CA1048938A - Control current generator for central dictation system - Google Patents

Abstract

Abstract of the Disclosure A control current generator for generating control currents of different magnitudes representing respective functions, and having particular application in a central dictation system. A constant current generator generates a constant current whose magnitude is determined by the resistance connected to the constant current generator. A plurality of resistors having different values is provided to be individually connected to the constant current generator, and thereby establish the magnitude of the constant current generated thereby. In addition, a signal generator is provided for super-posing a characteristic signal onto the constant current generated by the constant current generator, this signal generator being selectively energized in response to the operation of predetermined control switches. When differ-ent control switches are operated, the constant current of corresponding magnitude is generated without the superposed characteristic signal.

Description

:~)48938 This is a divisional of copending application Serial No.
242,610 filed December 24, 1974 by the Dictaphone Corporation.
mis invention relates to a central dictation system and, in particular, to the generation and detection of various function commands and to the manner in which such functions are controlled in response to such commands.
Central dictation systems are known wherein a central record/playback unit is adapted to be individually accessed by any one of a plurality of remote dictate stations so as to record dictated information on a record medium. In such systems, the central re~ord/
playback unit can be accessed by only a single dictate station at any given time. ~hile one dictate station is in communication with the central unit all other dictate stations are excluded, or locked out, from also communicating with the central unit.
The advantage of such central dictation systems is that individual dictators need not be concerned with the manipulation of various recording media, nor need they attend to the time consuming task of delivering recording media having dictation thereon to appropri-ate personnel for transcription. In the typical central dictation system, a recording medium having a relativcly large capacity for re-cording dictation is provided so that received dictation communicated from a remote dictation system is recorded on the medium and can be subsequently reproduced for transcription. In one type of central record/playback unit, the record medium consists of an endless loop of magnetic tape which is driven past a dictation transducing station and is also driven past a transcribing transducing station. mese stations are essentially operated independently of each other so that a dictation operation can be perf~rmed simultaneously with and 1~)4~938 independently of a transcribing operation. Thus, such a central dictation system advantageously permits the efficient use of dictating and transcribing apparatus. Moreover, dictated information can be almost immediately transcribed. A typical prior art central dictation system having an endless loop o magnetic tape is described in United States Patent No. 3,817,436, issued June 18, 1974, and is assigned to Dictaphone Corporation, the assignee of the present invention.
Central dictation systems of the aforenoted type can be readily adapted to accomodate a high volume of dictation by pro-viding plural record/playback units at a central location and by providing suitable switching apparatus which permits any one remote dictate station to gain access to any one of the plural record/playback units. However, it has been found that, as more central units are provided to thereby accomodate more remote dictate stations, the distance between many such remote stations and the central units becomes quite large. Consequently, it is necessary to provide con-ducting cables having extremely long length between such remote stations and the central units to permit information to be trans-mitted therebetween. The inherent resistance of very long con-ducting cables tends to deleteriously affect the levels of control commands which must be transmitted from the remote station to the central unit to control a dictation operation. Typically, such control commands have been represented by DC voltages of predetermined magnitudes or several magnitudes of resistances connected to the transmission path, each magnitude representing a control function, or command to be performed at the central unit. Unfortunately, the impedance loading effect attributed to the conducting cables dis-torts the control command magnitudes so that an erroneous command can be received at the central unit thus causing an improper :1~)4~38 function to be performedO
Although it is technically feasible to account for such loading effects prior to the installation of the central dictation system, it usually is impractical to a~just each remote dictate station function generator in accordance with the length of conducting cable extending between that station and the central unit. In addition, for those applications wherein a remote dictate station can gain access to any one of plural record/playback units, and wherein such record/playback units are disposed at various locations, the resultant variations in cable length from the remote stat}on to each central unit cannot be readily accounted for. Also, where the remote stations are connected through a switching apparatus, such as a conventional telephone PBX apparatus, various random cable lengths can be provided between the remote station and the record/
playback unit ultimately connected thereto.
In central dictation systems of the aforenoted type, it often is necessary for a dictator to be furnished with the immediate transcription of dictated information. However, since a large amount of dictated information previously recorded on the endless magnetic tape might be awaiting transcription, a delay can be expected until such dictated information is transcribed. Although sOme central dictation systems permit a transcribing station to be switched from connection with the transcription head to the dictation head :1~48938 so as to effectively by-pass the stored tape awaiting transcription, and to thus immediately transcribe the dictated information last recorded on the tape, it has been found that this mode of operation is accompanied by various disadvantages. For example, if the dicta-tion transducer of the record/playback unit is being used to perform a transcription operation, then that unit cannot be utilized to record dictation until such transcription operation is completed. Also, whereas the record/playback unit, when used in its normal modes of operation, advantageously permits the simul-taneous recording of dictation and transcription of recorded dictation, the use of the dictation transducer for a transcription operation requires that the dictated information first be completed. The simultaneous dicta-tion and transcription operation cannot be performed.

1~)4~5'38 It is an object of the present invention to provide an improved function signal generator capable of being used in a central dictation system whereby function command signals are generated and transmitted substantially without deleterious affects due to, for example, random cable lengths.
According to the present invention, there is provided a control current generator for generating control currents of predetermined magnitudes representing corresponding, predetermined functions for transmission from a first location, such as a remote dictate station, via a transmission channel to a second location, such as a record/reproduce station in a central dictation system, to thereby control predetermined functions at said second location, comprising current generating means for generating a constant current having a predetermined magnitude determined by resistance means selectively connected thereto and being independent of the load presented by the transmission channel; a plurality of resistance means having different values for determining the magnitude of said constant current; a plurality of manually operable switches for selectively connecting individual ones of said resistance means to said current generating means; signal generating means for super-posing a characteristic signal on the constant current generated by said current generating means; and energizing means responsive to the operation of predetermined ones of said switches for energizing said signal generating means.

Various other objects and advantages of the present invention will become apparent from the forthcoming detailed description thereof and the novel features will be particularly pointed out in the appended claims.
In accordance with this invention, a central dictation system is pro~ided including at least one record/reproduce station for recording dictated informa~ion on a record medium and for reproducing same, and having at least one remote dictate station adapted to communicate with the record/reproduce station, and lo wherein the functions of the record/reproduce station are controlled by a constant current generator provided at the remote dictate station, the constant current generator being actuated when the remote dictate station is operatively connected to a record/re-produce station to thereby transmit constant currents of pre-determined magnitudes which are determinative of functions to be performed; the magnitudes of the transmitted currents being sensed at the record/reproduce station by a current detector for decoding such currents into control signals; and the control signals being selectively applied to a function controller whereby the selective performance of predetermined functions at the record/
reproduce station is controlled. In one embodiment of the present invention, one of the controllable functions is a transfer function whereby a remote dictate station is switched from a record/reproduce station to an additional, predetermined record/
playback unit to enable dictated information to be recorded at the additional, predetermined unit.

i~48938 The present invention will now be described in greater detail with reference to the accompanying drawing in which:
Figure 1 is a block diagram representing a central dictation system of the type wherein the present invention finds ready application;
Figure 2 is a block diagram representing the connections between a remote dictate station and a record/
reproduce station in the central dictation system illustrated in Figure l;
Figure 3 is a schematic illustration of a control function current generator in accordance with the present invention;
Figure 4 is a schematic illustration of a current decoder for use with the generator of Figure 3;
The Central Dictation System_ Referring now to the drawings and, in particular, to Figure 1, there is illustrated a block diagram representing a central dictation system comprising a plurality of remote dictate stations, a plurality of record/reproduce stations and a plurality of transcribe stations. As depicted, N remote dictate stations can be provided and, in the interest of simplification, only four dictate stations 10, 12, 14 and 16 have been shown. Similarly, although any convenient number of record/reproduce stations can be provided, only three such stations 18, 22 and 26 have been shown. Typically, the record/reproduce stations may be provided at a central location and the remote dictate stations may be provided at any convenient locations and may be separated from the central location by any suitable distance.
For example, the remote dictate stations may be situated in various lo separate offices in an office building and the central location may be situated at a designated centralized location in such office building.
A typical record/reproduce station 18 is comprised of a record medium such as an endless loop of tape,in combina-tion with various transducing heads, tape drive mechanisms, audio electronics and control apparatus for effecting the recording and reproduction of audio information for achieving a dictation and a transcription operation. The record medium included in the record/reproduoe station is adapted to be driven so as to traverse a dictation site having a magnetic transducer such as a combination record/ playback/erase head, and a transcription site, also having a magnetic transducer such as a playback head. Although physically contained within the same structure, the dictation and transcrip-tion sites are independently operated. In addition, since dictation can proceed without a concurrent transcription operation, tape which has been dictated and which is awaiting transcription is adapted to be stored in serpentineefashion within a tape housing storage location between the dictation and transcription sites.

