Telephone line exclusion device

A device is disclosed for use on a telephone line where there is two or more telephones or other instruments connected in parallel to the same telephone line whereby when one of the instruments goes off-hook (in a telephone, raises the receiver) the telephone line exclusion device automatically locks out all other instruments connected in parallel with the instrument that went off-hook. Such a result is achieved by a pair of interconnected two-coil polarized normally closed reed relays which interface the incoming telephone line and the two instruments. The two lines which normally connect to each instrument on the telephone line utilizes the normally closed contacts of one relay to energize the coils of the other relay and thereby inhibit the other instrument on the telephone line by opening the normally closed contact of the second relay which is in line with the other instrument. Upon the first instrument going on-hook (in a telephone, returning the receiver to the cradle), the telephone line exclusion device returns to its quiescent state where either instrument upon the line may be utilized.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The field of the invention is devices that are placed on telephone lines to 
inhibit multiple instruments on the telephone line from interfering with 
each other. 
2. Description of the Related Art 
With the advent of so many different instruments which are adapted to 
attach to telephone lines, problems have developed with respect to 
interference between these different instruments when they are connected 
in parallel on a single telephone line. For example, it is common in 
business offices, and to some extent, in residential homes, to have 
multiple telephones on a single incoming telephone line or each to have 
access to the same telephone line, as well as other instruments, such as 
modems which permit attached computers to communicate with remote 
computers by sending and receiving data on the telephone line. 
With the use of high speed modems, such as the 1200, 2400, or more baud 
modems, data is sent over telephone lines at an ever increasing rate. In 
order for the data to be free of distortions, it is preferable to have a 
single line dedicated to the computer. However, leasing a telephone line 
solely for a computer may be rather expensive so it has become common 
practice to use the common telephone line and to share it with the office 
telephones and other instruments. 
However, results of using shared telephone lines by computers have resulted 
in distorted data being sent and received if a telephone or other device 
on the telephone line goes off-hook (receiver is picked up) during the 
time of data transmission. This injects electrical spikes and voltage 
fluctuations into the telephone line which distorts the data being sent 
and received by the modems resulting in error or, in some cases, even 
having the modems terminate transmission. 
It is common in situations where different instruments are on a common 
telephone line to place mechanically operated switches, preferably near 
the computer, which switch the telephone lines to the computer modem and 
switch out all other parallel telephones or other instruments connected to 
the line. This type of operations works well and does reserve the 
telephone line pair for the computer while the switch is holding the 
telephone line in that position, however, it does create problems if the 
computer operator neglects to re-position the switch back to the 
telephones or other instruments on the line after computer transmission is 
completed. If the telephone line computer switch is located in another 
room from the party seeking to use a telephone after computer use, and the 
switch has been left in the computer position, this requires that the 
party desiring to use the telephone or other instrument travel to the 
switch and put it in the correct position. Further, if one party is using 
telephone without the knowledge of the second party, and the second party 
has access to the telephone line computer switch, the first party will be 
cut off as the switch is operated to the computer position. 
In addition, other applications of the telephone line switch have been in 
commercial establishments, such as restaurants, where the proprietor has a 
public telephone on his business telephone line, and the proprietor makes 
the public telephone available whenever he is not using the line. If the 
telephone line switch is located near the proprietor's telephone, his 
forgetting to return the switch to the pay telephone line while his own 
telephone is not in use will result in lost revenues since the pay 
telephone is dead. 
Obviously then, there is a need for a device which will, upon any 
instrument connected to the telephone line line going off-hook (being 
readied for use) to inhibit the operation of all other instruments 
similarly connected to that same telephone line in order that no other 
instruments on the line may interfere with the instrument being used, and 
which device returns the telephone line to use by any of the paralleled 
instruments on the line after use of the first instrument on the line. 
This and other objects and needs are set out in the enclosed specification 
of the Applicant's invention. 
SUMMARY OF THE INVENTION 
The embodiment of the invention described consists of a pair of two-coil 
normally closed contact reed relays operably interconnected and interfaced 
between the incoming telephone line and a pair of instruments, such as 
telephones, computer modems, or the like, attached to the same telephone 
line. The subject telephone line exclusion device operates by permitting 
either of a pair of instruments, telephone, computer modem, or the like, 
connected to it to exclude the other from coming on line by use of the 
first. Such is accomplished without the use of switches, and either of the 
two instruments on the telephone line may be the first used instrument. 
Termination of the use of the first used instrument returns the system to 
its quiescent state. 
