Patent Publication Number: US-2007110252-A1

Title: Diagnostic circuit

Description:
BACKGROUND OF THE INVENTION  
      For a number of years, health clubs and gyms have provided their patrons with various items of exercise equipment. Once aerobic exercise became popular, the gym equipment companies started to manufacture such items as treadmills, stairsteppers, elliptical trainers, and stationary bicycles. One of the focal points of aerobic exercise is to exercise 3 to 5 times a week for a minimum of 30 minutes per workout. Users of such equipment quickly became bored and looked for ways to occupy themselves while putting in their exercise time.  
      Some users would try to read or perhaps listen to portable radios or audiocassettes. Health club management, in an attempt to cater to this new need of their clients, would provide a series of television monitors mounted in the club. These monitors would be tuned to several different television channels so playing the audio out loud from each monitor simultaneously was not feasible. To solve this problem, the first generation systems were designed so that the corresponding audio for each television channel that was being displayed would be broadcast using short range transmitters on unused broadcast radio frequencies. Signs would be placed on each monitor informing the clientele which radio frequency was being used to transmit the audio for that television monitor. The health club members would bring in their own portable radios and tune their radio to the corresponding frequency for the particular television monitor they wanted to watch.  
      This system was improved by utilizing small receiver boxes with volume and channel selectors built-in. These receiver boxes would be retrofitted to the desired pieces of workout equipment. The receiver boxes also included standard head phone jacks. To utilize this version, the user would only need to bring their own headset or purchase one from the gym, which would then be plugged into the jack on the receiver box. The user could, by using the controls on the box, select the audio channel and volume desired. Typically the receiver box would display a monitor number which would be matched up with the same numbered monitor showing the television program that the user was interested in watching.  
      One of the weakness of these systems is the headphone jack which is typically built into the housing of the receiver box. Because of the large number of users, headphones plugs are inserted and removed from the headphone jacks many times a day. Often times, the user forgets that his headphones are plugged in and walks away from the equipment without removing the headphone plug from the headphone jack. This results the plug being yanked out of the receptacle and subjecting the headphone jack to unnecessary wear and tear. The internal contacts in the headphone jack are subject to metal fatigue and possible corrosion and at some point actually break or no longer make adequate contact with the headphone plug. In either case, the result if a non-functioning headphone jack.  
      There is no way for the user to know ahead of time which headphone jacks are working. The user will get on a piece of equipment, place their paraphernalia (e.g. books, magazines, water, keys, cell phone etc.) onto the equipment and then plug in their headphones. If the jack is defective the user must then gather up all his paraphernalia and move to another piece of equipment. More often than not, the user doesn&#39;t take the time to inform the club personnel that there is a problem. Therefore, the equipment remains unrepaired and waiting to frustrate a subsequent user.  
      When the defect finally comes to the attention of the proper person, the device typically had to be taken out of service, and a factory service representative had to be called to either replace the whole console or disassemble and re-solder a new headphone jack into the circuit. Some improvement has been made by placing the headphone jack into a user replaceable module that can be easily replaced by club personnel. Broadcast Vision and Cardio Theater both have such options for their equipment. While a replaceable module facilitates the repair of the problem, it does nothing to help identify which units are defective and need repair.  
      It is an object of the present invention to provide a diagnostic circuit which can identify the most common reasons for headphone jack failure and provide a clearly discernable warning to others.  
      It is an object of the present invention to provide the diagnostic circuit with the ability to provide a warning of the defect to a remote location by way of any electric, electronic, computer or wireless means of information transmission  
      It is a further object of the present invention to couple the diagnostic circuit with a replaceable headphone jack module which can be easily replaced when the diagnostic circuit has indicated a fault in the headphone jack.  
      It is a further object of the invention to place as many of the components of the diagnostic circuit in the console so that there are a minimum number of components in the replaceable headphone jack module in order to reduce costs of the replaceable module.  