1(~4~938 Also, since transcription can proceed without a concurrent dictation operation, magnetic tape which has been transcribed and is awaiting subsequent reuse at the dictation site is adapted to be stored, also in serpentine fashion, at another location between the dictation and transcription sites. Accordingly, the record/reproduce station can be similar to the record/playback unit described in the aforenoted United States patent.
Since each remote dictate station is capable of communicating with any of the record/reproduce stations 18, 22 and 26, each record/reproduce station is connected to each of the remote dictate stations by a conducting cable. Accordingly, the record/
reproduce station 18 is connected by a conducting cable 18' to the N remote dictate stations. As shown, these remote dictate stations are connected in parallel to the conducting cable 18'. Similarly, the record/reproduce station 22 is connected via a conducting cable 22' to each of the N remote dictate stations. So also, a conducting cable 26' connects the record/reproduce station 26 to each of the N
remote dictate stations. Although all of the illustrated remote dictate stations are connected in parallel to each of the record/
reproduce stations, it will be shown hereinbelow that only a single dictate station can communicate at any given time with a single record/reproduce station. Hence, in an expected installation com-prised of many more remote dictate stations than there are record/
reproduce stations, it will be appreciated that, when each of the record/reproduce stations is communicating with a remote dictate station, any additional remote dictate station will be precluded from gaining access to a record/reproduce station. Suitable seizure and privacy control circuits are ~048938 provided for this purpose and will be described in greater detail hereinbelow.
A typical remote dictate station, such as the dictate station 10, is comprised of audio and function control apparatus which is connected by a conducting cable through a plurality of switches lOa, lOb, and lOc to the conducting cables 18', 22' and 26'.
The purpose of the switches lOa-lOc is to permit an operator at the dictate station 10 to select a particular record/reproduce station to which audio information and function control commands are to be lo transmitted. The switches lOa-lOc may, therefore, comprise con-ventionaly push button-type switches having visual indicators, such as lamps, associated or integral therewith. The purpose of such lamps is to indicate when a particular record/reproduce station is unavailable to be accessed by a remote dictate station, such as when that record/reproduce station is then communicating with another dictate station, and to thus enable an operator to properly 9elect an available record/reproduce station for communication. Thus, if the record/reproduce station 18 is available, an operator at the remote dictate station 10, by depressing the switch lOa will connect the audio and control function electronics 11 at the dictate station 10 to the record/reproduce station 18 via the conducting cable 18~.
Similarly, if the record/reproduce station 22 is available, the switch lOb, upon being closed, will connect the audio and control function electronics 11 to the record/reproduce station 22 via the conducting cable 22'. The operation of the switch lOc effects a similar con-nection between the remote dictate station 10 and the record/ re-produce station 26. If a switch associated with an unavailable record/reproduce station is depressed, the remote dictate 1~)4~938 station will not be operably connected thereto and, in one embodi-ment, a distinctive signal, such as a predetermined tone, will be provided at the remote dictate station to signify the unavailability or the selected record/reproduce station. The privacy and sie7ure control circuitry which insures that only a single remote dictate station can gain access to a record/reproduce station may be of the type described in United States Patent No. 3,835,261, which issued on September 10, 1974 and is assigned to the assignee of the present invention. A signal which is extended to all remote dictate stations from a record/reproduce station to indicate the status, i.e., availability, of such record/reproduce station is transmitted over one of the conducting channels included in the conducting cable, such as cable 18'.
The various function aommands generated from each of the remote dictate stations are transmitted to a record/reproduce station over another conducting channel included in the conducting cable, such as cable 18'. These command signals are constant currents of predetermined magnitudes and are generated in response to the selective manual operation of various switches disposed at the dictate station. Typical of such function commands are "dictate", "rewind", "stop", "play", and "fast forward". Each of these command signals serves to control the movement of tape past the dictation transducer site and, additionally, conditions the dictation transducer for a record or playback mode of operation. An example of mechanical driving apparatus which is used to move the magnetic tape is disclosed in United States Patent No. 3,934,774 which issued on January 27, 1976 and is assigned to the assignee of the present application.
Audio signals are transmitted from a remote dictate station to a record/reproduce station during dictation and iO4~938 are returned to the remote dictate station during a review of recorded information via a further conducting channel included in the conducting cable, such as conducting cable 18'. A further conducting channel included in the conducting cable is adapted to extend the system reference potential, such as ground, to a remote dictate station when the record/reproduce station is properly accessed by the remote dictate station.
In a typical remote dictate station, the sound trans-ducers for converting sound signals into audio signals and for transducing audio signals into sound signals are provided as a con-ventional microphone and loudspeaker. Such sound transducers are contained in a handset which is associated with various function control switches. ffl ically, the handset is adapted to be supported on a cradle having a cradle switch which is actuated when the hand-set is removed to thereby gain access to a record/reproduce station and is deactuated when the handset is returned to the cradle upon the completion of a dictation operation. To insure that subsequent dictated information which mi-ght be derived from another remote dictate station is not recorded over previously reoorded information, the deactuation of a cradle switch results in the automatic recording of a predetermined code immediately following a recorded message. This predetermined code is sensed when the tape is reversed past the dictation transducer site to automatically prevent further tape bearing prerecorded informa-tion from also being reversed past the dictation transducer. Thus, a subsequent dictation operation will not affect previously recorded information; nor will such previously recorded information be reproduced during a subsequent dictation or playback operation. The recording of such predetermined 1~)4~938 code and the sensing thereof is described in detail in United States Patent No. 4,041,249 which issued on August 9, 1977 and is assigned to the assignee of the present application.
Although each of the remote dictate stations is here illustrated as including plural station selecting switches, such as switches lOa, lOb and lOc, to thereby permit an operator to manually select a desired record/reproduce station for communication, in an alternative embodiment such manual selecting switches are replaced by an automatic switching matrix. Such switching matrix is conventional and is of the type generally used in telephone switching applications.
When such an automatic switching matrix is used, a remote dictate station is automatically connected to the first record/reproduce station which becomes available. The conditioning of a record/
reproduce station with respect to its availability can be a function of the amount of unused tape present therein and upon which informa-tion can be recorded.
As-a further feature of the central diotation system illustrated in Figure 1, an additional, predetermined record/playback unit 30 is provided and is intended to receive dictate information for recording when such information is of a high priority of importance.
As shown, the priority unit 30, which may be similar to the record/
reproduce stations 18, 22 and 26, is connected by a conducting cable 30' to each of the record/reproduce stations 18, 22 and 26. The cable 30l may include multiple conducting channels such as are included in each of the cables 18', 22l and 26l. The record/reproduce stations 18, 22 and 26 are connected in parallel to the conducting cable 30' by additional cables, each including multiple conducting channels.
~ccordingly, the priority unit 30 _ 14 -1~4~938 bears the same relationship to each of the record/reproduce stations as does a record/reproduce station to each of the remote dictate stations. As will be described in greater detail hereinbelow, when a "transfer" function command is transmitted from a remote dictate station to a record/reproduce station in communication therewith, such "transfer" command results in the switching of, for example, the dictate station 10 from communicating with, for example, the record/reproduce station 18, to now communicate with the priority unit 30. A conducting path will thus extend from the cable 18l, through the record/reproduce station 18 to the cable 30' and to the priority unit 30. While the remote dictate station is in communication with the priority unit, the record/reproduce station 18 will not be operatively coupled to the remote dictate station, but will maintain a quiescent or st~and-by condition until communica-tion with the priority unit is completed.
Each of the record/reproduce stations 18, 22 and 26 is connected to a transcribe station 20, 2~ and 28, respectively.
By suitable operation thereof, an operator of a transcribe station causes various transcribe control function signals to be transmitted to the associated record/reproduce station to thereby control the movement of the recording tape past the transcription transducer site ~o as to facilitate a transcribing operation. Generally, the transcribe station is provided with suitable switches, such as foot-pedal actuated switches, to control the movement of the tape past the transcription tr~sducer site. In addition, a sound re-producer, such as a loudspeaker or headphones, is provided to receive reproduced audio signals, and suitable audio electronics are pro-vided to permit an adjustment in the reproduced sound, as 1~)4~938 desired.
Although not shown herein, an alternative embodiment includes a supervisory console to supervise the operations of the record/reproduce stations, the transcribe stations and the priority unit. For example, suitable switching apparatus can be provided such that each transcribe station is connected through the supervisory con-sole to its associated record/reproduce station. In this configur-ation, a supervisor can, if desired, connect transcriber 20, for example, to the record/reproduce station 22. Such a connection might be preferred so as to not require an operator at, for example, the transcribe station 20 to relocate at, for example, the transcribe station 24 in order to transcribe the dictated information recorded at the record/reproduce station 22. Also, the skills of a particular transcriptionist may be readily matched to the amount of dictated tape awaiting transcription in a particular record/reproduce station. Also, a supervisory operator may intentionally dispose an otherwise available record/reproduce station into its "unavailable"
condition if it is determined that the capacity of that record/
reproduce station to receive additional dictation will soon be reached while another record/reproduce station exhibits far more acceptable capacity. me supervisory console might also be provided with audio communication equipment to permit a supervisory operator to communicate with an operator at a remote dictate station, if desirèd, and might furthermore manually transfer such a remote dictate station from communication with a record/reproduce station to communication with the priority unit.
me foregoing general description of a central dictation system of the type depicted in ~igure 1 is merely ~4~938 intended as a broad discussion of various functions, operations and features of such system and is not to be construed as limiting the central dication system only to those features which have been described.
Dictate Station - Record/Re~noduce Station Communication A block diagram illustrating the connections between a remote dictate station, such as station 10, and a record/reproduce station, such as station 18, is illustrated in Figure 2. The dictate station 10 is comprised of a privacy lo and seizure control circuit 50, a seizure switching circuit 54, a function control coding circuit 56, an audio switching circuit 58 and audio electronics 60. In addition, a micro-phone 62 and a loudspeaker 64 are shown as being connected to the audio electronics such that audio signals can be transmitted to and received from the record/reproduce station. The various functional components of the dictate station 10 are connected to conducting~channels included in the conducting cable 18'. It is recalled that this conducting cable extends from the record/reproduce station 18 to each of the remote dictate stations. For convenience, the individual conducting channels included in the cable 18' are designated as a ground line 42, a privacy line 44, a control line 46 and an audio line 48. The privacy line 44 is con~ected to the privacy and seizure control circuit 50 and is adapted to supply discrete DC voltages representing the availability of the record/reproduce station 18 to communicate with the remote dictate station 10. Such discrete DC voltages are used by the privacy and seizure control circuit 50 to energize the dictate station 10 to thereby permit a dicta-tion operation to be executed.

