Patent GB-869551-A (GB)
Title: Digit signalling arrangements between telephone subscribers and exchanges
IPC: H04M9/00
Filed: 1958-10-03
Abstract: 869,551. Automatic exchange systems. GYLLING & CO. A. B. Oct. 3, 1958 [Oct. 4, 1957], No. 31706/58. Class 40 (4). In an arrangement for signalling digits of wanted subscribers' numbers from a subscriber to an exchange four wires are used, contacts of a keyboard are arranged to connect one or other of a first pair of said conductors to one, either or both of a second pair of said conductors, and also to vary the impedance between the first pair of conductors (from a small value to complete disconnection as described). The two pairs of conductors used are actually those respectively connected to a microphone and loud-speaker during conversation. Digit sending equipment.-As shown, four wires a, b, c, d connect the subscriber to the exchange, the first and second pairs being also used to carry currents to the loud-speaker H and from the microphone M. Wires a and b are also normally connected in series via lamps r, gr. Push-buttons 0, 1, 2 connect wire a to d, c and both d and c, respectively, and push-buttons 7, 8, 9 connect wire b similarly. Push-buttons 3, 4, 5, 6 connect a or b to c or d in various combinations, at the same time opening the loop between a and b. Setting up call.-Two exchange batteries are employed, whose terminals are represented respectively by +, - and (+), (-). Terminals - and (+) are connected together. When a calling subscriber depresses a button + on R32, 22 or R32, 25 connected over the a or b wire passes to the c or d wire and thence over conductor CD to operate both a select magnet AKSO in an allotted free link (this magnet being associated with the calling subscriber's tens digit) and a hold magnet AKBO (associated with the calling subscriber's units digit). The corresponding cross-point connects + over the R-wire to bring up the subscriber's relay AROO. The wires a, b, c, d are now connected to wires as 106 of the link. Operation of AKSO operates R2 and also brings up relay R7 whereupon R32 operates, followed by R33, which connects up to the a, b wires of all unconnected subscribers' battery of such polarity that lamps r, but not qr are lit as an indication to them not to initiate a call at this moment. Magnet AKSO also operates R11 which connects wires a, b, c, d to wires 112, 113, 114, 115, Fig. 5. ( -) and + battery are thus applied over relays R20, R21 to the a and b wires and in this circuit the lamps r and gr light and R20, R21 come up provided the digit button depressed is not any of 3 . . . 6. Relays R20, R21 connect wires 114, 115 to pairs of oppositely polarized registration relays R22, R23 and R24, R25 and one out of each pair or one out of both pairs come up according to the digital button depressed. In the event of one of buttons 3 . . . 6 being depressed, the a, b loop is opened and R20, R21 fail to operate so that leads 114, 115 are connected to pairs of relays R26, R27 and R28, R29, one of which operates according to the button depressed. Operation of any relay R22 . . . R29 brings up R30 which connects + over a contact tree to one of wires 0 . . . 9 according to the digit received and this brings up a corresponding tens select magnet BKS1. When the press button is released and the registration relay de-energized R30 falls back and R4 is unbalanced and operates, releasing R2 and bringing up R3. When the units digit button is depressed operations proceed in a similar manner, the contact tree marking now bringing up a hold magnet BKBO corresponding to the units digit. + on the R-wire brings up the called subscriber's relay AR10, so that the called subscriber's a, b, c, d wires are now connected through to wires 124 . . . 127 of the link. When the button is released R13 operates due to unbalance, and R8 follows to release R11 which connects the speech wires 103 . . . 106 via wires 131 . . . 134 and R14 is also operated. The calling and called subscribers' c, d wires are now connected to the input terminals IN1, IN2 of a first and second amplifier whose output terminals UT1, UT2 are connected respectively to the called and calling subscribers' a, b wires. Operation of R8 releases R5 and R1 follows. Relay R5 is connected in a chain of such allotter relays (not shown) and brings up R5 in the next link which is thus preallotted for the next call. Called subscriber free.-When R14 operates R17 operates for a short period due to the charging current of capacity C17. Relay R17 couples the output UT1 to the input IN1 of the first channel amplifier to make it oscillate and this passes as a calling signal to the called subscriber via an attenuating network R53, R54 switched in by R17. Called subscriber busy.-In this case the subscriber receives - ve potential on his S wire from one or other of leads 160, 161 of the link he is using. In the link attempting to establish the call this brings up R16 before R14 can come up and this causes C17 to discharge through R18 which operates for a short period to backcouple the second amplifier whose resulting oscillation is reverted to the calling subscriber as a busy signal. Amplifier switching.-The amplifiers are normally arranged to be voice-operated only one amplifier being operative at a time. Any subscriber can intervene, however, by depressing the button T. Thus when conversation is in progress relay R12 is operated over the a. b wires and the calling subscriber's lamp circuit, and R15 is similarly operated over the called subscriber's lamp circuit. If the calling subscriber operates T, relay R12 releases, bringing up R19 which locks and biases off the second amplifier, i.e. the called subscriber's speech is blocked. When T is restored R12 re-operates and the blocking bias is transferred to the other amplifier. An over-riding control button Br is also provided. If the calling subscriber depresses this he releases R15 which releases R19 and the calling subscriber's speech is blocked. R19 is not re-activated unless the caller operates his T-button again. Release is effected by the calling station operating the A-button which connects b to both c and d. This brings up R9 to release R12 and R15. When A is released R10 is unbalanced and operates, releasing R14 and all the cross-bar switch magnets whereupon R9, R10 release. A partially set-up connection (i.e. when only one digit has been dialled) can be released by operating T which releases R20, R21, whereupon R31 follows to bring up R10 and release is effected as before. A time out circuit is provided so that if R7 remains operated too long a thermal relay V8 operates to bring up the release relay R10. All links busy. Contacts 16, 17 of relays R8 of the link are all connected in series to lead 109, Fig. 6, so that if all links are busy R32, R33 operate to connect (+) and (- ) to the a, b leads to light lamps r in the subsets.