Display device in electrical equipment

A display device includes a single meter which can be selectively employed as a signal meter indicating a strength level of a received radio wave and an output level meter indicating an output level of an amplifier. The display device is so designed that the meter is automatically caused to operate as the signal meter when a person touches the tuning knob of a tuner section, otherwise the meter operates as the output level meter. A switch may be provided to restrict the meter function to that of the signal meter regardless of a person's touching of the tuning knob.

BACKGROUND OF THE INVENTION 
This invention relates to display devices in electrical equipment, such as 
for instance a radio receiver, incorporating a tuner section and an output 
amplifier section (a preamplifier and a main amplifier). 
In general, the provision of a signal meter indicating the radio wave 
strength of an antenna input and a tuning meter indicating a tuning point 
with its pointer at the zero point in the scale thereof by utilizing the 
"S"-shaped characteristic curve of an FM demodulator is desirable in order 
to precisely indicate a tuning point of the tuner section of such 
electrical equipment as described above, and in addition it is also 
desirable to provide a pair of output level meters respectively indicating 
the right and left channel output levels for the output amplifier section. 
Accordingly it is necessary to provide the electrical equipment with four 
meters in total. Therefore the conventional electrical equipment of this 
type suffers from drawbacks that the area of the panel board where the 
meters are provided must be relatively large and accordingly the 
manufacturing cost of the electrical equipment is increased 
proportionately. 
SUMMARY OF THE INVENTION 
Accordingly a primary object of this invention is to provide a display 
device in electrical equipment in which the number of meters is reduced. 
Another object of the invention is to provide a display device is 
electrical equipment in which the manufacturing cost thereof can be 
reduced, and the area of a panel board available for use by elements other 
than meters is increased. 
A further object of the invention is to provide a display device in 
electrical equipment in which a meter switching operation is avoided so 
that the electrical equipment can be readily operated. 
This invention has been developed based on the fact that while a signal 
meter is scarcely needed when the station selecting operation or the 
tuning operation is not carried out, an output level meter is needed when 
a broadcast signal is received after completion of station selecting 
operation and when information recorded on a phonographic disk or in a 
magnetic tape is reproduced. 
The display device according to this invention comprises at least one 
meter, and a meter selection control circuit which operates to cause the 
meter to selectively display the radio wave strength of an antenna input 
in the tuner section of electrical equipment or the output level of the 
output amplifier section thereof. 
According to a preferred example of this invention, the aforementioned 
meter selection control circuit comprises a touch detection circuit which, 
when a person touches the tuning knob of the tuner section with his finger 
or hand, produces a touch detection signal, and a switching circuit which 
operates in response to the output signal of the touch detection circuit 
to control the meter in such a manner that the meter displays the radio 
wave strength when a person touches the tuning knob and the output level 
of the output amplifier section when the person does not touch the tuning 
knob. 
The novel features which are considered characteristic of this invention 
are set forth in the appended claims. This invention itself, however, 
together with additional objects and advantages thereof will be best 
understood from the following description taken in conjunction with the 
accompanying drawings which illustrate, by way of example only, some 
preferred embodiments of the invention. In the accompanying drawings, like 
parts are designated by like reference numerals or characters.

DETAILED DESCRIPTION OF THE INVENTION 
Shown in FIG. 1 is a circuit diagram illustrating a first embodiment of 
this invention, which comprises a pair of meters 1 and 2 arranged side by 
side for indicating voltage levels (hereinafter referred to as a left side 
meter 1 and a right side meter 2, respectively, when applicable). The 
output terminals 31A and 32A for the left and right channels of an output 
display circuit 3 are connected respectively to the negative terminals 1b 
and 2b of the meters 1 and 2. This output display circuit 3 is to perform 
logarithmic amplification of the amplified output voltages for the left 
and right channels applied to the input terminals 31B and 32B of the 
output display circuit 3 from an output amplifier section (not shown) and 
to output the voltages thus amplified through the output terminals 31A and 
32A. 
