US2348312A - Remote control apparatus - Google Patents

Description

y 9, 1944- F. M. SCHMIDT ETAL ,3 8,3 2

REMOTE CONTROL APPARATUS Filed June 11, 1941 3 Sheets-Sheet 1 INVENTORS.

' y 9-{1944- F. M. SCHMIDT EIAL 2,348,312

7 REMOTE CONTROL-l APPARATUS Filed June 11, 1941 3 Sheets-Sheet 2 BY 65A m a. 5% Q 7 7 6 3 /7 rok/vfxs.

y 1944- F. M. SCHMIDT ETAL 2,348,312

REMOTE CONTROL APPARATUS Filed June 11, 1941 3 Sheets-Sheet 3 I I77 u, fi 7 84 /74 l [7 .17 174 Will/14+ Will/4 II [b l q M5 w u I 15/ H L j I I50 o M m7 Zn 164 o 1w m INVENTORS.

Patented May 9, 1944 REMOTE CONTROL APPARATUS Francis M. Schmidt, North Tonawanda, and Gerald G. Smith, Kenmore, N. 1., asslgnors to The Rudolph Wurlitzer Company, Cincinnati,

Ohio, a corporation Application June 11, 1941, Serial No. 397,554

1; Claims.

This invention relates to a remote control apparatus which is particularly adapted to the selective control of automatic record changing phonographs but may be used for other purposes as well.

Certain features of the apparatus disclosed herein are shown and claimed in co-pending application of Charles J. Hull and Fred H. sborne, Serial No. 355,204, filed September 3, 1940, and which has become Patent 2,327,429, August 8, 1943.

One object of the present invention is to provide apparatus by means of which a controlled machine may be operated from a remote station which is connected only through the power mains which supply power for the controlled machine and for the remote station.

Another object of the invention is to provide remote control apparatus of this type which is able to discriminate accurately against spurious signals which might appear on the power lines and which might interfere with the operation of the controlled machine. For this purpose the controlling signals consist of a radio frequency carrier signal power modulated by a series of audio frequency impulses. The number of such impulses in a. series determines the selective operation of the controlled machine and the impulses preferably occur at definitely timed intervals. Selectivity against spurious signals is obtained first by accurate tuning of the sending and receiving apparatus for a particular frequency of'the carrier wave: second, by similar tuning for audio frequency impulses and third, by wasting a predetermined number of impulses at the beginning of each series. Preferably at least two such impulses are wasted, that is, a series of at least three impulses is required to efiect any operation of the controlled machine. While one or possibly two spurious impulses of proper radio and audio frequency might possibly be impressed on a power line from some outside source, the chance of ,three such impulses properly spaced is very remote. Thehigh degree of selectivity also insures against the unauthorized intentional operation of the machine by the generation of controlling impulses by other apparatus. Apparatus to produce the necessary impulses to operate the machine must be practically a duplicate of the authorized apparatus and must be similarly tuned.

Another means by which the apparatus discriminates against transient signals is by the use of suitable slow acting apparatus at the receiver which prevents operation by transient impulses. of short duration.

Another feature of the invention resides in a particular manner in which the radio frequency carrier is modulated. This arrangement permits power modulation with a minimum number of tubes and parts.

Other' objects and features of the invention will be understood from the accompanying drawings and the following description and claims:

Fig. 1 is a diagram of electrical connections and apparatus illustrating a preferred form of remote control station. Fig. 2 is a similar dia gram illustrating a preferred form of receiving apparatus. Fig. 3 is a perspective view of certain mechanical parts of the receiving apparatus with the stationary framework thereof omitted to show moving parts in more detail. Fig. 4 is a fragmentary view partly in section of a portion of the apparatus shown in Fig. 3. Fig. 5

is a diagram showing in conventional form the I relation of the remote station, the receiver and a controlled machine to the commercial power circuits by means of which they are supplied and over which controlling signals are transmitted.

The invention is best adapted for use in a home or commercial establishment which is provided with the usual electrical wiring having suitable outlet sockets to which the controlled machine and the remote control apparatus may bev connected by the usual socket plugs. For use in a commercial application such as a restaurant, the control will ordinarily be dependent upon the insertion of a coin. Obviously for home use the coin control may be omitted. In Fig. 5 there is shown a pair of conductors it which may be considered as the distributory conductors of a commercial power company leading to the premises on which the invention is to be used. Connected to the conductors Ill there is shown the usual local transformer ll having a secondary winding connected to power mains l2 supplying theiridividual customer of the power company. Suitable cutout switches and overload protection, not

shown, may be assumed to be connected be-' tween the transformer II and the mains l2.

