Abstract:
Some workers wear headsets to protect their hearing from loud persistent noises, such as airplane engines and construction equipment. These headsets are generally passive or active, with the active ones including ear speakers and automatic noise-reduction (ANR) circuitry to cancel or suppress certain types of loud persistent noises. One problem with active headsets, particulary those that are battery-powered, concerns battery life. Workers often take the headset off or store them without turning them off and thus wasting costly battery life. Accordingly, the inventor devised active headsets with automatic turn-on and/or turn-off circuits. One exemplary embodiment senses a condition of the headsets, for example, the light, pressure, or temperature within one earcup, and then turns the headset on or off in response to the sensed condition.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This patent application is a continuation of U.S. provisional patent application No. 60/123,150 filed Mar. 5, 1999. This application is incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention concerns headphones or headsets, particularly battery-powered headsets with automatic noise-reduction circuitry. 
     BACKGROUND OF THE INVENTION 
     Headsets typically include two earcups which are worn over ears of users to enhance or protect their hearing. For example, many workers wear headsets to protect their hearing from loud persistent noises, such as airplane engines and construction equipment. These headsets are generally passive or active. Those that are passive only cover the ears with a sound-muffling material, whereas those that are active include ear speakers and automatic noise-reduction (ANR) circuitry. The noise-reduction circuitry automatically cancels or suppresses certain types of loud persistent noises. Active headsets are often battery-powered and include an on-off switch to turn them on and off. 
     One problem with battery-powered headsets, particularly those with automatic noise-reduction circuitry, concerns battery life. Workers having these headsets generally put on and take off their headphones many times throughout a workday, often forgetting to turn them off and wasting costly battery life. Moreover, for those headsets that are used infrequently with long storage times between uses, the turn-off problem is worse not only because their batteries are more apt to die, but fresh batteries are too often unavailable or inconvenient to obtain. 
     SUMMARY OF INVENTION 
     To address this and other needs, the inventor devised active headsets with automatic turn-on and/or turn-off circuits and related mode-control methods for active headsets. One exemplary embodiment senses a condition of the headsets, for example, the light, pressure, or temperature within one earcup, and then turns the headset on or off in response to the sensed condition. Other embodiments that include automatic noise-reduction (ANR) circuitry use an ANR driver to sense engagement of an earcup with a user&#39;s head and an ANR microphone to sense disengagement of the earcup from the user&#39;s head. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram of a first exemplary headset  100  incorporating the present invention. 
     FIG. 2 is a block diagram of a second exemplary headset  200  incorporating the present invention. 
     FIG. 3 is a schematic diagram of an exemplary turn-on circuit  300  incorporating the present invention. 
     FIG. 4 is a schematic diagram of an exemplary turn-off circuit  400  incorporating the present invention. 
     FIG. 5 is a schematic diagram of an exemplary power-supply circuit  500  for with turn-on circuit  300  and/or turn-on circuit  400 . 
     FIG. 6 is a schematic diagram of an exemplary headset  600  incorporating turn-off circuit  400  of FIG.  4 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following detailed description, which references and incorporates FIGS. 1-6, describes and illustrates one or more specific embodiments of the invention. These embodiments, offered not to limit but only to exemplify and teach, are shown and described in sufficient detail to enable those skilled in the art to implement or practice the invention. Thus, where appropriate to avoid obscuring the invention, the description may omit certain information known to those of skill in the art. 
     FIG. 1 shows a first exemplary embodiment of an active, automatic-noise-reduction (ANR) headset  100  incorporating an automatic mode control feature in accord with the present invention. Headset  100  includes an earcup  110  attached to a bridge member  112 . Earcup  110  fits over an ear and against the head of a user, represented generally as surface  111  in the FIG. (For simplicity, the figure omits a second earcup.) Headset  100  also includes a mode sensor  120 , and a mode-control circuit  130 , an ANR sensor or microphone  140 , ANR circuitry  150 , and an ANR driver  160 . (ANR circuitry  150  includes one or more batteries and a power supply which are not shown.) (In some embodiments, the ANR function is implemented digitally.) 
