Patent Abstract:
A stereo sound level display device includes a single array of light emitting diodes aligned in a line. The left channel sound signal level is detected to display the left channel sound signal level from the left end of the light emitting diode array. At the same time, the right channel sound signal level is detected to display the right channel sound signal level from the right end of the light emitting diode array.

Full Description:
This application is a continuation of application Ser. No. 282,239 filed on July 10, 1981, now abandoned. 
    
    
     BACKGROUND AND SUMMARY OF THE INVENTION 
     The present invention relates to an analog display of the segmented type for displaying a level of a detected signal. 
     LED (light emitting diode) level meters have been used in audio reproduction systems for displaying the level of input signals. A typical drive system for controlling the number of lighted LEDs in response to the level of the input signal is disclosed in, for example, U.S. Pat. No. 3,796,951, &#34;SOLID STATE ELECTRONIC GAUGE&#34; issued on Mar. 12, 1974, and U.S. Pat. No. 4,017,796, &#34;ELECTRICAL CIRCUIT MEANS FOR USE IN ANALOGUE DISPLAY AND/OR CONTROL SYSTEM&#34; issued on Apr. 12, 1977. 
     When the above-mentioned LED level meter is used to display the level of the stereo sound signal, two sets of the LED level meters are employed in the conventional system for displaying the right channel signal level and the left channel signal level, respectively. 
     Accordingly, an object of the present invention is to provide an analog display of the segmented type which displays the levels of plural signals at a same time. 
     Another object of the present invention is to provide an LED level meter for displaying a stereo sound signal level through the use of one array of LEDs. 
     Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
     To achieve the above objects, pursuant to an embodiment of the present invention, a row of light emitting diodes are provided for indicating the level of one input signal from the left end of the row and for indicating the level of another input signal from the right end of the row. The one input signal can be the left channel sound signal, and the other input signal can be the right channel sound signal when the present level meter is used for displaying the audio signal level of the stereo sound. 
     In a preferred form, ten (10) light emitting diodes are aligned in a row to which a driver circuit is connected. The driver circuit functions to enable a preselected number of light emitting diodes from the left end of the row in response to the level of the left channel sound signal. The driver circuit further functions to enable a preselected number of light emitting diodes from the right end of the row in response to the level of the right channel sound signal. The driver circuit further functions to drive the light emitting diode which is located at the position where the number of diodes to be illuminated from the left end and the right end overlap each other at a brightness higher than the remaining light emitting diodes. 
     In another preferred form, a row of the light emitting diodes is connected to a driver circuit which functions to enable one light emitting diode representing the level of the input signal. More specifically, when the left channel sound signal has the level corresponding to four (4) LEDs and the right channel sound signal has the level corresponding to three (3) LEDs, the fourth LED counted from the left end of the row and the third LED counted from the right end of the row are enabled. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be better understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention and wherein: 
     FIG. 1 is a circuit diagram of an embodiment of a driver circuit of the present invention; 
     FIG. 2 is a circuit diagram of another embodiment of a driver circuit of the present invention; and 
     FIG. 3 is a block diagram of a level discriminator included in the driver circuit of FIG. 2. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows an embodiment of a level meter of the present invention, wherein the stereo sound signal level is displayed through the use of an array of ten (10) light emitting diodes LED 1  through LED 10 . 
     The left channel signal level is displayed from the left end of the LED array, and the right channel signal level is displayed from the right end of the LED array. When the left channel signal has the level corresponding to four (4) LED segments, the LEDs LED 1  through LED 4  are enabled. At the same time, when the right channel signal has the level corresponding to two (2) LED segments, the LEDs LED 9  and LED 10  are enabled. That is, the LEDs LED 1 , LED 2 , LED 3 , LED 4 , LED 9  and LED 10  are enabled. 