The left channel is made up of an electrolytic capacitor 301 whose positive 
terminal is connected to the input terminal 31B, an electrolytic capacitor 
302 whose negative terminal is connected to the negative terminal of the 
electrolytic capacitor 301, a resistor 303 connected in series to the 
electrolytic capacitor 302, an electrolytic capacitor 309 whose negative 
terminal is connected to the resistor 303, a resistor 308 connected 
between the junction of the resistor 303 and the electrolytic capacitor 
309 and the ground point, a transistor 310 whose base is connected to the 
positive terminal of the electrolytic capacitor 309, base bias resistors 
311 and 312 for this transistor 310, a load resistor 313 of the transistor 
310, an emitter bias (self-bias) resistor 314 of the transistor 310, an 
electrolytic capacitor 315 connected in parallel to the resistor 314 for 
shunting AC components, an electrolytic capacitor 316 whose positive 
terminal is connected to the collector of the transistor 310, a diode 318 
connected between the negative terminal of the electrolytic capacitor 316 
and the ground point, a diode 319 whose cathode is connected to the 
negative terminal of the electrolytic capacitor 316, a resistor 317 
connected between the junction of the electrolytic capacitor 316 and the 
diode 319 and a series-parallel connection of diodes 304, 305, 306 and 307 
which in turn is connected to the junction of the electrolytic capacitor 
309 and the resistor 303 to constitute a logarithmic amplifier together 
with the transistor 310, an electrolytic capacitor 322 connected between 
the anode of the diode 319 and the ground point, a parallel circuit 
constituted by two resistors 320 and 321, the parallel circuit being 
connected in series to the diode 319, and a resistor 323 connected between 
the output side of the resistors 320 and 321 and the ground point. 
The arrangement of the right channel is similar to that of the left channel 
described above. Since the operation of the output display circuit 3 is 
substantially identical to that of a conventional output display circuit 
employed in preamplifiers, main amplifiers, and so forth, the detailed 
description of the operation will be omitted. 
Connected to the positive terminal 2a of the right side meter 2 is a signal 
strength output terminal 5C of a signal meter circuit 5 adapted to pick up 
a radio wave strength of an antenna input to a tuner section 4. This 
signal meter circuit 5 is so designed that an intermediate frequency 
signal is obtained through a coupling capacitor from an intermediate 
frequency amplifier stage and is subjected to rectification (these 
elements being not shown). The positive and negative terminals 2a and 2b 
of the right side meter 2 are connected respectively to stationary 
contacts 6a and 6b of an electromagnetic relay 6, the stationary contacts 
being selectively grounded by means of a movable contact 6c of the 
electromagnetic relay 6. On the other hand, the positive terminal 1a of 
the left side meter 1 is connected to one 7b of the stationary contacts 7a 
and 7b of a first meter change-over switch 7, and is selectively set in 
grounded state and non-grounded state by the switching operation of a 
movable contact 7c of the change-over switch 7. 
A touch detection circuit 9a is to detect the fact that a person touches a 
tuning knob 8. More specifically, since interior wiring is installed in a 
room where electrical equipment such as a radio receiver is located, the 
room is filled with magnetic flux and therefore an induction voltage at 
the power supply frequency is developed in a person in the room. 
Accordingly, when the person touches the tuning knob 8, an induction 
voltage at the power supply frequency is applied to the touch detection 
circuit. In the case where a person does not touch the tuning knob 8, the 
potential at the output terminal 9D of the touch detection circuit 9a is 
maintained low. However, when he touches the tuning knob 8, the potential 
at the output terminal 9D is increased thereby to produce a touch 
detection output. The touch detection circuit 9a will be further described 
so as to be conducive to a full understanding of this invention. The touch 
detection circuit 9a is made up of a resistor 901 which is connected to 
the tuning knob 8, a capacitor 903 connected in series to the resistor 
901, a transistor 904 whose base is connected to the capacitor 903, the 
emitter thereof grounded, the collector thereof connected a power supply 
terminal 910 through a resistor 907, a series circuit formed by a resistor 
905 and a capacitor 906, (for stabilizing the base bias voltage), this 
series circuit being connected between the base of the transistor 904 and 
the ground point, a transistor 908 whose base is connected to the 
collector of the transistor 904, the collector of the transistor 908 
connected to the power supply terminal 910 through a resistor 909, the 
emitter of the same transistor 908 grounded through a resistor 911, a 
feedback path connecting the emitter of the transistor 908 and the 
junction of the resistor 905 and capacitor 906, and a transistor 912 whose 
base is connected to the collector of the transistor 908, the emitter of 
the transistor 912 connected to the power supply terminal 910, the 
collector of the transistor 912 grounded through an electrolytic capacitor 
913. 
