US2547216A

US2547216A - Remote controlled recording machine

Info

Publication number: US2547216A
Application number: US701896A
Authority: US
Inventors: Kobler Richard
Original assignee: Individual
Current assignee: Individual
Priority date: 1946-10-08
Filing date: 1946-10-08
Publication date: 1951-04-03
Anticipated expiration: 1968-04-03

Description

April 3, 1951 R. KOBLER REMOTE CONTROLLED RECORDING MACHINE 2 Sheets-Sheet 1 Filed Oct. 8, 1946 BYQ Patented Apr. 3, 1951 umrso REMOTE CONTROLLED RECORDING MACHINE Richard Kobler, San Francisco, Calif.

Application October 8, 1946, Serial N 0. 701,896

The present invention relates to systems adapted to permit use of a recording machine from a remote station, and more particularly it relates to electrical circuit arrangements enabling operation of an electronic'recording machine from a plurality of remote stations.

In the past it has been necessary in systems of this type to connect the recording machine with every remote control station through a plurality of difiierent lines, each serving a distinct function of its own. Thus, such systems required (1) a shielded line for each remote control station to feed the audio input to the recording machine, (2) a power line for starting and stopp ng the motor of the recording instrument, (3) an additional power line to activate or interrupt warning lights provided at all of the stations for the purpose of indicating the availability of the machine, and (4) frequently also a third power line to operate so-called stand-by lights at every one of the stations to indicate whether the machine (especially its electronic parts) was sufficiently heated to be in condition for use. It is self-evident that the necessity of having so many power lines in addition to a shielded audio line between the recording machine and every one of the remote stations rendered such systems complicated, costly, and difiicult to install. This is especially true for the power lines which have to be placed into B-X cables if they exceed 8 or 10 feet in length to satisfy fire prevention and building regulationsin most towns and cit es, to say nothing of the fact that the installation of such cables in addition to those installed during construction is expressly forbidden in a great number of modern ofiice buildings, and violation of any such rule may void all fire insurance claims.

The audio lines provided in known remote control systems of the type under consideration offered seriousadditional problems. The pick-up devices generally used in these systems were either crystal or high-impedance dynamic microphones requirin high-impedance lines for transmission. Such lines, however, are prone to pick up a considerable amount of hum and interferences fromv the adjoining power lines between the remote station and the recording device, and indeed from any other power line in the buildingv as well as the usual sources of radio interference. It was impossible, therefore, to include the audio lines in the same cable as the power lines; in fact, they had to be enclosed in special shields and had'to be conducted at random or placed a material distance apart from power lines. All these factors added materially to the cost of the known remote control systems and their I installation without entirely eliminating disturbances in the audio lines; therefore-in spite ofall precautions the effective range of operation of-these known remote control arrangements was severely limited,

12 Claims. (01. 17 96) because beyond a certain point the speech-tonoise ratio became too unfavorable for intelligible recording. To make matters worse, this disadvantage was still more accentuated by the necessity of employing powerful amplifiers in the recording machine due to the Weak out-put levels of the crystal or high-impedance dynamic microphones and the enormous line losses inherent in high-impedance lines, because the amplifiers did or other'interference.

not only amplify the sound output of the remote microphones but also the interferences picked up by the high-impedance line.

Thus, in spite of their very obvious value in business establishments, hospitals, government administration buildings, etc., remote controlled recording machines have not become popular because, (1) they were too expensive, (2) their installation was too costly and too complicated and frequently disfigured walls and ran counter to fire prevention regulations, (3) their rangepf operation was limited, and (4) the quality of the recordings obtained was not dependable and mostly unsatisfactory.

Broadly, it is an object of the present invention to provide a circuit arrangement for the operation of a recording machine from a number of remote stations, which is inexpensive and easy to install and operate.

It is another object of the present invention to provide a circuit arrangement of the type referred to, wherein the interconnecting lines constitute no fire hazard and comply in all respect with the contemporary building and insurance regulations.

'More specifically, it is an object of the present invention to eliminate the conventional use of 110 volt power lines between remote stations and the recording machine in systems of the types referred to while retaining the remote control functions previously performed'by these lines. 7

It is an additional object of the present invention to furnish a circuit arrangement adapted to permit operation of a recording device from a number of remote stations wherein the recording device requires only low amplification of the audio signals arriving from the remote stations.

