Abstract:
In an automotive radio system an amplifier is capable of detecting speaker faults. A fault signal from the amplifier is received by a microprocessor which sends a fault message to a radio display and/or stores fault data which can be accessed via a serial data link by a diagnostic tool. One embodiment of the amplifier has an output pin for outputting distortion signal, and that pin is used when distortion is not likely to also output a fault signal which reveals the presence of a fault. Another embodiment of the amplifier has a data storage register which receives data on the type of fault and the affected channel, and a data bus to send the data to the microprocessor.

Description:
FIELD OF THE INVENTION 
     This invention relates to the detection of speaker faults and particularly to detection and indication of speaker faults to a vehicle operator or to service personnel. 
     BACKGROUND OF THE INVENTION 
     In an automotive radio system, when a speaker fault occurs the radio or perhaps one channel shuts down, quits working, or is damaged. To prevent damage, many radios use audio amplifiers with built in protection which senses a speaker fault and shuts down at least the channel serving that speaker. Other radios lack that feature. In any event, the operator or service technician will not know the cause of the failure and will assume the problem is in the radio/amplifier, and replace that. Then the same problem will occur, and a search will be made for speaker faults or other system problems. It is desirable, then, that a speaker fault should be readily recognizable so that the service can be properly directed to correcting the problem. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the invention to detect speaker faults and indicate a fault to the operator or technician. 
     An audio amplifier with the capability to detect a speaker fault is configured to produce a signal when a fault occurs. A microprocessor responsive to such a fault signal sends a suitable message to the radio display to apprise the operator of the condition. Alternatively, the fault information is stored in memory associated with the microprocessor and is retrieved via a data bus by a diagnostic tool used by a service technician. 
     Fault detection begins when a radio is turned on. Then before an audio signal is applied, the amplifier is biased and a fault check is performed by the amplifier. At this stage, the fault detection feature can respond to a short to power or to ground and to an open load. If a fault is found the microprocessor executes a fault routine which effects an indication and/or stores fault data and limits the output of the radio from playing until the fault is repaired or otherwise cleared. If there is no fault or if a fault has been cleared, the operator may test for a shorted load by pressing designated radio buttons which cause a high current audio signal to be sent to the speakers. If a fault is detected then, the fault routine is entered but this time the radio is permitted to play at a reduced volume as long as the fault is present. Finally, if no fault is present, normal audio operation is provided and fault detection continues. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other advantages of the invention will become more apparent from the following description taken in conjunction with the accompanying drawings wherein like references refer to like parts and wherein: 
     FIG. 1 is a block diagram of radio hardware including an audio amplifier for speaker fault detection according to one embodiment the invention; 
     FIGS. 2 and 3 are flow charts illustrating the method of the invention; and 
     FIG. 4 is a block diagram of an audio amplifier for speaker fault detection according to another embodiment of the invention. 
    
    
     DESCRIPTION OF THE INVENTION 
     The ensuing description refers to an automotive radio. That term is used herein to include an audio source which may be, for example, a cassette player or other source as well as a tuner. 
     Referring to FIG. 1, a radio includes an audio source 10 providing a signal to an audio amplifier 12 which, in this example, has four output channels, each supplying at least one speaker 14. The amplifier is of the type which has built-in circuits 16 for detecting speaker faults in each channel and includes means for disabling any channel exhibiting a fault. The amplifier 12 also includes a distortion detection circuit 18 which is coupled to an output line 20 to impose a signal on the line when distortion is present. As thus far described, the amplifier is well known for use in automotive radios where the speaker fault and protection capability is desired. It is available from SGS Thomson Microelectronics, of Milan, Italy, as a bridge audio amplifier part no. QBA TDA7385. Similar devices serving only one or two channels are also available from the same source. Here it is proposed to configure the device to couple fault signals from the fault detection circuits 16 to the line 20, so that by monitoring the line when distortion is not likely to occur the state of the line will indicate the presence of a fault. 
     A microprocessor 22 is coupled to the line 20 to monitor its state and to discriminate between distortion and speaker fault signals. The microprocessor is connected to a serial data bus 24 to supply a fault signal or stored fault data to a normal dealership diagnostic tool 26 which is not part of the radio but is an instrument to be applied by a service technician. The radio has a display 28 which is coupled to the microprocessor 22 to display a speaker fault message as well as station identification and other information. Depending on the display capability, the fault message may be, for example, &#34;SPKR PRB&#34;, or an error code such as &#34;ERR3&#34;. Buttons 30 or other normal radio controls provide inputs to the microprocessor 22. 