     In operation, mode sensor  120 , which is shown in broken form to emphasize that its placement can be virtually anywhere in or on the headset, senses a condition of earcup  110  (or more generally headset  100 ) and outputs a corresponding electrical signal to mode-control circuit  130 . Mode-control circuit  130  processes the electrical signal, either switching the headset from a first operating mode to a second operating mode or leaving the headset in its current operating mode (or state.) For example, if the signal indicates that the earcup has been disengaged from the head of the user, mode-control circuit  130  deactivates ANR circuitry  150  or otherwise puts it in a standby mode to reduce power consumption. 
     However, if the signal indicates that the earcup has been engaged with the head of the user, mode-control circuit  120  enables or activates ANR circuitry  140  to control or otherwise affect the perceived acoustic energy within earcup  110 . This generally entails ANR sensor  140  outputting an electrical signal representative of acoustic energy within earcup  110  to the ANR circuitry. In turn, the ANR circuitry processes the electrical signal and outputs a responsive electrical signal to ANR driver  140 . ANR driver  140  ultimately produces an acoustic signal intended to cancel, suppress, or otherwise alter the acoustic energy within earcup  110 . 
     In some variants of this first embodiment, the sensor comprises one or more mechanical switches, photo-sensors, temperature sensors, or pressure sensors. As used herein, light or photoelectric sensor includes any electrical or electromechanical device or component with useful photon-sensitive characteristics, coupled for use as a sensor. Temperature sensor includes any electrical device or component with useful temperature-dependent characteristics, coupled for use as a sensor. Pressure sensor includes any electrical or electromechanical device or component with useful pressure-dependent characteristics, coupled for use as a sensor. 
     In some mechanical variants, a normally open or normally closed mechanical switch closes or opens on sufficient deflection of at least a portion of the earcup, such as an ear cushion, or deflection of a bridge between two earcups, upon engagement or disengagement of the headset with the head of the user (head surface or more generally user surface). Engagement or disengagement makes or breaks a normally open or normally closed electrical contact which in turn operates a switch (not shown) between a power supply and the ANR circuitry. 
     In some photo-sensing variants, the photo-sensors sense light or temperature levels or changing light or temperature levels within or without the earcup. For photo sensors within the earcup or for photo sensor on other interior (head-confronting) surfaces of the headset (such as a bridge between two earcups), engagement of the headset generally reduces the sensed light and disengagement generally increases the sensed light. 
     Some temperature-sensing variants place the temperature sensors the head of the user, for example within the earcup on the bridge member. Thus, the sensors generally see increases in temperature upon engagement of the headsets and decreases upon disengagement. 
     It is also contemplated that some photo-sensing or temperature-sensing variants would facilitate automatically changing operational modes as a user wearing a headset moves between indoor and outdoor environments or between two indoor environments. For example, one can tune the sensors and/or mode control circuit to distinguish indoor environments from outdoor environments, correlate the distinction to the intended use of the headset, and switch the headset on or off or otherwise change the acoustic control function of the headset. 
     FIG. 2 shows a second exemplary embodiment of an ANR headset  200  including an automatic mode control feature in accord with the invention. (FIG. 2 omits earcups for clarity.) Headset  200  includes an ANR microphone  140 , ANR circuitry  150 , an ANR driver  160 , and implements automatic mode control using a turn-off circuit  130   a , a turn-off circuit  130   b , and a power switch  130   c . Turn-off circuit  130  a is responsive to signals from ANR microphone  140  to control power switch  130   c , and turn-on circuit  130   b  is responsive to signals from ANR driver  160  to control the power switch. Thus, unlike headset  100  in the first exemplary embodiment, headset  200  omits a dedicated mode sensor, and instead uses ANR driver  160  and microphone  140  as respective headset engagement and headset disengagement sensors. 
     More specifically, engaging earcup  110  with the head of a user generally results in an appreciable mechanical deflection of ANR driver  150 , which responsively outputs an appreciable electrical signal to turn-on circuitry  130   a . If the signal exceeds a threshold, turn-on circuitry  130   a  activates power switch  130   c , thereby providing power to ANR circuitry  150 . 
