CA1049170A - Signalling device for key telephone systems - Google Patents

Abstract

Abstract of the Disclosure The present invention relates to a device which is to be used in conjunction with key telephone system, as for example, intercom system. More particularly, the invention consists of a device for decoding the pulse output from rotary dial telephones, indicating which digit has been dialed and selectively signalling the called party. Special features include acceptance of a wide rage of pulse speeds and ratios with decoding immunity to the initial hookswitch closure and the last opening. The latter per-mits the digit "1" to used, providing for an additional signal function. A decoding matrix operates a relay tree with provisions for either single or tow-digit codes. The device is intended for use in key telephone system which include rotary dial telephones.

Description

Brief Summ~ry Of The Inv tion This invention is directed to ~n improved sign~l detec-tion and c~ ng device for use with key telephone system~g as for example, intercom systems.
m e embodiment ~hown m~y utilize either s~ngle or ~wo~
digit codes, provid~ng for ~ sy~tem of up to 19 s~tlons.
Back~round Of The Invention In recent years the field of telephony h~s been adv~nced through the use of solid state sw~tching 8y8temS in which the 3ignalling informa~ion ~ processed using integrated ~ircuitry ~nd computer technology.
An ob~ect of the presen~ ention is to provide an Improved sign~ ng dcvice for key telephone systems u~ing CMOS
(complement~ry-symmetry metal oxide semiconductor) digital detec-tion which combines ~11 coun~ing ~nd decoding funct~ons in ~
~ingle de~ice. another ob~ect of ~his invention i~ to provide ~n intercom sign~lling device which allows the connection of up to 19 intercom st~tions. Stil7 3nother ob~ect of ~he inv8ntion i~
to provlde an intercom signalling d~vice which m~y utilize either ~ingle digit or two-digit codes. Stlll ~no~h~r objec~ of the invention ~ to provide a device in which the c~lling signals can be repeated wi~hout the necessity of operat~ng the swi~ch hook on the telephone ~nstrument, Yet ~nother ob~ect o~ ~he i~vention i8 to provide a device whlch includes ~ one second ~ignal contact closure whenever an lntercom 8ignal iS detec~ed. Yet ~no~her object of the invention is to provide ~ device which i~ ~o comp~ct and self-cont~ined that it m~y be installed in a fr~ction of the time ~nd ~ les~ C08t than prior art ~ys~em~.

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Broadly speaking, the above objects are met in a key telephone, intercom circui-t for operating with up to 19 stations, a calling system having a hook switch-controlled loop with keying means at ~ calling station to open and close the loop to generate a sequence of pulses, means to sense the closing of the loop when a calling -telephone is placed off hook, pulse conditioning circuit means, means to pass the sequence of pulses to the pulse conditioning means, digital counter and decoding means connected to the output of the pulse conditioning circuit means and generating decoded decimal outputs in accord-ance with the numbers of sequential pulses, diode matrix means connected to the outputs of the counter and decoding means, means connected to the diode matrix means to sense the decoded decimal outputs, relay tree means connected to the diode matrix means through the last-named sensing means and having respective branches connected to indicators at the telephones of the system, and means to selectively energize the indicators in accordance with the activation of the relay tree means.

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The above and other objects and adv~nt3ges of the invention will become apparent upon full co~sider~tion of the following detailed description ~ocompanying the drawings in which:
Figures lA to lD comprise, when t~ken together 7 a schematic di~gr~m of a decoder including regulated power ~upply~
time-ou~ circuits, and a line feed relay ~ccording to ~ preferred embodiment of the pre~ent invention.
Figure 2 i~ a schematic diagram of ~ relay tree ~nclu-din~ provision for ei~her one or two-digit s~gnalling.