The incoming telephone line necessary to permit operation of telephones, 
computer modems, or the like, consists of two lines, a tip and a ring 
line. Normally, when the telephone or other device is on-hook (receiver 
down), no dc path is provided through the telephone for the tip and ring 
lines and the open circuit voltage at the telephone is nominally 48 volts 
dc with the tip side being positive and the ring side being negative (or 
the return). When the telephone or other device goes off-hook (receiver 
picked up), resistance is placed between the ring and tip lines and the dc 
voltage nominally drops to about 8 volts dc. Upon this dc voltage is 
impressed the dial tone. When a telephone is on-hook and rings, a 105 volt 
30-cycle square wave is sent over the lines which passes a capacitor in 
the telephone set to the ringer which rings the bell which is heard. At 
that time, the phone receiver is picked up, and goes off-hook (telephone 
is placed in use). 
The relays which are utilized in the invention are commercially available 
reed type relays having normally closed contacts utilizing a pair of 
polarized coils to open the contacts. The coils are additive in their 
effect and must be connected so that the dotted side of each coil is 
connected to the positive side of the supplied dc voltage. The device is 
constructed to place the tip line to both the normally closed contacts of 
each relay at which time the lines are continued to one of the two coils 
of each opposite relay. Passing each relay coil, the lines then go to each 
of the two separate instruments as the tip line. The ring line then is 
directed to both the unconnected second coils on each of the relays where, 
after passing that second coil of each relay, then is directed to each of 
the pair of telephones or other instruments on the line as the ring side. 
The device operates when the first of the two telephones or other devices 
on the line goes off-hook and thus completes the circuit between that 
particular instrument's tip and ring lines. At this time, the tip line 
through the normally closed relay contacts energizes the first coil of one 
of the relays while the ring line energizes the second coil of the same 
relay in order that both coils of the same relay are now properly 
energized causing its contacts to go into the open position. At this, the 
other telephone or device on the line, having its tip line interrupted, is 
out of the circuit. If it should go off-hook, it does not come on to the 
circuit. 
When the first instrument has completed its call, and goes back on-hook, 
the connection between the tip end the ring is broken and the current 
through the coils of the previously energized relay is terminated and its 
contact returns to the normally closed position, thus opening up the 
telephone line to either of the instruments connected in parallel on the 
line. 
In an alternate embodiment, the telephone line exclusion device is 
connected in series with one of its outputs such that more than two 
telephones or other instruments may be connected in parallel upon a single 
incoming telephone line. 
In use, usual telephone type jacks and plugs are attached to the line so 
that the device may be readily available and conform with the types of 
connectors commonly in use on the telephone line system. 
Accordingly, it is an object of the present invention to provide automatic 
means by which a pair of telephones or other instruments upon a single 
telephone line provides uninterrupted connection for the first used 
instrument on the telephone line and automatically excludes the other 
telephone or other instrument on the line from use during the period of 
use by the first used telephone. 
It is another object of the subject invention to provide means which, after 
the first telephone or other instrument has completed its call, the 
telephone line is restored to its original quiescent condition in order 
that either of the pair of telephones or other instruments may then be 
used. 
Other objects of the invention will in part be obvious and will in part 
appear hereinafter. The invention accordingly comprises the apparatus 
possessing the construction, combination of elements, and arrangement of 
parts which are exemplified in the following detailed disclosure and the 
scope of the Application of which will be indicated in the claims.

In various views, like index numbers refer to like elements. 
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to FIG. 1, a partial schematic and partial block schematic 
diagram is shown of the prior art presently used to exclude second parties 
from coming on to a telephone line while the same line is being used by 
another instrument, such as a telephone or computer modem. Presently, a 
ganged double pole switch S1 is used which allows the computer modem, for 
example, to be switched on to the incoming telephone line and thereby 
exclude the telephone cr other device which normally uses the same 
telephone line. These switches work well, as they do prevent a person 
other than the person operating the computer modem from coming on the line 
and creating extraneous electrical signals which can harm the computer 
modem or distort the data that is being transmitted or received. The 
difficulty with the prior art is that it always does require the person 
operating the computer, or the telephone, to remember to place the switch 
in the correct position for whatever instrument is being operated. This 
may entail for a party seeking to use the telephone to go into another 
room where the computer modem is located to operate the switch since in 
most cases the switch is kept by the computer modem. In addition, as 
explained prior, having both the computer modem and the telephone on the 
same line without switch S1 serves to create utter havoc if, for example, 
the party picks up the telephone while data is being transmitted to or 
from the modem. 
In the FIG. 1, the switch S1 is set to selectively direct both the tip line 
6 and the ring line 8 to each of the blocks, namely the computer modem 2 
and the telephone 4. 