     Each anode electrode of the LEDs is connected to a DC power source +Vcc. Each cathode electrode of the LEDs is connected to a parallel circuit including a series circuit of a resistor R Li  and a transistor T Li , and a series circuit of a resistor R Rj  and a transistor T Rj . The transistor T Li  is connected to receive a switching signal from an input terminal Li for displaying the level of the left channel sound signal, and the transistor T Rj  is connected to an input terminal Rj to receive a switching signal for displaying the level of the right channel sound signal. A right channel sound signal level discriminator is provided for developing the switching signal to be applied to the input terminal Rj, and a left channel sound signal level discriminator is provided for developing the switching signal to be applied to the input terminal Li. 
     In the foregoing example, when the left channel signal has the level corresponding to four (4) LED segments, the input terminals L 1  through L 4  receive the switching signal of the high level. Further, when the right channel signal has the level corresponding to two (2) LED segments, the input terminals R 1  and R 2  receive the switching signal of the high level. Thus, the transistors T L1 , T L2 , T L3 , T L4 , T R1  and T R2  are switched on to enable the LEDs LED 1 , LED 2 , LED 3 , LED 4 , LED 9  and LED 10 . 
     If the left channel sound signal has the level corresponding to five (5) LED segments and the right channel sound signal has the level corresponding to seven (7) LED segments, the transistors T L1  through T L5  and T R1  through T R7  are switched on. Therefore, the LEDs LED 4  and LED 5  emit light higher than the remaining LEDs. More specifically, when the left channel signal level measured from the left end of the LED array and the right channel signal level measured from the right end of the LED array overlaps each other, the overlapped portion is driven to emit light stronger than the remaining LEDs. 
     FIG. 2 shows another embodiment of a level meter of the present invention, wherein the stereo sound signal level is displayed through the use of an array of five (5) light emitting diodes LED I  through LED V . In this embodiment, when the left channel sound signal has the level corresponding to one (1) LED segment and the right channel sound signal has the level corresponding to two (2) LED segments, the light emitting diodes LED I  and LED IV  are enabled. 
     Each anode electrode of the LEDs is connected to a DC power source +Vcc. Each cathode electrode of the LEDs is connected to a switching transistor TL i1  which receives a switching signal derived from a left channel sound signal level discriminator DL. Each of the cathode electrodes is further connected to a switching transistor TR j1  which is connected to receive a switching signal derived from a right channel sound signal level discriminator DR. 
     FIG. 3 schematically shows the construction of the right channel sound signal level discriminator DR. The level discriminator DR includes comparators C 1  through C 5 . A reference voltage signal VR 1  is applied to the reference input terminal of the comparator C 1  and the data input terminal of the comparator C 1  receives the right channel sound signal R in . The right channel sound signal R in  is applied to the each of the data input terminals of the comparators. The reference voltage signal VR 2  is higher than the reference voltage signal VR 1 . The reference voltage signal VR 5  is higher than the reference voltage signal VR 4  which is higher than the reference voltage signal VR 3  which, in turn, is higher than the reference voltage signal VR 2 . When the right channel sound signal has the level corresponding to two (2) LED segments, the comparators C 1  and C 2  develop a switching signal of the high level at output terminals R 1  and R 2 , respectively. The left channel sound signal level discriminator DL has the same construction as the right channel sound signal level discriminator DR. 
     In the embodiment of FIG. 2, when the left channel sound signal has the level corresponding to two (2) LED segments, the left channel sound signal level discriminator DL develops the switching signal of the high level at its output terminals L 1  and L 2 . The switching signal derived from the output terminal L 1  functions to switch on the transistor TL 11 . The switching signal derived from the output terminal L 2  functions to switch on the transistor TL 21 . The switching signal derived from the output terminal L 2  further functions to turn on a transistor TL 12 . When the transistor TL 12  is made conductive, the base electrode of the transistor TL 11  is forced to the ground level and, therefore, the transistor TL 11  is made non-conductive. Accordingly, the light emitting diode LED I  is disabled, and only the light emitting diode LED II  is enabled. The similar operation is conducted in the right channel side. Thus, when the left channel sound signal has the level corresponding to two (2) LED segments and the right channel sound signal has the level corresponding to one (1) LED segment, the light emitting diodes LED II  and LED V  are simultaneously enabled. 
     The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications are intended to be included within the scope of the following claims.

Technology Classification (CPC): 6