Abstract:
A data collection terminal is provided with an audible feedback system that self-compensates for changes in ambient noise levels. The data collection terminal comprises a central processor adapted to execute stored instructions and having at least a display, a keyboard and a communications interface operatively coupled thereto. An audio driver is operatively coupled to the processor. The audio driver includes a speaker for producing sounds responsive to functions performed by the central processor and a microphone for receiving audio input signals. The audio driver adjusts the output volume of the speaker responsive to variations in ambient noise detected by the microphone so that the speaker produces a substantially consistent volume level in relation to the variations of ambient noise.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to data collection and processing systems, and more particularly, to portable data terminals having a system for controlling speaker volume to compensate for varying ambient noise environments. 
   2. Description of Related Art 
   Portable data collection terminals are well known in the art for remote data collection applications such as inventory control, manufacturing and production flow management, and asset tracking. A mobile worker may use such a data collection terminal to collect, send and receive information while moving throughout a work area. The data collection terminal may either comprise a specialized device or a general purpose laptop computer or personal digital assistant (PDA) adapted for use in the particular application. Portable data collection terminals are also commonly used by sales persons, distributors, delivery persons, auditors, and the like, where it is advantageous to employ a portable data terminal in a route or otherwise mobile setting. Such applications include sales, distribution, control and inventory of products delivered, and delivery or tracking of products, packages, etc. 
   Portable data collection terminals typically include apparatus to facilitate efficient input and manipulation of data by a user. For example, a data collection terminal may include such apparatus as keypads, touch screens, laser scanners, optical indicia readers, and the like. Preferably, such apparatus allow the data collection terminal to read and manipulate data recorded in a variety of mediums and in many different formats. The data collection terminals often also include an audio output device, such as a speaker, to emit sounds in response to certain actions taken or functions performed. For example, it is known for a data collection terminal to emit a certain tones or beeps signifying that data (e.g., a bar code symbol) was faithfully collected by the terminal. Other sounds may be emitted for other purposes, such as to reflect failure to read the bar code symbol, entry of an improper key, receipt of an email message, rebooting of the terminal, and the like. The operator of the collection terminal may come to rely upon the audible feedback to ensure that data has been properly entered. 
   A drawback of these known audible feedback systems is that the data collection terminal is often used in work environments having varying levels of ambient noise. In a particularly loud work environment, such as on a factory floor, it may be difficult for the operator to hear the audible feedback over the ambient noise. To compensate, the operator may turn up the volume of the audible feedback, such as by adjusting a knob or manipulating a screen icon using a pointing device. When the operator exits the noisy environment and enters a quieter environment, such as a storage area or office floor, the operator must remember to turn back down the volume to prevent the amplified audible feedback from disturbing workers in that environment. As a result, the operator often finds that the volume must be continuously adjusted in correspondence with changes from one work environment to another. 
   Accordingly, it would be desirable to provide a data collection terminal in which the audible feedback volume does not need to be changed as the operator moves between different ambient noise environments. 
   SUMMARY OF THE INVENTION 
   The present invention addresses the shortcomings of the prior art systems and methods. In particular, the present invention is directed to a data collection terminal having an audible feedback system that self-compensates for changes in ambient noise levels. 
   In an embodiment of the invention, a data collection terminal comprises a central processor adapted to execute stored instructions and having at least a display, a keyboard and a communications interface operatively coupled thereto. An audio driver is operatively coupled to the processor. The audio driver includes a speaker for producing sounds responsive to functions performed by the central processor and a microphone for receiving audio input signals. The audio driver adjusts the output volume of the speaker responsive to variations in ambient noise detected by the microphone so that the speaker produces a substantially consistent volume level in relation to the variations of ambient noise. 