Referring now to FIG. 2, the subject line excluding device 10 is detailed 
showing the circuit and 
components operably interfaced between the computer modem 2, the telephone 
4, and the incoming telephone lines. The positive tip line 6 and negative 
ring line 8 of both the incoming telephone lines entering device 10 and 
entering the computer modem and the telephone are illustrated. As can be 
seen, normally closed telephone type reed relays K1 and K2 with contact 
opening coils are utilized to prevent either the computer modem 2 or the 
telephone 4 from coming upon the telephone line while the other instrument 
is operating. The relays are identical and each have two polarized coils 
which both must be operating in series aided configuration with positive 
dc voltage connected to the dotted side of the coil in order that the 
generated magnetic flux is in the correct direction to cause the relay 
contacts to go from the normally closed position to an open position. This 
means that current must be going through each coil in the same direction 
as determined by the dots proximate each coil. 
As detailed in FIG. 2, of the incoming telephone lines, tip side 6 is 
directed to pin 5 of both relays K1 and K2, pin 5 being one side of the 
normally closed contacts. Thereafter, the other side of the normally 
closed contacts, namely pin 6, is directed to the second relay coil of the 
opposite relay, i.e., pin 6 of relay K1 is directed to pin 4 of the second 
coil 19 of K2, and pin 6 of relay K2 is directed to pin 4 of the second 
coil 17 of relay K1. Both of these connections are to the dotted or 
positive side of each coil. Continuing, the other side of the second coil 
of each relay, pin 3, is then continued to the tip line 6 connected to the 
computer modem 2 and telephone 4, i.e., the output of second coil 17 of 
relay K1 is directed to the tip line 6 of computer modem 2 and the output 
of second coil 19 of relay K2 is directed to the tip line 6 of telephone 
4. With respect to the ring line, incoming telephone line ring line 8 is 
simultaneously directed to the first coil of each of the relays, i.e., the 
side opposite the dot of first coil 13 of relay K1 and first coil 15 of 
relay K2. This corresponds to pin 1 on each relay. Since the ring line is 
the negative side or return of the incoming telephone line, it does not 
connect to the dotted side of the relay coils. Thereafter, the dotted side 
of the first coil of each relay is then directed to the ring line of the 
computer modem and the telephone, i.e., the dotted side of first coil 13 
of relay K1 is directed to the ring line of computer modem 2 and the 
dotted side of first coil 15 is directed to the ring line 8 of telephone 
4. This corresponds to pin 2 of each relay coil. 
It is noted that each of the coils in each relay are connected in series 
through the tip and ring linesof one of the two instruments on the line 
while the normally closed contact is in the circuit of the opposite relay. 
Thus, completing the tip and ring line circuit for, as an example, the 
computer modem, essentially opens the normally closed contacts for the 
other instruments, namely the telephone. 
The circuit operates as follows. If the computer modem goes on the line, it 
closes the circuit between the tip and ring lines at which time current 
flows from the incoming telephone line tip side 6 through the normally 
closed contacts of relay K2, pins 5 and 6, to second coil 17 of relay K1 
(pins 4 and 3) and on to the tip line 6 of computer modem 2. At the same 
time, the ring line 8 circuit is completed in its connection to first coil 
13 of relay K1 (pins 1 and 2) and to the ring line 8 of computer modem. At 
that point in time, relay K1, having both first and second coils 13 and 17 
energized, and with the current flowing from tip (+) to ring (-) correctly 
through coils 13 and 17, breaks the normally closed contact between pins 5 
and 6 or relay K1, and thus the tip line 6 to the telephone is opened, 
disabling use of the telephone. So long as the computer modem is off hook, 
it closes the circuit between its' tip and the ring lines, and current 
will continue to flow through coils 13 and 17 of relay K1 and thus keep 
contacts between pins 5 and 6 open, constantly inhibiting the use of the 
telephone. It is noted that the first and second coils of relay K1 are 
connected in the series aided configuration shown by the dots so that 
current flow is in the correct direction and the coils do not oppose each 
other. 
When the computer modem goes off line, i.e., goes on-hook (no longer being 
used), the electrical connection between the tip line 6 and ring line 8 is 
broken, current ceases to flow, and relay contacts of relay K1 between 
pins 5 and 6 return to the normally closed position, thus placing both the 
computer modem and the telephone into a quiescent state where the first 
person to operate either one then proceeds to again exclude the other. 
For the telephone to operate, i.e., go off-hook, and assuming that the 
computer modem is not already operating, the tip line 6 and ring line 8 
into the telephone is closed. This then permits current to flow on the tip 
side 6 of the incoming telephone line through the normally closed contacts 
of relay K1, pins 5 and 6, and through second coil 19 of relay K2. 