~)41~938 The ground line 42 is connected through the seizure switching circuit 54 to the function control coding circuit 56 and to the audio electronics 60. The ground line 42 is provided with a reference potential for the central dictation system, such as a system ground. When closed, the seizure switching circuit 54 extends this system ground to the function control coding circuit and to the audio electronics such that these respective components are operably energized. As shown, the seizure switching circuit 54 is connected to the privacy and seizure control circuit 50 and is adapted to be closed thereby when a predetermined DC voltage is supplied to the privacy and seizure control circuits by the privacy~lline 44.
The function control coding circuit 56 is connected to the control line 46 and, when energized, is adapted to permit constant currents of predetermined DC magnitudes to flow there-over. The particular magnitudes of the constant currents are determinative of control functions which are to be performed by the record/reproduce station 18 in response to the manual selection thereof,as will bedescribed in greater detail here-inbelow. Suffice it to say that, because constant currents are transmitted as control function commands, and since a constant current magnitude is not affected by line impedance, substantially identical constant current magnitudes are received at the record/
reproduce station for identical function control commands, regardless of the length of the control line 46. That is, the inherent impedance of a long control line will not distort or degrade the magnitude of the constant current transmitted thereover.
The audio switching circuit 58 is effectively closed by the privacy and seizure control circuit 50 when a predetermined DC voltage is supplied to the privacy and _ 18 -~04893~3 seizure control circuit by the privacy line 44. The closing of the audio switch is adapted to establish an audio transmission channel between the audio electronics 60 and the audio line 48 to thereby permit audio information to be transmitted to the record/reproduce station 18 for recording on the record medium and f-or permitting reproduced~audio signals recovered from recorded information to be transmitted from the remote dictate station to the audio electronics 60. The audio electronics are comprised of amplifiers and filters for suitably operating upon audio signals to enable the proper transmission and reception thereof.
The privacy and seizure control circuit 50 is of the type described in aforenoted United States Patent No. 3,835,261. This circuit includes a switch 52 which may be, for example, the cradle switch described hereinabove with respect to Figure 1. This switch is normally open when the dictate station is not in use and, con-versely, is closed when a dictation operation is desired. It will be appreciated that, in accordance with the circuitry included in the privacy and seizure control circuit, when the switch 52 is closed, current flows through the privacy and seizure control circuit only if the predetermined DC voltage is provided on the privacy line 44.
This predetermined DC voltage is provided only if the record/reproduce station 18 is in an available condition so as to be capable of communicating with the remote dictate sta~ion 10. As described in the aforenoted patent, once current flows through the privacy and seizure control circuit, current flow therethrough will continue even when a second predetermined DC voltage is provided on the privacy line. However, if such second predetermined DC voltage is provided on the privacy line 44 when the switch 52 is first 104~938 closed, this voltage will not permit current to flow through the privacy and seizure control circuit. Hence, this second DC voltage is an indication that the record/reproduce station 18 is not avail-able for communication with the remote dictate station 10.
The record/reproduce station 18 includes a bias control circuit 70 connected to the privacy line 44, a voltage detecting circuit 76 connected to the audio line 48, a function decoding circuit 78 connected to the control line 46 and function control apparatus 80 and record/playback apparatus 82. The purpose of the bias control circuit 70 and the voltage detecting circuit 76 is to provide indications of the availability of the record/reproduce station 18 to communicate with a remote dictate station and to sense when a remote dictate station has gained access thereto. The bias control circuit 70 can be considered to be a switch, such as a change-over switch, having a first DC voltage supplied thereto by, for example, a first DC voltage source 72, and a second DC voltage supplied thereto via, for example, a second DC voltage source 74.
Depending upon the actuation thereof, as will be described below, the bias control circuit 70 is adapted to selectively apply the first DC voltage or the second DC voltage to the privacy line 44.
When the record/reproduce station 18 is in a quiescent state, that is, it is not communicating with a remote dictate station, and is available for such communication, the bias control circuit 70 supplies the first DC voltage from the voltage sourGe 72 to the privacy line 44. Such first DC voltage may exhibit a predetermined magnitude and/or polarity. However, if the record/reproduce station 18 is in communication with a remote dictate station, the bias control circuit is changed over _ 20 -to now apply the second DC voltage supplied from the second voltage source 74 to the privacy line 44. This second DC voltage may exhibit a second predetermined magnitude and/or polarity.
The voltage detecting circuit 76 is coupled to the bias control circuit 70 and is adapted to actuate the bias control circuit so as to change over the DC voltage applied to the privacy line 44.
The voltage detecting circuit 76 responds to a first voltage applied thereto by the audio line 48 to maintain the bias control circuit 70 in the condition whereby the first DC voltage applied by the voltage source 72 is applied to the privacy line. The voltage detecting circuit 76 is responsive to a second voltage applied by the audio line 48 to change over the bias control circuit 70 so that the second DC voltage supplied by the voltage source 74 is applied to the privacy line. me first voltage applied to the voltage detecting circuit 76 is produced when none of the remote dictate stations has accessed the record/reproduce station 18; and the second voltage is applied to the voltage detecting circuit when a remote dictate station has gained access to the record/reproduce station.
The function decoding oircuit 78 is responsive to constant currents of predetermined magnitudes representing control function commands which are transmitted to the record/reproduce station by a remote dictate station. These received currents are decoded into predetermined control signals which, in turn, are supplied to the function control apparatus 80 to thereby selectively control the various operations at the dictation transducer site in the record/reproduce station 18. The function decoding circuit 78 and the function control apparatus 80 will be described in greater detail hereinbelow.

