Power-saving device for a cable-information receiving/transmitting apparatus

A power saving device for a cable-information receiving/transmitting apparatus, for example, a facsimile machine or a computer. The device allows no AC power to be supplied to the apparatus during the stand-by time thereof. When ring signals arrives, or when the user picks up the handpiece of a telephone set attached to the apparatus, the Ac power supply is started. When the reception or transmission of information is over, the Ac supply is cut off after a predetermined time, thus allowing the after-reception work or after-transmission work to be finished. This device mainly comprises a relay (1) [or a SCR (1a)], a transistor (T), an optical coupler (3) [preferably consisting of a LED (31) and a CdS photoresistor (32)], and a tapping/rectifying circuit (2). It can totally eliminate the undeserved waste due to the consumption during the stand-by time.

The present invention relates to a power-saving device for a 
cable-information receiving/transmitting apparatus, in particular for a 
facsimile machine, to minimize the power consumption of the latter by 
eliminating the consumption during its stand-by time without thereby 
affecting the normal functions thereof. 
Such apparatus, for example, a facsimile machine or a computer, must always 
be kept in stand-by (or ready-to-work) state so as to be prepared for the 
sporadic arrivals of information without missing any of them. (Here the 
term "stand-by" means that the power line of the apparatus is connected to 
a power supply, but no information is being transmitted or received.) To 
keep the apparatus in stand-by state, a considerable amount of electric 
power is consumed (though not so much as what is consumed during the 
reception or transmission of information, when all parts of the apparatus 
are working). As a result, the total waste of power during the stand-by 
time is noticeable. For the currently used models of facsimile machines, 
the consumption is about 15-50W. 
Accordingly, it is the main object of this invention to provide a 
power-saving device which minimizes the AC power consumption of a 
cable-information receiving/transmitting apparatus (in particular a 
facsimile machine) by totally eliminating the AC power consumption during 
the stand-by time. 
To save the AC power consumption, it is necessary to start the AC power 
supply of a local facsimile machine or cut off it in the correct moment. 
In other words, in the case of reception of information from another (a 
remote) facsimile machine, the AC power supply must be started during the 
arrival of information, and be cut off shortly after the reception of 
information is over. In the case of transmission of information to another 
(a remote) facsimile machine, the AC power must be started when the user 
does the first step of transmission procedure (for example, when he picks 
up the handpiece of the telephone set attached to the local facsimile 
machine), and be cut off shortly after the transmission of information is 
over. (Note: the power supply should not be cut off immediately, but 
shortly after the end of the reception or transmission of information. The 
reason will be explained later.) 
To achieve this object, a power saving device must be responsive to various 
states. In other words, in the case of the reception of information, the 
device must be responsive to the arrival of an incoming transmission 
(Note: here we use the term "incoming transmission" instead of 
"information" because the central office always sends "ring signals" in 
advance before sending information to the local facsimile machine.) and 
the end of the reception of information. On the other hand, in the case of 
the transmission of information, the device must be responsive to the 
picking-up of the handpiece and the end of the transmission of 
information. 
A known device was developed to reduce the AC power consumption of a 
facsimile machine during its stand-by stage. But it is not altogether 
satisfactory because it only "reduces" and does not "totally eliminate" 
the AC power consumption during the stand-by time. Before explaining the 
reason of its imperfection, let's look at some well-known facts in 
facsimile transmission. 
When a local facsimile machine X is receiving information from another (a 
remote) facsimile machine Y, the central office will send ring signals to 
X in advance if X is in ON-HOOK state. The state of X is immediately (and 
automatically) changed from ON-HOOK to OFF-HOOK state upon reception of 
the ring signals. Then the central will perceive the OFF-HOOK state of X 
and sends information from Y to X. When the reception of information is 
over, the facsimile machine immediately returns to ON-HOOK state. If X is 
to transmit information to Y, when the user picks up the handpiece of X, 
the state of X immediately changes from ON-HOOK to OFF-HOOK. Once the 
transmission of information is over, the state of X immediate returns to 
ON-HOOK state. 
The known device uses a known "off-hook detector" to respond to the various 
states. The OFF-HOOK detector is always detecting the state of the local 
facsimile machine provided with this known device. Also, as a matter of 
fact, the ON/OFF of the AC power source is controlled by a relay. 
Referring to FIG. 1, the known device comprises, apart from the OFF-HOOK 
detector and relay, a controlling circuit interposed therebetween. The 
controlling circuit receives the output signal from the OFF-HOOK detector 
and controls the ON/OFF of the relay. During the arrival of an incoming 
transmission, the OFF-HOOK detector will perceive the OFF-HOOK state of 
the facsimile machine and gives corresponding signal to the controlling 
circuit, which in turn, switches on the relay to start the AC power 
supply. When the reception of information is over, the OFF-HOOK detector 
immediately perceives the ON-HOOK state of the local facsimile machine, 
and gives a corresponding signal to the controlling circuit to switch off 
the relay, and therefore the AC power supply after a predetermined time. 
