US3158814A

US3158814A - Pulse repeater employing alternately conducting devices responsive to control means alternately priming and cutting-off said devices

Info

Publication number: US3158814A
Application number: US251796A
Authority: US
Inventors: Donald A Brewin
Original assignee: General Dynamics Corp
Current assignee: General Dynamics Corp
Priority date: 1963-01-16
Filing date: 1963-01-16
Publication date: 1964-11-24
Anticipated expiration: 1981-11-24

Description

Nov. 24, 1964 D. A. BREWIN 3,158,814

PULSE REPEATER EMPLOYING ALTERNATELY CONDUCTING DEVICES RESPONSIVE TO CONTROL MEANS ALTERNATELY PRIMING AND CUTTING-OFF SAID DEVICES Filed Jan. 16, 1965 2 Sheets-Sheet l 65V. PULSE 42| 20 I40 I42 '23 SOURCE I30 I45 A OAB V 503 502 |2| A 221 EAB INVENTOR. DONALD A. BREW/IV g M WJQZZJ {QENT 245 EP i 220 230 223 244 PULSE REPEATER EMPLUYENG ALTERNATELY CONDUCTHNG DEVECES RESPONSKVE T CQN- TROLL MEANS ALTERNATELY PRIMING AND CUlTTiNG-QFF SAliD DEVICES Donald A. iirewin, Rochester, N.Y., assignor to General Dynamics Corporation, Rochester, N.Y., a corporation of Delaware Filed Jan. 16, 1963, Sci. No. 251,796 11 Claims. (Cl. 328-210) This invention relates in general to a pulse repeater and, more particularly, to a pulse repeater for driving a counter with increased accuracy.

Although the invention herein disclosed is suitable for more general application, it is particularly adapted for use in a system wherein it is necessary to count the number of pulses in a group of a first type which occur between pulses of a second type. For example, in toll ticketing telephone systems, information relating to a call is frequently transmitted as a coded series of first pulses separated by a distinctive second pulse. In systems such as that disclosed in Patent No. 2,877,311 to Morris et al., the first and second types of pulses are referred to as mark and space pulses, respectively. Experience has shown that a very satisfactory way to count groups of pulses of the type described is to use the input pulses to alternately operate, or fire, first and second tubes in a driver circuit. The driver circuit, in turn, provides output signals to a counting circuit which typically cornprises a chain of cold cathode gas tubes which are arranged in odd and even groups.

The effectiveness of the extinguishing action in the prior art circuits was reduced by the connection of the counting chain to the driver circuit. Furthermore, the prior art circuit required a potential clamping circuit to eliminate the production of a current spike from the load and the clamping circuit further reduced the effectiveness of the driver extinguishing circuit.

Accordingly, it is the general object ofv this invention to provide a new and improved counting circuit driver.

It is another object of this invention to provide a new and improved counting circuit driver wherein the load does not affect the extinguishing action.

It is another object ofthis invention to provide a new and improved counting driver circuit comprising a pair of tubes which are fired alternately and which are preextinguished.

It is another object of this invention to provide a new and improved counting driver circuit comprising a pair of cold cathode gas tubes which are fired alternately and wherein the extinguishing of one tube does not depend upon the firing of the other tube.

in accordance with a preferred embodiment of the present invention, the counting circuit driver comprises twocold cathode gas tubes and a bistable device. The input pulses which are to be counted by the counting chain driven by the driver are applied to the control anode of both of said gas tubes. The bistable device enables the tubes alternately and is shifted from one to the other of its bistable states as each of the gas tubes fires. Thus, when the enabled tube is fired by an input pulse,,the bistable device is operated, thereby removing the enabling potential from the fired tube and pre-extinguishing it. The enabling potential is thereupon applied to the other tube. Accordingly, the fired tube is pre-extinguished and,

3,158,814 Patented Nov. 24, 1964 therefore, does not need to be put out when the other tube fires. This permits a more accurate count without either introducing an unwanted spike into the load circuit or having the effectiveness of the extinguishing circuit be reduced by the load circuit, as in prior art counting circuit drivers.