1~4~938 The record/playback circuitry 82 is responsive to received audio information to thereby supply audio signals to the dictation transducer for recording on the record medium. In addition, during a playback mode, the record/playback circuitry receives audio signals recovered from the record medium by the dictation transducer and trans-mits such recovered audio information to a communicating remote dictate station.
The manner in which the illustrated components cooperate to permit the record/reproduce station 18 to be accessed and seized for communication by a remote dictate station, such as the station 10, now will be briefly described. Let it initially be assumed that the record/reproduce station is not then communicating with any remote dictate stations and is available to be accessed. Consequently, the bias control circuit 70 is disposed such that the first DC voltage supplied by the voltage s~urce 72 is applied to the privacy line 44 and is thus extended to all of the remote dictate stations connected to the conducting cable 18'. It is recalled that this first DC
voltage is sufficient to cause current to flow through a privacy and se~zure control circuit 50 at any remote dictate station which will be energized for communication. Also, since the record/reproducce station is not communicating with any remote dictate station, the audio line 48 is provided with a first voltage which is sensed by the ~oltage detecting circuit 76.
Now, if an operator of the remote dictate station 10 wIshes to communicate with the record/reproduce station 18 to execute a dictation operation, the switch 52 is closed. Cons-equently, current flows through the privacy and seizure control circuit 50 in response to the first DC voltage applied 104~938 thereto by the privacy line 44, resulting in the closure of the seizure switching circuit 54 and the audio switching circuit 58. When the seizure switching circuit is closed, the ground potential supplied by the ground line 42 is extended to the function control coding circuit 56 and the audio electronics 60. mese components are thus energized and now are adapted for operation.
When the audio switching circuit 58 is closed, current now is permitted to flow therethrough, resulting in a voltage change on the audio line 48. mis change in the voltage is representative of the fact that the remote dictate station 10 has gained access to the record/reproduce station 18. Accordingly, the voltage dete-cting circuit ?6 responds to this changed voltage to change over the bias control circuit 70 so that the second DC voltage supplied by the voltage source 74 is now applied to the privacy line 44 and, in turn, is extended to all of the remote dictate stations coupled to the con-ducting cable 18'. mis second DC voltage will prevent any other remote dictate station from gaining access to the record/reproduce station, but will not cause the privacy and seizure control circuit 50 at the remote dictate station 10 to be deactuated. Accordingly, the remote dictate station 10 now has gained access to the record/
reproduce station 18 and has seized the record/reproduce station in a manner such that the privacy of communication therewith is assured.
When the operator of the dictate station 10 has com-pleted a dicta~ion operation and no longer desires to communicate with the record/reproduce station 18, the switch 52 is opened. It is recognized that, by opening this switch, current no longer flows through the privacy and seizure control _ 23 -1C)48~38 circuit 50 with the result that the seizure switching circuit 54 and the audio switching circuit 58 are, respectively, deenergized. When the seizure switching circuit 54 is thus opened, ground potential is removed from the function control coding circuit 56 and the audio electronics 60 which deactivates these components. Also, when the audio switching circuit 58 is opened, the voltage at the audio line 48 now returns to its initial value which is sensed by the voltage detecting circuit 76. This sensed voltage now causes the voltage de-tecting circuit to change over the bias control circuit 70 to its lo initial condition whereby the first DC voltage supplied by the volt-age source 72 is again applied to the privacy line 44. Accordingly, the voltage detecting circuit 76 has sensed that the remote dictate station 10 is no longer in communication with the record/reproduce station 18 and the bias control circuit 70 now applies a voltage to the privacy line 44 indicative of the availability of the record/
reproduce station 18 to communicate with other remote dictate stations.
It is recognized that, when the remote dictate station 10 is in communication with the record/reproduce station 18, the second DC voltage applied to the privacy line 44 from the voltage source 74 by the bias control circuit 70 is of such magnitude and/
or polarity that, if the switch 52 in another remote dictate station is closed, this second DC voltage supplied to the privacy and seizure control circuit 50 in such other remote dictate station prevents a current flow through such circuit. Hence, the seizure switching circuit 54 and the audio switching circuit 58 at such other remote dictate station cannot be actuated and communication with the record/
reproduce station 18 is inhibited. Thus, when one remote dictate station is communicating with the ~04~938 record/reproduce station, all other remote dictate stations are locked out, and the privacy of communication is assured.
Function Control Codin~ Circuit A principle problem attending prior art central dictation systems is that the length of co~ducting cable which extends between a remote dictate station and a record/reproduce station is often long enough such that the inherent resistance therein presents a deleterious load to the dictate station. Although this loading effect usually does not significantly degrade the quality of the audio signals transmitted between the communicating stations, it can substantially affect the integrity of control signals which are transmitted as function commands from the remote dictate stations to the record/
reproduce station. For example, in central dictation systems wherein control signals are represented as discrete voltages such that a particular function command is associated with a corresponding voltage level, the intrinsic resistance of a long conducting cable causes a voltage drop in the control signal which ultimately is received at the record/reproduce station. Although in many instances such a voltage drop can be predicted and thus accounted for either by producing a higher voltage which is to represent a particular function command or by significantly amplifying the received voltage to increase its voltage level at the record/reproduce station. How-ever, as the actual length of conducting cable extending between a r~mote dictate station and a record/reproduce station might not be known at the time of manufacture or might be changed after an init~al installation, it ~ften is quite difficult to compensate for the loading attributed to a long conducting cable. Consequently, 10~938 the resultant voltage drop in a received function command can lead to an erroneous interpretation of such command.
Therefore, in accordance with one feature of the present invention, control signals representing function commands are produced in the form of constant currents of predetermined magnitudes, wherein a particular current magnitude is used as a command for a corresponding function. The function control coding circuit which is used in accor-dance with this feature is illustrated in Figure 3. This circuit is adapted to transmit constant currents over the control line 46 and is comprised of a constant current source 102, a first set of resistors 110 coupled to the constant current source, and a second set of re-sistors 112 connected to the constant current source and a tone oscillator 130. In one ~ypical embodiment, the constant current source 102 is comprised of complementary transistors 104 and 106 interconnected such that the collector electrode of the transistor 106 is connected to the base electrode of the transistor 104 and the collector electrode of the transistor 104 is connected to the emitter electrode of the transistor 106. Of course, other embodiments can be used if desired. A resistor 108 connects the collector electrode of the transistor 106 to the emitter electrode of the transistor 104 and, further, to the control line 46 through the diode 142. If the transistor 104 is a pnp transistor and the transistor 106 is an npn transistor, then current is seen to flow through the control line 46, through the diode 142 and through,the interconnected transistors 104 and 106 to the junction defined by the common-connected collector and emitter electrodes. This junction is connected to the first set of resistors 110 through the series-connected switched 114a, 116a, and 118a, and is further connected through a diode 126 to the second set of resistors 112 via the parallel-104~938 connected switches 120a and 122a. As shown, if each of the switches 114a, 116a and 118a remains in its illustrated opened state, a con-ducting path extends from the constant current source 102 through the diode 126 to the second set of resistors 112. However, if any one of the switches 114a, 116a or 118a is closed, such conducting path is interrupted.