Appliance outlet sockets l3 are connected to the mains H in the usual manner and may be placed at any desirable position on the premises. Adjacent any one of the outlets I! there may be ;installed a signal transmitter it having a cord l5 and socket plug it which may be connected to the socket [3. YA signal receiver l'l having a cord l8 and plug l9 may be similarly connected to another of the sockets It. The machine to be controlled is shown in Fig. 5 in the form of an automaticrecord changing phonograph 28 connected to the signal receiver by a cord 2|. If desired, the receiver I! may be placed within the cabinet of the phonograph 20.

Signal transmitter I to describe the same in detail.

There is also provided a multi-point manual selector switch 24 which may be operated by a suitable knob 25 on the face of the transmitter M. The switch 24 has a plurality of contact points 26 each connectedby one of a group of conductors 21 with a corresponding point 28 on a motor driven multi-point switch 29. Other electrical apparatus within the transmitter |4 includes an electromagnetic relay 38 adapted when energized to close a series of normally open switches 3|, 32 and 33 and a motor 34 adapted to operate the multi-point switch 29'and to rotate a series of cams 35, 36 and 31. The mechanical connections of the motor to the switch 29 and the respective cams are indicated schematically in Fig. 1 by broken lines and it is to be understood that these connections are such that each of the cams and the motor driven switch make one revolution in a definite period of time. The cams 35, 36 and 31 operate switches 38, 39 and 40, respectively. Said cams and switchesand the switch 29 are shown in Fig. 1 in their initial idle position. Each cycle of motor operation starts with the parts in this idle position and continues until all of said parts are simultaneously returned to said positions.

There are also. provided electron discharge tubes 4|, 42 and 43. Tube 4| is shown as a standard pentode tube and is used as a generator of radio frequency energy. Tube 42 is a twin triode tube. One of the triode elements is used as a radio frequency amplifier and modulator and the other as an audio frequency oscillator. Obviously two standard triode tubes could be used in place of the single tube 42. Tube 43 is shown as a diode tube connected as a half wave rectifier to supply the necessary D. C. plate voltages for tubes 4| and 42. In practice it is advantageous to combine the elements of tubes 4| and 43 in a single tube but separate tubes are illustrated in the drawing for the sake of simplicity.

Power for operating the transmitter is supplied from the plug IE to a pair of line conductors 44 and 45, in one of which there may be placed a cutout switch 46. A transformer 41 has its primary winding connected to the line conductors 44 and 45 and its secondary winding arranged to supply current for the rectifier tube 43 and for a signal lamp 48. One terminal of the secondary winding of transformer 41 is grounded and the opposite terminal is connected to the anode 50 of the rectifier tube 43. The cathode of said tube is connected to a distributory conductor 52 which is maintained thereby at a suitable potential above ground and supplies the necessary D. C. potential for the plate circuits of tubes 4| and 42. A condenser 53 connected between the cathode and ground serves to smooth out the D. C. voltage.

The cathodes o t e se e al tubes ma be heated by heating elements connected to suitable taps on the primary or secondary windings of the transformer 41 in a conventional manner.

The remaining electrical apparatus illustrated in Fig. 1 may best be described in connection with the circuits in which they are included.

In the operation of the transmitter the switch 24 is first set on one of the points 26 by means of the knob 25. Each of the points 26 corresponds to an operation of the controlled machine and in the case of a selective record changing phonograph each of said points corresponds to one of the records carried in the magazine of said phonograph. Obviously, as many such contact points as are needed may be used. In the drawing, for sake of simplicity, only eight are shown. The setting of the switch 24 may be indicated by a suitable scale visible to the operator and corresponding with a suitable index of record titles.

When the switch 24 has been properly set, a coin is deposited and switch 23 momentarily closed to complete a circuit from the line concluctor 44 through switch 23, the winding of relay 30 and a resistance 49 to the line conductor 45. The consequent actuation of the relay 39 closes switch 3| which is in parallel with switch 23 and thus retains the relay in energized condition after switch 23 has been opened.