' It is yet another object of the present invention I to provide a circuit arrangement enabling operation of a recording machine over the largest practicable distances in systems of the type under discussion, without harmful deterioration in the recording qualitydue to the introduction of hums At'the same time it is another specific object of the present invention to achieve these results without requiring special shielding for the audio lines.

.. It is a specificobject of the present invention to-provide a circuit arrangement of the type restations, wherein transmission of the audio signal from a remote station to the recording device and control of recording machine and warning lights are efiected through a single low voltage, low-impedance line.

It is also an object of the present invention to provide each remote station in systems of the type referred to, with a warning signal adapted to' in dicate engagement of the recording machine by another station whether the motor of the machine is running or not. Moreover, it is an object of my invention to so arrange this warning signal that it will act as a stand-by light as Well as a busy signal indicating not only availability but also readiness of the recording machine.

Lastly, it is an object of this invention to adapt the remote stations of my novel system to the reception for recording purposes,- of telephone messages by operation of a simple switchand with the highest degree of safety against shortcircuits of either the D. C. or the audio com ponent of the telephone line.

These and other objects of the present invention will be apparent from the following olescription of the accompanying drawing which illustrates certain preferred embodiments thereof and wherein:

Figure 1 is a circuit diagram representative of an electronic recording device and two remote stations;

Figure 2 is the circuit diagram of a. remote control station having a modified busy signal system;

Figure 3 is the circuit diagram of a remote control station having yet another busy signal system; and

Figure 4 is the circuit diagram of two remote control stations of simplified design.

In Figure 1 block A drawn in broken lines indicates the electronic recording machine; block B indicates the master control station which is usually in close proximity of the recording machine; and blocks C and D signify remote control stations.

The electronic recording machine A includes an amplifier It represented by a block drawn in full lines. Amplifier H) feeds amplified audio signals to the recording head II which may, for instance, be of the crystal type. An electric motor 12 is provided to drive the mandrel 12a of the recording instrument. Power from a suitable source such as a 110 volt light line is drawn at l3 which denotes a plug contact of the conventional type. switch 1 A is provided to permit convenient activation of the arrangement. When switch I4 is closed, power from the line is supplied through leads i5 and it directly to amplifier Ill to warm up its filaments (heaters and possibly plate power supplies) and prepare the amplifier for immediate use. At the same time power is supplied through leads l8 and [9 to the primary winding 2! of a step-down transformer 28 situated in master control station B the secondary winding 22 of which is connected across a selenium rectifier 23 of suitab e design. Thus the high voltage A. o. supplied from the line is stepped down in transformer 29 and appears as a pulsating 'D. C.

of materially lower voltage across output leads I 24 and 25 of selenium rectifier '23. A suitable filter system for instance in the form of a choke coil 26 and condensers 28 and 29 connected across leads 2G and 25 at either end of choke coil 26 serves to even out the pulsations of the lecti'fi'er A master control or stand-by output so as to provide a steady low voltage D. C. suitable for the transmission of telephonic messages originating in resistance type microphones.

While one side of the power line I9 is per manently connected to the motor through lead it and branch it, the closing of master switch 54 brings up the other side of the line to the motor through a branch I8 of lead 18 over a normally open switch 46 which may be closed by the operation of a relay 60 under conditions to be described hereinafter.

Likewise, while one side of the power line It is permanently connected to the primary winding 5% of a step-down transformer 58 through a branch [9, the closing of master switch It brings up the other side of the power supply line to the primary winding 51 through lead is, a portion of branch I8 and a secondary branch it" over a normally open switch it which may be closed by a relay 65 under conditions to be described hereinafter. Step-down transformer 58 has a secondary 52 adapted to supply the transformed A. C. voltage through leads 53 and 54 to sources of light 5% and 58 located in remote control stations C and D, respectively. It will be understood that lights 56 and as may also be supplied with a D. 0. current, for instance, by appropriate employment of a selenium rectifier.

Reverting to the output circuit of selenium rectifier 23, connected in series with choke coil 26 are two relays t0 and 65 arranged in series with one another and as previously mentioned adapted to close switches and respectively.

Relays

65 and 65 are designed to be of difierent sensitivity, relay 5!] requiring a greater current now in the D. C. circuit for operation of its armature than relay 65 for reasons which will presently appear.