Likewise, when the user picks up the handpiece of the local facsimile 
machine, the OFF-HOOK detector immediately perceives the OFF-HOOK state 
thereof, and the AC power supply is started. When the transmission of 
information is over, the OFF-HOOK detector immediately perceives the 
ON-HOOK state, so the AC power supply is cut off after a predetermined 
time. 
Thus it is the OFF-HOOK detector that enables the AC power supply to be 
started or cut off in the correct moments. But it is also the OFF-HOOK 
detector that results in the imperfection of the known device. The reason 
is simple. As stated before, the OFF-HOOK detector must "always" detect 
the state of the facsimile machine. Since the OFF-HOOK detector itself 
needs a basic AC power to drive its circuit, it is always consuming AC 
power, even in the stand-by time. As a result, the device can only reduce, 
but not totally eliminate the AC power consumption during the stand-by 
time. 
The present invention is directed to totally eliminating the AC power 
consumption during the stand-by time. 
As a matter of fact, on ON/OFF of AC power is control by a relay, as in the 
aforesaid device, or alternatively, by a thyristor (preferably a SCR). 
Both are well known elements in controlling the ON/OFF of AC power. 
To activate the relay or the SCR, and also to maintain it in ON state, a DC 
current or a positive bias must be applied (and then kept on being 
applied) to the coil of the relay or to the gate of the SCR during (and 
only during) the working state (and not during the stand-by stage) of the 
local facsimile machine. In the known device, the controlling circuit 
supplies the requisite DC current to the relay when the OFF-HOOK detector 
perceives the OFF-HOOK state of the local facsimile machine, and the 
required DC is interrupted short after the detection of the ON-HOOK state 
thereof. Since the OFF-HOOK detector consumes AC power supply, this 
invention involves no OFF-HOOK detector, and provides a circuit which 
consumes no AC power during the stand-by time. 
Once the relay or the SCR is activated and the AC power supply is thus 
started, it would be very easy to "tap" an AC current from the AC output 
of the relay or the SCR and to rectify the tapped AC current into a DC 
current, then apply the DC current to the coil of the relay or the gate of 
the SCR to keep the relay or the SCR in ON state. But the problems are, 
how to activate the relay or the SCR when the relay or the SCR is in OFF 
state and no such current is available, and how to deactivate the relay or 
the SCR when the relay or the SCR is in ON state and a current is 
continuously applied to the coil of the relay or to the gate or the SCR? 
To solve this problem, the device according to this invention utilizes a 
transistor, of which the collector-emitter (CE) path is in serial 
connection with the coil of the relay or connected to the gate of the SCR, 
and of which the base is in serial connection with a 
transistor-controlling element which is activated when the facsimile 
machine becomes OFF-HOOK and which becomes inactive immediately when the 
facsimile machine becomes ON-HOOK. Thus when the facsimile machine 
receives ring signals from the central office or when its handpiece is 
picked up, the transistor-controlling element is activated, and a current 
can pass through the transistor-controlling element and be applied to the 
base of the transistor, which is then conducted to allow a further current 
to flow through the coil of the relay and the transistor or through the 
transistor and be applied to the gate of the SCR, thus switching on the AC 
power supply. It is noteworthy that before the starting of the AC power 
supply, the required current (which flows through the 
transistor-controlling element and applied to the base of transistor, and 
which flows through the coil and the CE path, or through the CE path to 
the gate of the SCR) still has to be taken from the AC power supply. Since 
this current is taken before the activation of the relay or SCR, it must 
be taken from an upstream spot of the relay or SCR (i.e. in front of the 
AC input of the relay or the A terminal of the SCR) and not from a 
downstream spot thereof (i.e. behind the AC output of the relay or the K 
terminal of the SCR), so that the current can be taken even if the relay 
or SCR is in inactive state. To take such a current from the AC power 
supply and rectify it into a useful DC current, a tapping/rectifying 
circuit is provided. 
In stand-by state, the transistor-controlling element is not conducted, 
thus this current cannot flow through the transistor-controlling element 
to actuate the transistor, and therefore the relay or SCR. Once the 
transistor-controlling element becomes conducted, this current can flow 
from the tapping/rectifying circuit through the transistor-controlling 
element and applied to the base of the transistor, thus activating the 
latter. Then the tapped current can further flow through the coil of the 
relay (or be applied to the gate of the SCR) and keep the relay (or SCR) 
in activated state. This current keeps on supplying the 
transistor-controlling element and the transistor as well as the coil of 
the relay (or the gate of the SCR) until the transistor-controlling 
element becomes inactive again. 