General Clrcuit O~ tionfll Features Referring to Figures lA to lD9 the circuit provides the line rel~y coil Ll (Figure lA) which provides ~alk battery to the telephone or telephones while using the intercom ~y~tem.
Ql (Figure lA~ i~ used to deteot the output pulse~ from fl telephone which i~ d~ling on the intercom line7 When ~ tele-phone doe~ come off the hook on the inte~com lineg Ql ~en~e~ the current flow in the line and oper~tes the circui~ con~isting of Q2, whlch provides a relay contact clo~ure output ~nd fi transis-tor switch olo~ure output for the duration o~ ~ime ~h~t the intercom line is in u~e.
When ~he telephone whi~h h~ come off hook begins to dial, Ql p~se~ these di~l pulses ~long to ~ circuit con8~ing of part of ICl and p~r~ o~ IC:2 ~igure lC)gnamely, ICl~A), IC2(A) ~nd IC2(B~, which together form a pulse onditionlng circu~t, shown at 10.
The output of the conditioning clrcuit 10 drives I
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¦ digital coun~er/decoder and a re~riggerable one-shot circui~
~hown at ll. At the concluslon of the pul~ing, the decimal equ~valent of the number of pul~es di~led ~lll be on the output of the digital counter/decoder IC3.
The output of the digit~l counter/decoder goe~ into a diode m~trix and ~ sen~ing circuit. The enable sign~l, which i8 l~0 second in duration, come~ from the output of the retrigger-~ble one~shot ll, which includes part of ICl (Figure lC), i5l del~yed to ~ w the sensing circuit to est~blish if a digit "2"
or any digi~ from "6" to lo~ has been decoded.
For ~nst3nce, if ~ digit "2" w~s dialed, then relays K3 ~nd K4 ~Figure lB) would pull In and l~tch through l~tching c~rcuit Ql~, Ql3, and l/2 of IC4. Also~ Upon K3 ~nd Kh la~ching, ~ reset pulse would be gener~ted by the circuit Q7, QlO ~nd Ql2 (Flgurea lA ~nd lC). Thi~ reset pul~e would re~e~ the retrigger-able one-~hot's outp~t pulse, which in turn w~uld re~e~ the dig~tal coun~e~/decoder.
N~w the circuit i8 re~e~ ~nd re~dy to ~ccept ~nother sequence o~ di~l pulses ~rom Ql. With the ~ppllc~tlon cf ~nother ~equence of di~l pulses the ~ame procedure would be foll~wed a~
de~cribed be~ore. Ag~in~ the decimaI equi~alent of the number of pul~es ~pp~rs at ~he output of the digltal count~r/decoder.
Agflin ~he en~ble 8ign21 i8 de1ayed to ~llow sen~ing circu~s ~o e~blish if 3 d-lgit "2" or ~ny dig~t bet~een "6" ~nd "0" h~s been decoded, Since the fir~t dig~t di~led W~9 a dlgit "2'1, ~he ~en~ing circult for digit "2" detec~ i8 inh~blted by Q7 and Q5 (Figure lA)~ So the only ~en81ng circuit which i8 active , ~ ~49170 the sen3ing for a digit from "6" ~co "O", In the c~e ~7here Il the second digit ls ~ digit from "6" to "O", it will be sensed ¦¦ and relay K2 will pull in and l~tch through Qllg Q13, ~nd 1/2 of IC4 (P gure lB ) .
~o reset pulse is generated by the l~tehing of K2.
Therefore at ~he end of the delay period, which is approxim~tely !
20m~ec, ~he en~ble ~ applied to Q17 and Q16 ~igure lB).
Q16, when en~bled; proYides the oper2ting volt~ge for rel~ys K5 lthrough K9 (Figure lD).
Immedi~tely upon Q16 turning on9 the appropri3te rel~y -froTn K5 to K9 will pull ~n, depending upcn which relay ha~ been selected by the diode m~trix, When one o these rel~ys doe~ pull in, ~he signalling voltage i8 ~pplied to the ~ppropria~e tele-phone, ~hrough ~he contac~s of that relay ~nd ~che contact~ of ~2 ~nd el~her K3 or R~.
Upon termination oiE the en~ble ~ l, Q16 turns off ~ir~t, which all~w8 wh~chever rel~y w~s pulled in, from either K5 to K9, to rele~se. A time del~y is providea for by R50 ~nd C18 (Figure lB) ~o del~y the tr~iling edge o the enable 5~gnEIl from ~e~etting the transfer rel~ K3, Kh and relay K2. Naw the cir-cui~c ~8 back to its orig~nal quie~cen~ ~tate and is re~dy to ~ccep~c another ~erle~ of di~l pulse8 in the case where the ~me number w~nt8 to be redi~led or a di~ferent mJmber i8 di~led,, It can be ~een that due to the delay of the erlalble pul~e l~c alw~ys allows the transfer rel~ys K2 or K3 and R4 to oper~te (dry~, mE~t i8, ~1~ the t~me they operate and relea~e there i8 no ourrent ~lowing through ~heir con1:~ct5. The advantage of thi~ i~ tha~ it i~ not necess~ry to protec~ their cont~c~c3 again~t arcing whlch ._ .,- , . .
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~ ~ i ¦ result~ from high induc~ive load~ ~uch as buæzers and bell~ used ¦ in~ide ~elephones~ Xn this way the c~nt~ct~ of K5 through K9 are the only one~ which have to po8~e88 high curren~ capabilitiesl Q9 ~nd 1/2 of IC4 (Figure lC) ~ct together to gener~e .
S ~ rese~ pulse to re~e~ K3 a~d K4 in ~he event that ~ digit "2"
(tr~nsfer digit) i8 di~led ~8 the first digi~ ~nd then the tele-phone which i~ lni~ ting ~che c~ll h~ngs up, ~1~1~
mi8 device include~ provi~ion for supplying talkin~
battery volt~ge for the ~elephone ~n~trumen~s ~onnected to the sys~em.
. Referring to F~gure lA, Ll i~ ~ line feed coil. The I "IN" ~ide of the f~r~ wind~ng iB connected to "A" b~ery, ~nd ~he "OUT" side of the other winding i~ c~n~ectea to "A" ground.
The o~her s~de of e~ch winding i8 connected to ring ~nd tip respectlvely. Wikh ~ connection such ~8 this, the"A" grOuna and . .
the "A" b~ttery supply h~ a high ~ource of ~mped~nce. C2 serve~
~o bring L~ into re~onance ~t lawer frequeneie8, A 8elf-contained p~wer 8upply i8 ~nclud~d ~n the dev~ce ~o regula~e the ~upply vol~age ~nto the CMOS ~complement~ry-8~mnetry met~l oxide 8emiconductor) digit~l integr~ed clrcuit~
u8ed. mi~ i~ required 3ince the device i8 da8igned to oper~te ~rom telephone ~ys~emg ln which ~he supply volt~g~ is of the order of 18-28 volts D.C. 8pecifled for common telephone key 8y8tem equipment, Zener d~ode ZDl, resi~tor R10 ~nd Cap~citor C~
(Figure lA) comprise the vol~ge regul~tor used. ZDl m~in~in~
12 vol~s D.C, - lOqo ko ~he p~wer connection8 of ~11 XC device~
u~ed, namely, IGl, IC2, IC3 ,~nd IC4. Cap~cltor C5 provide~