It will be understood by those skilled in the art that the relays 60 and need not necessarily be connected in series but may be ar ranged parallel to one another and may yet be made to successively operate switches 45 and do as the current flow in the rectifier output sircuit increases. It should be noted that aside from their purpose of activating switches 48 and 45 the relays 6t and 65 in conjunction with condenser 38 form an additional stage of the previously mentioned filtering system, which increases the evenness of the D. C. output of rectifier 23.

The power supply system just described is part of the connecting circuit between remote stations C and D and master control station B. This circuit includes a carbon microphone 38 in remote station C and the primary 32 of an audio transformer 3| within the confines of master control station B the secondary 33 of said transformer 3| being connected across the input terminals of amplifier Ill. The connecting line between the remote control part and the master station part of the circuit is formed by

leads

35 and 36.

Within remote control station C, the circuit includes a resistor 39 and a selector switch 31. When switch 3! is closed in upward direction as viewed in Figure 1, it initiates a limited amount of current flow in the D. C. circuit provided stand-by switch I A has previously been closed. This current flow will be sufiicient to activate relay 65 which will close switch 45 but will be insuifici'ent to operate relay 60 so that switch will remain open. When switch 45 is closed, the power supply line through primary 5i f stepdown transformer 50 will be i closed and as a result thereof a low voltage A. C. .(or D. C.) will be supplied to lamp 58 in remote station C and lamp 56 in remote station D, and, indeed, to all the corresponding lamps in whatever additional remote control stations may be joined to the system of my invention. Thus, when 'aparty closes switch 31' in upward direction in remote control station C and lamp 56 in his station lights up, he will know that the standby switch 14 was closed and that the machine is ready for use, while light 56' lit up in control station D and any other associated remote station will warn other parties intending to dictate through any of the other remote control stations that the recording machine is engaged.

Current flow in the circuit initiated by the closing of switch 31, however, was not large enough, due to the presence of resistor 39, to cause operation of relay 6B for the purpose of closing switch 40, and motor l2 therefore re'-.

mained at rest. 7

To enable an operator to start the motor as soon as he is ready to dictate, means are provided to effectively eliminate resistor 39 from the circuit. For this purpose Wires Hi and II connected to either end of resistor 39'lead to a switch 12 which is normally held open by suitable means, and maybe adapted to be closed by the operators foot. When the operator steps on switch 12, wires Hi and H form a by-pass around resistor 39 and the resultant current increase in the D. C. circuit is sunicient to cause relay Bl] to close switch 40; in consequence thereof, power is supplied to motor l2 and the recording cylinder [2a will commence to revolve.

- If and when an operator wishes to interrupt there will be no waste of recording surface.

However, signal lights 56 in remote station C and the corresponding lights in any other remote stations that may be joined to my system, will remain illuminated, warning other prospective users that the machine is still engaged although the motor may not run at the moment. Only when the operator at remote station C has completed his work and returns switch 31 to its neutral position, will lights 56 go out to indicate at all remote stations that the system is now available to other users.

The manner in which a voice dictating into the microphone of a remote control station is transmitted to the recording device will be obvious to those skilled in the art from the foregoing description, but will briefly be outlined in the following: The resistancechanges occurring in carbon microphone 38 in response to vocal vibrations will modulate the direct current in the circuit imposing an alternating component upon the D. C. current flow. The resultant pulsating current will travel from microphone 38 through lead 35, to primary 32 of audio transformer 3|, with the alternating component returning through condenser 30, and lead 36 back tomicrophone 38. High-impedance secondary 33 of audio transformer 3| will respond to the alternatin'g component of the pulsating current passing through primary 32 and supply a corres'pond-' in'g'alternating potential to the input of ampliher It. Thus I am able to control operation of the 'motorhoi the recording machine from the remote station by use of the same low impedance line which I employ for transmission of audio messages and which constitutes no fire hazard and does not violate any fire prevention or insurance regulations.