The operation of relay 39 also closes switch 32 and completes a circuit through said switch to start the motor 34. The first movement of the motor 34 operates the cam 35 to close switch 38 and short circuit the switch 32. The motor thus continues to operate until cam 35 has made a complete revolution and the parts have returned to idle position even though switch 32 is opened at a later time in the cycle of operation. The operation of motor 34 also actuates cam 36 to open switch 39 and break a normally closed circuit for the lamp 48. Said circuit leads from ground through switch 39, a resistor54, lamp 48 and a portion of the secondary winding of transformer 41 back to ground. Switch 39 is not again closed until cam 36 has returned to idle position and thus the signal lamp 48 when lighted indicates that the motor 34 is not in operation.

The operation of motor 34 also rotates the finger 55 of the multi-point switch 29 in the direction of the arrow. In this rotation the finger 55 successively engages the contact points 23. When said finger reaches the point 28 connected to the point 26 on which the switch 24 is set, a shunt circuit is closed around the winding of the relay 30 and said relay is thereby deenergized. The provision of the resistor 49 prevents the formation of a dead short across the line conductors and thus serves as an overload protection.

It will be apparent that the length of time dur-' ing which the relay 3!! is energized depends entirely upon the setting of the switch 24 and tha after said relay is deenergized the finger 55 is returned to its normal idle position since the motor 34 continues to operate until cam 35 opens switch 38.. During the operation of the motor the signal lamp 48 is not burning. When said lamp is again lighted at the end of a cycle of motor operation, it indicates tint the apparatus is ready for the receipt of another coin. 1

' The actuation of the relay 30 also closes switch 33 to start the operation of the radio frequency oscillator tube 4|. Said tube is provided with a conventional anode-cathode circuit leading from the D. C. distributory conductor 52, through inductance 56 and tuning condenser 51 in parallel to the anode 58 and thence through I. coupled with an inductance 95, and said coupling the cathode 59 and switch 99 to ground. The gridcathode circuit leads from cathode 59 to control grid 69 through resistor 8| and' the parallel path formed by inductance 52 and condenser 63. Inductances (and 62' are coupledto give 4 the necessary feed-back for oscillation and the frequency of oscillation is controlled by the tun- Preferably oscillations of the ing condenser 51. order of 250 K; C. are used. Since switch 33 is included in the anode-cathode circuit, radio frequency'energy is generated in the circuits of said tube only when relay 39 is energized and switch 93 is closed.

The radio frequency energy generated in the tube H is amplified and power modulated by the tube 42 and associated circuits. In tube 42 the audio oscillator section consists of cathode 54, control grid 55 and anode 66. The radio frequency section of the tube consists of cathode 61, grid 98 and anode 69. The two cathodes 64 and 61 are connected together and are connected to ground through the lower half of a variable inductance 19 which is thus common to the oathode circuits of both sections of the tube. A condenser 1I serves as a radio frequency by-pass for the cathode circuits. The grid 65 is connected to the cathodes through a resistor 12 and to the inductance 19 through a resistor 13 and the switch 49. A condenser 14 is shunted across the inductance 19 to complete the audio frequency tuned circuit. The plate 66 is directly connected to the D. C. distributory conductor 52. The grid 68 is coupled to the grid of tube 4I through a condenser 15 and resistor 16. Inductance 11 serves as a radio frequency choke between grid 68 and the cathode circuits. Anode 59 is connected to the D. C. distributory conductor 52 through condenser 18, variable condenser 19 and inductan'ce 89 all connected in parallel and together forming a radio frequency tank.

In the electrical connections just described, the inductance 19 and condenser 14 form the tuned circuit of the audio frequency section of the tube 42. The grid 65 receives the necessary energy for oscillation from the tuned circuit, only when the switch 49 is closed. The lower portion of the inductance 19 also forms a part of the cathode circuit of the radio frequency sec tion of the tube 42, so that the potential of the cathode 61 is affected by the oscillating current in the inductance 19. Thus the inductance 19 serves the dual purpose of producing oscillation and controlling the potential of the cathode 61 to modulate the radio frequency energy.

Radio frequency energy from tube 4| is fed to the grid 68 through the condenser 15 and resistor 16 and is amplified, modulated and impressed upon the tank circuit 18-49-89 by the radio section of tube 42. The switch 49 is operated by the cam 31, and said cam is so formed that the switch 49 is alternately opened and closed at regular intervals. The modulationof the radio frequency is thus given the form of a series of power impulses, the frequency of which is determined by the tuning of the resonant circuit 19-14. Preferably, said circuit is tuned to a frequency of the order of 400 cycles per second.

