JPH0226745B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a level meter, and particularly to a level meter that can switch and display two or more of various voltages or signal levels such as signal level and battery level in audio equipment and the like.

Generally, a level meter has been developed for displaying the signal level of communication equipment, audio equipment, etc., in which the light emitting parts of several light emitting diodes are lined up and the light emitting diodes emit light according to the measured level to display the level. . Furthermore, this type of level meter employs a method of switching and displaying two or more signal levels using one level meter. For example, in a radio cassette recorder, a level meter consisting of five light emitting diodes is used to check the recording level as well as the battery level.

In this case, if the comparison levels of the comparators that drive each light emitting diode are A, B, C, D, and E in order, and a specific numerical example of each level is shown, A=-
10dB (0.31x), B = -5dB (0.56x), C = 0dB (1
D=dB (1.41 times), E=6 dB (2 times).
If a level meter with a level value corresponding to such signal level display is used as is for checking battery voltage, if the battery voltage level is set to display level E when the battery voltage level is sufficiently high, that voltage will be displayed. When the battery voltage reaches 1/2, level C is displayed, that is, a high level is displayed even though the battery is unusable, so it is not accurate as a battery check.

Therefore, a level meter has been proposed in which the step level width of the comparison level set in the comparator can be changed according to each object to be measured, and the level of the object to be measured can be appropriately displayed.

The present invention provides a level meter in which the stepwise level width of the comparison level set in the comparator can be changed according to each measurement object, and a control input terminal for inputting a switching control signal for changing the level width. By sharing the display element connection with the terminal, the number of terminals (IC pins) can be reduced.
To provide a level meter which has a circuit suitable for an IC and which simplifies the operation of changing the display level.

The present invention includes a level comparison circuit that individually compares comparison levels set in a plurality of stages and an input to be measured, and a level comparison circuit provided corresponding to the comparison level setting stage and driven by the output of the level comparison circuit. A plurality of display elements, a switch inserted in series in one of the display elements to switch the comparison level, and level switching by detecting electrical changes occurring at the terminals of the display elements by opening and closing of the switch. A level switching circuit that generates a signal, and a level setting in which the step level width of a comparison level formed by dividing the output voltage of a constant voltage source into a plurality of stages can be changed by a level switching signal generated by the level switching circuit. It is characterized by being composed of a circuit.

Embodiments of the invention will be described in detail with reference to the drawings. FIG. 1 shows an embodiment of the level meter of the present invention. In the figure, an input to be measured is applied to an input terminal 2 from a signal source or a voltage source (not shown), and this input is converted to a DC level by a rectifier amplifier circuit 4. The rectifier amplifier circuit 4 includes an amplifier, a diode, an externally connected smoothing capacitor, and the like. That is, the input signal is amplified by an amplifier, rectified by a diode, smoothed by a capacitor, and converted to a DC level. This DC level output is given to the level comparison circuit 6, and is compared with a comparison level set stepwise by the level setting circuit 8.

The level comparison circuit 6 includes five comparators 10 and 1 that individually compare the input signal with the comparison levels set in multiple stages by the level setting circuit 8.
2, 14, 16 and 18 are installed, and transistors 20, 22, 2 as switching elements are installed at the output terminal of each comparator 10 to 18.
4, 26 and 28 are connected.

In addition, the level setting circuit 8 is configured to set comparison levels in a plurality of stages and to change the level step width of the comparison levels. In this embodiment, two types of comparison levels can be set by switching the division allocation using a switching input. It is designed to be obtained. That is, resistors 34, 36, 38, 40, 42, and 44 are connected in series as a plurality of voltage dividing elements to a constant voltage source 32 driven by a DC voltage Vcc applied to a power supply terminal 30. Resistors 46, 48, 50, 52, 54 are used as voltage dividing elements, and transistors 56, 58, 6 are used as switching elements.
They are connected in parallel via 0, 62, and 64.
At the base of each transistor 56 to 64 are constant current sources 66, 68, 70, 72, 74 and switching transistors 76, 78, 80, 82,
The bases of the transistors 76 to 84 are connected in common, and a level switching signal is applied from the level switching circuit 86 to the bases.