Since the output level of a resistance type microphone, and especially of' a microphone of the carbon type, is relatively high, the alternating voice potential supplied by secondary 33 to amplifier II] will likewise be relatively high so that itwill not be necessary to employ powerful and expensive amplifiers inthe recording device to produce satisfactory recordings. Additionally, since the path travelled by the alternating component of the modulated D. 0. current is predominantly of low-impedance, and the high-impedance path between secondary 33 and the input of amplifier It] will usually be very short, very little interference will be picked up by the line, and the dictation supplied to the amplifier will beremarkably free from hum or other disturbing noises. Also there will be no practical limit as to the permissible length of the connecting line between remote station and inaster'station such as exists in the known remote control systems employing high impedance lines wherein the noise level will soon drown out the diminishing voice level as the length of the line in creases.

Aside from a position of rest and a position adapted to close the above described D. C. circuit through microphone 38 for the purpose of dictation, switch 31 also has a third or downward position as shown in Figure 1 whereinit connects the secondary 82 of a transformer across

main leads

35 and 36 for the purpose of recording telephone messages. The primary 8| of transformer 80 is connected through attenuating potentiometer 83 across telephone tapping leads 81 and 88 each of which contains a blocking condenser and 86, respectively, to prevent the D. C. component of the telephone circuit from.

reaching the transformer 80. As an added safety againstaudio or D. C. short circuits over the protection afiorded by blocking condensers 85 and 86, potentiometer 83, and transformer 89, I provide aresistor 84 between primary winding BI and blocking condenser 85. The principal protection, however, whichI secure in accordance with my invention for the telephone net work, flows from the fact that'here no A. C. or

D. C. power lines are installed in the proximity of the audio lines as was the case in the conventional remote control recording systems. Thus, the danger ever present in the known systems, of getting one or both sides of the power line connected to the audio line is eliminated in its entirety.

When a telephone message arriving at remote 'stationC is to be recorded, switch 37 is turned to connect secondary 82 of transformer 89 across leads 35 and 55, for which reason secondary 82 should be designed to have approximately the same resistance as microphone 38. Secondary 8 2 of transformer 80 now forms anintegral part of my low voltage D. C. control circuit in that its insertion closes said circuit and activates relays 60 and 65 and the switches 40 and 45 controlled by said relays, while elimination of secondary 62 from the circuit by operation of switch 3T-will stop the motor and extinguish the warning lights. In thetelephone tapping circuit, condensers '85 and 86 while blocking the D. C. of the telephone line, permit the audio component tlii'areof...tci-pa'ssthrough resistor =84 and potentiometer 33 to the primary 8| of transformer 80 inducing corresponding potentials in the secondary 82 thereof which are imposed upon the D. C. of the communication circuit and are transmitted to the amplifier II! of the recording machine over audio transformer 3! in master station B in the manner previously described.

It should be noted that since the communication circuit connecting remote station and master station is adapted to a carbon type microphone as described above, no line balances will have to be incorporated in the system of my invention when used for the purpose of recording telephone messages, because the output of a carbon microphone and that of a telephone tapping system of the type described are in close proximity, and whatever attenuation may be required when a remote control station is set for the recording of a telephone message may be provided by regulation of potentiometer 84.

Any number of additional remote control stations may readily be joined to my system as exemplified by remote control station D in Figure 1. Station D differs from station C merely in so far as it has no provision for the recording of telephone conversations but is otherwise identical with station C, and equivalent elements in remote station D have therefore been identified by the same reference numerals as in station C except that a prime has been added to the numerals in station D. As may be seen from Figure 1, all that is necessary to join remote station D to the system of the present invention, is to connect leads 35, 36', 53, and 54 of remote station D to the corresponding leads 35, 36, 53, and 54 at any suitable points thereof, and the newly added remote station D may be manipulated, and will operate, in exactly the same manner as station C.

While each of the remote stations of my novel system is provided with a warning light 56 or 56', respectively, to indicate whether the recording machine is available or not, it may be desirable under certain circumstances to have additional audible signalling means to warn a prospective user who may absentmindedly have overlooked lamp 56, that he is about to spoil another partys recording. For this purpose a suitable sound reproduction device 90 may be connected across leads 35 and 36 in shunt of microphone 38 and resistor 39 (or 35' and 35 in station D) as shown in Figure 1, a blocking condenser 9| (or 9| respectively) being provided in one of the leads to prevent direct current flow through the shunt line. Thus, when switch 31 is set to one of its operative positions the voice of any party that may dictate into the recording machine through another remote control station such as station D will become immediately audible and warn the intended user that he overlooked busy signal 56.