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sufficient filtering of the AoC~ component of the regulated D.C. ¦
The signalling system utilized with rotary di~l type ¦ telephone in~rum~nt8 i8 common kn~wledge in ~he telephone indus-~ try. It con~ists of ~ sequentialty openTng ~nd clo~ing contact which is in æeries with the line circuit~ Thi8 series of open-~ngs and clo9ings form~ "dial pulse~". A sequence of ~hese pulse8 relate to the number di~1ed, or ins~nce: di~ling a digit "l" c~uses ~he di~l con~c~s ~o op~n and clo~e on¢e~ di~l~ng ~
digi~ "2" causes the dial contact8 to open, ~lose, open ~nd close ag~in, ~nd thus a sequence of two dl~l pu~ses correspond~ to ~
digit "2" being di~led. This type of sequence occurs relative to the digit di~led. The digit "O" c~uses lO dlal pul~es to be sequenced. A ~equence of di~l pul8es ha~ ~ cert~in repe~ition rate a8soci~ted with them and a cert~in duty cycle~
When a telephone instrument i8 off hook on the intercom l~ne~ there is ~n effective lSO 0~ loop across the tip and ring connections. Thi~ condition ceuses current to fl~w from "A"
battery ~hrough one wind~ng of Ll ou~ ~he r~ng termin~l through the other w~nding of Ll, through Rl, through D2 ~nd b~ck to the other ~ide of the 8upply "A" ground.
When ~ sufficient curr~nt flow~ with~n the loop to develop Approximately 0.75 volts ~oro8~ Rl~ the b~se emitter ~unction of Ql becomes fo~w~rd bl~sed, and Ql turn~ on, conduct-ing current ~rom "A" ground down through the ne~work R2~ R3 and Rh~
With Ql conducting, c~p~ci~or Cb~ charge~ through D3, and also, Q2 turns on, causing rel~y Kl (Figure lA) to pull in.
W~th Q2 now oonducting, Q24 is turned on. The rel~y cont~c~

