Telephone signalling method and apparatus

The disclosed signalling apparatus provides a different identifying signal in response to a ringing signal for one or more telephone station sets connected by a common line to a centralized switching, control and signalling machine. The different identifying signals are generated in response to the number and timing of ringing signals applied to the line. If a first ring is sensed and within a predetermined first time a second ring is sensed, a first identifying signal is initiated. If a first ring is sensed and after the predetermined first time but before a predetermined second time a second ring is sensed, a second identifying signal is initiated. If a first ring is sensed, but a second ring is not sensed before the predetermined second time, the signalling apparatus is reset to initial conditions. In the disclosed preferred embodiments of the invention, the second identifying signal may be used to provide a signal to a second telephone connected to the common telephone line, or it may be used to control the operation of a remote appliance.

BACKGROUND OF THE INVENTION 
This invention pertains in general to the field of telephone circuitry. 
Specifically, the invention relates to logic circuitry and method for 
generating different output signals applied to a telephone line to which 
one or more telephone station sets are connected. 
There has been an unfilled need for a device by which two or more persons 
who use a common telephone line can be individually signalled. One such 
need is where a secretary and an individual who directs or supervises the 
secretary (hereafter simply referred to as "boss") use the same telephone 
line on a business PBX or key telephone system. The boss does not wish to 
answer the telephone, if the caller desires to talk to the secretary. On 
the other hand, if the call is for the boss, the boss desires to be 
signalled. Thus, a need exists for a device which can interpret the number 
and timing of rings, controlled by the calling party, to provide two 
different identifying signals, one indicating that the boss is being 
called, the other that the secretary is being called. If the caller, 
wishing to speak with the secretary, would follow a predetermined sequence 
of the number and timing of ringing signals, the caller could produce 
information sufficient to enable suitable apparatus to distinguish such a 
caller's ringing signals from the ringing signals of all other callers. 
Another need exists whereby an ordinary telephone line may be used to 
signal the control of a remote appliance, e.g. an air conditioner unit in 
a home, office or factory. 
SUMMARY OF THE INVENTION 
According to a first embodiment of the invention a logic circuit is 
provided which is responsive to the number and timing of ringing signals 
on a telephone line and is used to control the generation of one of two 
different identifying signals, thereby indicating which one of the two 
parties for which the call is intended. 
The inventive logic circuit is intended for use with one or more telephones 
in which the usual bell or audio signalling apparatus has been adjusted so 
as not to generate an audible tone. Nevertheless, the periodic electrical 
ringing signal sequence, which would otherwise generate the audible tone, 
remains detectable in the telephone set or sets. A periodic ringing signal 
sequence comprises a periodic ringing signal for T1 units of time followed 
by an idle period for T2 units of time. A ringing detector is provided for 
sensing the electrical ringing signal on the line and for generating 
ringing pulse signals at the start of each ringing signal on the telephone 
line. 
A counter is provided for counting the number of ringing pulse signals 
sensed on the line. The counter generates a ring count output signal when 
the number of ringing signals counted equals a predetermined number of 
rings, e.g. two rings. 
A clock provides a first time measurement signal when T3 units of time have 
passed from the occurrence of the first of the ring pulse signals and a 
second time measurement signal when T4 units of time have passed from the 
occurrence of the first of the ring pulse signals. The unit of time T3 is 
taken to be greater than the sum of T1 and T2 units of time; T4 is taken 
to be greater than T3 units of time. 
A logic circuit determines whether or not the ring count output signal has 
occurred (e.g. whether or not two rings have occurred) before the first 
time measurement signal has occured (e.g., before T3 units of time have 
occurred from the first ring). If the ring count output signal occurs 
before the first time measurement signal, a first identifying signal is 
generated. The first identifying signal is typically an audio signal which 
is generated by applying a first audio tone enable signal to a first audio 
signal generator which may or may not be adapted to sound in synchronism 
with ringing signals on the telephone line. 
A second logic circuit determines whether or not the ring count output 
signal (e.g., two rings) has occurred after the first time measurement 
signal (e.g., T3 units of time), but before the second time measurement 
signal (e.g., T4 units of time). If the ring count output signal is 
present after the first time measurement signal and before the second time 
measurement signal, a second identifying signal is generated. The second 
identifying signal is typically a second audio signal which is generated 
by applying a second audio tone enable signal to a second audio signal 
generator which may or may not be adapted to sound in synchronism with 
ringing signals on the telephone line. 