      It is another object of this present invention to provide a replaceable headphone jack module which contains all of the components of the diagnostic circuit necessary to perform the diagnostic function and alert personnel to failure of the headphone jack module. Placement of all of the diagnostic circuit elements within the replaceable headphone jack module allows for easy updating or upgrading of the diagnostic circuit.  
      It is an object of the present invention to provide a replaceable retrofitable diagnostic headphone jack module which can be used with existing equipment by plugging into an existing headphone jack without the needed to modify any aspect of the existing equipment.  
     BRIEF SUMMARY OF THE INVENTION  
      The present invention pertains to an electronic diagnostic circuit that is either located  
      a) entirely within the console,  
      b) partially within the console and partially within the replaceable module;  
      c) entirely within the replaceable module but obtaining power from the console or  
      d) entirely within the replaceable module including the source of power.  
      a. Entirely within the Console. 
          This embodiment is primarily intended for new devices where the diagnostic circuit can be incorporated into the overall design. However it does not preclude the option of retrofitting an existing console by adding the components needed for the diagnostic circuit within the console.        

      b. Partially with the Console. 
          Certain of the components of the diagnostic circuit, such as the operational amplifier or voltage comparators may be subject to malfunctioning at a greater rate than other components. Those components deemed to have shorter functional life can be placed in the replaceable headphone jack module so that they can be easily be replaced.        

      c. All Component within the Replaceable Headphone Jack Module, Except Power 
          In order to facilitate the complete replacement or upgrade of the diagnostic circuit, all of the active components of the diagnostic circuit can be placed within the Replaceable Headphone Jack Module. Power for the active components of the diagnostic circuit can be provided from the console to the diagnostic circuit within the Replaceable Headphone Jack Module.        

      d. All Components Entirely within the Replaceable Module Including a Source of Power. 
          It is possible to place all of the components for the diagnostic circuit in an entirely separate module including a source of power. This would be used in conjunction with existing audio sources. The separate module can be plugged into a headphone jack on the existing device. A user would then plug their headphones into the headphone jack on the separate module. By use of a separate module, wear and tear on the headphone jack in the existing equipment is almost completely eliminated because users would be using the headphone jack in the separate headphone module instead of the headphone jack in the existing equipment.     Power for the separate module can be obtained from batteries or an external standard AC to DC power module. If the diagnostic circuit detects any defects in the headphone jack on the separate module, then some form of notification can be made.     This embodiment would provide a way to reduce maintenance of existing equipment without the need for any retrofitting or modification to the existing equipment.        

      The diagnostic circuit will determine the proper operation of other circuits. If the diagnostic circuit determines that the other circuit is not operating within predetermined parameters an initial fault signal is generated.  
      Additionally, this fault signal may be provided to logic circuits which would evaluate such parameters as the length, timing and frequency of the initial fault signals and provide an end User fault signal. This use of additional logic circuits may be implemented if a particular installation, because to its location, local electromagnetic interference, 120 volt line noise or fluctuations, or the particular type of hardware, may have false positives than can be screened out by the additional use of logic circuits.  
      Reference to the diagnostic circuit refers to those electrical components which are added solely for the purpose of performing the diagnostic function. Though some of the diagnostic circuits make use of conductivity through the headphone jack and related elements, these elements are not considered for this purpose to be part of the diagnostic circuit because those headphone jack elements would have been present, regardless of whether there was or was not a diagnostic circuit. 
    
    
     BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWING  
      The present invention is hereinafter described in conjunction with the appended drawings, in which:  
       FIG. 1  shows a perspective view of the main console and the replaceable headphone module;  
       FIG. 2  shows an exploded view of the main console with the Replaceable Headphone Module and Module Cover shown removed from the Main Console for viewing purposes;  
       FIG. 3  is block diagram showing the main features of the diagnostic headphone jack circuit;  
       FIG. 4  is a block and detailed schematic of the Headphone Switch Detection Circuit;  
       FIG. 5  is detailed schematic of the Current Limited DC Bias Source;  
       FIG. 6  is a block schematic of the DC Level Detection Circuit;  
       FIG. 7  is a detailed schematic of the DC Level Detection Circuit; and  
       FIG. 8  is a detailed circuit schematic of an alternative embodiment of the invention. 
