo-ohms, preferably in the multiple mega-ohms range (e.g., 1 to 100 mega-ohms), thereby reducing the current consumption during scanning from tenths of milliamperes to microamperes. A slow recovery time is avoided by a special step in the scanning process. Each time a depressed key is detected, and before the corresponding output pin is put back into a high impedance state, the output pin is momentarily driven high to recharge the stray capacitance of the wire. The slow recharge through the large pull-up resistor is therefore avoided. Thus, even though a much larger pull-up resistor value than that in the prior art is used, the universal keyboard of the present invention does not result in a keyboard with slower responsiveness. 
   Accordingly, the low-power keyboard scanning method in accordance with the present invention is more energy efficient than prior art keyboards. The low-power keyboard scanning method of the present invention allows keyboards of the present invention to use two low-cost CR2032 coin batteries for up to six months under a typical usage of two hours of continuous typing per day. Prior art keyboards required batteries that are capable of a higher electrical current and a higher energy capacity. 
   The above-described embodiments of the present invention are merely meant to be illustrative and not limiting. Various changes and modifications may be made within the scope of this invention. Therefore, the appended claims encompass all such changes and modifications.