   In another embodiment of the invention, a method for controlling output audio level of a data collection terminal comprises the steps of: (1) sampling ambient noise levels; (2) receiving operator input defining a desired relative audio output level; and (3) adjusting an actual audio output volume responsive to variations in the sampled ambient noise levels so that the actual audio output level is substantially consistent in relation to the variations in the sampled ambient noise. The method further comprises producing a plurality of sample tones and receiving an operator selection of a desired volume level for the sample tones. 
   A more complete understanding of the data collection terminal with an audible feedback system that self-compensates for changes in ambient noise levels will be afforded to those skilled in the art, as well as a realization of additional advantages and objects thereof, by a consideration of the following detailed description of the preferred embodiment. Reference will be made to the appended sheets of drawings which will first be described briefly. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a block diagram of an exemplary portable data collection terminal; 
       FIG. 2  is a block diagram of a self-compensating audible feedback system for the portable data collection terminal in accordance with an embodiment of the invention; and 
       FIG. 3  is a flow diagram illustrating a method of receiving user volume setting signals for use with the self-compensating audible feedback system. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   The present invention provides a data collection terminal with an audible feedback system that self-compensates for changes in ambient noise levels. In the detailed description that follows, like element numerals are used to describe like elements illustrated in one or more figures. 
   Referring first to  FIG. 1 , a block diagram of an exemplary portable data collection terminal is illustrated. In a preferred embodiment of the invention, the data collection terminal is intended to be a handheld, microprocessor-controlled device used for collection of data such as bar codes and RFID tags, and for communication via a wireless local area network to a base station (not shown). Though not expressly described herein, it is understood that the hand-held data collection terminal and all of its circuits are powered by an internal battery power source. The data collection terminal will typically be provided with the capability of being plugged into a docking station for connection to the base station through a wired (e.g., Ethernet) network for data download and for battery recharge. 
   More particularly, the data collection terminal includes a microprocessor  12  that functions as a microcontroller and as an interface for communicating data and control signals to and from the base station. The microprocessor  12  is coupled to a keyboard interface  14 , a communications interface  16 , and a scanner interface  16 . The keyboard interface  14  includes a keyboard enabling entry of data and commands into the device by the operator, and associated driver circuitry for interfacing the keyboard to the microprocessor  12 . The communications interface  16  includes an antenna and a radio transmitter/receiver for communicating RF messages to and from the base station. The scanner interface  18  includes sensing circuitry and optical systems for reading bar code symbols or for providing input data from other external sources. Alternatively, or in addition, the scanner interface  18  may include suitable circuitry for reading and/or writing to RFID tags. The microprocessor  12  may be provided by any suitable device, such as a conventional microcontroller with on-chip masked ROM, RAM and built-in timers, ports, analog to digital converters and a serial interface. In addition to the on-chip memory capacity, an external EEPROM  20  and an external RAM  22  may be coupled to the microprocessor  12  through a suitable bus to provide additional data processing, programming and communication capacity. The data collection terminal further includes a display controller/driver circuit  24  coupled to the microprocessor  24  through the bus. The display controller/driver circuit  24  is adapted to drive an LCD display  26 . It should be appreciated that each of the foregoing aspects of the data collection terminal are considered conventional, and that alternative arrangements of these circuit components may be advantageously utilized by persons having ordinary skill in the art. 
   The data collection terminal further includes an audio driver circuit  30  coupled to the microprocessor  12 . The audio driver circuit  30  is further coupled to a microphone  32  and a speaker  34 . The audio driver circuit  30  is further adapted to receive a volume control input. The volume control input may be an electrical signal that is varied by an input device mounted to a housing of the data collection terminal, such as a rotatable or slidable potentiometer. Alternatively, the volume control input could be produced by keyboard entries of by a touch screen display. The audio driver circuit  30  provides the function of driving the speaker  34  to produce audio output signals in response to certain actions taken or functions performed by the microprocessor  12 . The volume control input permits manual control by the operator of the data collection terminal over the audio output volume produced by the speaker  34 . 