The transistor-controlling element itself is further controlled by a 
transistor-controlling-element controlling element (hereinafter referred 
to as TCE-controlling element) which is only accessible by the cable 
current but not by the tapped current. Thus, once the reception or 
transmission of information is over, the TCE-controlling element itself 
can become inactive due to the change in the cable despite the fact that 
the tapped and rectified current is still supplying the transistor and the 
transistor-controlling element. The inactivation of the TCE-controlling 
element causes the transistor-controlling element to become 
non-conductive, thus the tapped and rectified current can no longer be 
supplied to the base of the transistor, which therefore becomes 
non-conductive too, thus the relay or SCR is inactivated. In so doing, the 
aforesaid problems are solved. 
Practically, the aforesaid TCE-controlling element and the 
transistor-controlling element are respectively an optical emitter and an 
optical receiver which, together make an optical coupler. Preferably the 
TCE-controlling is a LED (though it can also be a bulb), and the 
transistor-controlling element is a CDS photoresistor (though a 
photodiode, a photo-transistor or a photocell can also be used). It is 
found that only an optical coupler can achieve satisfactory control of the 
AC power supply. If we used other elements to replace the optical coupler 
(for example, a reed or a DIAC-TRIAC set) the result will be inferior. 
It is noteworthy that in stand-by state, the connection between the central 
office and the local facsimile machine (now in ON-HOOK state) is not 
built. Once the facsimile machine becomes OFF-HOOK, the connection will be 
built and information can be transmitted from the central office to the 
local facsimile machine or vise versa. In other words, the connection is 
built in two cases: When the user picks up the handpiece of the local 
facsimile machine, or when the local facsimile machine receives ring 
signals from the central office (Both cases lead to the OFF-HOOK state of 
the facsimile machine.). Once the connection between the local facsimile 
machine and the central office is built, the LED can be supplied by the 
current from the cable, thus maintaining all related elements (the CDS 
photoresistor the transistor, and the relay or SCR) in active state. 
In stand-by state, the potential at the cable terminal of a facsimile 
machine is 48 V. During the presence of ring signals, the potential 
slightly increases (to about 56 V) and the polarity is inverted. Then 
during the reception of information, the polarity is recovered, but the 
potential falls to 6-7 V. It is not until the reception is over that the 
potential recovers to 48 V. This phenomenon is well-known to anyone 
skilled in the field of telecommunication. 
In order to ensure the cable current to flow always in the forward 
direction of the LED, a rectifying circuit is provided. (This rectifying 
circuit is not to be confused with the aforesaid tapping/rectifying 
circuit!) If a bulb, which has no polarity is used instead of a LED, the 
rectifying circuit is not necessary. But a LED is more preferred. 
Therefore, the power-saving device of this invention basically comprises an 
AC-controlling element (a relay or a thyristor), a tapping/rectifying 
circuit, a transistor, an optical coupler (preferably consisting of a LED 
and a CdS-photoresistor), and, if necessary, a rectifying circuit. 
Theoretically, the AC power supply can be immediately cut off after the end 
of a reception or a transmission of information, but in actual use, this 
is not the case. A facsimile machine still has some after-reception work 
or after-transmission work to do after the reception or transmission of 
information. For example, it must give a confirmation of safe receipt to 
the remote facsimile machine which sent information to it, or make sure if 
the transmitted information is safely received by the remote facsimile 
machine. The necessary work is generally finished within 20 seconds and 
requires AC power. For this reason, the AC power cannot be immediately cut 
off when the reception or transmission of information is over. For this 
purpose, a capacitor is provided to delay the switching-off of the AC 
power supply. Practically, the capacitor is in parallel connection with 
the coil of the relay or the BE route of the transistor (when SCR is 
used). When the reception or transmission of information is over, the 
capactor starts to discharge until its potential reaches a lower value. 
The discharge causes a current to flow through the coil of the relay or to 
the gate of the SCR. Thus the relay or the SCR can remain in ON state for 
a predetermined time, which depends on the capacitance of the capacitor. 
The capacitor must have a definite polarity, and is preferably an 
eletrolytic capacitor. The reason will be explained later. 
It is preferred that the device of this invention can be directly applied 
to a facsimile machine without modifying the structure thereof. 
Practically the device has a socket into which the plug of the power line 
of a facsimile machine can be inserted, and two (or three) pins defining a 
plug to insert into a socket of a power source. Since the device also 
involves the transmitted signals in the cable, it must respectively be 
connected to a cable from the central office and the cable of the 
facsimile machine. Therefore, this device also has a first jack (or first 
terminal set) to connect with the cable from the central office (telephone 
cable) and a second jack (or second terminal set) to connect with the 
cable of the facsimile machine. Thus, when one applies this device to an 
ordinary facsimile machine, one only needs to connect the telephone cable 
and the cable of the facsimile machine respectly to the first and the 
second jacks, and then insert the plug of the power line of the facsimile 
machine into the socket of the device and insert the pins of the device 
into a socket of an AC power source. In so doing, a conventional facsimile 
machine can be easily converted into a power-saving facsimile machine 
without modification of its structure. 