     On the other hand, after engagement, the earcup and surface  111  define a substantially closed volume that changes with user movements, such as head and jaw movements and the pulsating flow of blood through the confronting surface. In turn, these volume changes cause momentary pressure changes within the earcup, which are generally inaudible low-frequency events correlated only to engagement of the earcup with surface  111 . In response to these events, microphone  140  produces a low-frequency electrical signal which turn-off circuitry  130   b  monitors. If the turn-off circuitry detects that this signal is absent for a sufficient period of time, such as 2 or 3 or 5 or more minutes, it deactivates power switch  130   c.    
     FIG. 3 shows details of an exemplary embodiment of turn-on circuit  130   a . In this embodiment, the turn-on circuit includes a high-pass filter  310 , a preamplifier  320 , threshold detector  330 , an inverter  340 , a processor  350 , a switch  360 , power supply terminals V+ and Vgnd, and a positive battery terminal Vbattery+. V+ and Vgnd are respectively +2.5 and zero volts in the exemplary embodiment. (Not shown in the diagram are one or more batteries, for example, AA batteries, and a switching regulator which provides the voltages of +2.5 and −2.5 volts.) In operation, turn-on circuitry draws on the order of 10 microamps from one or more supplied batteries. Hence, its impact on battery life is generally negligible. 
     More particularly, filter  310  comprises a 100-nanofarad capacitor C 4   k  and a resistor R 6   k . Capacitor C 4   k  has first and second terminals, with the first terminal coupled to the output of the ANR circuitry, or more precisely the ANR driver. The second terminal of capacitor C 4   k  is coupled to ground via resistor R 6   k  and to the input of preamplifier  320 . 
     Preamplifier  320  comprises an LT1495 operational amplifier U 1   a , a one-mega-ohm resistor R 6   k , a 33 kilo-ohm resistor R 7   k , a 470-kilo-ohm resistor R 15   a , and 100-kilo-ohm input resistor R 16   a . Amplifier U 1   a  has a negative and positive inputs and an output. The positive input is coupled via resistor R 16   a  to a second terminal of capacitor C 4   k , and the negative input is coupled to terminal Vgnd via resistor R 7   k . Resistor R 6   k  is coupled between the second terminal of capacitor C 4   k  and ground, and resistor R 15   a  is coupled between the output and the negative input of amplifier U 1   a . The output of amplifier U 1   a  is coupled to the input of threshold detector  330 . 
     Detector  330 , which detects signals swings greater than 50 millivolts, includes an LT1495 operational amplifier U 1   b , a 1N914 diode D 1 , and a one-mega-ohm resistor R 8   k . Amplifier U 1   b  has a positive input coupled to the output of amplifier U 1   a , and a negative input coupled to the positive terminal of diode D 1 . The negative terminal of diode D 1  is coupled to ground, and resistor R 8   k  is coupled between the positive terminal of diode D 1  and positive supply terminal V+. Inverter  340  has its input coupled to the output of amplifier U 1   b , and its output coupled to an input of processor  350 . 
     Processor  350  responds to an output signal indicating engagement of the headset with the user by activating switch  360 . Activating switch  360 , which in this embodiments comprises a p-channel mosfet transistor, connects power to the ANR circuitry enabling it to cancel or otherwise alter the acoustic energy within the earcup. A terminal of the mosfet is coupled to a shutdown pin of integrated switching regulator. 
     FIG. 4 shows an exemplary embodiment of turn-off circuit  130   b . Turn-off circuit  130   b  includes a microphone preamplifier  410 , a bandpass filter  420 , a threshold detector  430 , a processor  450 , a switch  460 , respective positive and negative power-supply terminals V+ and V−, and a positive battery terminal (or node) Vbattery+. In the exemplary embodiment, terminals V+ and V− respectively provide 2.5 and −2.5 volts. 
     In operation, ANR microphone  140  senses pressure within earcup  120 . When engaged with each other earcup  110  and surface  111  defines a substantially closed space with a volume that changes with user movements, such as head and jaw movements and the pulsating flow of blood through surface  111 . In turn, these volume changes cause momentary pressure changes within the earcup, which are generally inaudible, low-frequency events. On the other hand, when disengaged from surface  111 , earcup  110  is not pressed against surface  130  and thus no longer defines a volume subject to user movements. Thus, microphone  140  generally provides preamplifier  410  a signal with low-frequency content that changes during engagement of earcup  110  with surface  130  and that remains relatively constant after disengagement. 