Output terminals 88, 90, 92, 94 and 96 for connecting display elements are formed at the collectors of each of the transistors 20 to 28 of the level comparison circuit 6. Each output terminal 88 to 94 has a light emitting diode 98, 100, 1 as a display element.
02, 104 are connected individually, transistor 2
The driving current is supplied in accordance with the switching operation from 0 to 26. In the case of this embodiment, as is clear from the configuration of the level setting circuit 8, the display level of each of the output terminals 88 to 96 is such that the output terminal 88 is used for displaying the lowest level, and the level increases sequentially from the output terminal 88 and is outputted. terminal 96
is designed for the highest level display. In this embodiment, an output terminal 96 for displaying the highest level is also used as a control input terminal for the switching control signal of the level switching circuit 86, and a light emitting diode 106 is connected to this terminal 96 via a level switching switch 108. A resistor 110 is connected in parallel to the light emitting diode 106.

The level switching circuit 86 is connected to the switch 108.
The level switching signal is formed by detecting electrical changes occurring at the terminal 96 in response to opening and closing of the terminal 96 . That is, this embodiment is configured as a discrimination circuit including a comparator that discriminates the level change of the terminal 96, and the transistors 112, 114,
116, 118, diode 120, 122, 1
24, a resistor 126, and constant current sources 128 and 130. A driving power is supplied to the power supply terminal 132 in common with the light emitting diodes 98 to 106.

In the above configuration, when the switch 108 is closed and the base potential of the transistor 20 is at a high level, the transistor 20 becomes conductive and current Io flows, and this current lights the light emitting diode 106. do. At this time, assuming that the power supply voltage is Vcc and the forward voltage drop of the light emitting diode 106 is Vfled, the potential Va at point a becomes Va=Vcc-Vfled (1). Furthermore, when the base of the transistor 20 becomes low level and the transistor 20 becomes non-conductive, the current Io flowing through the transistor 20 is
Io=0, but if the resistance value of the resistor 110 is _R1 and the current flowing through this resistor 110 is _Io1 , the potential Va' at the point a is Va'=Vcc- _R1・_Io1 ...(2 ) becomes. In this case, the resistance value R ₁ of the resistor 110 and the current Io ₁ are set to the condition that R ₁ ·Io ₁ <Vfled. Furthermore, when the switch 108 is opened, the a
The potential at the point becomes low level, and the potential at this point is
On the other hand, if the potential at point b of the level switching circuit 86 is Vb, then this potential is
The forward drop voltage of 2,124 is given by 2Vf,
The magnitude relationship between this b potential and the point a potentials Va, Va', Va'' is set as Va''<Vb<Va or Va' (3), and the opening and closing of the switch 108 causes the point a potential to change.
The operation of transistors 112, 114 is reversed by being switched such as Va, Va' or Va''.

When switch 108 is closed, transistor 112 becomes conductive according to the above conditions;
A current Ic as a level switching signal applied to the level setting circuit 8 flows through the transistor 118, and this current Ic flows through the bases of the transistors 76 to 84. When this current causes transistors 76-84 to become conductive, transistors 56-64 become non-conductive. In this state, each resistor 46-54 is replaced by each resistor 34-4.
4, the constant voltage source 3 becomes electrically open state.
Only the resistors 34 to 44 are connected in series to the output of 2. As a result, the output voltage of the constant voltage source 32 is divided by the resistance values of the resistors 34 to 44, and the comparison levels of the comparators 10 to 18 are set by the voltages formed at the connection points of the resistors 34 to 44. Therefore, the input applied to the input terminal 2 and converted to a DC level by the rectifier amplifier circuit 4 is compared with the comparison level, and one or more of the comparators 10 to 18 output a high level depending on the input level. In response to this output, one or more of the transistors 20 to 28 become conductive, and the light emitting diodes 98 to 106 emit light in response to the input level. At this time, even if the transistor 20 becomes conductive to display the highest level, the level switching circuit 86
The operation of will not change in any way.

In addition, in order to change the measurement target, the switch 108
When opened, the operation of transistors 112 and 114 of level switching circuit 86 is reversed to that described above, and current Ic in transistor 118 is released, resulting in transistors 76 to 84 being non-conductive. Therefore, the output current of the constant current sources 66 to 74 flows into the base of each transistor 56 to 64, and each transistor 56 to 64 becomes conductive. As a result, each resistor 36 to 4
4, resistors 46 to 54 are connected in parallel via transistors 56 to 64,
The resistance ratio of the resistance ladder connected to the constant voltage source 32 will be changed. That is, the resistance values of the resistors 46 to 54 are now set so that the comparison levels set by the resistors 46 to 54 are logarithmic, and the resistors 46 to 54 are individually connected in parallel to the resistors 34 to 44. If the resistance values of the respective resistors 46 to 54 are set so that they have the same resistance value in this case, the comparison level set to each of the comparators 10 to 18 will be determined by dividing and distributing the output voltage of the constant voltage source 32. Instead, the comparison level is changed to a level step width different from that in the above case. As a result, one or more of the light emitting diodes 98 to 104 can be caused to emit light in accordance with this comparison level, and appropriate display can be performed depending on the object to be measured, such as battery voltage. In this case, since the switch 108 is open, display by the light emitting diode 106 becomes impossible, and the highest level display is moved down to the light emitting diode 104, and the level display is performed by the four light emitting diodes 98 to 104. In this embodiment, the control input terminal of the level switching circuit 86 is shared by the output terminal 96 that generates the highest level output, but it may be shared by any one of the other output terminals 88 to 94. A control input signal having the same effect as described above can be obtained.