This invention will be better understood when read in connection with the 
drawing, in which three different practical embodiments are shown. In the 
first and second embodiments, a relay is used, while in the third 
embodiment, a SCR is used to control the AC power supply. In the first and 
third embodiments, the power-supply-side circuit and the cable-side 
circuit are isolated from each other, but in the second embodiments, they 
are connected with each other. In these embodiments, like references 
designate like elements.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
Referring to FIG. 2, the present invention is practically made in form of 
an adapter A which has two pins defining a power plug PP to insert into a 
socket PS of AC power supply, a socket FS for the plug FP of a power line 
of an ordinary facsimile machine (not shown), a first jack (or terminal 
set) J1 for a cable CC to the central office, a second jack (or terminal 
set) J2 for a cable FC of the facsimile machine. An indicator light I can 
be provided to indicate whether or not the AC power supply is switched on. 
Two switches SW1, SW2 can be optionally provided. Their functions will be 
stated later. 
It is to be announced that in the first and the third embodiments, the 
polarity of the cable terminals is of no importance. In other words, the 
user need not carefully connect the positive and negative terminals of the 
jack J1 and jack J2 to the corresponding positive and negative terminals 
of the cable terminals of the cables CC and FC. But in the case of the 
second embodiment, the terminals of like polarity must be connected with 
each other. The reason will be explained later. 
Referring to FIG. 3, the device A basically comprises, as stated before, a 
relay 1, a tapping/rectifying circuit 2 with four diodes D21, D22, D23, 
D24, a transistor T, an optical coupler 3 including a LED 31 and a CdS 
photoresistor 32, a rectifying circuit 4 including four diodes D41, D42, 
D43, and D44, and a capacitor C1. As stated hereinbefore, in this 
embodiment, the power-supply-side circuit CKT1 and the cable-side circuit 
CKT2 are isolated from each other. Their connection is only via the 
LED-CDS optical coupling. 
The function of the device in various states of the facsimile machine (i.e. 
during the reception and transmission of information, or used as a 
photocopier) is described in the following: 
A. RECEPTION OF INFORMATION 
In stand-by state, the connection between the facsimile machine and the 
central office is not built, thus the cable-side circuit CKT2 is not 
supplied by the cable CC, and the LED, [and therefore, the CDS 
photoresistor 32 resistor, the transistor T, and the relay 1] are all in 
inactive state. Thus no AC power is supplied to the facsimile machine. The 
potential at the terminals of jack J1 is 48 V. 
If a remote facsimile machine dials the number of the local facsimile 
machine, the central office, which is always detecting the state of all 
the telephones and facsimile machines in its territory, will make 
different response depending on the state of the local facsimila machine. 
If the local facsimile machine is found to be busy (i.e. it is receiving 
or transmitting information), of course its power supply must have been 
started. Therefore the equipped local facsimile machine makes no 
difference with an ordinary facsimile machine without the device of this 
invention in this busy state, and a statement is not necessary. 
If the local facsimile machine is not busy (i.e. in ON-HOOK state) the 
central office will send ring signals to the local facsimile machine, and 
the polarity of the terminals of jack J1 is inverted. As stated before, in 
this embodiment the polarity of the terminals of jack J1 is no importance, 
thus the ring signals may travel from either terminal of jack J1 via the 
rectifying circuit 4 to point P11 and then through the LED and diode D43 
to the facsimile machine. When the ring signal passes through the LED, 31 
the latter lights up, thus activating the CDS photo-sensitive resistor 32. 
Once the CdS photoresistor 32 becomes conductive, a tapped current can flow 
through diode D21, switch SW2 [if this switch is provided], the coil 11 of 
relay 1, and the CdS photoresistor 32 and applied to the base of the 
transistor T, thus actuating the transistor T. As a result, the tapped 
current can also flow through the CE path of the transistor T, and 
therefore the coil 11 of relay 1, thus starting the AC power supply. 
After actuating the relay, the tapped current keeps on flowing from the 
tapping/rectifying circuit 2 and to the CdS photoresistor 32 and the 
transistor T to provide the required current flowing through the coil 11 
to keep the relay 1 in activated state. The tapped current occupies only a 
negligible portion of the AC power, which is mostly supplied via the AC 
output of the relay to the facsimile machine. 
When ring signals enters the facsimile machine, the latter immediately 
changes from ON-HOOK to OFF-HOOK state, which is immediately perceived by 
the central office. Thus the central office stops sending out ring 
signals, and builds up its connection with the local facsimile machine. 