The induction AC voltage applied through the tuning knob 8 is amplified by 
the transistors 904 and 908. The induction voltage thus amplified is 
employed to change the base bias of the transistor 912. In its negative 
cycle, the transistor 912 is rendered conductive, and current is allowed 
to flow into the capacitor 913 from the power supply terminal 910. As a 
result, the capacitor is charged to increase the potential at the output 
terminal 9D (or to produce the touch detection signal). In the case when 
the person does not touch the tuning knob 8, the transistor 912 is 
maintained non-conductive. Therefore the capacitor 913 is not charged and 
accordingly the potential at the output terminal 9D is maintained low. In 
other words, it can be said that the tuning knob 8 and the touch detection 
circuit 9a form a touch response switch 9. 
In FIG. 1, reference numeral 902 is intended to designate a shield wire for 
shielding the lead wire extended between the tuning knob 8 and the 
resistor 901. That is, the provision of the shield wire prevents the 
induction of voltage in the lead wire by the external magnetic flux. The 
diode 914 serves as a connection circuit to an AFC (automatic frequency 
control) circuit for instance. 
The above-described touch response switch 9 forms a meter selection control 
circuit with a switching circuit 10 which operates in response to the 
output signal from the touch response switch 9 so that the radio wave 
strength is displayed on the meter 2 when a person touches the tuning knob 
8 and the output levels of the left and right channels of the output 
amplifier section are displayed on the meters 1 and 2 when the person does 
not touch the tuning knob. The output terminal 9D of the touch detection 
circuit 9a is connected to the above-described switching circuit 10 
including the aforementioned electromagnetic relay 6. The output terminal 
9D is grounded through a capacitor 43 on the one hand and is connected to 
a transistor 21 through a resistor 44 on the other hand. The switching 
circuit 10 comprises a relay operation control circuit made up of the 
transistor 21 whose base is controlled in response to variations in the 
voltage level at the output terminal 9D whereby its conduction state is 
changed, and a transistor 22 whose base is controlled in response to 
potentials at the collector of the transistor 21. The switching circuit 10 
further comprises a transistor 30 which is base-controlled in response to 
potentials at the collector of the transistor 22. In the collector circuit 
of the transistor 22, or between the collector of the transistor 22 and 
the power supply terminal 11 there are provided a second meter change-over 
switch 12 and the above-described electromagnetic relay 6 connected in 
series. The transistor 30 is connected between the negative terminal 1b of 
the left side meter 1 and the ground point so that when the transistor 30 
is rendered conductive, the negative terminal 1b is grounded. The second 
switch 12 is interlocked with the first switch 7 and is adapted to open 
and close the collector circuit of the transistor 22. In the case when the 
movable contact 7c in the first switch 7 is tripped over to the stationary 
contact 7a so that the positive terminal 1a of the left side meter 1 is 
disconnected from the ground, the movable contact 12c of the second switch 
12 is connected to the stationary contact 12a thereof so that the flow of 
current to the collector of the transistor 22 is interrupted. In contrast, 
in the case when the movable contact 7c of the first switch 7 is connected 
to the stationary contact 7b so as to ground the positive terminal 1a of 
the left side meter 1, the movable contact 12c of the second switch 12 is 
connected to the stationary contact 12b thereof so that current is 
supplied to the collector of the transistor 22. Furthermore the 
electromagnetic relay 6 is so designed that upon energization the movable 
contact 6c is so moved as to be connected to the stationary contact 6a so 
as to ground the positive terminal 2a of the right side meter 2, while 
upon deenergization the movable contact is so moved as to be connected to 
the other stationary contact 6b so as to ground the negative terminal 2b 
of the right side meter 2. 