The first set of resistors 110 is comprised of a plurality of resistors 114, 116 and 118 which are adapted to be connected to the respective switches 114a, 116a and 118a so that an individual one of these resistors will thus be connected in series with the constant current souree 102. For example, if the switch 114a is closed, then the resistor 114 is connected to the constant current source 102 and, moreover, in view of the series-connection of the switches 114a, 116a and 118a, no other resistor can then be con-currently connected to the constant current source. Similarly, if the switch 116a is closed such that the resistor 116 is connected in series with the constant current source 102, then a conducting path cannot be extended from the constant current source to the switch 118a and, therefore, the resistor 118 cannot concurrently be connected to the constant current source. However, should the switch 114a now be closed, the previous connection of the resistor 116 to the constant current source 102 will be interrupted and the resistor 114 thus will be connected to the constant current source. It there-fore is apparent that the switches 114a, 116a and 118a are coupled to the constant current source 102 in a predetermined hierarchy such that the closure of certain ones of these switches will override a previous closure of other switches.
The switch 118a not only serves to selectively 104~938 connect the resistor 118 to the constant current source 102 but, additionally, serves to connect the second set of resistors 112 to the constant current source. The second set of resistors is com-prised of a resistor 120 which is adapted to be connected in series with the constant current source 102 by a switch 120a. Additional resistors 122 and 124 are adapted to be selectively connected in series with the constant current source by the particular operating state of a switch 122a. For example, if the switch 122a is a single-pole/double-throw switch, then the resistor 122 will be connected to the constant current source when the switch 122a is in a first position and the resistor 124 will be connected to the constant current source when the switch is in a second position. The switch 122a also has a neutral, or isolated, position. It will, or course, be apparent that the operation of the switches 120a and 122a will have no effect upon the constant current source unless all of the switches 114a, 116a and 118a are opened, as illustrated.
me resistance values of the resistors 114 and 120 are selected to be equal. Also, the resistors 116 and 122 are of equal resistance value. Finally, the resistors 118 and 124 are of equal value. Thus, as is recognized, when the resistor 114 or the resistor 120 is connected in series with the constant current so~rce 102, the same constant current of a first predetermined magnitude will be caused to flow in the control line 46. Similarly, if either the resistor 116 or the resistor 122 is connected in series with the con-stant current source, the same constant current of a second pre-determined magnitude will be caused to flow in the control line.
Finally, if either the resistor 118 or the resistor 124 is connected in series with the constant current source, the same constant current of a third predetermined magnitude will be caused to flow in the control line.
Because of the particular hierarchy of interconnections between the switches 114a, 116a and 118a, only a single one of the first set of resistors can be connected to the constant current source 102 at any given time. Thus, there is no ambiguity in the generation of a constant current if two of these switches are closed at any given time. This is because the switch associated with a higher position in the hierarchy will override a previously closed switch associated with a lower hierarchial position. Although the switches 120a and 122a can be similarly interconnected in a prearranged order of hierarchy, the switch 120a and the resistor 120 are~-illus-trated as being in parallel with the switch 122a and either of the resistors 122 and 124. It is thus possible for both of these switches to be closed without any overriding affects, resulting in the connection of parallel resistors to the constant current source. However, the resistance values of the resistors 120, 122 and 124 are selected such that the effective parallel resistance of the resistors 120 and 124 results in the generation of a constant current of approximately the same magnitude as that which would be generated only by the re-sistor 124. Similarly, the effective parallel resistance formed of the resistors 120 and 122 results in the generation of a constant current of a magnitude which is approximately the same as the magnitude of the constant current generated when only the resistor 122 is con-nected to the constant current source. Thus, the resistance values of the resistors 120, 122 and 124 are selected in a hierarchial order to prevent any ambiguity in the constant current generated by the constant current source.
The resistors 114, 116 and 118 included in the first 10485~38 set of resistors are connected in common to the base electrode of a switching transistor 134 and thence through a base biasing resistor 136 to ground through the seizure switching circuit 54. ~he collector-emitter circuit of the switching transistor 134 serves to connect the tone oscillator 130 to ground through the seizure switching circuit.
It is appreciated that, when current flows through the bias resistor 136, the switching transistor 134 is rendered conductive to thereby connect the toneoscillator 130 to a ground potential.
The tone oscillator 130 is supplied with an operating voltage from a suitable voltage supply 80 through a current limiting resistor 132. When operatively connected to the voltage supply, the tone oscil-lator generates an alternating signal of predetermined frequency.
Accordingly, the tone oscillator 130 may comprise a conventional re-laxation oscillator~ a multivibrator, or other free running circuit capable of generating a predetermined tone frequency. me output of-the tone oscillator 130 is connected through a resistor 138 and the capacitor 140 to the diode 142 so as to superimpose a tone signal onto the constant current flowing in the control line.
A bias circuit formed of the parallel combination of a potentiometer 144 and a zener diode 146 is connected to the constant current source 102 fo-r the purpose of insuring that an equal voltage is applied across any of the resistors 114, 116 and 118, regardless of the particular switch which is closed. Accordingly, this bias circuit is coupled to the voltage supply by the current limiting resistor 132.
It should be recognized that the bias circuit is coupled to ground through the seizure switching circuit 54. The movable contact of the potentio-meter 144 is connected to the base electrode of the transistor 106 and is adjusted to obtain ~48938 the aforenoted equal voltage across each of the selected resistors.
It is recognized that, if a constant voltage is applied across a resistor, the current flowing therethrough is then determined by the resistance value. Hence, since a constant voltage is insured across any one of the resistors to be selected, the resultant constant current which is caused to flow in the control line 46 is a function of the resistance value of the particular resistor which is selected.
Although all of the illustrated switches may be of identical construction, in one embodiment the switches 114a, 116a and 118a are formed as push button switches. If desired, these push button switches may be interlocked ~o insure that only a single one can be operatively depressed at any given time. The switch 120a may be a spring biased push button switch which is normally biased to its open condition. The switch 122a, in addition to comprising a single-pole/double-pole switch having a neutral position, may also be formed as a toggle-type switch.
Where ~ remote dictate station includes a handset and a cradle support structure, the switches 114a, 116a and 118a may be disposed on the cradle support structure; and the switches 120a and 122a may be disposed on the handset. Of course, the particular loca-tions and types of switches employed may be selected as desired and form no part of the present invention per se.
As a typical example, the switch 120a may be designated the DICTATE switch such that, when closed, a dictate operation is selected. Of course, as is apparent, the actual generation of a dictate function control current is dependent upon whether the switches 114a, 116a and 118a are all open. The switch 122a may be designated the REWI~D/