    
    
      Although the Replaceable Headphone Module is shown with a mechanical connector which allows the Replaceable Headphone Module to receive the audio signal, it is within the scope of the invention that this connection can be made by wireless, optical or any other form of form of audio communications between the console and the Replaceable Headphone Module which is compatible with the diagnostic circuit.  
      Although the specification refers to headphone jacks (and corresponding plugs) which have the industry typical configuration of being round and 2.5 or 3.5 mm in diameter with two electrically isolated conductors along the length of the jack and a ground connector made by an annular contact located at the open end of the jack, any type of electrical connection which allows for the removable connection of a headphone, monaural or stereo, to a circuit is within the scope of this disclosure.  
     DETAILED DESCRIPTION OF THE INVENTION  
      Referring now to  FIG. 1 , the Main Console  100  is shown with Lower Clamp  105  and Upper Clamp  110  for mounting the Main Console to a rigid support, typically part of the frame of an exercise device. Along one end of Main Console  100  is shown Module Cover  125  which attaches to the front of Main Console  100 . Module Cover  125  physically retains Replaceable Headphone Jack Module  120  within the Main Console  100 . Module Cover  125  contains an opening therein which permits access to Headphone Jack  130  while the Replaceable Headphone Jack Module  120  is contained within Main Console  100 .  
       FIG. 2  shows Main Console  100  with the Replaceable Headphone Jack Module  120  and Module Cover  125  shown removed from the Main Console  100 . Replaceable Headphone Jack Module  120  includes Headphone Jack  130 , Circuit Board  140  and Module Connector  135 . Headphone Jack  130  is adapted to physically and electrically receive a headphone plug, typically one that is 2.5 mm in diameter. Module Connector  135  is physically and electrically adapted to mate with a corresponding connector located within Main Console  100 . Main Console  100  includes a Headphone Module Receiving Cavity  123  into which is disposed the Replaceable Headphone Module  120  and a portion of Module Cover  125 . Module Cover  125  includes a pair of Retaining Tabs  126  which contain Mounting Holes  127 . Mounting Screws  128  are positioned through Mounting Holes  127  and engaged with threaded holes in the body of Main Console  100 . Circuit Board  140  includes a pair of Locking Tabs  142  located one on each side of Circuit Board  140 . Locking Tabs  142  are adapted to engage a corresponding pair of Locking Notches  144 , located one on each side of Module Cover  125 . In this embodiment, Circuit Board  
       FIG. 3  shows a block schematic of the diagnostic headphone circuit. Detailed schematics for various the functions described and shown in block form in  FIG. 3  shall be shown and discussed in subsequent figures provide herein. A Left Audio Source  302 A and Right Audio Source  302 B are provided as inputs to Headphone Amplifier  300 . The output of Headphone Amplifier  300  is labeled as A and B on this and other figures presented herein. The outputs of Headphone Amplifier  300  are ultimately conducted to Headphone Jack  130 .  
      A pair of capacitors  305 A and  305  B are placed in series with the outputs of Headphone Amplifier  300 . A DC Voltage is placed on the output of the Capacitors  305 A and  305 B at locations C and D in the schematic. DC Biased Left Audio Signal  304 A and DC Biased Right Audio Signal  304 B are the output of Capacitors  305 A and  305 B plus the applied DC bias.  
      The Capacitors  305 A and  305 B function as audio coupling and DC blocking capacitors to isolate the applied DC voltage from the Headphone Amplifier  300 , to isolate the DC voltage generated by the Headphone Amplifier  300  from the rest of the circuit and to allow the audio signal to pass from the Headphone Amplifier  300  to the portion of the circuit on other other side of the blocking capacitors.  