The circuit is also provided with means responsive to the first or second 
audio tone enables signals for resetting the ring counter and the clock to 
zero conditions when the first and second audio tone enable signals are 
generated. 
A second clock is provided which starts its timing function on the 
occurrence of the ring count output signal (e.g., two rings). The second 
clock, reset on the occurrence of each ringing signal, detects the absence 
of a periodic ringing signal and applies a signal to reset the entire 
logic circuit. Absence of a periodic ringing signal indicates that the 
telephone station has been answered or that the calling party has ceased 
signalling. 
According to a second embodiment of the invention the control unit 
described above is used to control one or more appliances in response to a 
given coded ringing sequence on the telephone line.

DESCRIPTION OF THE INVENTION 
FIG. 1 illustrates the prior art signalling method whereby one or more 
telephone station sets are connected to the same line to a central 
signalling, switching and control apparatus such as a telephone central 
office, a PBX switching machine or a key service unit in a key telephone 
system. At least one telephone station 10 has an audio signalling circuit 
11 which responds to a periodic ringing signal on line conductor pair 30. 
One or more other station sets 20 may be typically attached to line 30 and 
may or may not be equipped for generating an audio signal in response to 
the periodic ringing signal on line conductor pair 30. 
The audio signalling means shown in FIG. 1 are bells 11 and 12, but may 
also typically be small speakers associated with each telephone. If there 
are two or more parties using telephone 10 or telephones 10 and 20, there 
is no way for the parties to determine for whom a call is intended without 
answering a telephone and determining from the caller the identity of the 
called party. If a calling party should signal the line with a prearranged 
calling code, normally both parties using the line would be exposed to 
rings corresponding to the predetermined calling signal. For example, the 
following predetermined calling code might be established: continuous 
ringing if the call is intended for party #1; one ring followed by a 
period less than thirty seconds after which the telephone station is again 
signalled if the call is intended for party #2. Where there is merely one 
station, party #1 would not wish to be disturbed with the first ring 
signal of the predetermined calling code. Where there are two or more 
stations, such as telephone station sets 10 and 20 and the sets are 
sufficiently remote from one another, the audio signal associated with 
station 10 would not be heard at station 20 and vice versa. In such a case 
it is desirable that party #1 not be disturbed by hearing an audible 
signal intended for a call to party #2 and vice versa. 
FIG. 2 schematically shows how the prior art audio signalling arrangements 
have been modified in accordance with this invention. The bells 11, 12 (or 
alternatively, speakers) have been rendered inactive, yet the electrical 
ringing signal flowing through the bell coil 13, (or speaker transformer) 
remains in at least one telephone 10. Associated with the bell coil 13 (or 
speaker transformer) is a ring sensor 14 which senses the electrical ring 
signal flowing through coil 13. The sensing is preferably made by magnetic 
induction so that no electrical connection to the telephone line 30 is 
required. The invention is not limited, however, to the particular means 
for sensing the ring signal on line conductor path 30. Signals from ring 
sensor 14 are applied to a control unit 15 which assesses the number and 
timing of the ring signals to enable either a first audible tone generator 
40 or a second audible tone generator 41. The enabling signals may 
alternatively be used to control other indicating means such as lights, 
bells, horns, etc. 
The preferred embodiment of the invention is for use in conjunction with a 
predetermined calling code by which a calling party who wants to signal 
party #2, allows the telephone ringing sequence initially to last for only 
one ring. After the one ring, the calling party inhibits the ringing by 
hanging up the receiver (depressing the hookswitch). He then must ring 
again within a preset time, approximately 30 seconds, in order to enable 
the apparatus of the invention to commence signalling party #2. All other 
callers are presumed to belong to a group that simply wishes to call party 
#1. In the case of such other callers, continuous ring signalling on line 
30 enables audio tone generator 40. 