Now information can be transmitted from the remote facsimile machine to 
the local facsimile machine. Meanwhile the polarity of the terminals of 
jack J1 recovers, and the potential falls to 6-7 volts. Since the 
connection between the central office and the facsimile machine has been 
built, the cable-side circuit can be supplied via the cable CC to maintain 
the LED in activated state. Now information can travel from J1 directly to 
J2 or through the rectifying circuit to J2 and enter the facsimile 
machine, depending on the polarity of the two terminals of J1. 
When the reception is over, the facsimile machine becomes ON-HOOK again, 
and the connection between the central office and the facsimile machine is 
broken. The potential at the jack J1 recovers to 48 V. Now the cable-side 
circuit is no longer supplied via the cable, so the LED 31 immediately 
becomes inactive. the inactivation of LED results in the inactivation of 
the CdS photoresistor 32 and the transistor T. Thanks to the capacitor C1, 
which starts to discharge at this moment to delay the switching-off of the 
relay for 40-50 seconds, thus allowing the after-reception work to be 
finished. 
In stand-by state, the potential difference between the two electrodes of 
the capacitor C1 is 0 volts, thus no current can flow from its positive 
electrode to its negative electrode, and the relay remains inactive. Once 
the relay is activated, the power-supply side circuit CKT1 is supplied by 
the tapped and rectified current which has a voltage of 110 V or 220 V. 
Thus the capacitor C1 is charged by the tapped current to 110 V or 220 V. 
At his moment, the potential in the circuit CKT1 is also 110 V or 220 V, 
hence no charge can flow from the positive electrode of to the negative 
electrode of the capacitor C1. When the reception of information is over, 
the LED, CdS photoresistor 32 and transistor T become inactive, and the 
potential in the circuit CKT1 falls to 0 volts, thus allowing a current to 
flow from the positive electrode of capacitor C1 through coil 11 to the 
negative electrode thereof. The potential difference between the two 
electrode gradually falls. When the potential difference falls below a 
value (for example, about thirty volts), the current becomes too weak to 
keep the relay in active state, so the AC power supply is cut off. But the 
capacitor C1 still continues to discharge until the potential difference 
between its two electrodes approaches 0 volts. 
B. TRANSMISSION OF INFORMATION 
If the user picks up the handpiece, the connection between the local 
facsimile machine and the central office is built, thus the cable-side 
circuit CKT2 is supplied via the cable, and the LED 31 is actuated, which 
in turn, causes a chain reaction of the activation of the CdS 
photoresistor 32, transistor T, and raley 1, thus the AC power supply is 
started. Meanwhile the local facsimile machine changes from ON-HOOK to 
OFF-HOOK state. When the user dials the fax number of the remote facsimile 
machine, if the latter is not busy, the central office will build up the 
connection between the central office and the remote facsimile machine. 
Now, information can be transmitted from the local facsimile machine via 
the central office to the remote facsimile machine. The information may 
travel from jack J2 directly to jack J1 or through the rectifying circuit 
4 to jack J1, depending on the polarity of the terminals of J2. When the 
transmission of information is over, the state of the facsimile machine 
changes from OFF-HOOK back to ON-HOOK, and the central office will 
perceive the ON-HOOK state of the local facsimile machine, and the 
connection between the local facsimile machine and the central office is 
broken. Now the cable-side circuit is no longer supplied via the cable, 
and the LED becomes inactive. This results in the inactivation of the CdS 
photoresistors 32 and the transistor. Here too, thanks to the capacitor 
C1, the inactivation of the relay is delayed by 40-50 seconds so that the 
facsimile machine can still be energized to finish the after-transmission 
work. 
C. USED AS A PHOTOCOPIER 
Some of the models of facsimile machines can be used as a photocopier for 
xeroxographic duplication purpose. In such case, a facsimile machine 
provided with this invention can only be supplied with AC power when the 
user picks up the handpiece and keeps it away from the hook during the 
duplication. This is not desirable. In order to start the power supply 
without picking up the handpiece, the best way is to "short-circuit" the 
power-supply-side circuit CKT1, so that a current can pass through the 
coil 11 without passing through the transistor T. In so doing, the power 
supply is always in switched-on state regardless of the state of the 
trasistor T. For this purpose, a normally open switch SW1, which is in 
parallel connection with the transistor T, is provided. When the local 
facsimile machine is used as a photocopier, the user only need to switch 
SW1 to its ON (close) position, and the power supply will be started. 
Now the functions of the major elements of the device has been described in 
details. Some minor elements of the first embodiment are described in the 
following. 
As a matter of fact, a resistor R1 is connected in series with the LED 31 
to protect the latter. 
To further protect the LED, another resistor R2 is connected in parallel to 
limit the current flowing through the LED 31. 
To facilitate information (which are alternating signals) to pass through 
the cable side circuit CKT2, a capacitor C2 is provided, so that 
information can travel from J1 to J2 or vise versa directly or merely via 
the capacitor C2 without passing through the more difficult resistors R1, 
R2, LED and reactifying circuit 4, thus the loss in intensity of the 
signals in the rectifying circuit can be minimized. The capacitor C2 is 
used to provide a shunt for the signals, not for storage purpose. Since 
the polarity of the terminals of jack J1 is inverted during the presence 
of ring signals, the capacitor C2 should not have definite polarity. 