1C~4~938 PLAYBACK/STOP switch. mis switch, when connected to the resistor 122, results in the generation of a current representing a rewind function command. When the switch 122a connects the resistor 124 to the con-stant current source 102, a constant current representing a stop or a playback function command is generated. me dual results attained through this resistor 124 will be described in greater detail hereinbelow.
The switch 114a is designated the PRIORITY switch which cause~ a constant current representing a transfer function command to be generated when this switch is closed. me switch 116a is designated the ATTENDANT CALL switch which causes a constant current representing an attendant call function command to be generated when closed. Finally, the switch 118a is designated the FAST FORWARD switch which cause a constant current representing a fast forward function command to be generated when close~.
Briefly, the operation of the illustrated function control coding circuit is such that the constant current source 102 is not capable of generating a constant current unless a reference potential, such as ground, is connected to the circuit. It is recalled that ground potential cannot be applied to this circuit until the seizure switching circuit 54 is closed. mu~, the function control coding circuit is effectively inoperative until the remote dictate station at which this circuit is positioned has gained access to the record/
reproduce station.
When ground potential is coupled to this circuit, a con-stant current of predetermined magnitude is generated depending upon the closure of a particular switch. Of course, if no switch is closed, then zero current is generated.

1~)4~93~
If any one of the first set of switches is closed, a constant current having a magnitude determined by the particular resistor connected in series with the constant current source 102 is caused to flow through the control line 46, through the diode 142, through the constant current source 102, through the selected resistor and through the base bias resistor 136 to ground. As a consequence of the current flowing through this base bias resistor, the switching transistor 134 is en-ergized to couple the tone oscillator 130 to ground. Thus, when any one of the first set of switches is closed, a corresponding constant lo current source is generated and the tone signal produced by the oscil-lator 130 is superposed thereon.
When any one of the second set of switches is closed, a constant current having a magnitude determined by the particular re-sistor connected to the constant current source 102 is caused to flow through the control line 46, the diode 142, the constant current source 102, the diode 126 and the particularly selected resistor to ground. It is seen that the constant current flowing through the selected one of the second set of resistors does not flow through the base bias resistor 136. Consequently, the switching transistor 134 is not energized and ground potential is not coupled to the tone oscil-lator 130. Hence, when any one of the second set of switches is closed, a constant current flows and no tone signal is superposed thereon. Hence, the presence or absence of the tone signal is seen to result in twice the number of function control commands which can be generated without requiring a corresponding number of control cur-rents. In the illustrated example, three predetermined currents can be used to select six discrete functions. Of course, if desired, 1~4~938 the first and second set of resistors all can be differently valued so that six predetermined constant currents will be generated to con-trol six corresponding functions. However, as is recognized, an in-crease in the number of current levels which are used correspondingly reduces the range of permitted variation of each current level. This, in turn, requires that current detecting apparatus of higher resolution be used at the record/reproduce station.
Since current flows through the base-emitter junction of the switching transistor 134 when any one of the first set of switches is closed, but curren$;does not flow through this junction when any one of the second set of switches is closed, the diode 126 is provided to simulate this base-emitter voltage drop when current flows through the second set of resistors. Thus, the predetermined currents which flow in response to the selection of any one of the resistors 114, 116 and 118 are equal to the predetermined currents which flow in response to the selection of any one of the resistors 120, 122 and 124, respectively. Of course, a control function current which is generated when the switches 120a or 122a are closed will be overriden by the closing of any one of the switches 114a, 116a or 118a. Simi-larly, the closure of the switch 116a will override a previous closure of the switch 118a and a closure of the switch 114a will override a previous closure of the switch 116a. Accordingly, constant currents of predetermined magnitudes are caused to unambiguously flow through the control line 46 in accordance with the particular function switch which is closed by an operator at a remote dictate station.

1C~4~38 Function Decoding Circuit The predetermined constant currents and superposed tone signal transmitted to the record/reproduce station by the function control coding circuit at a remote dictate station is detected and decoded by the function decoding circuit schematically illustrated in Figure 4. mis circuit is comprised of a current-to-voltage converter 150, a tone separator 154, a threshold detecting circuit 160, an out-put signal generating circuit 180 and logic gating circuitry 260. The current-to-voltage converter 150 is adapted to convert a DC current into a DC voltage of corresponding magnitude. Such converting circuits are well known to those of ordinary skill in the art and further description thereof need not be provided. Suffice it to say that a voltage is produced by the converting circuit 150 having a magnitude which is a direct function of the magnitude of the constant current transmitted to the record/reproduce station. Hence, predetermined voltages are derived which represent the aforedescribed control function commands. These output voltages are processed to produce control signals which are used to control various functions at the record/reproduce station to facilitate a dictation or playback operation.
The DC voltage output derived by the current-to-voltage converter 150 is separated from the received superposed tone signal by a low pass filter 152 and is supplied to the threshold detecting circuit 160. me low pass filter 152 is adapted to permit a DC voltage to be transmitted there-through, but sufficiently attenuates the higher frequency tone signal.
The tone detecting circuit which, for example, may 10~938 comprise a band pass filter 154, is also coupled to the current-to-voltage converter 150 and is adapted to detect the received tone signal.
me band pass filter 154 serves to produce an output DC signal of a first magnitude and/or polarity when a tone signal is detected and a DC voltage of another magnitude and/or polarity when a tone signal is not detected. For the purposes of establishing a consistent convention throughout, it here will be assumed that a relatively higher level DC
signal is produced when a tone signal is detected and a relatively lower level DC signal is produced when a tone signal is not detected.
o Further in accordance with this convention, the higher level DC signal will be designated a binary "1" and the lower level DC signal will be designated a binary "0". Of course, if desired, a binary "1" may be represented by a positive signal and a binary "0" may be represented by a negative signal. In addition, the aforenoted representations corresponding to a binary "1" and a binary "0" may be interchanged, if desired. mose of ordinary skill in the art will recognize that conventional logic circuits are commerGially available to operate with the various binary signals just described.
me threshold detecting circuit 160 is adapted to sense the relative magnitude of the DC voltage supplied from the current-to-voltage converter and to produce an output signal corresponding to such sensed voltage level. Accordingly, the threshold detecting circuit is comprised of a plurality of threshold detectors 162, 164 and 166 con-nected in common to the current-to-voltage converter through the low pass filter 152. Each threshold detector is capable of comparing the voltage applied thereto to a predetermined reference voltage. A
resistance voltage divider network is connected to a source 1~48938 of reference voltage and is adapted to divide this reference voltage to obtain successively lower reference levels. Accordingly, resistors 172, 174, 176 and 178 are connected in series to the source of refer-ence voltage and each junction defined by adjacent series-connected resistors is connected to a corresponding threshold detector to thereby supply a reference level thereto. Thus, the threshold detector 162 is supplied with the lowest reference level, the threshold detector 164 is supplied with a higher reference level and the threshold detector 166 is supplied with the highest reference level.
lo Each of the individual threshold detectors preferably comprises a comparison circuit such as a differential-type amplifier.
A conventional differential amplifier includes positive and negative input terminals and is adapted to provide an output voltage having magnitude and polarity dependent upon the difference between the voltages applied to the respective input terminals. For example, a positive output voltage is produced if the input voltage applied to the positive input terminal is greater than the input voltage applied to the negative input terminal. Conversely, a negative output voltage is produced if the voltage applied to the negative input terminal exceeds the voltage applied to the positive input terminal. The thres-hold detectors 162, 164 and 166 are preferably formed of such difer-ential amplifiers. The reference levels produced by the voltage divider network are supplied to the respective positive input terminals of the differential amplifiers and the voltage produced by the current-to-voltage converter is supplied to each of the negative input terminals.
Hence, when the voltage produced by the converter 150 exceeds the reference threshold ~4~938 level, the output voltage produced by the corresponding differential amplifier is changed from a positive to a negative voltage. Of course, if desired, the converse may obtain.
The threshold detecting circuit 162 is connected to the output signal generator 180. The purpose of the output signal generator is to produce output signals of suitable magnitude and polarity in response to the sensed level of the voltage produced by the current-to-voltage converter 150, the output signals corresponding to a binary 'l1" or "O" which is compatible with the logic gating circuit 260 to cause suitable control signals to be generated. The output signal generator 180 comprised of a plurality of transistors 182, 184 and 186, each including a base electrode coupled to a corresponding threshold detector 162, 164 and 166, respectively. In particular, the threshold detector 162 is connected through a diode 192 and a voltage divider comprised of resistors 196 and 198 to the base electrode of the transistor 182. In addition, an R-C delay circuit 194 is connected between the cathode of the diode 192 and ground. Operating current is supplied to the transistor 182 from a suitable source of operating potential +V through a current limiting resistor 200 to the collector electrode of the transistor.
The base electrode of the transistor 184 is similarly connected to the output of the threshold detector 164 through a diode 202, a voltage divider network formed of the resistors 206 and 208 and an R-C delay circuit 204. In a similar fashion, the transistor 186 is connected to the output of the threshold detector 166 through a diode 222, a voltage divider circuit formed of the resistors 226 and 228 and a delay circuit 224.