For any call on line 30, the audio signal is delayed until after the first 
ring: when called party #1 is being called, the first audio signal 
generator 40 is not enabled until the second ring signal is sensed by ring 
sensor 14; when called party #2 is being called, the second audio tone 
generator 41 is not enabled until the second ring signal is sensed within 
the preset delay period after the first ring. 
FIG. 2a shows a preferred ring sensor circuit for use with this invention. 
A reed relay 50 is provided in proximity with telephone coil 13. The 
relay's contacts close when an alternating current voltage appears across 
coil 13. FIG. 2b illustrates the ringing sequence of the voltage E 
appearing across coil 13. Alternating voltage occurs for the ringing 
period T1 followed by an idle period T2. The total period of ringing 
sequence is the sum of the ringing period and the idle period, T1+T2. When 
the contacts of reed relay 50 close, the voltage e.sub.1 appearing across 
resistor R1 rises to E volts, the value of d.c. source 51. When reed relay 
50 contacts open, voltage e.sub.1 falls to zero volts. The voltage e.sub.2 
across resistor R2 initially rises to E volts but exponentially decays to 
zero as the voltage E rises on charging capacitor C. When the ringing 
signal stops, and the idle period begins, a negative pulse e.sub.2 appears 
across resistor R2 as shown in FIG. 2d. Diode D1 allows only positive 
pulses e.sub.3 to appear across the output terminals of the ring sensor to 
be applied to control unit 15. The pulses e.sub.3, are illustrated in FIG. 
2e and occur at the start of each ringing signal. 
FIG. 3 illustrates the logic by which the control unit is designed in order 
to distinguish the called party on the basis of the number and timing of 
incoming ring signals. 
FIG. 3a shows that if two ring pulses are sensed before a predetermined 
time T3, selected to be greater than the one ringing sequence time period 
(T1+T2) but less than two ringing sequence time periods, then a first 
audio generator will be enabled starting with the second ring pulse. 
FIG. 3b shows that if a first ring pulse is sensed, at time t.sub.1, and a 
second ring pulse only occurs between t.sub.1 +T3 and t.sub.1 +T4, then a 
second audio generator will be enabled, starting with the second ring 
pulse. 
FIG. 3c illustrates the condition where a first pulse is sensed at time 
t.sub.1 and no second pulse is received before t.sub.1 +T4. When this 
condition occurs, the control circuitry must be reset to initial 
conditions. 
FIG. 4 illustrates in block diagram form the hardware necessary to carry 
out the logic functions illustrated in FIG. 3. Ring sensor 14 generates 
one pulse on lead 62 at the start of each ringing signal of the ringing 
sequence appearing at coil 13. Ring number counter 60, responding to the 
pulses on lead 62, produces a ring count output on lead 61 when two ring 
pulses have been received. Clock "1" (80) is enabled with the first ring 
pulse on lead 81 from ring sensor 14. Clock "1" (80) produces outputs on 
leads 84, 85 and 86 if time has reached T3, T4 or greater than T4 units of 
time. 
Comparator logic circuit 82 compares the ring count output on lead 61 with 
the first time measurement output signal on lead 84 to determine if, for 
example, two rings have occurred before time has reached T3 units of time 
after the first ring. If comparator logic circuit 82 determines that two 
rings have occurred before T3 units of time, then an output signal on lead 
87 is applied to a tone #1 generator 100 (or other suitable identifying 
device) to enable it. 
As shown in FIG. 4, tone #1 generator 100 also has an input from ring 
sensor 14 via lead 63. Applying the signal from an output of ring sensor 
14 to tone #1 generator 100 indicates that a first audible tone on output 
lead 110 will be in synchronism with the ringing signals of the ringing 
sequence applied to the telephone station from the central signalling, 
switching and control apparatus. It should be realized that tone generator 
#1 signal 110 need not necessarily be in synchronism with the ringing 
sequence from the central signalling switching and control apparatus but 
rather, may operate independently. 
Comparator logic circuit 83 determines if two rings have been received, as 
indicated by the output on lead 61, before time has reached T4 units of 
time as indicated by an output on lead 85. If so, an output signal on lead 
90 enables tone #2 generator 101 for producing an audio signal on lead 
111, thereby indicating that party #2 is being called. 