Further objects and advantages of the invention will become apparent as the following description proceeds, and features of novelty which characterize the invention will be pointed out in particularity in the claims annexed to and forming a part. of this specification.

For a better understanding of the invention, reference may be had to the accompanying drawings in which:

FIG. 1 illustrates a counting circuit driver incorporating the invention; and

FIG. 2 illustrates a typical counting circuit driven by the driver.

It is to be understood that only the details of the circuit necessary to understand the invention have been shown. For example, the means for producing the first and second types of pulses has not been shown. These pulses could be derived from many sources. For example, the first type of pulse could be activated by a typical counter mechanism, such as a trafiic counter, while the second pulse might be activated at fixed time intervals so that the number of counts per unit time could be readily determined; or the first and secondpulses may be indicative of mark and space pulses, respectively, as read from a toll ticketing tape recorder, as described in the above cited Morris et al. patent. In addition, only a typical counter is shown. it will be appreciated that, depending upon what is being counted and the need for registering the count, that one or more counters and/ or registers may be required and that a steering circuit may be employed to steer the output signals from the driver or of pulses is subsequently transferred, in coded form, to a selected one of a plurality of registers.

It is believed that the operation of the invention can best be understood by considering the following detailed description in conjunction with the accompanying figures. The tubes ill, 222, 4%, and the tubes of FIG. 2 may be cold cathode gas tubes, such as RCA type5823. These tubes have a starter anode-to-cathode breakdown volt age of approximately seventy-three volts minimum and an anode-to-cathode potential drop of approximately sixty volts. However, as the tube ages, this potential may increase. In addition, there is included in FIG. 1 a bistable device 5ii having contacts 5&2 and 503 which may be mercury wetted. Current in one direction through coil 5% will cause contacts 592 to close, while current in the other direction through coil Silt) will cause contacts 5% to close. Either set of contacts, once closed, will remain closed even though the current in coil 50%) ceases to flow. Upon reversal of a direction of current in coil 50%, the contacts 502 and 5423 will reverse themselves, that is, the closed contacts will open and the open contacts will close. The operation of the counting driver circuit will not be afiected by whether or not the

contacts

502 and 503 are bridging contacts.

All terminals marked are connected together and to the reference or system ground. Accordingly, these terminals will hereinafter be referred to as ground. The terminals marked are connected to a potential which I 3 is sixty-five volts positive with respect to ground. The terminal marked B+ is at a positive potential of one hundred and sixty-five volts with respect to ground.

As will be seen, it Will be convenient to refer to tubes ill and 222 as the odd and even tubes, respectively. Ac cordingly, these tubes have been given distinctive odd and even numbers to facilitate the association of their function with their designation. In addition, elements Whose functions are most closely associated with tube 111 have been given designations starting with the digit 1; While elements whose functions are most closely associated with tube 222 have been given designations starting with the digit 2. in a similar manner, elements which are most closely associated with tube dill have been given designations starting with the digit 4.

It will be observed that while contacts see are closed, the B+ potential will be applied through the common load resistor 221 to the lead designated EAB (even anode bus). In a similar mannenwhen contacts 5t)? are closed, the B+ potential will be applied through the common load resistor 121 to the lead designated GAB (odd anode bus).

When contacts 503 are open, it will be seen that capacitor 130 is discharged as the two sides thereof are connected to ground through resistors 12% and 123, respec tively. Later, when contacts 5% close, the left terminal of capacitor 136 will be suddenly raised to the 3-}- potential. Capacitor 134) will charge to a potential of plus sixty-five volts, the potential connected to the cathode of diode 142. Accordingly, a sixty-five volt pulse is applied to the OP (odd pulse) lead in response to the closing of contacts 503. In a similar manner, it will be obvious that capacitor 2% performs in the same manner to apply a sixty-five volt pulse to the EP (even pulse) lead when contacts 502 close.