     The method of detecting and indicating speaker faults is illustrated by the flow charts of FIGS. 2 and 3 wherein the functional description of each block in the charts is accompanied by a number in angle brackets &lt;nn&gt; which corresponds to the reference number of the block. The method involves manual inputs, operation by the amplifier 12 and the fault circuits 16, and operations performed by the microprocessor 22. Each time the radio is first turned on &lt;40&gt; a DC bias is applied to each channel of the amplifier and the fault circuits 16 check for faults &lt;42&gt;. At this time no audio signal is applied and faults due to open load, shorts to ground or shorts to power will be revealed. If a fault is present &lt;44&gt;, a fault circuit changes the state of line 20 and a fault routine is entered &lt;46&gt;. The fault routine &lt;46&gt; is detailed in FIG. 3. The microprocessor responds to the state of line 20 by setting a fault flag and indicating a fault &lt;48&gt; by sending a message to the radio display and storing the fault flag for future examination by the diagnostic tool 26. If the radio is turned off while the fault routine is being executed &lt;50&gt; the fault detection will end &lt;52&gt;. If the radio remains on, a limited audio performance may be allowed &lt;54&gt; but it is preferred to keep the sound off during this initial fault test; however for later tests the limited audio (low volume) is permitted. Next another fault check is made &lt;56&gt; so that if the fault remains &lt;58&gt; the fault routine continues until the radio is turned off. Whenever the fault is cleared either due to a repair or due to an intermittent condition, the fault flag is reset, the fault indication is removed, and a fault occurred flag and fault information will be stored &lt;60&gt;. 
     Then when the fault is cleared &lt;62&gt; (returning to FIG. 2) the operator has the option of testing for internal speaker shorts. This test requires operator action and results in a loud unpleasant sound and will not be performed except when the operator or technician suspects there is a speaker fault. The operator action is, for example, the pressing of two buttons simultaneously, say the #1 and #4 preset buttons. If the buttons are pressed &lt;64&gt; an audio signal is sent to the speakers and a fault check is performed &lt;66&gt;. The signal has high current but is insufficient to cause distortion. This fault check is able to detect a shorted load. If a fault is present &lt;68&gt; the fault routine is entered &lt;70&gt;. This is the same routine (FIG. 3) used above and this time low volume audio performance is permitted. If the fault is cleared &lt;72&gt; or if the button had not been pressed &lt;64&gt; normal audio operation is provided and fault checking continues &lt;74&gt;. If a fault is present &lt;76&gt; it is determined whether the fault detection and distortion detection share the same line 20 as in FIG. 1 &lt;78&gt;. This is done because the same method can be used with other amplifier arrangements. A flag could be set to identify a combined detection arrangement when the software is installed, and the flag is read to answer the inquiry &lt;78&gt;. If the combined detection configuration is used, and the volume setting is high &lt;80&gt;, it is assumed that the fault signal is the result of distortion and normal operation continues. If the volume setting is not high &lt;80&gt; the fault routine is entered &lt;82&gt;. This is the same routine (FIG. 3) used above and this time low volume audio performance is permitted. During the fault routine limited audio performance is allowed and if the fault is cleared &lt;84&gt; the normal operation is restored. 
     The fault circuits 16 of the amplifier are able to identify for each channel the specific type of fault; however there is no convenient way to extract that information for diagnostic purposes. The amplifier may be modified to include communication capability to output the detailed fault information. As shown in FIG. 4, a modified amplifier 12&#39; includes a data storage register 90, and a clock bus 92 and a data bus 94 connect the register to the microprocessor 22. The fault circuits 16 for the several amplifiers channels each have four outputs for coupling specific fault data to pre-assigned bits D0 to D15 of the register 90. The fault outputs are short to B+ (power), short to ground, shorted load and open load. Whenever a fault check is made, the register data is clocked onto the data bus and read by the microprocessor to determine specific fault information and to provide appropriate indication. This data is independent of the distortion signal, although this communication capability can include distortion data if desired. 
     In operation of the system as modified by the FIG. 4 communication capability, the method of FIGS. 2 and 3 remains the same except that the high current used in step &lt;66&gt; does not have to be limited to a non-distorting level, and the steps &lt;78&gt; and &lt;80&gt; are omitted. Since more specific fault information is available, specific diagnosis may be accomplished by the diagnostic tool 26 as it accesses the information. Depending on the extent of the radio display 28, specific information may be shown there as well. 
     It will thus be seen that the detection of speaker faults according to the invention simplifies the diagnosis of radio problems and if there is a speaker fault, avoids the time and expense of unnecessary removal and testing of radios, which is usually the first step in analyzing such problems. Moreover, when the modified amplifier is used, the problem is narrowed to a particular fault in a specific channel, thereby greatly facilitating repair. In addition customer satisfaction is improved by detecting and repairing speaker faults in new vehicles at the factory or at the dealership before delivery to the customer.