The inductance 89 is coupled with an inductance 8|, connected in series with an inductance 82 and a condenser 83. The inductances 8| and 92, and the condenser 83 form a link circuit in .which currents induced by the coupling with ininduces corresponding high frequency energy therein. One terminal of each of the inductances 94 and is connected to the line conductor 44, and the opposite terminals of said inductances may be selectively connected to the line conductor 45 by a switch 99 connected tothe last mentioned line conductor through a condenser 91.

-By means of the connections just described, the amplified and modulated radio frequency output of tube 42 is impressed upon the line conductors 44 and 45. byeither one of the inductances 94 and 85, the particular one otsaid inductance to be used being chosen by manual operation of the switch 86, and the choice depending upon the impedance of the external circuit between the remote station and the local station and conse-' quent strength of signal required.

The cam 91 and the switch 29 are both operated by the motor 94 and the audio frequency impulse produced by the operation'of switch 49 ma thus be accurately timed with relation to the movement of switch 29. It will be noted that in the movement of switch 29 from the initial idle position, the finger 55 travels some distance before the first of the contact points 29 is reached. Preferably, the cam 31 is so shaped that itproduces three audio impulses during this time.

Thus three audio impulses are generated and im pressed upon the line conductors before the finger 55 reaches the first of the contact points 28. During the movement of the finger 55; between each of the succeeding contact points, an additional audio frequency impulse is produced. Thus, if the switch 24 is set on the contact point 26 corresponding to the first of contact points 28, a series of three audio frequency impulses is transmitted before the relay 39 is deenergized to stop the production of radio frequency oscillation. Similarly, the setting of the switch 24 on any one of the other contact points 26, results in the production of a series of impulses of correspondingly greater number.

v Receiver Power for operating the receiver I1 and the controlled machine 29 is supplied from the plug cathode of said tube is connected to a D. C. distributory conductor I95 which is grounded through a resistor I99. The mid-point of the secondary winding of the transformer I93 is connected to a conductor I91 which is grounded through a resistor I99. The rectifier tube I94 thus serves as afull wave rectifier to maintain a suitable D.C.'potential difference between conductors I95 and I91. The resistances I96 and I99 are so chosen that conductor I95 carries a suitable potential for the plate circuits of the several tubes used in the receiver and the conductor I91 carries a negative potential.

The electrical apparatus of the receiver also includes a radio frequency transformer I99, a pentode tube II9 used for radio frequency amplification, a radio frequency transformer III, a tube II2 having a diode rectifier-section and a triode amplifier section used for audio frequenc amplification and a similar tube II3. Other electrical elements shown in Fig. 2 will be described in connection with the circuits in which they are included.

The primary winding of the transformer I03 is connected to the line conductors I40 and Ill through condensers H4 and H6 adapted to transmit radio frequency energy but to block the usual 60 cycle commercial current. Thus the modulated radio frequency signals generated in the transmitting apparatus are conducted from the transmitter I4 through the line conductors I2 and line conductors I06 and III to the transformer I09 and said signals induce corresponding currents in the secondary winding of said transformer. A tuning condenser H6 is connected in parallel with the secondary windings oi the transformer I to complete a resonant circuit which may be tuned to the radio frequency of the incoming signals. The resulting signal is impressed on the control grid II1 of tube H0. The cathode II8 of tube H0 is connected to ground through a conventional biasing resistor H9 and condenser I20 and the anode I2I of said tube is connected to the positive D. C. distributory conductor I46 through a tuned circuit consisting of the primary winding of transformer III and'a tuning condenser I22. The connections just described constitute a conventional stage of radio frequency amplification by means of which the incoming signals are amplified and impressed upon the primary winding of transformer II I.

The secondary winding of transformer III is provided with a tuning condenser I23 in parallel therewith to complete a tuned secondary circuit. one terminal of which is connected to the anode I24 of the rectifier section of the tube H2. The opposite terminal of said tuned circuit is connected to the cathode I25 of said tube through resistors I26, I21 and I28. The D. C. voltage produced in the circuit just described by operation of the rectifier section of tube II2 appears across the resistors I26, I21 and I26 and is applied to the control grid circuit of tube IIO through a conductor I 29 and a filter network consisting ,of a resistor I30 and condensers I3I and I32 to provide automatic volume control.