The operation of the first example of this invention will be described with 
reference to FIGS. 2 to 4 in which only essential elements thereof are 
shown and essential conducting lines are indicated with heavy lines. 
FIG. 2 illustrates a state in which the movable contacts 7c and 12c of the 
first and second switches 7 and 12 are connected to the stationary 
contacts 7b and 12b, respectively, and a person is not touching the tuning 
knob 8. In this case, as the detection output terminal 9D of the touch 
detection circuit 9a is maintained at a low potential, the transistor 21 
is in non-conductive state so that the base of the transistor 22 is 
maintained at a high potential. In addition, as the collector of the 
transistor 22 is connected through the electromagnetic relay 6 and the 
second switch 12 to the power supply, the transistor 22 is in conductive 
state. As a result, the electromagnetic relay 6 is energized. Accordingly, 
the movable contact 6c of the electromagnetic relay 6 is connected to the 
contact 6a thereof and the positive terminal 2a of the right side meter 2 
is connected to the ground, while the negative terminal 2b is disconnected 
from the ground. That is, while the signal strength output terminal 5C of 
the signal meter circuit in the tuner section 4 is grounded, the negative 
voltage from the right channel output terminal 32A of the output display 
circuit 3 is applied to the negative terminal 2b of the right side meter 
2. Therefore the right side meter indicates the right channel output level 
of the output amplifier section. In this operation, as the transistor 22 
is rendered conductive to lower the collector potential, the transistor 30 
is rendered non-conductive. Therefore the left channel output terminal 31A 
of the output display circuit 3 is not grounded and the left channel 
output level of the output amplifier section is indicated on the left side 
meter 1. 
Now, under the condition that the first and second switches 7 and 12 are 
maintained as shown in FIG. 2, if a person touches the tuning knob 8 for 
the tuning operation of the tuner section 4, then the state of the 
circuitry will be changed as indicated in FIG. 3. More specifically, as 
the potential at the detection output terminal 9D of the touch detection 
circuit 9a becomes high, the base potential of the transistor 21 is raised 
to a high level and therefore transistor 21 is rendered conductive. 
Therefore the base potential of the transistor 22 is lowered to a low 
level and accordingly the transistor 22 is rendered non-conductive, 
thereby interrupting the flow of current to the electromagnetic relay 6. 
As a result the movable contact 6c of the relay 6 is moved so as to be 
connected to the stationary contact 6b and the negative terminal 2b of the 
right side meter 2 is grounded. In other words, as the right channel 
output terminal 32A of the output display circuit 3 is grounded, the right 
channel output level of the output amplifier section is not displayed by 
the right side meter 2 and instead the input signal strength from the 
signal meter circuit 5 of the tuner section 4 is displayed thereby. Since 
under this condition the collector potential of the transistor 22 is high, 
the transistor 30 is rendered conductive so that both negative terminal 1b 
of the left side meter 1 and left channel output terminal 31A of the 
output display circuit 3 are grounded. Therefore the left channel output 
level of the output amplifier section is not indicated on the left side 
meter. 
If the movable contacts 7c and 12c of the first and second switches 7 and 
12 are connected to the stationary contacts 7a and 12a, respectively, as 
illustrated in FIG. 4, then the positive terminal 1a of the left side 
meter 1 is disconnected from the ground to render the left side meter 1 
inoperable, which does not indicate the left channel output of the output 
amplifier section. In addition, as the collector circuit of the transistor 
22 is opened, no current flows in the electromagnetic relay 6 regardless 
of the potential level at the detection output terminal 9D of the touch 
detection circuit 9a. Therefore the movable contact 6c of the 
electromagnetic relay 6 is maintained connected to the stationary contact 
6b thereof and accordingly the positive terminal 2a of the right side 
meter 2 is free from the ground potential and the negative terminal 2b is 
in turn grounded. Thus, similarly as in the case of FIG. 3, the right side 
meter 2 does not indicate the right channel output level of the output 
amplifier section but indicates the signal strength from the signal meter 
circuit 5 of the tuner section. Unlike the afore-described case, this 
condition is not affected by the potential level at the touch detection 
output terminal 9D. Therefore no change is observed whether the person 
touches the tuning knob 8 or not. In other words, by tripping the movable 
contacts 7c and 12c of the first and second switches 7 and 12 to the 
stationary contacts 7a and 12a, respectively, the right side meter 2 can 
be held to indicate the radio wave strength of the antenna input at all 
times. 