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~9~L7~ i ¦l (KlA~ of Kl ~erve~ the purpo~e of oper~ting the ~ntercom button light~ through KlA ~nd L (F~gure 2) on all telephone instrument~
~n the system to ~ignify th~t the system is in use. Q24 (Figure IA) prov~de~ a l~tching ground through PC SFigure 2) for 3uxili~s~y equipment .
me time constant ~s~oci~ted w~th C4, R8 and R9 (Figure ~A) provides the current to keep Q2 and Q24 conduc~ing while Ql i~ turning on ~nd oICf followlng dial pulses. When ~he loop across tip and ring open~ ~nd remains open or ~ time period that exceeds the time const~nt of C4, R8 and R9, then Q2 wil~
stop conduct~g~ Kl ~ill release and Q24 will turn off. Thi~
act~on wi~l c~u~e ~he ~ntercom busy l~mp bwtton on e~ch telephone¦
instrumen~ to go ou~c, signifying th~t th0 sy~tem i~ m~t in u~e.
A~ described, Ql detect~ on hook and of hook conditions, as well ~ aetects di~l pulse~. As de~cr~b~d ~bove, ~suming an o~f hook conditio~ ha~ been detected9 Ql ~urns on~ c~us~ng Q2 ~nd Q24 to turn on. To illustrate how this d~vice prevents 8 digit "1" from being de~ected upon coming off hook ~ith ~n instru , m~nt, re~er to the pulse oond1tioning circuit 10 con8isting of ICl(A) and IC2(A) ~nd ~B) (Figure lC). With Ql turned on, ~
po~i~ive potenti31 i8 applied to the junctlon of C6, D4 ~nd C21 (F~gure ~C). The t~me cvn~t~nt of R2 (Figure lA) ~nd C21 (F~gure lC~ prevents ~ny hook 6witch bounce from being pas~ed through ~he pulse conditionlng ~ v~lid dial pul3e~ If Ql conducts long enough, 10 milliseco~ds9 ~hen C7 ~rts to ~h~rge through D4 ~nd RS, ~nd ~l~o ~ posl~ive di~erenti~ed pulse ~8 coupled through C6 to one ~nput of the NAND gate IC2~), which i~ only 5 milli~econas in width, ~nd the other ~npu~ i~ held 1GW

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until C7 ch~rges to the thre~h~ld volt~ge of ICl(A)9 and the output of IC2(B) rem~ns hi8h (l~V,~. When C7 does charge to the threshold voltflge o~ ICl(A), the output of ICl(A) ~witches l~w, ~nd this level is inverted by IC2(A) and ~pplie~ ~ high level (12 V.) to the other input of NAND gate IC2(B~. It take~
~ h~gh level s~gnal ~t both input~ to NAND G~te ~C2(B) fo~ its output to go low. It taka~ appr~xim~tely 200 milll~econds for C7 to ~harge ~o ~hig threshola vol~age, consequen~ly the firs~
pulse coupled by C6 to one inpu~ of NAND gate IC2(B) ~rri~es there before ~he other ~nput of IC2(B) goes high~ ~nd con-~equently ~he output from IC2~B) ren~ins high, In this way the device iB m~de ~ e ~o hook swi~ch bounce upon coming off hook and the tran~ition to ~n off hook cond~tion.
When golng back on hook5 ~g~n the pul~e conditioning clr~uit prevent~ a digit "1" from being di~led. When the te~e-phone in~rument i~ placed b~ck on hook, the posit~ve potential ~s removea from the junc~ion of C21, D4 ~nd C6. Thi~ ~au~es d nega~iYe~go~ng di~feren~iated pulse ~o be co~pled through C6, which is o the wrong pol~r~y to cause NA~D gate IC2(B)'s ou~put to ch~nge, hence no digit will be de~ec~ed, Cont~nuing on wi~h the sequence o$ event~ after ini-ti~lly coming off hook, i~ hus ~lre~dy been descr~bed th~t Ql turn~ on along w~th Q2 and Q24, ~nd 200 milli~econds l~ter XC2(B) is en3bled and the devlce i8 now re~dy to ~ccept di~l pulse~.
~i~h the dial~ng of ~ number on ~he ~elephone ~hich ~
off hook, a series of opening ~d closing ~c~u~tian~ o the loop ; ~re made. Ql detects the~e openin~s and ~loslng~ of the loop (dial pulse~) and ~urn3 on when the loop i8 elo~ed ana ~urn~ 0 . . .., , .
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~49~713 ¦l ~hen the lo~p is opened, thereby present~ng a series of positive pulse~ to the pulse conditioning circuit. W~th IC2(B) bein~
en~bled nGw, e~ch positi~e pulse coupled to ~he o~her lnpu~ o IC2(B) c~use~ its output to go low for the dur&tion of time th~t ¦
the pulse is pre~ent, ~pprox~m~tely 5 milliseconds.
The first negat~ve pul~e from the putpu~ of IC2(B) is coupled through D8 to the input of ICl~B) (F~gure lC) ~nd the t~me const~nt ne~cwork C10 ~nd R21, which cornbine to m~ke the retriggerable one-~ho~.:.ll which ~erve~ ~s ~n ln~erdigit timer.
mi~ neg~tive pulse discharge~ C10 ~nd holds ~he input to ICl(B) low, c~using ~ts ou~put to go high. If C10 does not cont~nue ~o be di~charged every 100 milliseconds9 it ~ill ch~rge positively to ~he ~hre~hold voltage of ICl(B), c~using its output ~o switch ~egative.
The neg~ti~e pul~e~ coming from the output of IC2(B) are u8ed to ho~d C10 discharged ~nd the output of ICl(B) high.
These pulses are also inverted by ICl(C~ and applied to the clock inputs of bo~h ~he digit~l counter/aecoder ~nd IC4(A) (Figure lB~
By applying ~hese pul~es to the clock ~nput of IC4~A) ~he "Q"
output will sw~tch to ~ high level. m~8 will enable Qll ~Flg-ure lB) wh~ch w~ll c~use Q13 ~o be turned on, presentlng ~
latching ground to ~he normally open cont~cts K21~, K3F ~nd K4F
of relays K2, K3 and Kh. The digi~a~ counter/decoder IC3 (Fig-ure lD) adv~nces on the positi~e-golng edge of each pul~e. The pul~es are counted ~nd appe&r on the ou~put af IC3 in ~ 1 ~a 10 fora~t, S~nce the ou~putY o:E IC3 ar~ cont~nu~lly ch~nglng ~8 long as the input i8 receiving pul~es, the QUl:pUt vf the diode m~trix, which decodes ~che output of IC3, is del~y~d ~rom being enabled un~cil pulsing h~s stopped , ; , . . . . . .