Further, the ring line 8 circuit is completed through first coil 15 of 
relay K2 from telephone 4 to the incoming telephone line. Thus, first and 
second coils 15 and 19, being energized correctly in the series aided 
configuration, results in the normally closed contacts between pins 5 and 
6 of relay K2 opening resulting in an open line connecting second coil 17 
of relay K1 and thus preventing the computer modem 2 from going on line. 
When the telephone hangs up and goes on hook, the electrical connection 
between the tip line 6 and the ring line 8 at the telephone is broken, and 
thus current is prohibited from flowing through first coil 15 and second 
coil 19 of relay K2 which allows the contacts of the relay K2 (pins 5 and 
6) to return to the normally closed position. 
If one is to follow current flowing, say from tip to ring on the incoming 
telephone line, it is quickly seen that the flow of current through the 
coils is additive, in accordance with the polarity of the coils such that 
both coils operate to increase the magnetic flux opening the reed relay 
contacts, and the coils do not oppose each other such as to cancel each 
other. 
In order to apply the invention to the situation where more than two 
telephones or other devices are attached to a common incoming telephone 
line, an arrangement similar to that shown in FIG. 3 is utilized. Since 
the construction of the basic device affords operation for only two 
parallel telephones or the like, a first telephone line excluding device 
10, characterized by the Numeral 31 in FIG. 3, receives the tip line 6 and 
ring line 8 of the incoming telephone line. One of the two outlets of the 
line excluding device is immediately made available for attachment to 
whatever telephone line instrument is desired. That is shown as the "T" 
and "R" (tip and ring) terminals 33. The second set of tip and ring lines 
from the first situated device 31 leads to the input for the second line 
excluding device 35. Here the first set of tip and ring lines emerge to 
terminals 37 and the second set to the following line excluding device 39. 
This scenario is repeated until all desired pair of tip and ring lines are 
available for connection to the devices operating on the telephone line. 
As shown in FIG. 3, four line excluding devices permit a total of five 
telephones or other instruments connected to the tip and ring lines. 
With the above interconnection, and instrument on any one of the tip-ring 
pairs (33, 37, 41, 45, and 47) being used would inhibit use by any other 
instrument on any other tip-ring line. 
Lastly, referring to FIG. 4, a typical installation is shown wherein the 
subject invention, the telephone line excluding device 10 (not shown) is 
encased in a container 51 where, emerging from the left hand end is the 
tip and ring lines (shown as one bundled line 53) terminated with a 
standard telephone type RJ-11 type plug 55. This connects to the incoming 
telephone line. At the opposite end of container 51 housing the line 
excluding device are a pair of jacks, labeled J1 and J2. These jacks are 
adapted to receive the tip and ring line pairs, shown as individually 
bundled wires terminating with plugs P1 and P2. Again, the standard RJ-11 
type plugs are suggested for the connectors P1 and P2, the plugs Pl and P2 
adapted to be joined to the jacks J1 and J2. At the opposite ends of the 
lines 55 and 57, each of which contain one tip and one ring line, are the 
various types of equipment which may be attached to telephone lines. For 
example, block 59 may represent the key service unit (KSU) normally 
utilized by the telephone companies for multi-line PBX's or terminals. The 
PBX system or multi-line terminal is represented by block 61. Similarly, 
line 55 which connects Pl to the other device residing on the telephone 
line, is represented by block 63. Block 63 then may be a pay telephone, a 
standard telephone, a computer modem, or as desired. 
In all cases, use of one of the pair of tip and ring lines in cables 55 or 
57 will inhibit the use of the lines by the other. 
In the construction of the subject invention, the reed relay which has been 
utilized is a reed relay manufactured by the Wabash Relay And Electronics, 
Inc., company, a subsidiary of Wabash Magnetics, Inc., of Wabash, Ind., 
and more particularly, its Model 1670-4-3 relay. This relay conforms with 
the FCC Part 68 requirements and is characterized by normally closed 
contacts which open when a current of 18 ma. flows in the correct 
direction (entering the dotted side) through the series aided configured 
coils and once opened, will drop out (close) when the current drops to 6 
ma. Further, the coil resistance of each coil is 20 ohms, and the unit 
provides 1500 volts dc coil to contact isolation as required. Although the 
subject invention does insert resistance into the telephone lines, 
nominally 20 ohms into each line for a total of 40 ohms, yet that is less 
than 10% of the normal resistance placed across the tip and ring lines by 
the telephone or modem and as such, does not degrade the quality of the 
transmission. 
Although in the preferred embodiment of the device, together with an 
alternate embodiment, has been shown and described, it will be understood 
that there is no intent to limit the invention by such disclosure, but 
rather it is intended to cover all modifications and alternate 
constructions falling within the spirit and the scope of the invention as 
defined in the appended claims.