     More particularly, preamplifier  410  has a gain of 20 decibels and comprises an input capacitor C 10   a  of 470 nanofarads, an input resistor R 10   a  of 470 kilo-ohms, an LMV324 operational amplifier U 1   d , and feedback resistors R 12   a  of 6.8 kilo-ohms and R 14   a  of 62 kilo-ohms. Amplifier U 1   d  provides an output signal proportional to the signal from preamplifier  410  to band-pass filter  420 . (In some embodiment, preamplifier  410  also functions as a portion of ANR circuitry  150  (shown in FIG.  2 ). 
     Band-pass filter  420 , which defines a one-to-five hertz passband with an approximate gain of 30 decibels, comprises a resistor R 1   k  of 330 kilo-ohms, a resistor R 2   k  of 330 kilo-ohms, a resistor R 3   k  of 33 kilo-ohms, a resistor R 4   k  of 1 kilo-ohm, a resistor R 5   k  of 620 kilo-ohms, and a resistor R 1   m  of 470 kilo-ohms. Filter  420  also comprises three 100-nanofarad capacitors C 1   k , C 2   k , and C 3   k , and one 470-nanofarad capacitor C 1   m . Filter  420  also comprises an operational amplifier U 5   b  which provides a pressure signal indicative of the pressure in earcup  120  via capacitor C 1   m  to threshold detector  430 . 
     Threshold detector  430 , which comprises an LMV324 operational amplifier, a 470-kilo-ohm resistor R 2   m , a 1-kiloohm resistor R 3   m , and a 10-kilo-ohm resistor R 4   m , compares the pressure signal to a 225-millivolt reference voltage at a node C and outputs a signal indicating the result of the comparison to processor  440 . When the pressure signal at node B is greater than the reference voltage at node C, detector  430  outputs a low signal, which indicates an “on-head” event, that is, engagement of earcup  110  with surface  111 , to processor  440 . 
     In response to receiving an “on-head” event, processor  440  starts a timer which runs for a predetermined period of time, for example, two to three minutes. If during this period, another “on-head” event does not occur, that is, there are no sensed low-frequency events of sufficient magnitude, processor  440  assumes that the headset has been removed and sends an appropriate turn-off signal to a power-supply shutdown circuit, which turns off the headset. In some embodiments, processor  440  directly drives a shut-down pin on a switching regulator that provides the V+ and V−.supply voltages. 
     FIGS. 3 and 4 are shown as separate stand-alone circuits which are adaptable to virtually any active ANR headset to provide automatic mode control. When used together in the same headset, certain components of the circuits are shared to reduce the number of parts. For example, some embodiments use a single programmable processor and power switch. Moreover, some embodiments implement all or one or more portions of the circuit as an integrated circuit. 
     FIG. 5 shows an exemplary embodiment of a power supply  500 . Supply  500  includes, among other things, battery connection terminals  510   a  and  510   b , one or more batteries  520 , and a integrated switching regulator circuit  530 . Regulator circuit  530  includes a shutdown pin, which in the exemplary embodiment, ultimately coupled to a terminal of switch  360  or switch  460  in the turn-on and turn-off circuits of FIGS. 3 and 4. The present invention is not limited to any particular power supply arrangement. 
     FIG. 6 shows an exemplary embodiment of active headset  600  including a turn-off circuit in accord with the invention. FIG. 6 also shows details of an exemplary ANR circuitry. 
     Conclusion 
     In furtherance of the art, the inventor has presented one or more embodiments of active headsets incorporating an automatic mode control feature. One exemplary embodiment provides an turn-on and turn-off circuits which automatically detect engagement and disengagement of a headset to or from the head of a user to activate or deactivate the headset. The turn-off circuit is especially useful to conserve battery life in battery powered ANR headsets. However, the invention is generally applicable to automatically control the operational mode of any active headsets or headphones, regardless of the power source. 
     The embodiments described above are intended only to illustrate and teach one or more ways of practicing or implementing the present invention, not to restrict its breadth or scope. The actual scope of the invention, which encompasses all ways of practicing or implementing the concepts of the invention, is defined by the following claims and their equivalents.