Apparatus for indicating telephone line state

A power saving type indicator apparatus for a telephone line. Existence of one of input signals on a telephone line is indicated by actuating an indicator and existence of the other is indicated by deactuating the indicator so that the consumption of electric power in indicating the presence and absence of the input signals is reduced substantially. Furthermore, in connection with another indicator apparatus which indicates the presence of the other input signal by actuating the indicator, indication of signals is so controlled as not to indicate the same signal by actuating two indicators at the same time. Thereby, a further saving of electric power in indicating such signals will be attained. By saving the electric power consumed in signal indication in this manner, a substantial extention of useful life of such a communications system is attained.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to apparatus for indicating the state of a 
telephone line by indication means, and more particularly the present 
invention is directed to means for effecting power saving in such 
indicator apparatus. 
2. Description of the Prior Art 
In the art there is well known a full-duplex data transmitting and 
receiving system on a telephone line employing acoustic couplers provided 
in terminal apparatus at both ends of the telephone line. FIG. 1 is a 
schematic block diagram useful in understanding the common procedure of 
data transmission and reception in such a full-duplex system. 
In FIG. 1, reference numerals 1 and 4 designate terminal equipment and 
numerals 2 and 3 denote acoustic couplers used for transmitting and 
receiving data. When some data has to be transmitted and received through 
the shown system, at first the calling subscriber originates a call 
directed to the called station by means of its telephone station and makes 
an arrangement by a voice communication. Then, the calling subscriber sets 
his or her handset on the acoustic coupler 2 and sets the calling-called 
switch to its "calling" position on the operation console of the coupler. 
On the other side, the called subscriber sets his or her handset on the 
acoustic coupler 3 and sets the switch to its "called" position. Upon a 
completion of the setting, a continuous signal having frequency f.sub.3 is 
transmitted to the acoustic coupler 2 from the acoustic coupler 3 over the 
telephone line. 
The acoustic couplers 2 and 3 have the same structure which is shown in 
detail in FIG. 2. A sound from the handset energizes a microphone 8 and is 
applied to a filter 6 through an amplifier 7. Thus, a received signal 
detection signal CD is obtained as an output from the filter 6. The signal 
CD is introduced into the terminal 1 or 4 to turn on the lamp L.sub.1 or 
L.sub.4 on the terminal. The received signal detection signal CD from the 
filter 6 is also applied to a modulator 11 to generate a continuous signal 
of frequency f.sub.1 or f.sub.3, which enters the acoustic coupler 3 or 2 
at the other station over the telephone line. 
As readily understood from the foregoing, the turning-on of lamps L.sub.1 
and L.sub.4 at both terminals 1 and 4 indicates that the communications 
system is prepared for start of a communication. Therefore, after the 
turning-on of the lamps at both stations, a communication can be started 
with a so-called frequency shift signal FS of frequencies f.sub.1 and 
f.sub.2 at the calling party and a frequency shift signal FS of f.sub.3 
and f.sub.4 at the called party. 
However, in the above process required for preparing the system for start 
of a communication, note should be taken of the fact that up to the end of 
the arrangement step, transmission of all the necessary information must 
be carried out solely with voice. This fact means that deaf-and-dumb 
people can never prepare the system for start of comunication. For such 
people, therefore, it has been proposed to provide the acoustic couplers 2 
and 3 with particular lamps L.sub.2 and L.sub.3 for indicating the state 
of a telephone line. In the known system for this purpose, the particular 
indicator lamps L.sub.2 and L.sub.3 are turned on and off in accordance 
with a ringing tone, busy tone, etc. In general, such communications 
system is designed to be portable so that a deaf-and-dumb person may carry 
it with him and in many cases there is used a battery as the power source 
for the portable system. As the indicator lamps there are usually used 
light emitting diodes (LEDs) or the like because of their high speed in 
response. However, use of such indicator lamps involves a large 
consumption of electric power. Therefore, the useful lifetime of the 
battery is shortened. This is a significant drawback of such communication 
system hitherto known. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the invention to provide indicator 
apparatus useful for the above-mentioned type of communications system 
which indicates an instant state of a telephone line by indicator means. 
It is another object of the invention to provide indicator apparatus which 
enables duplication of indication to be avoided in connection with another 
apparatus involved in the communications system, thereby saving electric 
power. 
It is a further object of the invention to provide indicator apparatus 
which enables the useful life of the communications system to be extended 
by reducing the power consumption in the apparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring first to FIG. 2 the operation of the acoustic coupler will be 
described in detail. 