~049~L70 With the cess~tion of pulsing, C10 (Figure lC) i~
all~wed ~o ~tar~ charg~ng through R21 ~o the threshold volt~ge of ICl(B). Upon C10 reaching the threshold ~olt~ge, the output of the ICl(B) swi~ches negative. This neg~tive ex~ursion dis-charges C12 ~o zero vol~s, which causes the input ~o ICl(D) to go to zero volts and its output to go high (+12 V.). C12 immediately starts charging bark to -~12 V. ~hrough R28. The network of R28, C12 ~nd ICl(D~ (Figure iC) m~kes up the output timer, which controls how long ~he output rel~ys of this device st~y pulled in, delivering ~n ~udible supply curren~ to the ~elephone selected.
~pon the output of ICl(D) going posit~e, it is del~yed from en~blin~ the output relays b~ ~he t~me const~n~ o ~37 ~nd C16 (Figure lC). This time constant is approxim3tely 20 milli-seconds, This time del~y is provided so that outputs "6" and o~
and ~l~o output "2" of IC3 (Figure lD) c~n be interrog~ted ~or the presence of ~ high level (-~12 V.), signifying that that particular digit h~d been di~led. S~nce the ~utputs of IC3 ~re declm~l, oné and only one output will be high a~ a given t~me, Also, ~he posit~ve-going output of ICl(D3 (Figure lC) D
which is the leading edge o the en~ble pulse~ i8 fed ~nto the clock ~nd cle~r inpu~ of IC4(B) (Figure lC)~ ~hich c~ases the i Q output to go high, turning on Q3 (Figure lA), When Q3 turns on it forward-bi~es Q4 ~nd en~bles Q15 (Figure lD), W~th Q~
conduct~ng3 ~ ~positive potent~l is placed on the emitter o:E Q6 (Figure L~) ~hrough diode D6 and no~lly turned on tr~n8istor QS
Assuming th~t ou~put "2" of IC3 w~8 high, it would signify th~t a digit "2" h~d been di~led, which i~ perm~nently ,. , , ~ .................. . . . . . .
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~¦ ~ssi~ed as the tr~nsfer digit :l~or ~ two-digit int~rcom number.
With the ou~put "2" of IC3 high, Q8 (Figure lA~ will turn on, hence causing Q6 to now conduc~ and ~pply the pull-~ volt~ge for relays K3 ~nd K~ (Figure lB), Both rel~3y K3 ~nd K~, upon pulling in, will latch up vi~ cont~ct K4F of rel~y IC4 ~nd tr~nsist :or Q13. Contact K3F of rel~y K3 is norm~lly open9 wlth one ~ide of ~t connected to "B" b~ttery while the other side connects to the base of Q7 ~F~gure lA). When rel~ys K3 ~nd K~ pull in, con-t~ct K3F oloses, placing "B" b~ttery on the ba~e o~ Q7. This bias on the b~se turn~ Q7 on, ~pplying ~ po~ti:ve potenti~l through diode D~ to the b~e of Q5 which c~uses it to be held turned off, ~hich removes the forw~rd bias from the emitter of Q6 caus~g it to be held of, Al~o, when Q7 turns on9 thi~ posi~:ve potential i8 coupled to the base of QlO (Figure lA) through Cll.
Q10 is driven into conduction by thi~ pul~e ~nd by this ~tion pull~ the b~se of Qï3 (F~gure lC) low, which tu~ng lt on. me pul~e p~ssed by Cll ~8 only a few milllsecond~ ~n width. Con-sequently, Q10 ~n~ Q12 are only conducting for ~ few milli~econd~
When Q12 turns on it effectively short~ the re~is~or . .
R28, Thi8 Rction c~use~ C12 to ch~rge b~ck up to the threshold vo7tage o ICl(D) very r~pidly. Con~equently, the output from ICl(D) returns to a low level before the time con~nt of R37 and C16 ~Figure lC3 ha~ had ~ime ~pproximately 20 milliseconds) to charge up to the thre3hold volt~ge of XC2(C) (Figure lD), which when enabled by thi~ signal would have p~ssed the en~ble pul~e out to pull in the sign~lling relay~, W~h ~he output o~ ICl(D) (Figure lC) going b~ck to a low level, IC4(B) (~igure lC) i9 cleared, thereby turning Q3 ~Figure LA) off. When Q3 turns o~f it9 collector goe~ b~ck high, '"' , ,, ~ , . . .