FIG. 2 shows another embodiment of the present invention, in which the control input terminal of the level switching circuit 86 is shared with the output terminal 88 for displaying the lowest level, and two contacts s are used in place of the switch 108. ₁ , s ₂ is used, and this switch 134
A contact s ₁ is connected to the terminal 88 and inserted between the terminal 88 and the light emitting diode 98, and the contact s ₂ is connected to the reference potential point (GND) via the resistor 136 and connected to the light emitting diode 98. resistance 138
are connected in parallel. That is, since the resistor 136 is connected to the contact _s2 , the switch 134
When switching to contact s ₂ , light emitting diode 98
A bypass is formed through which a drive current flows, and the light emitting diode 98 emits light by passing this drive current.
In the case of this example, unlike the case of the previous example,
A light emitting diode connected to the control input terminal can also be made to emit light. If you configure it like this,
Is it possible to use the output terminal 96 for the highest level as the terminal shared with the control input terminal? Since the light emitting diode 106 on the highest level side emits light separately from the level display, the light emitting diode 98 on the lowest level side is made to emit light. This is advantageous in terms of level display and confusion. The other functions are the same as those in the previous embodiment, so their explanation will be omitted.

Further, in the case of the above embodiment, for changing the comparison level, the resistors 46 to 54 and the transistor 56
However, the resistors 46 to 54 may be replaced with other voltage dividing elements. For example, the same effect can be obtained even if the resistors 46 to 54 are replaced with diodes. The transistors 56 to 64 can be replaced with electronic switches only. Alternatively, a mechanical switching element such as a relay may be used instead. Further, in the above embodiment, a resistor 4 as a voltage dividing element is used for each resistor 36 to 44.
6 to 54 are connected in parallel, but the voltage dividing element may be connected in parallel to one or more of the resistors instead of connecting the voltage dividing element to all the resistors in parallel.

Further, in the above embodiment, the level change is explained as two types, but if the number of parallel connection of voltage dividing elements and switching elements for level change is increased to a plurality,
A plurality of different levels can be displayed by switching control. In this case, according to the embodiment described above, it is necessary to provide each switching element with a constant current source and a switching transistor as a switching circuit.

In addition to the light emitting diode of the embodiment, a light bulb or the like may be used as the display element.

As explained above, according to the present invention, in a level meter in which the stepwise level width of the comparison level set in such a comparator can be changed according to each measurement object, a switching control signal for changing the level width is provided. By sharing the control input terminal for input with the display element connection terminal, the number of terminals (IC pins) can be reduced, making the circuit suitable for ICs, and also simplifying display level and changing operations. can.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a level meter according to the invention, and FIG. 2 is a circuit diagram showing another embodiment of the invention. 6... Level comparison circuit, 8... Level setting circuit, 86... Level switching circuit, 88, 90, 9
2, 94, 96...output terminal, 98, 100, 1
02, 104, 106... Light emitting diode as a display element, 108, 134... Switch.

Claims (1)

[Claims] 1. A level comparison circuit that individually compares comparison levels set in a plurality of stages and an input to be measured, and an output of the level comparison circuit that is provided corresponding to the comparison level setting stage. a plurality of display elements driven with and a level switching circuit that generates a level switching signal by dividing the output voltage of the constant voltage source into a plurality of stages to form a comparison level whose step level width can be changed by the level switching signal generated by the level switching circuit. A level meter comprising a level setting circuit. 2. One of the display element connection terminals formed on the output side of the level comparison circuit is shared as a control input terminal for a switching control signal of the level switching circuit, and one display element is connected to this terminal via the switch. 2. The level meter according to claim 1, wherein a switching control signal is applied to the control input terminal by opening and closing the switch. 3. At least one of the terminals for connecting the display element that generates the highest level output or the lowest level output is shared as a control input terminal for the switching control signal of the level switching circuit, and the terminal connected to this terminal via a switch Claim 2, characterized in that a bypass is formed in the display element in response to the switching operation of the switch to enable the flow of driving current.
Level meter as described in section.