In contrast, the capacitor C1 is used for storage purpose. Thus it is 
should have a definite polarity and is preferably an electrolytic 
capacitor (Since in the case of electrolytic the required capacitance can 
be smaller). But this is not its exclusive function. The capacitor C1 can 
also stabilize the relay during the presence of ring signals. When ring 
signals arrives, the power-supply-side circuit is not yet supplied by a 
tapped rectified current, and thus the voltage therein is not stable. 
Since the ring signals are pulses, which may cause the pulsative 
activation of the LED, and therefore the pulsative activation of the CdS 
photoresistor, of the transistor and of the relay, thus resulting in the 
"rattling" of the relay. With the capacitor C1 the undesired pulsation can 
be absorbed. To adapt to different voltages of AC power source (for 
example 110 V or 220 V), there is provided a selector switch SW2 in the 
power-supply-side circuit CKT1. 
The functions of the first embodiment has been explained in detailes. The 
second embodiment will be further discussed in he following. 
Referring to FIG. 4, like the first embodiment, this variants also 
comprises the major elements such as a relay 1, tapping/rectify circuit 
2', a transistor T an optical coupler 3 consisting of a LED 31 and a CdS 
photoresistor 32, and a capacitor C1. Apart from the major elements, this 
variant also comprises like minor elements such as resistors R1 and R2, 
switches SW1 and SW2, a rectifying circuit 4' and a capacitor C2. Since 
the functions of all these elements are the same as or similar to that in 
the first embodiment, their detailed description is not necessary. The 
function of tapping/rectifying circuit 2' is similar to that of the 
tapping circuit 2 in FIG. 3. Likewise, the function of the rectifying 
circuit 4' is similar to that of the rectifying circuit 4 in FIG. 3 . But 
in this embodiment, the cable-side circuit and the power-supply-side 
circuit are not isolated (The reason will be explained later). Therefore 
it is necessary to ensure that the tapped current cannot get access to the 
LED. For this purpose a second rectifying circuit 5 is provided. But this 
is not the only function of the second rectifying circuit 5. The reason 
will be explained later. 
In view of a fact that in some remote areas, the ring signals may be too 
weak and may be insufficient to activate the LED 32, an auxiliary circuit 
comprising a diode D3 and resistor R3 is provided. Thus in the presence of 
ring signals, a portion of the ring signals can flow through this 
auxiliary circuit and directly applied to the base of the transistor. 
Thus, even through the ring signals applied to the LED is not sufficient 
to light it up, the transistor T can still be ensured to become 
conductive. 
In the first embodiment the tapped current is directly applied to the coil 
11, CdS photoresistor 32 and transistor T without transformation. Hence 
the voltage of the tapped current is alo 110 V or 220 V. Accordingly, the 
elements 11, 32 and T must be able to withstand such high voltage, thus 
necessitating a relatively high cost. In the second embodiment, a 
transformer 6 is provided to reduce the voltage of the tapped current to 
48 V, so that the required specification of these elments 11, 32 and T is 
not so critical, and the cost of production can be reduced. 
The use of a transformer causes another problem. It is well known that even 
if the second winding of a transformer is open-circuit, if its primary 
winding is close-circuit, a certain consumption of power is still 
inevitable. For this reason, the primary circuit of the transformer must 
be connected to the relay and kept normally open. In so doing, the 
consumption of the primary winding of the transformer during stand-by-time 
is avoided. 
But another problem arises. In the first embodiment, the required current 
to drive the elements 32, T and 1 is taken from the AC power source. If 
even the primary circuit of the transformer is open, such a current will 
not be available. 
To solve this problem, a third capacitor C3 is provided which provides a 
current to drive these elements 32, T and 1, in the early stage of a 
working cycle (i.e. during the appearance of ring signals, or when the 
user picks up the handpiece). Once the relay is activated, a current can 
be tapped from the transformer 6 via the tapping/reactifying current to 
drive these element 32, T and 1, so the capacitor C3 no longer need to 
supply this current. 
The capacitor C3 must have a definite polarity to ensure the current to 
flow in the forward direction of the transistor T. It is preferably an 
electrolytic capacitor. The reason is the same as why the capacitor C1 is 
preferably an electrolytic capacitor. 
It is necessary to allow the current from the cable CC to flow to the 
capacitor C3 in definite direction so as not to counterbalance the stored 
charge thereof during the inversion of the polarity at the terminals JR1. 
JT1. This avoidance is also achieved by the second rectifying circuit 5. 