1~)48938 It is appreciated that, if the voltage produced by the current-to-voltage converter 150 exceeds the reference threshold level applied to the threshold detector 164, then it will also exceed the reference threshold level applied to the threshold detector 162, thereby causing negative output voltages to be produced by both thres-hold detectors. Similarly, if the reference threshold voltage applied to the threshold detector 166 is exceeded, all reference threshold levels will be exceeded. It is preferable to inhibit the output voltage produced by the threshold detector associated with the next lo lowest reference threshold level from being applied to its output signal generator when an output voltage is produced by the threshold detector associated with the adjacent, next higher reference threshold level. To this effect, a switching transistor 212 is conneGted to the cathode of the diode 192 and is adapted to suppl~ a positive voltage thereto when the threshold detector 164 produces an output voltage of negative polarity. Accordingly, the collector electrode of the transistor 212 is connected through a diode 218 to the cathode of the diode 192. me collector electrode is additionally connected through a collector resistor 220~ to a source of operating potential +V. me base electrode of the transistor 212 is connected to a voltage divider circuit formed of the resistors 214 and 216 which extend between the output of the threshold detector 164 and ground. A similar switching transistor 232 is connected to the cathode of the diode 202 and is adapted to apply a positive voltage thereto when the threshold detector 166 produces an output voltage of negative polarity. Accordingly, the collector of the transistor 232 is connected through a diode 238 to the cathode of the diode 202 and, additionally, is connected through 1~)41~938 a collector resistor 240 to a source of operating pctential +V. The base electrode of the transistor 232 is connected to a voltage divider circuit formed of the resistors 234 and 236 which are connected between the output of the threshold detector 166 and ground.
As will be described in detail hereinbelow, the transistor 182 is adapted to produce a binary "1" or "0" in accordance with the output voltage supplied thereto by the threshold detector 162. This binary "1" or "0" serves to determine the control signal produced by the gating circuit 260. Accordingly, the collector electrode of the transistor 182 is connected in common to the coincidence circuits 242 and 244 included in the gating circuit 260. A typical coincidence circuit is formed of an AND g~te which is adapted to produce a binary "1" output only if each input thereto is supplied with a bina~y "1".
If this condition is not satisfied, the AND gate produces an output binary "0". As shown, the AND gate 242 includes another input con-nected to the output of the band pass filter 154. The AND gate 244 include another input which is connected through an inverting circuit 156 to the band pass filter 154. An inverting circuit is a conventional logic signal inverter which produces a binary "1" output in response to a binary ~'0" input and, conversely, produces a binary "O'i output in response to a binary "1" input. If desired, the inverting circuit 156 may comprise a conventional inverting amplifier.
The gating circuit 260 further includes AND gates 246 and 248 which include first inputs connected in common to the transistor 184 and second inputs which are connected to the band pass filter 154 and to the inverting circuit 156, respectively. The gating circuit 260 also includes AND gates 1~)48938 250 and 252 which include first inputs connected in common to the transistor 186 and second input which are connected to the band pass filter 154 and the inverting circuit 156, respectively.
As will now be described, the illustrated function de-coding circuit is adapted to selectively produce control signals which respectively control the performance of "dictate", "rewind/playback", I'stop/playback'', "priority", "attendent call" and "fast forward"
operations. mese control signals are produced as a function of the magnitude of the constant current transmitted to the record/reproduce lo station ar,d, additionally, are determined by the presence or absence of a superposed tone signal. Let it initially be assumed that an operator at the remote dictate station wishes to perform a dictate operation.
By suitable operation of the aforedescribed function control switches, such as by closing the switch 120a in Figure 3, a constant current having, for example, the lowest current level, is transmitted over the control line 46. Also, this current is not accompanied by a superposed tone signal.
me current received at the record/reproduce station is applied to the current-to-voltage converter 150 and is converted to a voltage having a corresponding magnitude. This voltage magnitude, which is here assumed to be the lowest magnitude, is supplied through low pass filter 152 to each of the threshold detectors 162, 164 and 166.
It will be appreciated that this voltage exceeds only the reference threshold level which is applied to the threshold detector 162. It should be noted that, before any current is supplied to the current-to-voltage converter, each of the threshold detectors 162, 164 and 166 producesa positive output voltage. This positive output voltage is supplied through each of the diodes 192, 202 and 222 to the transistors 182, 184 and 186, respectively.
As a result of this supplied positive output voltage, each transistor is rendered conductive so that a binary "0" is produced at each col-lector electrode. Consequently, each AND gate included in the gating circuit 260 produces a binary "0~ control signal. However, since the reference threshold level associated with the threshold detector 162 is now exceeded, this threshold detector will produce a negative out-put voltage. As is appreciated, such a negative output voltage is not capable of maintaining the transistor 182 in its conducting state.
Consequently, the voltage provided at the collector electrode of this transistor now rises to correspond to a binary "1" which is supplied to the common-connected inputs of the AND gates 242 and 244. However, at this time, the threshold detectors 164 and 166 continue to produce positive output voltages, resulting in the conduction of the transis-tors 184 and 186.
Since a dictate function has been selected, a superposed tone signal is not provided. Consequently, the output of the band pass filter 154 is a relatively low voltage which, after being inverted by the inverting circuit 156, causes a binary "1" to be supplied to the second input of the AND gate 244. As a consequence thereof, the AND gate 244 is the only circuit which produces a binary ~'1" output, corresponding to a dictate control signal. Of course, if, instead of closing the switch 120a, the switch 114a at the function control coding circuit was closed, the same current level would be supplied to the current-to-voltage converter 150, but now a tone signal would be superposed thereon. This tone signal, would, of course, be detected by the band pass filter 154 to supply a binary "1" to the AND gate 242 and to the inverting circuit 156. Hence, - 42 _ 104~5 38 although the transistor 182 would, in this case, supply a binary "1"
to the common-connected inputs of the AND gates 242,and 244, only the AND gate 242 is supplied with a binary "1" at its second input, thereby resulting in the production of a priority control signal.
Let it now be assumed that a constant current flowing through the control line 46 exhibits the next higher magnitude. As is appreciated, this control current can be produced by closing the switch 122a in Figure 3 to connect the resistor 122 to the constant current source 102 or by closing the switch ll~a. Depending upon which switch is closed, a rewind or attendent call function is selected As is appreciated, the presence or absence of a superposed tone signal indicates which of these control functions has been selected.
In either event, the voltage now applied to the threshold detecting circuit 160 by the current-to-voltage converter is high en-ough to exceed the reference threshold level applied to the threshold detector 164 as well as the reference threshold level applied to the threshold detector 162. Consequently, both of these threshold detectors now produce negative output voltages.
The negative output voltage produced by the threshold detector 164 is applied to the base electrode of the transistor 212, thereby rendering this transistor nonconductive. Accordingly, the potential appearing at the collector electrode of this transistor now rises toward the level +V and is supplied by the diode 218 to the cathode of the diode 192. Since the threshold detector 162 is also producing a negative output voltage, it is recognized that the diode 192 is reverse biased so that the positive voltage supplied by the collector of the transistor 212 is coupled to the base electrode of the transistor 1&2, there-i~J4~938 by driving that transistor into its conducting state. Consequently, a binary ~'0" is produced by the transistor 182; but since the threshold detector 164 produces a negative output voltage, the transitor 184 is driven out of its conducting state in response to such negative voltage to thereby apply a binary "1" to the common-connected inputs of the AND gates 246 and 248. If no tone had been superposed on the constant current, indicative of a rewind function, then a binary "1" is supplied to the AND gate 248 by the inverting circuit 156 to thereby produce a rewind control signal. However, if the attendant call function had been selected, then a superposed tone signal is received and is detected by the band pass filter which supplies a binary ~'1" to the AND gate 246, resulting in the production of the attendant call control signal.
Since the reference threshold level applied to the thres-hold detector 166 has not been exceeded at this time, it is seen that this threshold detector produces a positive output voltage which renders conductive the transistor 186 and also the transistor 232. Hence, at this time, the potential at the collector electrode of the transistor 232 is not sufficient to prevent the negative output voltage produced by the threshold detector 164 from being supplied to the transistor 184.
However, if the current flowing through the control line 46 now is assumed to exceed the highest reference threshold level, corresponding to the selection of a stop/playback or the selection of a fast forward function, then the voltage now applied to all of the threshold detectors by the current-to-voltage converter will exceed all of the reference threshold levels. Consequently, all of the threshold 1~)4~938 detectors will produce negative output voltages. However, as in the previously described operation, the collector of the transistor 212 supplies a positive voltage to reverse bias the diode 192, thereby inhibiting the negative output voltage produced by the threshold detector 162 from being supplied to the transistor 182. Now, in a similar fashion, the negative output voltage by the threshold detector 166 is supplied to the transistor 232 to bias this transistor to its nonconductive state. Accordingly, the potential at the collector electrode of the transistor 232 rises to a relatively high positive level and is supplied by the diode 238 to reverse bias the diode 202.
Consequently, the negative output voltage produced by the threshold detector 164 is inhibited from bèing supplied to the transistor 184.
Accordingly, only the transistor 186 is now rendered nonconductive.
Thus, a binary "1~' is supplied by this transistor to the common-con-nected inputs of the AND gates 250 and 252. If a stop/playback func-tion had been selected, then no tone signal is superposed on the received control current and, consequently, the inverting circuit 156 supplies a binary "1" to the AND gate 252. As a consequence thereof, the stop/
playback control signal is produced. However, if the fast forward function had been selected, then a superposed tone signal will be detected, resulting in a binary "1" supplied to th~ AND gate 250 by the band pass filter 154. Hence, a fast forward control signal will be produced.
It is recognized that a band pass filter conventionally exhibits an intrinsic delay. Hence, a perceptible delay will be provided until the band pass filter 154 produces a binary ~rll~ in response to the sensed tone signal. However, since the DC operating circuits comprising the threshold 93~