A second example of the invention is shown in FIG. 5 in which transistor 
means is employed in place of the above-described electromagnetic relay 6 
thereby providing a contact-less type display device. In FIGS. 5 and 1, 
like parts are designated by like reference numerals. Therefore the 
detailed descriptions of these like parts will be omitted. 
In FIG. 5, the output terminal 5C of the signal meter circuit 5 and the 
left and right channel output terminals 31A and 32A of the output display 
circuit 3 are connected to the respective terminals of the meters 1 and 2 
similarly as in the case of FIG. 1. The positive terminal of the left side 
meter 1, as in the case of FIG. 1, is connected to the stationary contact 
7b of the first switch 7. The negative terminal 1b of the left side meter 
1, the negative terminal 2b and the positive terminal 2a of the right side 
meter 2 are respectively connected to the collectors of the transistors 
27, 23 and 24 whose emitters are grounded. The left and right channels of 
the output display circuit 3 are connected to the collectors of 
transistors 28 and 29 whose emitters are grounded. The output terminal 9D 
of the touch detection circuit 9a is grounded through a capacitor 43 and 
is further connected through a resistor 44 to the base of a transistor 25 
whose emitter is grounded. The collector of the transistor 25 is connected 
to the power supply terminal 11 through a resistor 46 and is further 
connected through a resistor 48 to the base of a transistor 26 whose 
emitter is grounded. The collector of the transistor 25 is further 
connected through a resistor 51 to the base of the aforementioned 
transistor 24. The collector of the transistor 26 is connected through a 
resistor 47 to the power supply terminal 11 and is further connected 
through resistors 49, 50, 52 and 53 to the bases of the aforementioned 
transistors 27, 23, 28 and 29 respectively. Furthermore the collector of 
the transistor 25 is connected through a resistor 51 to the base of the 
transistor 24 and is further connected to the movable contact 12c of the 
second switch 12 operating in association with the first switch 7. Thus 
the collector of the transistor 25 is selectively connected to and 
disconnected from the ground by the operation of the switch 12. 
In the second example thus constituted, if the movable contacts 7c and 12c 
of the first and second switches 7 and 12 are connected to the stationary 
contacts 7b and 12b, respectively, under the condition that a person does 
not contact the tuning knob 8, the potential at the output terminal 9D of 
the touch detection circuit 9a is maintained at the low level to render 
the transistor 25 non-conductive. Therefore the collector of the 
transistor 25 is at a high potential and the transistors 26 and 24 are 
rendered conductive. Upon the transistors 26 becoming conductive, the 
transistors 27 and 23 are rendered non-conductive. In other words, the 
positive terminal 1a of the left side meter 1 is grounded through the 
first switch 7, while the negative terminal 1b is not grounded because of 
the transistor 27; the positive terminal 2a of the right side meter 2 is 
grounded through the transistor 24, while the negative terminal 2b is not 
grounded because of the transistor 23. Therefore, similarly as in the case 
of FIG. 2, the left side meter 1 indicates the left channel output of the 
output amplifier section and the right side meter 2 indicates the right 
channel output of the output amplifier section. 