   In accordance with an embodiment of the invention, the microphone  32  provides an electrical signal corresponding to a periodic sample of the magnitude of the ambient noise present in the environment within which the data collection terminal is operating. The ambient noise measurement is used by the audio driver circuit  30  as a baseline for determining the relative audio output volume produced by the speaker  34 . When an operator selects a desired audio output volume, the audio driver circuit  30  adjusts the output volume relative to the ambient noise measurement. Thereafter, as the ambient noise measurement changes, such as due to movement of the operator through a factory, the audio driver circuit  30  will continue to adjust the relative output volume to compensate for the noise level changes. As a result, the data collection terminal will produce a relatively consistent audio output level as the ambient noise level changes. 
   It should be appreciated that the microphone  32  should be located on the exterior housing of the data collection terminal such that it can adequately sample the ambient noise environment. Mounting places to avoid would include under handstraps or anywhere in which an operator&#39;s hand would block the microphone during ordinary use. The microphone  32  may be dedicated for use with the audio driver circuit  30  for sampling ambient noise, or may be shared with other applications operating on the data collection terminal, such as for communicating voice messages. 
   Referring now to  FIG. 2 , a block diagram of an exemplary audio driver circuit  30  is shown in accordance with an embodiment of the invention. The operator defines the desired audio output volume using a setting mode (described below), which defines a digital value that is stored in a corresponding register (not shown). The register provides a corresponding digital value to multiplexer  66 , which provides a digital signal to digital potentiometer  62 . While a 16-bit multiplexer is shown in  FIG. 2 , it should be understood that the size of the multiplexer  66  would depend on the desired amount of volume adjustment resolution. The digital potentiometer  62  includes a variable resistor  64  that defines a resistance value corresponding to the digital signal from multiplexer  66 . The variable resistor  64  is coupled between a voltage source (+V) and ground, such that the digital signal from multiplexer  66  defines a variable voltage between +V and ground. The variable voltage provides a reference voltage (REF 1 ) that corresponds to the desired audio output volume set by the operator. The reference voltage REF 1  will be higher for higher volume levels selected. 
   The audio driver circuit includes an audio processor  44  that receives a plurality of audio inputs from the microprocessor  12  (see  FIG. 1 ) and produces an audio output signal. The audio processor  44  selects from among the audio inputs to produce an output signal that is delivered to the speaker  34 . The audio processor  44  also receives a noise sampling signal from the microphone  32 , which passes through input amplifier stage  42 . The audio processor  44  produces an output that corresponds to the sampling signal from the microphone  32 . The output passes through a rectifier/filter  58  that provides full wave rectification and average filtering, and produces a reference output (REF 2 ) that corresponds to an average RMS value of the sampling signal from the microphone  32 . An RC network defined by resistor  54  and capacitor  56  coupled to the output of the rectifier/filter  58  provides high-pass filtering of the reference output REF 2 . The characteristics of the rectifier/filter  58  can be selected depending on the desired “sampling rate” of the input. Larger values will result in a longer time constant resulting in ambient noise being “remembered” for a longer period of time. Sampling can also be accomplished in other ways, such as using registers within the audio processor  44 . 
   Comparator  52  compares the reference voltage REF 1  (i.e., the user selected sound level) with the reference voltage REF 2  (i.e., the sampled noise level), and produces a difference signal. The difference signal will be smaller as the difference between the reference voltages REF 1 , REF 2  is smaller; conversely, the difference signal will be larger as the difference between the reference voltages REF 1 , REF 2  is larger. For example, if the operator chooses a loud setting and the ambient noise level is high, the output of the comparator  52  will be low. 
   The output from the audio processor  44  passes through two amplifier stages before reaching the speaker  34 . The first amplifier stage has gain controlled by reference voltage REF 1 , and the second amplifier stage has gain controlled by the difference signal from comparator  52 . In other words, the first amplifier stage determines a level of amplification based on the volume setting defined by the user, and the second amplifier stage provides additional amplification as necessary to overcome background noise. 