For this purpose I find it especially advantageous to use a combined microphone and receiver of the type used in modern telephones, and I so arrange matters that lifting of the receiver from its rest for the purpose of dictating into the recording machine automatically sets switch 31 to operative position and activates light 56. Thus, when a person lifts the receiver and places it to his head in the manner of an ordinary telephone receiver, he will immediately hear the voice of whatever party may at the time dictate into the machine, and will therefore refrain from using the machine.

In Figure l I have shown the warning lamps 56 in the remote control stations as operated by a transformed A. C. current drawn from the main power line at I3 and supplied to the remote stations through a step-down transformer 50 situated in the master station and over low voltage lines 53, 54 and 53', 54, respectively. It may be preferable, however, if the number of control stations is considerable, to modify the warning light system to the form shown in Figure 2, wherein like numerals are used to identify parts analogous in form and function with parts shown in Figure 1. A relay me is substituted for the incandescent warning light 56, and said relay is adapted to actuate a normally open switch I02 to close a circuit IIlI including a neon lamp I03 and a local source of power 1M which may be a conventional power supply of 110 volts. By using this modified warning light system, the number of control stations can be greatly expanded without consuming any more current in the various relays I than is ordinarily consumed by about five warning lights 56 of the incandescent type shown in Figure 1.

Figure 3 shows another modification of the warning light system. In this particular embodiment the flow of D. C. current in the communication circuit initiated by the closing of switch 3'! is arranged to operate a relay I I0 provided in the circuit within the confines of the remote control station. When relay III] is excited, it closes a normally open switch I I I to complete a circuit H2 drawing power from a local source of power H3 which may again be a conventional power line of volts. A step-down transformer IIA having its primary H5 in circuit H2, supplies a low voltage A. C. through secondary I5 to an incandescent type lam 111. Thus, lamp II! will light up as soon as current flows in the D. C. circuit upon closing of switch 3?. In a remote control system employing a warning light arrangement of this type, master control station and remote stations will in fact be connected by only a single low voltage D. 0.

line

35, 35, plus ground.

Other variations Of my warning light system will readily occur to those skilled in the art once they have familiarized themselves with my disclosure.

All the remote control stations so far described were provided with individual warning lights and two control switches; one for indicating, by illumination of the warning lights, to all other remote control stations that the machine was engaged, and a second one in the form of a foot pedal or hand switch to start and stop actual operation of the machine. It will be understood, that for certain purposes remote stations of a much simpler construction may sufifice which have no warning light and only one control switch. Two such simplified stations are shown in Figure 4, each com-prising merely a microphone I38 connected across leads I35 and I35 of a D. C. communication circuit, and a foot pedal or hand switch II2 adapted to close the D. C. circuit for transmission of audio messages to the recording machine. Closing of foot pedal switch I72 will at the same time cause operation of the motor. A system using exclusively remote control stations of this type requires only one relay coil in the master station to close the power circuit of the motor upon the closing of foot pedal switch I12.

A simplified system of this type is particularly appropriate in cases where one and the same person may wish to dictate notes from a pluralassociated with said microphone means for regr iaia 9 ity" or difierent rooms with no likelihood of another person using the same machine, such as in a doctors office having several examination rooms. In a practical embodiment of my invention constructed according to the diagram of Figure l are employed the following circuit constants:

Contact 13 110 volt power line Stepdown transformer 20: 1 Primary 21 110 v. A. 0,

Secondary 22 ;L 18 v. A. C. 10 Audio transformer 31:

Primary 32 100 ohms impedance Secondary 33 100,000 ohms impedance 'Stepdown transformer 50:

Primary 51 110 V. A. O.

' 10 v. A. C. Audio transformer 80 15 Primary 81. 10,000 ohms impedance 100 ohms impedance 2.3 henrics, 65 ohms D. G.

resistance Secondary 8 Choke coil 26.--

Relay 60 35 milliwatts Relay 65 5 milliwatts Rectifier 23, selenium rectifier." 12-14 v. D. 2A. 8v. D. 0.3A. -2() Condenser 2S Condenser 29 40 mi. 40 mi.