      In normal operating conditions the DC voltage on each audio channel will be conducted through the Headphone Jack  130 , the inserted headphones plugged into Headphone Jack  130 , and back through Ground Contact  160  on Headphone Jack  130  to Circuit Ground  315 .  
      Therefore, in the normal operating conditions just described, DC Level Detection Circuit  320  will not detect any significant DC voltage. With there being essentially zero volts on the audio channels the Headphone Fault Detection Signal  325  will not be activated. However, if there is a break in the circuit, usually due to a break in the headphone jack and occasionally due to a break in the inserted headphone set, then the DC voltage supplied by Current Limited DC Bias Source  310  will be detected by DC Level Detection Circuit  320  and Headphone Fault Detection Signal  325  will be activated.  
      Because the flexible contacts in Headphone Jack  130  are subject to breakage, the Headphone Jack  130  is incorporated into a Replaceable Headphone Jack Module  120  which is removably attachable to the Main Console  100 . Replaceable Headphone Jack Module  120  includes Module Cover  125  which is adapted to electrically and physically mate with a corresponding jack mounted within Main Console  100 . If a defect is identified in Headphone Jack  130 , then the whole Replaceable Headphone Jack Module  120  can easily be removed and replaced by persons who don&#39;t have any specialized training.  
      Headphone Jack  130  includes Audio Signal Contacts  150 A and  150 B which typically make contact with the tip and ring of the headphone plug. Contact  160  is typically contacts the sleeve on headphone plug and is connected to Circuit Ground  315 .  
      In addition a Headphone Switch  135  is incorporated into Headphone Jack  120 , which connects Headphone Switch Line  140  with Audio Signal Contact  150 B. If there is no headphone plug inserted into Headphone Jack  130 , then Headphone Switch Line  140  makes contact with Contact  150 B and conducts the DC bias voltage on DC Biased Left Audio Signal  304 A (also shown as (C) in  FIG. 3 ) to Headphone Switch Detection Circuit  322  located within the Main Console  100 . When a headphone plug is inserted into Headphone Jack  130  then the contact between Headphone Switch Line  140  and Contact  150 B is broken and the applied DC voltage is no longer present on Headphone Switch Line  140 .  
       FIG. 4  depicts a block and a detailed schematic of the Headphone Switch Detection Circuit  322 . Headphone Switch Line  140  (also shown as (I) in  FIG. 3 ) passes through a Low Pass Audio Filter  410 , which is comprised of Resistor  412  and Capacitor  414 , and connects to the non-inverting input  415  of Voltage Comparator  420 . Threshold Voltage Source  425  is connected to the Inverting Input  430  of Voltage Comparator  420 . The voltage supplied to Inverting Input  430  is provided by Voltage Source  427  and Voltage Resistors  428 A and  428 B.  
      If there is no headphone plug inserted into Headphone Jack  130 , then Headphone Switch  135  is closed and the voltage supplied by Current Limited DC Bias Source  310  is present at the Non-Inverting Input  415 . The circuit has been designed such that the Threshold Voltage Source  425  will be slightly less than the voltage on the Non-Inverting Input  415  when there is no headphone plug inserted into Headphone Jack  130 . In this circumstance, the Voltage Comparator  420  is non-conducting.  
      Headphone Detection Signal  440  normally provides 3.3 volts which is the voltage provided after the Voltage Source  445  passes through Pull-Up Resistor  447 . As previously described, when no headphone plug is inserted into Headphone Jack  130 , Voltage comparator  420  is non-conducting and there is no change to the voltage level on Headphone Detection Signal  440 .  
      However, if there is a headphone plug inserted, then the applied DC voltage from Current Limited DC Bias Source  310  on Headphone Switch Line  140  is not present and there is a difference in the voltages present on the non-inverting and inverting inputs to Voltage Comparator  420 . Thus Voltage Comparator  420  will be conducting and will short Voltage Source  445  to ground though the pull-up resistor  447  and Headphone Detection Signal  440  will be essentially zero.  
