JPS6046465A - Meter driving circuit - Google Patents

Abstract

PURPOSE:To perform invariably optimum display by detecting a signal level and switching automatically the range of display level of a meter. CONSTITUTION:When the levels of power amplifiers 1 and 1' are lower than some level, transistors (TR) 26-29 are made off, so resistances 33 and 33' and capacitors 34 and 34' are disconnected from the input circuit of the meter. Consequently, the meter has a proper deflectin with a small volume of sound, and TR30 turns off to turn on a light emitting element 32, displaying a low range at this time. Then, the amplifiers 1 and 1' increase to the large volume of sound, and TRs 26-29 turn on with the time constant determined by capacitors 12, 15, and 18 and resistances 13 and 16; and the resistances 33 and 33' and capacitors 34 and 34' are connected to the meter circuit to reduce the driving voltage of the meter. Consequently, the meter indicates a proper deflection even with a small volume of sound, and a light emitting element 31 turns on to show a high range.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a meter drive circuit for a signal strength meter, etc., and is configured to automatically switch the display level range of the meter.

Figures 1 and 2 show conventional meter drive circuits, where 1 is a power amplifier, 2 is a resistor for setting the meter display level, 3 is a rectifier diode, 4 is a smoothing capacitor, and 5 is a rectifier diode.
is a speaker, 6a is an output terminal, 7 is a selector switch, and 8 is a range switching resistor. 3(a) and 3(b) show meters driven by the drive circuits of FIGS. 1 and 2, and 9 shown in FIG. 3(,) is a moving coil meter,
FIG. 3(b) shows a meter in which a plurality of light emitting elements 11a to 11d such as light emitting diodes (LEDs) and FL (fluorescent) are sequentially turned on by a driver 10. 6b in Figures 3(a) and (b) is shown in Figure 1,
This is a terminal connected to the output terminal 6a in FIG. 2.

In the case of Figure 1, the meter is driven according to the output level of power amplifier 1, but setting the level using resistor 2 is very difficult, and if you set it so that it has an appropriate vibration when the volume is high, it will not work at low volumes. When listening, the meter hardly moves, and the display effect disappears. Also, if you set it to have an appropriate deflection when the volume is low, the pointer will not swing completely when the volume is high, or all the light emitting elements 11a
There is a problem that ~11d remains lit.

In the case of Fig. 2, the display level range can be changed according to the switching of switch 7, so the double problem can be solved. If you forget, the same problem as shown in Figure 1 will occur, and the L7J replacement operation is still extremely troublesome.

The present invention provides a meter drive circuit that solves these conventional problems.

An embodiment of the present invention will be described below with reference to FIG.

In FIG. 4, parts with the same symbols as in FIGS. 1 and 2 have the same functions. 12 is a capacitor for improving transient response, 13.16 is a resistor for setting the range switching level, 14.17 is a rectifying diode, 15.18 is a smoothing capacitor, and 26 is a transistor for level detection. , 19 is its collector resistance, 27 to 30 are switching transistors, 20 to 23 are its base resistances, 24.
25 is the collector resistor of the transistor 29.30, 31.degree.'B2 is a light emitting element for indicating the range, and 33.34 is a gain adjustment resistor and capacitor. Note that 1' to 34'
indicates the other channel for stereo reproduction, and corresponds to 1 to 34 above.

A signal level detection circuit is constituted by a capacitor 12 to a resistor 22 and a transistor 26, and when a high range is reached, the signal level remains unchanged for a time constant determined by a capacitor 18 and resistors 20 to 22.

In the above configuration, when the level of the power amplifiers 1, 1/ is below the level, the transistor 26 is turned off;
Since transistors 27 to 29 are also turned off, resistor 33.
33' and capacitors 34 and 34' are connected to one from the meter's input circuit. For this reason, the meter shows appropriate deflection at low volumes. Also, since the transistor 30 is on at this time, the light emitting element 32 lights up to indicate that the current range is low.

Next, when the power amplifier 7'1.1 becomes loud and the transistor 26 is turned on, the bases of the transistors 26 to 29, which have a time constant (T1) determined by the capacitor 12°15.18 and the resistor 13.16, are turned on. Electric potential rises. Therefore, resistors 33, 33' and capacitors 34, 34' are connected to the meter circuit and serve to reduce the meter drive voltage. For this reason, the meter shows appropriate vibration even at high volumes. At this time, the light emitting element 31 lights up to indicate that the range is high. When the power amplifier level becomes low again, the potential of the capacitor 15 is discharged through the resistor 16, but the potential of the capacitor 18 is discharged from the transistor 26 to
29 and resistors 20 to 22, the discharge time constant (T2) is (capacity of capacitor 18 x transistor 2
The circuit is configured and the constants are selected so that the current amplification factor (hFE) of 6 x parallel combined resistance of 20 to 22 resistors becomes TI.

Therefore, switching from a low range to a high range is almost instantaneous, while switching from a high range to a low range requires a few seconds.
Once you reach a high range, try to stay in that state for a few seconds. By doing so, it is possible to prevent unstable operation due to minute level fluctuations near the switching level. It goes without saying that the range may be changed over three or more steps.

As described above, since the present invention detects the signal level and automatically switches the range of the meter display level, it is possible to always provide the optimum display from the small signal level to the large signal level 1. can.

4. Simplified drawing 11 theory! 11 Figures 1 and 2 are circuit diagrams of conventional examples, and Figure 3 is a circuit diagram of a conventional example.

(b) is a diagram showing an example of a meter, and FIG. 4 is a circuit diagram of one embodiment of the present invention.

1...Power amplifier, 5...Speaker, 6a...Output terminal, 12-22.26...
...Signal level detection times 9.27, 28...
Transistors forming switching circuits, 33.34
...Gain adjustment element.

Claims (1)

[Claims] a meter that is driven according to the signal level; a gain adjustment element connected to the input circuit of the meter; a signal level detection circuit that detects the signal level and outputs it with a predetermined time constant; and a switching circuit that is turned on and off by the output of the level detection circuit, and the range of the display level of the meter is automatically switched by controlling the gain adjustment element according to the on/off state of the switching circuit. IKl+ circuit.