The control grid I33 of the amplifier section of tube H2 is connected through a coupling condenser I 34 to a point in the rectifier circuit just described where suitable variations in voltage are obtained for the operation of said amplifier section. Said grid is connected to ground through a conventional grid coupling resistor I34A. The cathode I35 is connected to cathode I25 and is biased to ground in a conventional manner. The anode I36 is connected to the D. C. distributory conductor I05 through a resistance I31. The connections just described complete a conventional stage of audio frequency amplification as a result of which a pulsating current of audio frequency corresponding to the transmitted impulses is generated in the circuit of anode I36.

The anode I36 is coupled by means of a condenser I38 to a circuit consisting of a variable inductance I40 and condenser I connected in parallel and a high frequency choke I and resistor I46 connected in series therewith and connected to the negative D. C. conductor I01. In this circuit the inductance I40 and condenser I4I form a tuned portion which may be adjusted to the particular frequency of the signal impulses. Voltages due to the signal impulses appear across the tuned portion of the circuit while voltages due to transient higher frequency enpedance to high frequency current is high as compared to that for lower frequency currents.

A rectifier circuit consisting of the rectifier anode I39. cathode I44, resistor I42 and condenser I43 is connected in parallel with the tuned portion of the circuit just described, but the connection is exclusive of the choke I45. Current flow in the rectifier circuit is thus controlled by the low frequency voltagesacross the tuned portion and is substantially unaffected by higher frequency voltages across the choke I45. This arrangement therefore provides an additional valuable means for discriminating against transient or spurious signals.

The current appearing in the rectifier circuit just described is a pulsating direct current of a predetermined audio frequency and flows only during the brief period of each of the signal impulses. During each impulse, the upper or cathode end of the resistor I42 is at a considerably higher potential than the lower end. The lower end of said resistor is connected through choke I45 and resistor I46 to the negative D. C. conductor I01 and the opposite end of said resistor is connected to the control grid I41 of the second section of tube H3. The cathode I48 of said second section is grounded and the anode I49 is connected through the winding of a relay I50 to the positive D. C. conductor I05. Because of the negative potential of the conductor I01 which is impressed upon the grid I41 when no current flows in the rectifier circuit, the second section of tube H3 is normally biased to cutoff and no anode current is drawn. During the receipt of a signal impulse, the voltage appearing across the resistor I42 raises the potential of the control grid I41 sufllciently to permit current flow in the anode circuit to energize the relay I50. Thus. said relay is momentarily energized in response to each of the signal impulses.

The relay I50 preferably is adjusted for relatively slow action by use of a copper core or other well known means so that transient impulses of short duration cannot energize the re lay. However, the speed of operation of the relay is not reduced sufliciently to prevent a distinct actuation for each signal impulse and a distinct release of the relay between the impulses.

ergy appear across the choke I45 since its im- .Referring now to Figs. 3 and 4, there is illustrated therein certain mechanical apparatus forming a part of the receiver and actuated by operation of the solenoid I50. In said figure only movable parts of the apparatus are shown and it will be understood that said parts may be supported on any suitable stationary structure. Said apparatus includes a shaft I60 carrying a contact finger I6I adapted to engage a series of contact points I62 as the shaft I60 is rotated in the direction of the arrow. The shaft I60 also carries a ratchet wheel I63 and is urged in the clockwise direction by a torsion spring I64, one end of which is secured to said shaft and the opposite end to a part of the stationary structure. An electromagnet I65 is mounted in a stationary position and is adapted to attract an armature I66 which is pivotally mounted on a pin I61. A finger I68 is pivotally mounted by means of a pin I69 on the armature I65 and is held against a stop pin I10 by a tension spring "I, the end of which is anchored to a stationary portion of the apparatus. The finger I68 is iii position to engage the teeth of the ratchet Wheel,

I63 and to move the ratchet wheel a distance corresponding to one tooth each time the magnet I65 is energized. A pawl I12 is mounted on a pivot pin I13 and may be held in engagement with the teeth ofthe ratchet wheel I68 by a tension spring I14. Said pawl is adapted to hold the ratchet wheel in the positions in which it is placed by operation of the magnet I65.