Resistor 84 5000 ohms 25 Potentiometer S3. 15,000 ohms Lamps 56, 56 6-8 V., ,15 A.

ulating the current flow in saidcommunication circuit and a visual signalling device having a normally interrupted power supply circuit; said first relay being adapted to close the power supply circuit for said signallin device in response 0 to current fiow in said communication circuit and said second relay being adapted to close the power supply circuit for said motor in response to a predetermined increase in said current flow over that required to activate said first relay.

2. An arrangement for recording sound from a plurality of remote points including a centrally positioned recording machine having an electronic amplifier, a motor and a normally open power'supply circuit therefor; a communication circuit inductively coupled to said amplifier and comprising a source of D. C. voltage, a first relay, a second relay requiring a. stronger current fiow for activation than said first relay and a plurality of remotely positioned resistance type microphones connected in series with said relays but parallel to one another; and associated with each microphone means for regulating the current flow in said communication circuit and a visual signalling device having a normally interrupted power supply system common to the signalling devices associated with all of the other microphones; said first relay being adapted to close the power supply system of said signalling devices in response to current flow in said communication circuit, and said second relay being adapted to close the power supply circuit for said motor-in response'to a predetermined increase in said current flow over that required to activate said first relay.

3. Arrangement for remote control operation of a recording machine of the type having an,

electronic amplifier, a motor and a normally interrupted power supply circuit therefor; said arrangement including a communication circuit having a source of D. C. voltage, a first relay, a second relay requiring stronger current flow in said circuit for actuation than said first relay, a winding forming part of an audio transformer operatively connected to said amplifier, a remotely positioned resistance type microphone and associated therewith a resistor, a, first switch adapted to close said communication circuit through said resistor, a second switch adapted to -by-pass said resistor, and a visual signalling device havin a normally interrupted power supply system, said first relay being arranged, upon closing of said first switch, to close said power supply system for said signalling device, and said second relay being arranged, upon closing of said second switch, to close said. power supply circuit for said motor.

4(Arrangement for remote control operation of a recording machine of the type having an electronic amplifier, a drive system and a normally interrupted control circuit therefor; said arrangement including a communication circuit, having a source of D. C. voltage, a first relay, a second relay requiring stronger current fiow in said circuit for actuation than said first relay, a winding forming part of an audio transformer operatively connected to said amplifier, a plurality of remotely positioned resistance type microphones connected in series with said relays and said winding but in parallel to one another, and associated with each microphone a resistor, a first switch adapted to close said communication circuit through said resistor, a second switch adapted to by-pass said resistor; and signalling means associated with said microphones respectively and having a common, normally interrupted power supply system, said first relay being adapted, upon closing of any one of said first switches, to close said power supply system for all said signalling means independently of activation of said second relay, and said second relay being adapted, upon closing of any one of said *second switches, to close said control circuit for said drive system.

5; An arrangement for recording sound from a remote point, including a recording machine having an electronic amplifier, a power circuit to heat said amplifier, a, drive system and a normally interrupted control circuit effective when closed to render said drive system operative; a communication circuit inductively coupled to said amplifier and including a relay, a plurality of remotely positioned resistancetype microphones in series with said relay and parallel to one another and a manually operable switch associated with each of said microphones to close said communication circuit for operation, a power supply circuit including a rectifier adapted to supply said communication circuit with direct current; and common to all said power supply circuits a source of power and a master control switch adapted to connect said source of power simultaneously into said power circuits, said relay being arranged to close said normally interrupted cosm c ma ly in err p d power i it tor contr lli said-drive system; a communication circuit indu ti lv c u l to s am lifie n i c udin a number of relays'responsive to'D. 'C. currents 01- different magnitudes," a remotely positioned r s st nc e icro e owe su l ir- Quit in l i a c i e a pt d o sim l sa d com nic t ciicuit th d ect curren and associated with said microphone means ior controlling the flow of D. C. current in said cornmunication circuit; a signalling system including a source of light in proximity of said microphone, a normally interrupted power supply circuit to energize said signalling system; and common to all said power supply circuits a source of power and a master control switch adapted to connect Sa d so rc of powe simultaneously i to a l aid power circuits, said relays being arranged to close idnc m fly rru d DQ Q 'QiE iii in p se t d cc c r cn flq i i said comm nication circuit.