Output signals from comparator 82 on lead 87 and output signals from 
comparator 83 on lead 90 are each applied to a reset logic circuit 120 
which in turn resets clock "1" (80) and ring number counter 60 via lead 
121. If clock "1" (80) generates an output on lead 86, indicating that 
greater than T4 units of time have passed since the first ring pulse on 
lead 62, the signal on lead 86 is applied to reset logic circuit 120 for 
resetting clock "1" 80 and ring number counter 60. 
The clock "2" circuit 130 is provided for resetting the logic circuitry of 
the invention after tone #1 signal on lead 110 is established or after 
tone #2 signal on lead 111 is established, but either the telephone 
station has been answered or the calling party has stopped signalling. 
Clock "2" (130) is enabled from lead 61 from ring number counter 60 
indicating that two rings have been received. The clock "2" (130) is reset 
from ring pulse signals on lead 81 via lead 62 occurring with every ring 
pulse. An output on lead 132 from clock "2" (130) will only appear if T3 
units of time have passed before clock "2" (130) is again reset by a ring 
pulse on lead 62. Thus, an output on lead 132 indicates that too great a 
time has elapsed since the last ring signal was received. The signal on 
lead 132 is applied to logic reset circuitry 120 for resetting all logic 
circuitry in the circuit arrangement. 
FIG. 5 shows a detailed schematic drawing of a preferred embodiment which 
is used to accomplish the functional features outlined in FIG. 4. Ring 
sensor circuit 14 applies ring pulse signals on lead 62 which are applied 
to counter 60 via a "clock in" lead 63. Counter 60 is a decade counter 
enabled via a clock enable lead 64 by a d.c. voltage E. Decade counter 60 
has ten output leads, each having a voltage placed in sequence thereon as 
determined by the number of pulses on lead 63 received by it. Output lead 
61 from output 2 will be enabled once the counter 60 has received two ring 
pulse signals via a "clock in" lead 63. 
Counter #1 (200), in conjunction with oscillator 300, serves to measure 
time in this embodiment of the invention. If the ring sequence cycle is as 
it is shown, for example, in FIG. 5A where the ringing signal T1 is 1.5 
seconds and the idle period of the ringing sequence T2 is 4.5 seconds, 
then a preferred period T for oscillator 300 is approximately 4 seconds, 
as shown in FIG. 5. The output from oscillator 300 on lead 301 is applied 
via diode D11 to the "clock in" lead 302 to decade counter #1 (200). The 
decade outputs of counter 1 represent integral multiples of period T of 
oscillator 300. A decade output 1 from counter #1 (200) represents 4 
seconds, decade output 2 represents 8 seconds, etc. Lead 84 on decade 
counter #1 (200), when enabled, indicates that approximately 8 seconds 
have occurred from the time counter #1 (200) was initially enabled from 
the output of flip-flop 5 (FF5), which is set to a "one" output on the 
occurrence of the first ring sensor output pulses of lead 62. An output 
signal on decade output 8 of counter #1 (200) indicates that approximately 
32 seconds have occurred from the first ring pulse signal. An output on 
decade lead 9 of counter #1 (200) indicates that a time period greater 
than 32 seconds has passed from the occurrence of the first ring pulse. 
The output from counter 60 on lead 61 is applied to one input lead 400 of 
AND gate A1. The "zero" output of lead 401 from flip-flop 1 (FF1) is 
applied to a second input lead of AND gate A1. An output from lead 401 is 
present on flip-flop (FF1) when all of the circuitry is set to zero or 
initial conditions and before an input to the one input of flip-flop 1 
(FF1) has been received. An output is received on lead 403 OF AND gate A1, 
if, and only if, two ring pulses have been received by counter 60 before 
counter 200 produces an output on lead 84, indicating that 8 seconds of 
time (T3) have passed since receiving the first ring pulse. If an output 
is produced at the output of AND gate A1 on lead 403, flip-flop 3 (FF3) 
has its "one" input pulsed, thereby producing an output from the "one" 
output lead 404 of flip-flop 3 (ff3). An output on lead 404 is applied to 
one input lead of AND gate A3. The other input lead of AND gate A3, lead 
404, applies ring synchronism voltages from ring sensor 14 via resistor 
R1, which has a d.c. voltage E placed thereon during the ringing signal 
applied on telephone line 30. The output of AND gate A3 on lead 405 is 
applied to tone generator #1 (100) (or any other indicating means such as 
lights, bells, horns, etc.) which produces a first output signal on lead 
110 for producing a first audio output signal. If two ring pulses have 
been received before T3 units of time have passed, an output signal on 
lead 403 on the output of AND gate A1 is also applied on lead 406 to reset 
counter 60 and counter 200. 