A lever arm I16 is adapted to engage the tail of the pawl I18 and to disengage the same from the pivotally mounted within a time delay device I11 which may be of a common commercial form, the details of which form no part of the present invention. It is sufilcient to say that the device has an action somewhat similar to that of a dashpot. That is, the lever arm I16 may be rapidly lifted by a small force in opposition to the action of a tension spring I18. When the lifting force is withdrawn, the spring I18 returns the lever I16 to its lower position but the time delay device I11 operates to slow the return movement to a predetermined slow speed which may be adjusted as desired. For lifting the lever arm I16 there is provided a vertical rod I19 the upper end of which is pivoted to the lever arm I16 and the lower end of which is reduced and extends through a loosely fitting opening in the armature I66, as shown in Fig. 4.

In the normal idle position of the apparatus, the lever arm I16 is held in its lower position by the spring I18 and engages the pawl I12 to free the same from the ratchet wheel I68. Said ratchet wheel carries a stop pin I86 engaging a the power lines I66 and m for a relay m. Said relaywhen actuated closes a switch I86.

teeth of the ratchet wheel. Said lever arm is In the operation of this portion of the apparatus, the first signal impulse received causes an actuation of magnet I65 to lift the lever I16 to close switch I88 and thereafter open switch I84. The operation of switch I83 energizes the relay I85. The movement of the lever I16 in the upward direction is relatively rapid so that switch especially slow acting relay be used for opersuitable stationary stop I8I which holds the.

ratchet wheel in an initial idle position when the pawl I12 is disengaged therefrom. In this position the contact finger I6I is out of engagement with the contact points I62 and is positioned at a sufllcient distance from the first of said contact points so that three actuations of the magnet I65 are required before said contact finger reaches said first contact point. Each actuation of the magnet I66 moves the ratchet wheel I68 and the contact finger I6I one step in the counterclockwise direction. The first such actuation causes the lever arm I16 to be lifted free of the pawl I12 and permits said pawl to hold the ratchet wheel. After each actuation of magnet I65 the slow downward movement of the lever I16 is begun but each succeeding actuation returns said lever to its upper position. Thus, if a series of actuations of the magnet I65 occurs with sufficient frequency the time delay device I11 prevents the arm I16 from freeing the pawl I12 between actuations. At the end of a series of such actuations, the lever arm I16 moves slowly downward and eventually engages the pawl I12, releasing the same from the-ratchet wheel and permitting the ratchet wheel to return to normal idle position.

Referring again to Fig. 2. the relay I56 actuates a switch I82 to close a circuit from line conductor I66 through magnet I65 to the line conductor I6I. The switch I82-is closed each time the relay I56 is energized. Thus the magnet I65 acts as a repeater for the relay I56 and is momentarily actuated in response to each signal impulse received from the transmitter. The lever I16 in its uppermost position is adapted to engage and operate a pair of switches I83 and I84, the switch I88 being closed, and the switch I64 being opened when so engaged. Said switches are preferably adiusted so that in the upward and downward movement of the lever arm I16 each of said switches is closed before the other is opened. The

ation of switch I86. However, .a slow acting relay may be used if necessary since it is desirable to open switch I84 before switch I86 is closed. At the end of a series of signal impulses, the contact finger I6I has been placed by operation of magnet I65 on one of the contact points I62. In

this connection it is to be noted that the initial position of said contact finger is sufficiently far from the first of thecontact points I62 so that a series of three impulses is required before said finger reaches the first of said contact points. Thus each of the contact points I62 corresponds to one of the contact points 26 and the point I62 selected by operation of magnet I65 is determined by the setting of switch 24.

The cessation of signal impluses permits the lever I16 to move slowly downwardly. In this movement the switch I84 is closed considerably before switch I88 is opened. The operation of switch I84 completes a circuit from line conductor I66 through switch I64 and switch I86 to the contact finger I6I and thence from the selected contact point I62 to one of a series of electromagnets I15, each of which has its opposite terminal connected to the line conductor I6I. At the same time, a circuit is completed through the switches I84 and I86 for an electromagnet I58. The electromagnets I58 and I15 form part of a controlled machine which may be of the type disclosed in Wilcox Patent No. 2,002,236 and the magnets I58 and I15 may correspond to the magnets I58 and I15 in said Wilcox patent. In that patent each of the magnets I15 controls the selection of a predetermined record and the magnet I58 initiates one operation of the machine. For selection of the record and initiation of the operation only momentary actuations of the magnets I58 and I15 are required. As the downward movement of lever I16 continues, switch I83 is opened to deenergize magnet I85. Switch I86 of which may be varied between wide limits with-' out departing from the scope of the invention as defined by the appended claims.