As will be seen, the tubes 111 and 222 respond alternately to successive pulses on lead MK and the circuit is reset in response to each pulse on the lead designated Si irrespective of which of the two tubes 111 or 222 was last fired. The pulses applied to the MK lead will be applied to the starter anodes of both the odd and even tubes and pulses applied to the SP lead will be applied to the starter anodes of the even tube and the auxiliary tube designated 222 and 4%, respectively. In addition, the SP pulse is applied to the Reset lead of the counter circuit of FIG. 2 through capacitor 433.

t will be assumed that no tube of FIG. 1 is fired and that contacts Sill are closed, thereby applying a 13-}- potential to the anode A of tube 111 at the time that the first pulse appears on the MK lead. As will be seen, this is the condition which prevails after the receipt of an SP pulse. The application of a sixty-five volt pulse to the MK lead will cause a sixty-five volt pulse to be passed through

capacitors

216 and 116 to raise the potentials of the starter anodes of tubes 222 and 111, respectively, to approximately one hundred and thirty volts since they are biased to sixty-five volts by resistors M22 and sea. Since a B+ potential is connected to the anode A of tube 111 and its cathode K is at ground potential, tube 111 will be fired, thereby raising its cathode terminal to a potential of approximately one hundred volts. The cathode poten tial will be equal to the B+ potential minus the anode-tocathode potential of the tube, which is approximately sixty volts, and minus the potential drop in resistor 195. Tube 222 will not be fired as its anode is at ground potential. The one hundred volt positive potential on the cathode oftube ill will cause a current to flow in the operating coil of bistable relay Still. The circuit is comand 222.

The application of the 13-}- potential to the anode of tube 222 does not cause tube 222 to be fired at this time as the pulse from the MK lead has been dissipated and the starter anode of tube 222 has been returned to sixtyfive volts, a potentail which is below the firing potential.

The application of the 13-}- potential to the DAB lead will apply the B+ potential through the common load resistor 12?; to the anodes of the odd tubes of FIG. 2, as will be described later. In addition, a sixty-five volt pulse will be applied to the OP lead, as mentioned before, and, as will be shown, this pulse will be used to fire the first odd tube of the counting chain of HG. 2. Accordingly, when a steady state condition has been reached after the first MK pulse, none of the tubes of FIG. 1 will remain fired, but contacts 5% will remain closed.

The next sixty-five volt pulse to be applied to the MK lead will again be applied to the starter anodes of both the odd and even tubes. However, since only the even tube 222 has a 13+ potential applied to its anode, only this tube will be fired. In response to the firing of tube 222, its cathode will be raised to approximately one-hundred volts and, therefore, a current will flow through resistor Sill and relay coil 50%, thereby operating the relay and causing contacts 5% to open and contacts 592 to close. The opening of contacts 563 will extinguish tube 222 and e closing of contacts Sill will re-apply the B+ potential to tube 111, thereby preparing it to fire upon receipt of the next sixty-five volt pulse on the MKlead. In a manner similar'to that already described, the closure of contacts 5% will apply the B+ potential through the common load resistor 221 to the EAB lead and a sixty-five volt pulse will be applied to the EP lead to fire the first even tube in the counting chain of FIG. 2, as will be described below.

The operation continues in the manner described with successive MK pulses causing the odd and even tubes to be fired alternately.

By means which do not form a part of this invention a sixty-five volt pulse is applied to the SP lead periodically, or at the end of each series of MK pulses. Techniques for providing such pulses are Well known to those skilled in the art and, therefore, are not shown herein. It is evident that an SP pulse may be applied after any number of MK pulses. That is, the SP pulse may occur when either contacts 502 or 563 are closed. The application of an S? pulse will be used to reset the driver circuit and to reset the counter circuit and/or to shift the connections through a steering circuit so that the information represented by a subsequent series of pulses will be registered in another register. Obviously, the driver circuit may or may not happen to be in its reset condition at the time of the occurrence of the SP pulse. The reset condition of the driver circuit is with contacts 562 closed. If the driver is already in its rest condition, there is no need for the SP pulse to alter the drive circuit of FIG. 1. However, if the drive circuit must be reset by the SP pulse, the drive circuit must be prevented from providing another pulse to the counting circuit.