       FIG. 5  depicts details of Current Limited DC Bias Source  130 . Voltage Source  550  provides 3.3 volts which passes through series Resistors  555 A and  555 B to ground. Resistors  555 A and  555 B are typically 1 k ohms each. The actual voltage provided by Current Limited DC Bias Source  130  is taken at the junctions of Resistors  555 A and  555 B. Resistors  555 A and  555 B form a voltage divider network and be sized to provide the desired voltage. Two Current Limiting Resistors  557 A and  557 B, one each placed in series with each of the connections made to DC Biased Left Audio Signal  304 A and DC Biased Right Audio Signal  304 B (also shown as (C) and (D) in  FIG. 3 )  
       FIG. 6  depicts a block level schematic for DC Level Detection Circuit  320 . The circuit is composed of two voltage comparators  605 A and  605 B which each monitor the DC voltage on one of the DC Biased Left and Right Audio Signals  304 A and  304 B. If either comparator detects a fault condition on the particular DC Biased Audio Signal it is monitoring, then Fault Detection Signal  325  is activated.  
      The inputs (C and D from  FIG. 3  and  FIG. 5 ) to each comparator passes through Low Pass Audio Filters  610 A and  610 B. These filters are provided to reduce and/or eliminate the effects of any voltage fluctuations due to the audio signal which might effect the operation of the comparators while allowing the average DC voltage from the L/R Audio+DC Bias to pass through. However, audio signals containing a high amplitude bass components may pass sufficient signals through the Low Pass Filters to effect operation of the comparators.  
      Each Voltage Comparator  605 A and  605 B looks at two voltages. The first voltage is provided by Threshold Voltage Source  620  which is designed to provide a somewhat lower voltage than the voltage level as Current Limited DC Bias Source  310 . When all circuit elements are functioning properly, the DC voltage on each DC Biased Left and Right Audio Signal  304 A and  304 B has been shorted to ground through the Headphone Jack  130  and the headphone circuit. Since this voltage is less than the Threshold Voltage level (which is typically 1 volt) the Voltage Comparator is non-conducting.  
      However, if there is an open circuit due to a defect in the headphone jack, a defect in the headset that is plugged into the headphone jack or there is no headset plugged into the headphone jack, the voltage appearing on one or both of the inverting inputs of the two Comparators will be higher. Under these conditions, one or both of the comparators become conducting and provide a closed circuit from the output of the Comparators to ground.  
      The Fault Detection Signal  325  is connected to Voltage Source  625  through Pull-Up Resistor  627 . In normal operating conditions, both Voltage Comparators  605 A and  605 B are non-conducting and therefore have no effect on the voltage level on Fault Detection Signal  325 . However, when there is a defect in the circuit or no headset is plugged into Headphone Jack  130 , one or both of Voltage Comparators  605 A and  605 B are conducting and short the voltage from Voltage Supply  625  to ground resulting in an essentially zero voltage level on Fault Detection Signal  325 .  
       FIG. 7  shows a more detailed schematic for the DC Level Detection Circuit  320 . Resistor  710 A and Capacitor  715 A form Low Pass Filter  610 A. Resistor  710 B and Capacitor  715 B form Low Pass Filter  610 B  
      Voltage Source  720 , and Resistors  722  and  724  form Threshold Voltage Source  620 . The voltage at the junction of Resistors  722  and  724  is connected to the non-inverting input of Comparators  605 A and  605 B through Resistors  730 A and  730 B. The Outputs  732 A and  732 B of each Comparator is connector to the non-inverting input through Hysteresis Resistors  735 A and  735 B, which prevent oscillation in the circuit. The remaining parts of the circuit have already been described.  