104917(~
~n this case (GRD~ which dis~bles Q14 (Figure lD) and ~lso ¦ couple~ a positive pulse vi~ C17 ~o ~he "cle~r" inpu~ of IC3.
The "clear" pulse to IC3 resets ~ll outputs to ~ l~w l~vel, except for digit "0" output which is norm~lly high~ until the S input to IC3 receives its flrst pulseO
- W~th the conclus~on of the re~et pul~e, the retrigger-~b~e one-ghok 11~ the output timer R28, C12, ICl(D) ~nd the coun~ing/decoding circui~ry IC3 ~re all reset, ~w~iting the nex~
digit of th~ two-digit number t3 be di~led. W~th the next digit di~led the ~m~ ~equence of events t~kes place ex~ep~ for ~he pulse that resets the output timer, When the di31 pulses stop ~g~in, the decimE~l equiv~lent of the number of di~l pulses ~re presen~ ~t the o~tput of IG3. Also, again the en~ble pul~e i~
delayed to allow ~he sen~ing ci~cui~ fo~ ~ digit ~om "6" ~o "0"
to be detected. The sens~ng circuit for digit "2" i~ d~sabled now because the digit "2" w~s detec~ed ~s ~he fir~t dig~t di~led, Con~equeffl ly, itsisensing circuit is dis~bled.
Assume th~t ~he 3econd digit w~s a dig~t "6'1. Then, the decim~l output "6" of IC3 will be h~gh ~nd ~pplied through D23 to ~che emi~ter of Q15 (Figure lD). QlS, being enabled from Q3, wlll now turn on, c~using Q23 to turn on, wh~ch c~uses Q14 (Figure lB~ 1:o turn on. When Q14 turns on, rel~y K2 pulls in.
Rel~y K2, upon pulling in, w~ll latch up through i~8 awn cont~et Et2F and Q13. At the end o~ the t~me delay period" the en~ble sign~l is g~ted ~hrou8h IC2(C3 (Figure lD) ~nd is inverted by ICl(E). me en~ble ~ now a positive sign~l which ~u~ns on Q17 ~(Fi~re lB~, ~nd by Q17 turning on Q16 is turned on~