The pulse applied to the SP lead Will be conducted to the starter anodes of tubes 4% and 2122. However, if the driver circuit is already in the reset condition, i.e., if contacts 5492 are closed, then the SP pulse will not fire either of the tubes 4% or 222, but the SP pulse will be applied through capacitor 433 to the Reset lead to the counter circuit. f a plurality of registers are used, the SP pulse on the Reset lead can be applied to a steering circuit to cause the digital information counted by the counter to be transferred to a selected one of the plurality of registers. If the driver is not already in the reset condition, contacts 5&3 will be closed, thereby applying the 3+ potential to the anodes of tubes 4% Therefore, upon the application of the SP pulse to the starter anodes of these tubes, they will both be rendered conducting and relay coil 5% will be energized to open and close contacts 593 and 5%, respectively.

' lead.

With tube 400 conducting, its cathode will be raised to approximately a,.sixty-fi-ve volt positive potential, thereby Charging capacitor 431, which will tend to maintain the upper terminals of

resistors

405, 406 and 407 at this potential after the B+ potential is removed from the anodes of tubes400 and 222. The resistor 421 is employed to keep the cathode of tube 400 from rising volt pulse, which is passed through capacitor 430, tends to increase the charge on capacitor 432, thereby passing a pulse on the Reset lead.

Since tube 400 had not been rendered conducting before contacts 502 closed, diode 444 had been effectively back biased by the plus sixty-five volt potential connected at resistor 715 and, therefore, no pulse below sixty-five volts can be transmitted to the Reset lead through capacitor 432. However, when tube 400 fires, a sixty-five volt potential will also be applied to the junction of capacitor 432 and diode 444 through resistor 406, thereby nullifying the back bias on diode 444 and thereby permitting the transmission of pulses to the Reset lead.

Detailed Description Counting Circuit FIG. 2 illustrates a typical counting circuit of a type which might be driven by the pulse repeater o-fFlG. 1. As with FIG. 1, the elements of FIG. 2 which have similar functions have been given three digit designations with the last two digits identical. As has already been shown, the pulse repeater of FIG. 1 starts in its reset to the driver, the B-{- pulse is maintained on, or shifted in response to a; first pulse on the MK lead, shifts the B+ potential to the CAB lead and applies a sixty-five volt pulse to the OPlead. In response to the next pulse on the MK lead, the B+ potential is shifted back to the EAB lead and a sixty-five volt pulse is, applied to the EP In response to a pulse applied to the SP lead to the driver, the B+ pulse is maintained on, a shifted to, the EAB lead, but no pulse is applied to the EP lead.

the Reset lead.

It will be assumed for'the present that the Home tube 600 of the counting circuit has already been fired and that the B+ potential is applied to the EAB lead. It will be seen later that this is thecondition which prevails after a reset pulse.

.Theresistors 601 and 602 are selected as a voltage divider so that when tube 6% is conducting the common point of the two resistors is at a sixty-five volt potential. It should be recalled that the tubes have approximately a sixty volt anode-to-cathode potential when conducting. The pair of resistors connected between ground and the cathode of each of the tubes of FIG. 2 have the same function as resistors dilland 602 and, therefore, when their respective tube is conducting, the common resistor point is at a sixty-five volt potential.

When the driver circuit removes 13+ potential from the EAB lead, the Home tube 6&0 is extinguished, but the .charge 'on-capacitor 60d maintains the common point anodeof the diode 637 is at ground potential since no current is flowing in

resistors

621, 622 and 623.