      An alternative configuration would be to provide a Fault Detection signal for each of DC Biased Left and Right Audio Signals  304 A and  304 B. If no headphone is plugged in, then a Fault Detection Signal would be activated for each of the Audio Left and Right Signals. Since it&#39;s not very likely that there would be an open circuit in both channels simultaneously, a Fault Detection on both channels would more likely indicate that a headphone was not plugged in. It would be possible to eliminate the circuitry needed for the Headphone Switch Detection Circuit  322 .  
      Both Fault Detection Signals would be provided as input to a logic circuit which would make a determination that only one of the Fault Detection Signals was activated and if it met other criteria, generate an End User Fault Signal.  
      The following is a list of the specific components used in the circuits shown in  FIGS. 3-7 .  
                                                       Value or       Fig. No.   Type   Ref. No.   Part No.                      Capacitor   305A   220 microfarads               305B   220 microfarads           Resistors   410   100K               412   110K               428A   33K               428B   10K               447   2.2K           Capacitor   414   0.1 microfarad           Differential   420   LM339D           Comparator           Resistors   555A   1K               555B   1K               557A   1K               557B   1K           Resistors   710A   10K               710B   10K               722   10K               724   1K               730A   10K               730B   10K               735A   1 Meg               735B   1 Meg               627   2.2K           Capacitors   715A   0.1 microfarads               715B   01. microfarads           Differential   605A   LM339D           Comparators   605B                  
 
      A second alternative embodiment is shown in schematic form in  FIG. 8 . This circuit is composed of two portions which are essentially identical up to point Q in the circuit. The following discussion will be directed to the circuit which interacts with Left Audio Source  302 A. The circuit which interacts with Right Audio Source  302 B is identical up to point Q. This circuit is dynamic in nature and requires an audio signal in order to detect a fault condition.  
      Load Sense Resistor  805  is placed in series with Left Audio Source  302 A. A differential amplifier is used to read the voltage drop across Load Sense Resistor  805 .  
      Except for an open circuit condition, when there is an audio signal source in the left channel then there will be a voltage drop across Load Sense Resistor  805 . A voltage divider circuit is formed with Load Sense Resistor  805  and the impedance in the headphone that is plugged into Headphone Jack  130 . Usually Load Sense Resistor  805  is 1/10 of the impedance of the headphones. So if typical headphones are 32 ohms then Load Sense Resistor  805  would be 3.2 ohms, but the actual value of Load Sense Resistor  805  can be sized for particular equipment.  
      Leads coming from both sides of Load Sense Resistor  805  go to Inverting Input  820  and Non-Inverting Input  815  of Operational Amplifier  810 . There is voltage on Output  825  if there is a signal differential between Inverting Input  820  and Non-Inverting Input  815 .  
      There is voltage on Output  825  only if there is current flow through Load Sense Resistor  805  which causes a signal differential between Inverting Input  820  and Non-Inverting Input  815 . Output  825  is connected to Inverting Input pin  830  of Operational Amplifier  835 . Non-inverting Input  840  of Operational Amplifier  835  comes from a lead just before Load Sense Resistor  805 . Therefore Non-Inverting Input  840  gets the full signal of the output from the Headphone Amplifier  300 , even if there is no current flow in Load Sense Resistor  805 .  
      Operational Amplifier  810  and supporting components are designed to provide the same signal level as Non-Inverting Input  840  will get, in normal operating conditions. If the signal voltages at Non-Inverting Input  840  and Inverting Input  830  of Operational Amplifier  835  are the same then there is no signal voltage on the Output  845  of Operational Amplifier  835 .  
      However, if there a break in Headphone Jack  130  or a break in the headset that is plugged into Headphone Jack  130 , then there will be no current in Load Sense Resistor  805  which results in a difference in voltages at Inputs  840  and  830 . Therefore there will an audio signal at Output  845 .  
      Capacitor  846  and Diodes  847  and  848  form a rectifying circuit which provides DC voltage.  