In the case where the first and second switches 7 and 12 are maintained as 
described above and a person touches the tuning knob 8 for the tuning 
operation or the like, the output terminal 9D of the touch detection 
circuit 9a is maintained at a high potential to render the transistors 26 
and 24 non-conductive. Upon the transistor 26 becoming non-conductive, the 
transistors 27, 23, 28 and 29 are rendered conductive. Accordingly the 
negative terminal 1b of the left side meter 1 is grounded through the 
transistor 27 and the negative terminal 2b of the right side meter 2 is 
grounded through the transistor 23 while the positive terminal 2a of the 
right side meter 2 is brought into non-grounded state. Thus, similarly as 
in the case of FIG. 3, the left side meter 1 is rendered inoperable, while 
the right side meter 2 indicates the radio wave strength of the antenna 
input in the tuner section 4. In this operation, there may be the 
possibility that the left and right channel outputs of the output 
amplifier section applied to the negative terminals 1b and 2b of the 
meters 1 and 2 are not shorted completely to the ground potential due to 
the existence of the saturation resistances of the transistors 27 and 23 
so that a mixture of the amplifier output voltage signals to the meters 
thereby causing indication errors. However, since the left and right 
channel output signals in the output display circuit 3 are shorted to the 
ground through the lines 300a and 300b upon the transistors 28 and 29 
becoming conductive, such signal mixing can be positively prevented. 
When the movable contacts 7c and 12c of the first and second switches 7 and 
12 are connected to the stationary contacts 7a and 12a thereof 
respectively, the positive terminal 1a of the left side meter 1 becomes 
free from the ground, while the collector of the transistor 25 is 
grounded. Accordingly the transistors 26 and 24 are rendered 
non-conductive irrespective of the state of the transistors 25. When the 
transistors 26 becomes non-conductive, the transistors 27, 23, 28 and 29 
are rendered conductive. In this operation, the negative terminal 1b of 
the left side meter 1 is shorted to the ground through the transistor 27, 
while the negative terminal 2b of the right side meter 2 is shorted to the 
ground through the transistor 23 and its positive terminal 2a is brought 
into non-grounded state. Thus, similarly as in the case of FIG. 4, the 
left side meter 1 is rendered inoperable, while the right side meter 2 
indicates the radio wave strength of the antenna input of the tuner 
section 4 irrespective of whether a person touches the tuning knob 8 or 
not. 
In this instance also, the transistors 28 and 29 become conductive and 
therefore the output signals prior to logarithmic amplification in the 
output display circuit 3 are shorted to the ground. Thus, signal mixing in 
the output amplifier section can be prevented. 
In the above-described two examples, the left side meter 1 is employed for 
indicating only the left channel output level of the output amplifier 
section and the right side meter 2 is employed for indicating both the 
radio wave strength of the antenna input and the right channel output 
level of the output amplifier section. However, if necessary, the left 
side meter 1 may be employed concurrently with a tuning meter. It is, of 
course, possible to use the left side meter for the indication of the left 
channel output level and the radio wave strength of the antenna input. 
As is apparent from the above description, in this invention, a common 
single meter (or the right side meter in the examples) is employed as a 
signal meter indicating the radio wave strength of an antenna input and as 
an output level meter indicating the output level of the output amplifier 
section and the functions of the meter can be selected with the aid of the 
selecting means. Accordingly it is possible to reduce the number of meters 
provided in such electrical equipment as a receiver having a tuner section 
and an output amplifier section. As a result, the manufacturing cost of 
such electrical equipment can be reduced and the space required for the 
meters of the electrical equipment can be reduced, which leads to 
miniaturization of the electrical equipment and to increase in freedom of 
an ornamental design of the equipment, especially the front panel board 
thereof. In addition, in the case where the selecting means is constituted 
with the tuning knob as the touch responsive switch, the meter can be so 
designed that it functions as an output level meter during the normal 
operating period and it is automatically changed to function as a signal 
meter when a person touches the tuning knob for the tuning operation. This 
will eliminate the meter switching operation to realize simplified 
operation of the electrical equipment. 
While the invention has been described by reference to preferred 
embodiments thereof, it will be obvious to those skilled in the art that 
various changes and modifications may be made therein without departing 
from the invention and it is intended, therefore, to cover in the appended 
claims all such changes and modifications as fall within the true spirit 
and scope of the invention.