'7. An arrangement for recording scund from a number of remote points including a recording ma hin ha n e e troni amp ifies a new r c r t t a sa pl e a m o and. a normally interrupted power circuit to drive said motor; a c mmunica n rcui iidiw i lv l t d am fi nd' i ud ne a umbe of re ys r p si e D.- C- curre t 0i ffi ifeiii magnitudes, a plurality of. remotely positioned parallel-connected carbon microphones, a power supply circuit including a rectifier adapted to supply said communication circuit with direct current and, associated with each microphone means for controlling the now of D, C, current in said communication circuit; a signalling syst r nc udi a mora y f se ies. ne d lam s o e a h s c ated. w th, ever 1 9 10.,- phone, a normally interrupted power supply circuit for energization of said signalling system; nd common to l, aid w is ipp y cir it 3 source of power and a master control switch adapted to connect said sourceoi power, sim'ul taneously into allsaid power circuits, said relays being arrangedto close said normallyinterrupted power supply circuits in response todirec t curl flo in a d c mmi iii i ori W 1 a a ow irs i i e ivi ie ri v tems of the type described, a rectifier having out; put terminals, in combination with a filter arrangement connected, across said terminals, saidfilter arrangement including a choke coil and a number of relay'coils connected in series'with said choke coil at'the' low potential end thereof and, a number of condensers connected across said terminals at the low potential ends of said choke'coil and said relay "coils.

9. In an arrangement for remote control operation of a recordin machine of the type having a recorder, a drive system and a control circuit forputting said drive system into and out of operation: the combination of a communication circuit serially includin a source of direct current, a remotely positionedresistance type micro phone, a primary winding forming part of an audio transformer, a, relay oil having an associated pair of contacts, and a manual switch adjacent to said microphone for closing said com munication circuit to cause direct current to flow therein; means connecting said relay con-'- tacts in said control circuit to cause the latter to be closed to render said drive system operative upon closing of said manual switch; a secondary winding included in said audio transformer; cir- Qui means. conn ct n sa d ec ndar wind n t sa d e o e o sup l th re o u io. module,- oiits imposed on th d r u r i said s me munication circuit by said microphone; and a sound condenser in said communication circuit forming a by-pass for the audio currents around said relay coil and D.-C. source.

10. The combination set forth in claim 9 wherein said source of direct current comprises a rectifier and a filter, said filter comprising said relay coil acting as a choke.

11. In an arrangement for remote control operation of a recording machine of the typefhaving a recorder, a drive system and a control circuit for putting said drive'system into. and out of operation: the combination of a communication circuit serially including a source" or direct cur:- rent, a remotely positioned resistance type microphone, a primary winding forming part or an audio transformer operatively connected to said recorder, a first relay, a second relay requiring a stronger current fiow in said communication circuit for activation than said first relay, and a first switch adjacent to said microphone for. cl'os ing said communication circui t to cause direct current flow therein and activation of said relay; a signaling device controlled by said. first relay to render 'it operative when the'relay is activated; means associated with said communi cation circuit and including a second switch adjacent to said microphone and operable to: increase the current flow in said communication circuit to cause activation of said second relay; and means connecting said second relay to said: con trol circuit to placesaid drive system in operation when said second switch is operated.

' 12. In an arrangementincluding a dictation recording machine having a'reccrder and a drive system and including a remote stationiorf con: trolling said machine: the combinationof a can munication circuit leading'from said station'to said machine and including a source or direct current, a resistance type microphone, a resistor and a'first switch closable to cause flow of direct current in said circuit; a first control device for said machine connected in said'communicatiofi circuit and activatable by the direct current therein when said first switch is closed; a n'o'rmally-open second switch connected in shunt with said resistor for shorting the latter to cause an increase in now of direct current in saidcoin' munication circuit; a second control device for said machine. connected insaid communication circuit fol-activation by the direct current therein, saidsecond control device requiring a higher valueiof direct current for activation than said first controldevice andbeing activated only when both said first. and second switches are closed, said microphone being operable to modulate the direct current in said"communicatiori'circuit when both said first and said second switchesare closed; "and means for feeding audio modulations in saidconimunication circuit tosaid recorder."

e r RIcHARn oBnEr-t REEZQBENCES CITED The following references are of reco rd in,tne

file r this patent:

' U irEa r r TEus au s ee- -9 3