      An identical circuit is used to monitor the current flow in Right Audio Source  302 B. If there is break in the either the Left or Right Audio Source then the DC voltage that is generated by the either circuit will charge Capacitor  850 . Resistor  855  limits current to the base of Transistor  860 . Resistor  856  is used as a discharge path for the voltage stored in capacitor  850 .  
      Voltage Source  865  and Resistor  867  normally provide a 3.3 voltage on Headphone Fault Signal  325 . If there is no DC voltage generated by either detection circuit there will be no DC voltage developed across Capacitor  850  or on the base of Transistor  860 . If there is no voltage on the base of Transistor  860  then Transistor  860  does not turn on and there is no change in the voltage appearing on Headphone Fault Signal  325 . If there is a voltage developed on Capacitor  850  due to a reduction in the voltage drop across Load Sense Resistor  805 , the Transistor  860  becomes conducting and shorts Voltage Source  865  to ground an causing Headphone Fault Signal  325  to become essentially zero.  
      In summary, signal voltage output from the Headphone Amplifier  300  is compared to the voltage drop across Load Sense Resistor  805 . In normal operating conditions these two signals are in a fixed ratio and Output of  845  of Operational Amplifier  835  provides no output. However, if there is no current in Sense Resistor  805  and therefore no voltage drop (open circuit) or there is a short in the headphone jack and/or headphone (i.e. a much larger amount of current in R 11 ), then the ratio of the two measured values will be different and there will be voltage present on Output  845  of Operational Amplifier  835  which will turn on Transistor  860  and short the Headphone Fault Detection Signal to an essentially zero voltage. This circuit is dynamic in nature and requires an audio signal to determine a fault condition. Without an audio signal present, the Headphone Fault Signal  325  will necessarily go to a non-fault indicating state (voltage remains high).  
      These various conditions with audio signal present are summarized in the table below.  
                                                   Load Sense           Headphone Fault       Conditions   Resistor 805   Output 825   Output 845   Detection Signal 325                  Normal   Normal current   Normal   No voltage because   Voltage Remains           level in R11   signal level   input 830 and Input 840   High                   are designed to be the                   same in normal                   operating conditions       Break in   NO CURRENT   No voltage   There is output because   Voltage drops to       headphone   IN R11       Pin 10 still sees the   essentially zero       jack,           same voltage as before,       headset or           but now pin 9 has no       headset not           signal present-       plugged in           generating output and                   turning on Q1       Short in   High current in   High signal   There is output because   Voltage drops to       headphone   R11   voltage   Input 830 now has   essential zero.       jack or           higher than designed for       headphone           voltage and Comparator                   Operational Amplifier                   835 senses this disparity                   and provides voltage on                   Output 845, which turns                   on Transistor 860.                  
 
      Though the diagnostic circuit of the invention has been described as being incorporated into an entertainment module for the detection of a malfunctioning headphone jack, all embodiments of the invention described above can also be used to detect malfunctioning speakers or defects in the wiring leading to and from the speakers, particularly remotely mounted speakers.  
      For example, paging systems in hospitals, speakers in movie theaters or other business often have speakers mounted in a great number of locations and often mounted in auditoriums having high ceilings. Emergency notification systems such as community hurricane warning systems and industrial plant evacuation warning systems may have speakers mounted over a wide geographic area. Actual determination of the functioning of these speakers would require costly and potential dangerous physical inspection of each one. By utilizing the diagnostic circuit of the present invention, each speaker could have its own diagnostic circuit and an associated notification system. All of the notification systems could be located in one place so that it would be easy to monitor a single display to verify the functioning of all of the speakers being monitored.  
      While the invention has been described in conjunction with the preferred specific embodiments thereof, it is to be understood that the foregoing description as well as the example are intended to illustrate and not limit the scope of the invention. Other aspects, advantages and modifications within the scope of the invention will be apparent to those skilled in the art to which the invention pertains.