The-invention claimed is: 1

l. A signal transmitter including a generator adapted to produce electrical energy of high frequency power modulated by a series of signals of lower frequency, switching means and associated circuits adapted to start and stop the operation of said generator, initiating means for operating said switching means to start said generator, and apparatus automatically operable thereafter to reverse said switching means to stop said generator, said apparatus being selectively operable to predetermine the number of low frequency signals impressed on said circuit prior to said reversal.

2. A signal transmitter including a high frequency oscillator, a low frequency oscillator, a modulator and associated circuits adapted to apply to the output of said high frequency oscillator a power modulation the frequency of which is determined by said low frequency oscillator, a make-and-break device in said modulator circuits adapted to limit said modulation to a se- -ries of signals occurring at predetermined time intervals, and controlling means adapted to stop the operation of said high frequency oscillator to limit the number of signals generated, said controlling means being selectively operable to vary said number.

3. A signal transmitter including a high frequency oscillator, a low frequency oscillator, said low frequency oscillator having a cathode circuit and a control grid circuit, an electronic discharge amplifier having a control grid connected to said high frequency oscillator and having a cathode circuit, an inductance element at least a portion of which is connected in said low frequency oscillator control grid circuit and at least a portion of which is common to the low frequency oscillator cathode circuit and the amplifier cathode circuit. said inductance element controlling the potential of the amplifier cathode to modulate the output of said amplifier, switching means in said oscillator control grid circuit, and means operating said switching means to control said modulation.

4. A signal transmitter including a generator adapted to produce electrical energy of high frequency modulated by a series of signals of lower frequency, switching means and associated circuits adapted to start and stop the operation of said generator, initiating means for operating said switching means to start said generator, and apparatus automatically operable thereafter to reverse said switching means to stop said generator, said apparatus being selectively operable to predetermine the number of low frequency signals generated prior to said reversal.

5. A signal transmitter including a high frequency oscillator, a low frequency oscillator, a modulator and associated circuits adapted to apply to the output of said high frequency oscillator a power modulation the frequency of which is determined by said low frequency modulator, a make-and-break device in said modulator circuits adapted to limit said modulation to a series of signals occurring at predetermined time intervals, and controlling means adapted to stop the operation of said high frequency oscillator to limit the number of signals generated, said controlling means being selectively operable to vary said number.

quency oscillator, a lowfrequency oscillator, said low frequency oscillator having a cathode circuit and a control grid circuit, an electronic discharge amplifier having a control grid connected to said high frequency oscillator and having a cathode circuit, an inductance element at least a portion of which is connectedin said low frequency oscillator control grid circuit and at least a portion of which is common to the low frequency oscillator cathode circuit and the amplifier cathode circuit, said inductance element controlling the potential of the amplifier cathode to modulate the output of said amplifier, switching means in said oscillator control grid circuit, and means operating said switching means to control said modulation.

7. A signal transmitter including a high frequency oscillator, a low frequency oscillator, a modulator and associating circuits adapted to apply to the output of said high frequency oscillator a power modulation the frequency of which is determined by said low frequency oscillator, a make-and-break device in said modulator circuits adapted to limit said modulation to 6. A signal transmitter including a high frecircuits controlling the operation of said motor through a predetermined cycle during which said make-and-break device is operated a predetermined numberof times, and controlling means operated by said motor during said cycle to stop the operation of said high frequency oscillator, said means being selectively operable to predetermine the number of operations of said makeand-break device prior to cessation of operation of said high frequency oscillator.

8. A signal transmitter including a high frequency oscillator, a low frequency oscillator, a modulator and associating circuits adapted to apply to the output of said high frequency oscillator a power modulation'the frequency of which is determined by said low frequency oscillator, a make-and-break device in said modulator circuits adapted to limit said modulation to a series of signals occurring at predetermined time intervals, a motor operating said make-and-break device, means for initiating the operation of said motor and the operation of said high frequency oscillator substantially simultaneously, circuits controlling the operation of said motor through a predetermined cycle during which said makeand-break device is operated a predetermined number of times, and controlling means operated by said motor during said-cycle to stop the operation of said high frequency oscillator, said means-being selectively operable to predetermine the number of operations of said make-andbreak device prior to cessation of operation of said high frequency oscillator.

FRANCIS M. SCHMIDT. GERALD G. SMITH.

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