When the device is connected to the facsimile machine, a tlephone cable and 
a power supply, the capacitor C3 is charged from 0 to 48 V by the 48 V 
potential at the terminals R1, JT1 and then always kept at this value. The 
charging route in stand-by state is as follows: from terminal JR1 via 
diodes D51, resistor R4 (of which the function will be stated later) to 
the capacitor C3 and then via diode D54 to terminal JT1. 
In this embodiment, ring signals can only reach the transistor from 
terminal JT1, but not from terminal JR1. Therefore it is necessary to 
correctly connect the terminals R1, JT1 to the current terminals of the 
cable CC of like polarity. 
Since the capacitor C3 must be charged by the cable, it must be connected 
to the cable-side circuit. Also, since capacitor C3 is used to supply the 
elements 32, T and 1, it must be connected to the power-supply-side 
circuit. For this reason, the cable-side circuit and power-supply-side 
circuit may not be isolated with each other. 
Therefore the second embodiment comprises a transformer 6, a second 
reactifying circuit 5 and a third capacitor C3 [and probably also an 
auxiliary circuit D3, R3] which are absent in the first embodiment. 
In stand-by time, the polarity at the terminals of jack J1 is JR1 (+) and 
JT1 (-), and the potential is 48 V. When ring signals arrives, the 
polarity is inverted to JR1 (-) and JT1 (+). The ring signals can travel 
from JT1 to the LED 31 and the elements 32, T and 1. But we cannot utilize 
the ring signals to drive the elements 32, T and 1 without using the 
capacitor C3. If we do so, a considerable portion of the ring signals will 
be consumed by the element 32, T and 1 and the remaining ring signals 
passing through the LED and entering the facsimile machine may become too 
weak to carry out their normal task (to light up the LED and to change the 
facsimile machine from ON-HOOK to OFF-HOOK). 
When the user picks up the handpiece, the connection between the central 
office and facsimile machine is built, and the potential at the terminals 
JR1, JT1 falls to 6-7 volts. (It is not until the transmission is over 
that the potential recovers to 48 V.) Though at this moment, the circuit 
can be supplied via the cable, the 6-7 V voltage is only enough to 
activate the LED (as it is in the first embodiment), but far from 
sufficient to drive the more difficult elements 32, T and 1. Therefore, we 
once more understand that the capacitor C3 is indispensable in the second 
embodiment. 
The operation of the second embodiment in various conditions is stated in 
the following. 
A. RECEPTION OF INFORMATION 
When ring signals arrives, the polarity of terminals JR1, JT1 is inverted. 
The ring signals can travel from JT1 via points P1, P2 to point P3. From 
here they can either travel via the auxiliary circuit D3, R3 and directly 
applied to the base of the transistor T to actuate it, or travel from 
point P4 via one of the following three routes to point P5: firstly, via 
resistor R1, LED 31 and diode D41'; secondly, via resistor R2, and diode 
D41'; and thirdly, simply via capacitor C2. Then the ring signals enter 
the facsimile machine from terminal JT2 and leaves the facsimile machine 
from terminal JR2 and return to the terminal JR1, thus finishing a loop. 
As the ring signals pass through LED 31, the LED 31 and therefore the 
elements 32, T are activated. Thus a current can flow from the positive 
electrode capacitor C3 through the coil 11 and the transistor and back to 
its negative electrode. Therefore the relay 1 is activated. Now a current 
can be tapped from the secondary winding of transformer 6 through the 
tapping/rectifying circuit 2' to supply the elements 32, T and 1. The 
current flows from the secondary winding of transformer 6 via diode D61 or 
diode D62 via a diode D5, coil 11 and then either via CdS photoresistor 32 
and be applied to the base of transistor C or through the CE path of the 
transistor C and back to the secondary winding. Therefore it is obvious 
that the capacitor C3 only provide the current in the early stage of a 
working cycle. 
When the facsimile machine receive the ring signals, it immediately changes 
from ON-HOOK to OFF-HOOK. Thus the central office will buil its connection 
with the local facsimile machine. Now the potential at the terminals JR1, 
JT1 falls to 6-7 V, and the polarity thereof recovers to JR1 (+) and JT1 
(-). The 6-7 V voltage is still enough to keep the LED 31 in active state. 
The current (and alos the information) travels from JR1 to JR2 and enters 
the facsimile machine, and then travels through JT2, P5 to point P6 either 
via diode D42' or via capacitor C2 and diode D44', and then travels from 
point 7 to point 8 either via R1 and LED 31 or via resistor R2, and 
finally travels via diode D34' and points P4, P3, P2 and P1 back to 
terminal JT1. Thus the LED is kept active during the reception of 
information. 
When the reception of information is over, the potential at the terminals 
JR1, JT1 recovers to 48 V, and the connection between the central office 
and the facsimile machine is broken, thus no current flows through the LED 
31. As a result, the elements 32 and T become inactive. But the relay 1 is 
switched off 40-50 seconds later because of the discharging of the 
capacitor C1. 