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~! The oper~ting voltage for rel~ys I~ ~hrough K9 (Flgure lD~ i~ n~w i applied to one side of the rel~y coils of I~ through K9. The hig~
level ou~put from the IC3 on decim~l output "6" is ~pplied through D22 ~nd R55 to the b~se of Q22 (Figure lD) ~hroughout S thi~ del~y period, but now th~t Q16 (Figure lB) h~s turned on and applied the operating voltage, Q22 w~ll immediately turn on~ I
pulling in K9, Referring ~o Figure 2, relays K5 to K9 ~re ~ingle form "A" ~ont~et relay~, One ~lde o all these cont~c~ se~ ~re commoned together and connect to the 3udible ~upply. Now~ ~5 the¦
cont~cts of relay K9 close, the ~ud~ble ~upply is roul:~ed through¦
these cont~c~s ~nd on to cont~c~ K2E of rel~y K2. Since K2 (Figure lB) is pulled in, the audible supply vol~ge is rou~ed . .
through the norm~lly open eont~ct~ and on ~o contacts K4E of relay K4. K4 (~igu~e lB) is ~lso pulled in 90 the ~udible 3upply volt~ge i8 routed through the norm~lly open c~nt~ct~ ~nd out to terminal T20. Term~l T20 goe~ to the telephone instru-ment assigned to ~he corresponding number in the in~ercom ~ys~cem.
When the audible supply volt~ge re~ches the ~celephone, the aud~ble device with~n the telephone wil~ sound un~il the ~udible supply voltage i8 removed.
At the end o~ the time out period ~he outpu~ of the tim er R28, C12~ ïCl~D) goes lo~, thereby remov~ng ~he o~ward bi~s ~rom Q17 (Figure lB), which l:uyrl8 Q16 off, remov~ng the oper~t~ng ~oltage from K5 ~o K9, which ~llows whichever rel~y ~a~ pulled in to release, The cont~cts of K5 through K9 will ~lways open the c Lr-cuit to the ~udible device within ~he ~elephone while current ~
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still fl~wing. Re~ys K2, K3 and K~ ~re still operated ~t thi~
t~me. Con~equently, thQ cont~cts of rel~y8 K5 to K9 h~ve to h3ve ~ high currPnt-h~ndling c~pablllty wh~le ~11 of the other relays do not, due to the f~ct th~t they ~.3w~ys operste while S there is current flowing in ~he circuit.
In ~ddition to turning Q17 off, ~he trailing edge of the timeout period (en~ble pul~e) pl~ce~ ~ low on the "cle~r"
input to IC4~B) (Figure lC), clearing it. When IC4(B) is ~le~red~
its "Q: ou~put goes low, which ~urn8 off Q3(Figure lA)., When Q3 turns off it causes a positive pul~e to be coupled-through C17 ~o the "clear" input of IC3 (F~gure lD). This c~u~es the output~ of IC3 ~o go to zero volt~ge~ except for output "O", which ig cle~red to ~ high level, logic one. At the s~me time : that IC3 i8 cleared, diode Dll i~s back bia~ed, remGv~ng the ~5 enable drive from the b~e of Q15 (Figure lD), A150D ~i~h Q3 turnin~ off, Q4'~ b~se i~ allowed to be pulled b~ck to the .
em~tter of Q4 through Rll, turning Q4 off, With Q4 turned off ~he forw~rd bi~s from QS~8 emitter i8 remwed.
In ~ddltion to turn~g Q~7 ~Figure lB~ off, the l~w level a~ the outpu~ of ICl(E) ~igure lD) i8 ~n~erted by IC2(D) ~Figure lB) and ~pplied ~o the charging c~rcui~ of R50 ~nd C18.
~hen C18 charge~ to the pos~t~ve ~hreshold volt~ge of ICl(F) (Figure lB), the outpu~ of ICl(F) 8wi~ches nega~ive (logic æero), the~eby coup~ing ~ neg~tive ~pike through Cl9 to the "cle~r" inp~ t of IC 4(A). Upon IC4 being cle~red, the "~" output swi~che~ low~
turning Qll off~ When Qll turns off ~he forw~rd bias is removed from Q13, c~using i~ t; turn off. W~en Q13 turns off i~

," ,,, ~

j' removes the locking ground p~th for rel~ys K2~ K3 ~nd K~, ~
! Consequently~ whichever ones were pulled in c~n n~w rele~se It ¦
c~n be seen that relays K2, K3 and K~ rele~se a definite del~yed I period af~er ~he rele~se of ~elays K5 through K9, me purpose of Q9 (Figure lC) is to clear IC4~) when the ~irst digit of a two~digit number is dialed; then the calling¦
party goes back on hook. This ~ction occurs ~ue to the f~ct that when the calling p~rty does go on hook after dialing ~ digit 'l2", . .
the output of XCl(D) (Figure lC) is still l~w~ holding IC4~B3 in the cle~r mode, with "Q~ l~w~ With "Q" being l~w a neg~lve potential is ~pplied to the emitter of Q9, C~p~c~ter C7 (Figure lC) starts discharging ~nd when it re~ches the threshold voltage of ICl(A) ~he output of ICl(A3 switohes posltive. C8 couples a posit~ve pulse to ~he b~se of Q9, c~using it to turn of~ briefly~ pulling the "clear" input of IC4~A) (Figure lB) to "B" battery (low level), thereby c~using the "Q" output to swi~ch l~w, which disables Qll and Q13 (Figure lB), wh~ch removes the latching ground for relays K2, K3 ~nd K4, thereby rele~sing rel~ys K3 ~nd K4 which would h~ve been pulled in if the diglt "2" h~d been di~led, , While a specific embod~ment o~ an improved ~ign~lling de~ice for key telephone systems h~s been disc~osed in the fsre-go~ng d8criptiong it will be understood the~ v~r~ous modific~tion~ ;
within the 8pirit o the invention may o~cur ~o those skilled in the art, There~ore it is intended th~t no ~imitation~ be p~ced on the invention except as deined by the scope o~ the ~ppended cl~im3.
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Claims (15)

What is Claimed Is:

1. In a key telephone intercom circuit for operating with up to 19 stations, a calling system having a hook switch-controlled loop with keying means at a calling station to open and close the loop to generate a sequence of pulses, means to sense the closing of the loop when a calling telephone is placed off hook, pulse conditioning circuit means, means to pass the sequence of pulses to said pulse conditioning means, digital counter and decoding means connected to the output of said pulse conditioning circuit means and generating decoded decimal outputs in accordance with the numbers of sequential pulses, diode matrix means connected to the outputs of said counter and decoding means, means connected to said diode matrix means to sense said decoded decimal outputs, relay tree means connected to said diode matrix means through said last-named sensing means and having respective branches connected to indicators at the telephones of the system, and means to selectively energize the indicators in accordance with the activation of said relay tree means.