If counter 600 does not count two ring pulse signals before T3 units of 
time have passed, flip-flop 1 (FF1) will have its "one" input cell enabled 
via lead 84 when T3 units of time have passed, thereby disenabling an 
output on lead 401 and preventing the enablement of tone generator #1 
(100). However, if counter 60 registers two ring pulse counts by producing 
an output on lead 61 before T4 units of time have passed (32 seconds), 
then all of the input leads of AND gate A2 have inputs: lead 410 has an 
input when lead 61 is energized, lead 411 has an input because the "1" 
output of flip-flop 1 (FF1) is high, because more than T3 units of time 
have passed, and lead 412 from the "zero" cell of flip-flop 3 (FF3) is 
high, because the input to the "one" cell from lead 413 has not yet been 
produced. Thus, on the condition that two rings have been counted after T3 
units of time have passed, but before T4 units of time have passed, an 
output from AND gate A2 on lead 414 is present, which is then applied to 
the "one" cell of flip-flop 4 (FF4). The output of the "one" cell on lead 
415 is applied to the one lead of AND gate A4. The other input lead of AND 
gate A4 via lead 416 connected to lead 404 then produces an output from 
AND gate A4 from lead 417 in synchronism with the ring signals applied 
from the signalling, switching and control apparatus, thereby enabling 
tone generator #2 (101) (or any other indicating means) for producing 
audible tones on lead 111. The output of AND gate A2 via lead 420 is 
applied to reset the counter 60 and counter 200. 
If the time length after the first ring pulse is greater than T4 units of 
time, and two rings have not been sensed on lead 61, then a decade output 
9 on counter 200 produces an output on lead 430, which is applied to bus 
431 for resetting all of the logic circuitry of the invention. A reset 
signal on bus 431 is applied to the zero inputs of flip-flops FF1, FF2, 
FF3, FF4 and is also applied to reset counter 60 and counter #1 (200) and 
to the "zero" input or flip-flop 5 (FF5), which is used to enable counter 
(200). 
If counter 60 counts two ring pulses before it has been reset, then as 
indicated above, either tone generator #1 (100) or tone generator #2 (101) 
is enabled. On this condition flip-flop 6 (FF6) is enabled via lead 440 
connected to lead 61 so as to enable counter #2 (210). Counter #2 (210) is 
reset via lead 450 with each ring pulse from lead 62 via lead 500. Counter 
210 has its "clock in" input lead 460 pulsed by oscillator pulses on lead 
301 from oscillator 300. Thus, counter #2 (210) incrementally counts the 
units of time from the last ring pulse on lead 62, because it is reset 
with each ring pulse of lead 450. Decade lead 2 at the output of counter 
#2 (210) will be energized only when 8 seconds have passed since the 
beginning of the last ring signal. The output from decade lead 2 of 
counter 210 is applied to bus 431 for resetting all of the logic circuitry 
of the circuit arrangement. 
Diodes D11 and D12 insure that the zero input of flip-flop 6 (FF6) is only 
enabled by an output from decade lead 2 of counter 210. Diodes D2 and D3 
insure that only counter #1 (200) and counter 60 are reset on the 
occurrence of outputs from AND gates A1 or A2. Thus, it is seen that 
counter #2 (210) applies an output of decade lead 2 for application to bus 
413 for resetting the entire circuit when greater than 8 seconds have 
passed from the beginning of the last ring pulse, a condition indicating 
that either the called party has picked up his telephone set or the 
calling party has ceased ringing. 