B. TRANSMISSION OF INFORMATION 
When the user picks up the handpiece, the connection between the central 
office and the local fascimile machine is immediately built, and the LED 
can be supplied via the cable. Meanwhile, the voltage at the terminals 
JR1, JT1 falls to 6-7 V. The activation of the LED results the activation 
of the CdS photoresistor 32, thus a current can flow from the capacitor C3 
through the coil 11 and the CdS photoresistor resistor 32 to the base of 
transistor T to actuate the transistor, and then directly through the coil 
11 and the CE path of the transistor T back to the capacitor C3, thus 
starting the AC power supply. Once the AC power supply is started, a 
current can be tapped from the transformer 6 via the tappin/rectifying 
circuit 2' to drive these elements 32, T and 1. 
The path of the current that energizes the LED is the same as the route 
which information travels during the aforesaid reception of the 
information. 
After the user has dialed the fax number of the remote facsimile machine, 
if the latter is not busy, information can be transmitted from JR2 via the 
same route as the aforesaid path to JT1, and then to the remote facsimile 
machine. 
When the trasmission of information is over, the potential at the terminals 
JR1, JT1 recovers to 48 V, and the connection between the central office 
and the facsimile machine is broken, thus no current flows through the LED 
31. As a result, the elements 32 and T become inactive. But the relay 1 
becomes inactive 40-50 seconds later because of the capacitor C1. 
C. USED AS A PHOTOCOPIER 
Like the first embodiment, the second embodiment also has a normally-open 
switch SW1 for like purpose. When the switch SW1 is switched to its close 
position, a current can flow from the capacitor C3 through the coil 11 and 
switch SW1 without passing the transistor T, thus the AC power supply can 
be started. 
The major functions of the second embodiment has been described 
hereinbefore. The functions of its some minor elements will be explained 
in the following. 
To prevent the capacitor C3 from being charged too rapidly, a resistor R4 
is provided. The resistor R4 also prevent ring signals to be absorbed by 
the capacitor C3. 
To prevent the probable fluctuation of the tapped current from causing the 
pulsative ON/OFF of the relay, a capacitor C4 is provided to absorb the 
peaks. Since the current passing through the capacitor C4 is rectified DC 
current, it must have definite polarity, and is preferably and 
electrolytic capacitor. 
The second embodiment has been explained in details. The third embodiment 
will be described hereinafter. 
Referring to FIG. 5, the third embodiment differs with the first embodiment 
only in that it uses a SCR instead of relay to control the AC power 
supply. Since here the cable-side circuit CKT2 is exactly the same as the 
cable-side circuit CKT2 of the first embodiment in FIG. 3, the details 
thereof are not repeated. Like the first embodiment, the third embodiment 
also comprises a transistor T, an optical coupler 3 consisting of a LED 31 
and a CdS photoresistor, a tapping/rectifying circuit 2, two switches SW1 
and SW2, and a capacitor C1. The emitter of the transistor T is connected 
to the gate of the SCR 1a so that when the transistor is activated, a 
current can pass through the CE path of the transistor and be applied to 
the gate of the SCR 1a, thus activating the latter to allow the AC power 
to the supplied to the facsimile machine. 
The various functions of the third embodiment are substantially the same as 
the first embodiment, thus their detailed description is not necessary. 
However, it is to be noted that the capacitor C5 serves only for filtration 
purpose. Although it is well known to an electronic specialist that a 
capacitor stops DC and allows AC to pass through, if the capacitance is 
very small, a capacitor does not allow an AC current to pass through. Here 
the capacitance of capacitor C5 is so small that it allows no AC current 
to pass through. 
The RC circuit connected in series with the SCR is an ordinary protective 
meansure for thyristors. 
Apart from a facsimile machine, a computer which is on line with the 
central office can also utilize the present invention for like purpose. It 
is noteworthy that when a computer is on line with the central office, its 
signal I/O jack must be connected to an interface (a so-called "modem") 
which is connected to a cable. When the present invention is used for such 
a computer, the cable is connected to the jack J1 of this invention, and 
the cable line of the interface is connected to the jack J2. Since both 
the computer and the interface need and AC power to drive them, a socket 
extender which provides two sockets can be inserted into the socket FS, 
then the plugs of the power lines of the computer and the interface are 
recpectively inserted into the two sockets of the socket extender. 
When a computer is connected on line with the central office, it is also 
provided with a telephone set (or the like) to dial the fax number of a 
remote station. Therefore in the case of transmission of information, when 
the user picks up the handpiece (or gives an equivalent instruction via 
the keyboard) the interface will build up the connection between the 
computer and the central office. In the case of reception, it is also the 
interface that build up this connection when receiving ring signals. Thus, 
when used for a computer, the function of this device is substantially the 
same as when it is used for a facsimile machine.