2. The calling system of claim 1, and "busy line"
indicating means connected to said telephones, and means to activiate said "busy line" indicating means responsive to the operation of said loop closure-sensing means.

3. The calling system of claim 29 and wherein said "busy line" activating means comprises a transistor controlled by said loop closure-sensing means and a rely controlled by said transistor.

4. The calling system of claim 1, and retriggerable one-shot circuit means driven by said pulse conditioning circuit means and generating a timed enable signal, means to apply said enable signal to said decoded decimal output sensing means, means to delay the transmission of said enable signal to said decoded decimal output sensing means, and means to activate said relay tree means when said enable signal is applied to said decoded decimal output sensing means.

5. The calling system of clam 4, and means to reset said retriggerable one-shot circuit means and said digital counter and decoding means responsive to the reception of sequence of pulses corresponding to the digit "2".

6, The calling system of claim 4, and wherein said relay tree means includes transfer relay means for shifting from one-digit to two-digit operation, means to energize said transfer relay means responsive to reception of a sequence of pulses corresponding to the digit "2", means to generate a reset pulse responsive to the energization of said transfer relay means, means to apply said reset pulse to said retriggerable one-shot circuit means to reset same, and means to reset said digital counter and decoding means when the retriggerable one-shot circuit means resets.

7. The calling system of claim 6, and wherein said relay tree means includes further relay means to sense a digit from "6" to "O".

8. The calling system of claim 7, and means to delay the release of said transfer relay means and said further relay means upon termination of said timed enable signal.

9. The calling system of claim 7, and means to release said transfer relay means in the event that pulses corresponding to the digit "2" are received followed by the hanging up of the calling telephone.

10. The calling system of claim 1, and retriggerable one-shot circuit means driven by said pulse conditioning circuit means and generating a timed enable signal, means to apply said enable signal to said digital output sensing means, means to delay the transmission of said enable signal to said digital output sensing means, and means to activate said relay tree means when said enable signal is applied to said digital output sensing means, wherein said relay tree means includes transfer relay means for shifting from one-digit to two-digit operation, means to energize said transfer relay means responsive to the reception of a sequence of pulses corresponding to the digit "2", means to generate a reset pulse responsive to energization of said transfer relay means, means to apply said reset pulse to said retrigger-able one-shot circuit means to reset same, means to reset said digital counter and decoding means when said retriggerable one-shot circuit means resets, interdigit timer means in said pulse conditioning circuit means, means to activate said interdigit timer means responsive to the reception of sequential pulses by said pulse conditioning circuit means, and means pro-viding a latching ground for said transfer relay means respon-sive to the operation of said interdigit timer means,

11. The calling system of claim 10, and means to advance the digital counter and decoding means responsive to the reception of said last-named sequential pulses and place the pulse count on the output of said counter and decoding means in a 1 to 10 format.

12. The calling system of claim 11, and output timer means between the pulse conditioning circuit means and the relay tree means controlling the length of energization of the relay tree means.

13. The calling system of claim 1, and an audible signal current supply terminal, and wherein said relay tree means includes transfer relay means for shifting from one-digit to two-digit operation, further relay means to sense a digit from "6" to "0", and respective single-contact branch circuit relays whose contact are connected between said audible signal current supply terminal and the contacts of said further relay means, means to energize said transfer relay means responsive to recep-tion of a sequence of pulses corresponding to the digit "2", wherein the relay tree means has output terminals connected to the contact of said transfer relay means, means to delay energi-zation of said single-contact branch circuit relays until the further relay means and the transfer relay means have closed their contacts, and means to delay deenergization of said further relay means and said transfer relay means until after said single-contact branch circuit relays have become deenergized.

14. The calling system of claim 1, and means providing a time delay between the operation of said loop closure-sensing means and said pulse conditioning circuit means when the calling telephone goes off hook to prevent a digit "1" from being falsely detected,

15. The calling system of claim 14, and means to generate an inhibiting signal between the loop closure-sensing means and said pulse conditoning circuit means when the calling telephone goes back on hook which inhibits operation of said pulse conditioning circuit means to further prevent false digit detection.