   More particularly, the first amplifier stage includes operational amplifier  72 , having a non-inverting input coupled to ground through resistor  76  and an inverting input coupled to the output of the audio processor  44  through resistor  46 . A feedback loop between the output of the operational amplifier  72  and the inverting input is provided by field effect transistor  74 . The gate terminal of the transistor  74  is driven by reference voltage REF 1 . As the value of REF 1  increases, corresponding to an increase in the volume setting by the user, the drain-source resistance of the transistor  74  will increase and thereby increase the gain of the first amplifier stage. Thus, the volume setting through multiplexer  66  defines the “floor” level of amplification for the audio signal. 
   The second amplifier stage includes operational amplifier  82 , having a non-inverting input coupled to ground through resistor  86  and an inverting input coupled to the output of the first amplifier stage through resistor  78 . A feedback loop between the output of the operational amplifier  82  and the inverting input is provided by field effect transistor  84 . The gate terminal of the transistor  84  is driven by difference signal from comparator  52  (corresponding to the difference between reference voltages REF 1  and REF 2 ). As the value of REF 2  increases relative to REF 1 , corresponding to an increase in the detected noise level, the drain-source resistance of the transistor  84  will increase and thereby increase the gain of the second amplifier stage. Thus, when there is no background noise, there will be a unity gain through the second amplifier stage. The result will be a volume level that overcomes background ambient noise. Since the audio output waveform is effectively subtracted from the reference voltage difference signal, feedback caused by the user setting the volume too high is avoided. 
   It should be appreciated that the audio processor  44  can also be programmed to ignore several harmonics beyond the fundamental to assure that a potential feedback path is minimized. In the present embodiment, the audio processor  44  precludes the audio signal from passing directly from the audio inputs to the first and second amplifier stages, as such direct communication would be undesirable in many applications. Of course, it should be appreciated that the function of the audio processor  44  could be provided by other circuitry, such as the microprocessor  12  or could be eliminated altogether in other applications. 
     FIG. 3  illustrates a method of receiving user volume setting signals for use with the self-compensating audible feedback system. As noted above, the operator initiates a volume setting process  90 , such as by selecting an icon on the LCD display or by pushing a button or turning a knob on the data collection terminal. The volume setting process  90  may be provided in the data collection terminal as a stored software or firmware program that is executed by the microprocessor  12 . At step  92 , the speaker  34  of the data collection terminal begins producing a series of sample tones. These sample tones may correspond to the specific sounds that the data collection terminal would produce in response to certain functions or events. Alternatively, the tones may be dedicated for use in the volume setting process, and may have no other application. The sample tones allow the operator to make a subjective determination that the volume of the tones is acceptable. At step  94 , the operator would have the opportunity to alter the volume setting while listening to the tones, such as by adjusting a radio dial on the LCD display or adjusting a slidable or rotatable potentiometer (as discussed above). This way, the operator can identify a volume setting that is optimal. 
   The volume setting process makes a determination at step  96  as to whether the volume setting has changed from a previous volume setting operation. This determination is made by comparing a numerical value corresponding to the volume level to a previously stored numerical value. If the volume setting has changed, at step  98 , the new value is loaded into a corresponding register, thereby replacing the previous value. This register value is then used to provide volume setting information to the audio driver  30  as discussed above with respect to  FIG. 2 . The volume setting process then ends at step  100  and returns to permit the microprocessor  12  to execute other functions. Conversely, if the volume setting has not changed, the process skips step  98  and ends at step  100 . 
   Having thus described embodiments of a data collection terminal with an audible feedback system that self-compensates for changes in ambient noise levels, it should be apparent to those skilled in the art that certain advantages of the system have been achieved. It should also be appreciated that various modifications, adaptations, and alternative embodiments thereof may be made within the scope and spirit of the present invention. The invention is further defined by the following claims.