Another feature of this invention relates to its use for remote control of 
home, office or factory appliances. For example, there can be the desire 
to activate or control equipment in a remote location by means of 
telephone commands. As illustrated in FIG. 6, rather than connecting two 
telephones to the same line, equipment such as an air conditioning unit 
600 may be substituted for the telephone #2 (20) as illustrated previously 
in FIG. 2. The embodiment of the invention illustrated by FIG. 6 could be 
identical in all respects to that described previously with the exception 
that coded dialing would produce a start signal to air conditioning unit 
600 rather than initiating an enable signal to the tone generator 
associated with a telephone. The control unit 15 could be identical to 
that illustrated in FIG. 5 with the exception that line 417 would be 
connected to a start switch of air conditioning unit. 
The embodiment illustrated in FIG. 6 (with the control unit 15 being 
constructed as illustrated in FIG. 5) would allow signalling of telephone 
calls to telephone 10 to be made, the ringing or tone signalling beginning 
with the second ringing sequence. On the other hand, if the ringing signal 
or telephone line 30 were only one ring signal within T3 units of time, 
followed by at least one other ring signal between T3 units of time and T4 
units of time, the air conditioning unit would be enabled. The use of an 
air conditioning unit in this description of an alternative embodiment of 
the invention is only by way of one example. Other examples of systems 
which could be remotely controlled in the manner illustrated are burglar 
alarm systems, electric lights, garage doors, ovens, furnaces, etc. 
It is possible, of course, to construct control unit 15 so that it may 
respond to two, three or even more codes of the nature described above, in 
order that two or more appliances can be remotely controlled via a 
telephone line. The codes would be combinations of numbers of rings 
occurring within predetermined timing sequences. For example, where two 
appliances must be controlled, a first appliance could be controlled 
according to a code described above with the added condition that only one 
ring be detected between T3 and T4. 
A second appliance could be controlled according to a second code as 
follows: 
one ring only between the start of the first ring and a time T3 from the 
start of the first ring, T3 being selected to be greater than T1 plus T2 
where T1 is the length of the ring signal and T2 is the length of the idle 
period of the ringing sequence, 
one second ring only between time T3 and T4, and at least one ring signal 
between T4 and T5 where T4 would be selected to be approximately equal to 
twice the length of time T3, and T5 would be selected to be a sufficient 
time length greater than T4 to allow the user to initiate the third ring 
signal. The control unit would be constructed to generate a first 
appliance enable signal for the first appliance in response to the first 
coded signal, a second appliance enable signal for the second appliance in 
response to the second coded signal, and a tone enable signal for the 
telephone signal in response to a continuous ring signal. Thus, as shown 
in FIG. 4, the first appliance enable signal is on lead 90 from logic 
circuit 83 and is fed to a first appliance to, for example, start or stop 
it. The second appliance enable signal is generated by the logic circuit 
108 shown in FIG. 7. Logic circuit 108 is responsive to the ring count 
output signal on line 61 and to the first, second and third time 
measurement signals on lines 84, 85 and 86, respectively, of FIG. 4 for 
generating the second appliance enable signal (a third identifying signal) 
on line 106 when the first ring count output signal occurs after the first 
time measurement signal but before the second time measurement signal 
occurs, and the second ring output signal occurs after the second time 
measurement signal but before the third time measurement signal occurs. 
The second appliance enable signal is fed to the second appliance on line 
106, for example, start or stop it. Additional appliances could be 
controlled by other codes using additional logic circuits 109. The second 
appliance enable signal and enable signals from additional appliances are 
fed to Reset 120 of FIG. 4 to provide for resetting of the logic 
circuitry. 
Another embodiment of this invention relates to the addition to the control 
unit of FIG. 6 of a clock by which two or more signals may be generated 
depending on the time of day. The clock 650 shown in dashed lines at the 
bottom of FIG. 6 when initiated by an output signal 417 from control unit 
15 as a result of a coded ringing sequence applied to telephone line 30 
produces an output on lead 601 during the "daylight" hours of the day and 
an output on lead 602 during the evening hours of the day. Appliances such 
as an air conditioner or an oven might be connected to the daylight enable 
lead 601 while house lights or a burglar alarm might be connected to the 
evening enable lead 602. 
It is to be understood that the invention is not limited to the exact 
details of construction, operation, or identical embodiments shown and 
described, because obvious modifications and equivalents will be apparent 
to one skilled in the art. The invention is therefore limited only by the 
scope of the claims which follow.