detecting circuit 160 and the output signal circuit 180 operate with slight delays, it is recognized that it would be possible for a false control signal to be momentarily produced during the intrinsic delay of the band pass filter For example, if a priority function is selected, because of the delay in the operation of the band pass filter it is possible that a binary "1" will be supplied to both inputs of the AND 244, resulting in a dictate control signal to be produced initially. Of course, such dictate control signal will be terminated and a priority control signal will be produced at the conclusion of the band pass filter operating delay. Nevertheless, in an effort to avoid this false production of control signals, the delay circuits 194, 204 and 224 are provided between the threshold detecting circuits 162, 164 and 166 and the transistors 182, 184 and 186, respectively. The purpose of these delay circuits is to effectively match the intrinsic delay of the band pass filter 154. Thus, the transistors 182, 184 and 186 will not be selectively operated in response to the sensed current levels before the band pass filter has had an opportunity to produce an output indicating the presence or absence of superposed tone. Hence, these delay circuits permit the band pass filter to respond to the tone signal (if it is present) before a control signal can be produced.

Claims (6)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A control current generator for generating control currents of predetermined magnitudes representing corresponding, predetermined functions for transmission from a first location, such as a remote dictate station, via a transmission channel to a second location, such as a record/reproduce station in a central dictation system, to thereby control predetermined func-tions at said second location, comprising current generating means for gener-ating a constant current having a predetermined magnitude determined by re-sistance means selectively connected thereto and being independent of the load presented by the transmission channel; a plurality of resistance means having different values for determining the magnitude of said constant current; a plurality of manually operable switches for selectively connecting individual ones of said resistance means to said current generating means;
signal generating means for superposing a characteristic signal on the constant current generated by said current generating means; and energizing means responsive to the operation of predetermined ones of said switches for energizing said signal generating means.

2. A control current generator in accordance with Claim 1 wherein said plurality of resistance means comprises a first set of differently valued resistors and a second set of resistors equal in value, respectively, to said first set, said first set of resistors being connected in a current path to said energizing means such that when any one of said first set of resistors is connected to said constant current generating means, current flows therethrough to said energizing means to thereby energize said signal generating means.

3. A control current generator in accordance with Claim 2 wherein said first set of resistors all are connected at one end thereof to a first common junction coupled to said energizing means, the other end of each re-sistor in said first set being connected to a first terminal of a respective manually operable switch; and wherein said secomd set of resistors all are connected at one end thereof to a second common junction coupled to a refer-ence potential, the other end of each resistor in said second set being connected to a first terminal of a respective manually operable switch; all of said switches being arranged in a predetermined order such that only a single resistor is connected in circuit with said current generating means even if more than one switch is closed.

4. A control current generator in accordance with Claim 3 wherein each switch is a two-position switch having a movable contact selectively engage-able with said first terminal thereof to connect the resistor connected there-to to said current generating means and with a second terminal to which the next switch in said predetermined order is connected so that the next switch in said predetermined order is capable of connecting the resistor connected thereto to said current generating means provided the movable contact of the preceding switch in said order is connected to its second terminal.

5. A control current generator in accordance with Claim 1, 2 or 3 wherein said current generating means comprises a pair of complementary transistors, the collector electrode of one transistor being connected to the base electrode of the other, the collector and emitter electrodes of respective transistors being connected together, and the base electrode of said one transistor being connected to a reference voltage source so that current flows through the interconnected transistors via said transmission channel.

6. A control current generator in accordance with claim 1, 2 or 3 wherein said signal generating means comprises an actuable tone oscillator having an output coupled to said transmission channel; and wherein said energizing means comprises transistor means whose col-lector-emitter circuit is operative to connect said tone oscillator to a reference potential for actuating said oscillator and whose base electrode is supplied with an energizing voltage when predetermined ones of said switches are operated.