As previously described, the microphone 8 receives sound from the telephone 
handset 15. The received sound signal is amplified by the amplifier 8 and 
then connected to filter 6 and differential amplifier 10. The filter 6 
passes only such signals having frequencies f.sub.1 and f.sub.2 at the 
calling station and those having frequencies of f.sub.3 and f.sub.4 at the 
called station. This change-over of the passing bands is effected in 
response to the above mentioned "calling-called" switch provided on the 
operation panel. The signal passed through the filter 6, namely frequency 
shift signal FS, is demodulated by a demodulator 5 to form a pulse signal, 
namely, a received signal RD which is applied to the terminal 1 or 4. On 
the other hand, from the signal applied to the differential amplifier 10 
only those signal components which are higher than a certain determined 
level are picked up to exclude noise or the like. The signal thus obtained 
from the differential amplifier 10 is applied to a driver 9 for lamp 
L.sub.2 or L.sub.3. Therefore, all the signals formed from the sound 
received by the microphone 8 and higher than the determined level turn the 
lamp L.sub.2 or L.sub.3 on. 
When data signal SD is applied to a modulator 11 from the terminal 1 or 4, 
it is modulated by the modulator into frequency shift signal FS of 
frequencies f.sub.1 and f.sub.2 at the calling station and that of 
frequencies f.sub.3 and f.sub.4 at the called station. After being 
amplified by the amplifier 12, the signal FS is converted into sound by 
the loudspeaker 13 and then sent over the telephone line through the 
telephone handset. 
Since the acoustic couplers 2 and 3 operate in the manner described above 
and the indicator lamps L.sub.1 and L.sub.2 in the terminals 1 and 4 are 
turned on in response to the generation of received signal detection 
signal CD, it is no longer necessary to indicate the detection of the 
received signal by turning the lamps L.sub.2 and L.sub.3 on in the 
couplers 2 and 3. Therefore, it is made possible to turn the lamps L.sub.2 
and L.sub.3 off by the received signal detection signal CD employing a 
circuit as shown in FIG. 3 for the purpose of power saving. Lamps L.sub.2 
and L.sub.3 become turned on only when, for example, a ringing tone or 
busy tone is generated from the telephone handset 15 before the output of 
received signal detection signal CD. 
The operation of the circuit shown in FIG. 3 will be discussed. 
A series of pulses obtained as an output signal from the differential 
amplifier 10 is introduced into the input terminal B of the circuit and 
then applied to the base electrode of transistor Tr2 through a connection 
circuit constituted by capacitor C1 and resistor R1 and through an 
integrator circuit. Since the transistor Tr2 is made conductive by this 
application of the pulse series, the lamp L.sub.2 or L.sub.3 receives a 
voltage V so that in turns on. The integrator circuit between the 
connection circuit C1, R1 and the base of transistor Tr2 comprises 
resistors R2, R3 and a capacitor C2 to transform the input voltage in the 
form of pulse into a DC voltage. By this conversion of voltage form, the 
brightness of light emitted from the light emitting diodes or the like 
constituting the lamps L.sub.2 and L.sub.3 is increased. 
The circuit shown in FIG. 3 further comprises transistor Tr1 the collector 
electrode of which is connected to the connection between the resistors R2 
and R3 contained in the integrator circuit mentioned above. With this 
arrangement, when a received signal detection signal CD is applied to the 
base of transistor Tr1 from the input terminal A through resistor R4, the 
transistor Tr1 is turned on and therefore the connection point between the 
resistors R2 and R3 assumes a position as if grounded through the 
transistor Tr1. In this position, the pulse series signal applied to the 
input terminal B can no longer reach the base of transistor Tr2 and 
therefore the display lamp L.sub.2 or L.sub.3 turns off. 
In this manner, according to the embodiment of the present invention, the 
indicator lamp L.sub.2 (L.sub.3) provided on the acoustic coupler for 
indicating the state of the telephone line is turned on only before the 
reception of a frequency shift signal FS, and turned off when the lamp 
L.sub.1 (L.sub.4) on the terminal is turned on by the reception of the 
signal FS. In other words, lamp L.sub.2 (L.sub.3) continues to be on only 
during the time of signals other than data signal being received. Thus, 
duplication of indication of the state of the telephone line by both of 
lamps L.sub.1 (L.sub.4) and L.sub.2 (L.sub.3) is avoided, which in turn 
prevents the electric power from being wastefully consumed by the 
indicator lamps. Therefore, according to the invention, the useful life of 
a battery mounted, for example, in the acoustic coupler circuitry will be 
expanded substantially as compared with the prior art system. 
While a preferred embodiment of the invention has been described using 
specific terms, such description is for illustrative purpose only, and it 
is to be understood that changes and modifications may be made without 
departing from the spirit and scope of the following claims.