ever, the back bias on diode 617 has been nullified by .virtue of the potential across

resistors

601 and 602 from Howcharged capacitor 604. That is, the anode and the cathode of diode 617 are both at a plus sixty-five volt potential a The SP pulse is either applied directly or repeated to v 6 and, therefore, the starter anode of tube 610 is at a plus sixty-five volt potential. Accordingly, the application of the sixty-five volt pulse to the OP lead will pass through capacitor 613 and diode 617 to raise the potential of the starter anode oftube 610 to one hundred and thirty volts which will cause the tube 610 to tire and start conducting. The firing of tube 610 causes capacitor 614 to be charged and thereby nullifies the back bias of diode 62.7, which had been back biased in the same manner as diode 637. Accordingly, when the 13+ potential is removed from the CAB lead and applied to the EAB lead, the tube 620 will be enabled to be fired upon receipt of a sixty-five volt pulse on the EP lead. The removal of the B] potential from the anode of a conducting tube provides a positive extinguishing of that tube.

In this manner, each of the successive tubes in the counting circuit of FIG. 2 are sequentially fired and extinguished. FIG. 2 may include as many stages as desired and they may be ring connected and coupled to another counting unit which records thenurnber of completed rings that have been advanced through in response to the alternate pulses on the OP and EP leads.

When a pulse is applied to the SP lead in FIG. 1, the B+ potential is connected to the EAB lead, if it is not already so connected, and a sixty-five volt pulse is applied to the Reset lead. If at the time of an SP pulse the B+ pulse is on the CAB lead, then the removal of the 13+ potential from the CAB lead to transfer it to the EAB lead will'extinguish whichever one of the odd tubes which had been conducting. if the B+ potential is on its anode is approximately sixty volts above the cathode potential and, therefore, the potential of the EAB lead is momentarily pulled down from the B+ potential to a potential of approximately sixty volts. The increased current through the common anode resistor 221 also facilitates the reduction in the potential on the EAB lead. With the potential of the EAB lead reduced to approximately sixty volts, the even tube which had been conducting will be extinguished as the potential of the anode thereofis momentarily reduced below the potential required to sustain conduction. For example, if even tube 620 has been fired, its cathode capacitor 624 is charged to a potential of approximately seventy-five volts and, therefore, when the potential of the EAB lead is temporarily reduced significantly below one hundred and sixtyfive volts, the even tube will be extinguished as the potentiai between the anode and cathode will be reduced below the value required to sustain conduction. As already stated, the Honte tube does not react in the same manner as its cathode capacitor 604 is not charged. Accordingly, in response to the application of an SP pulse to the driver circuit, the counting circuit is restored to its starting, or reset, condition irrespective of'whether the last tube that had been fired was an odd or even tube.

When 5823-type' tubes are employed, the following values have been found to give satisfactory results:

Value 47 Element designation and/or function:

562-, N2, 202, 6%5, 615, 625, 635 kilohms All resistors connected to .+65 volt potential,

lthough the purpose of some elements may not have been described in detail, it is believed that their function will, for the most part, be evident from their similarity to other elements which have been described. The remaining elements form obvious current limiting, clamping, or discharge circuits which are all obvious and well known to those skilled in the art to which this invention pertains.

While there has been shown and described what is considered at present to be the preferred embodiment of the invention, modifications thereto will readily occur to those skilled in the art. it is not desired, therefore, that the invention be limited to the embodiment shown and described, and it is intended to cover in the appended claims all such modifications as fall within the true spirit and scope of the invention.

What is claimed is:

l. in a pulse repeater, first and second devices each having an anode, a cathode, and a stanter anode, a source of pulses having a predetermined minimum potential with respect to a reference potential, a bistable device, first circuit means for applying the pulses from said source to the starter anodes of both of said first and second devices, said bistable device including conlrol means for rendering said first device conductive in response to the application of one of said pulses to its starter anode only when said bistable device is in a first of its stable states and for rendering said second device conductive in response to an application .of one of said pulses to its starter anode only when said bistable device is in a second of its bistable states, second circuit means coupled to said first and second devices for setting said bistable device to its first and second states when said second and first devices, respectively, are rendered conducting, first and second output terminals, and means for producing an output pulse at said first and second terminals in response to the setting of said bistable device to its first and second states, respectively, whereby pulses are alternately applied to said first and second terminals in response to successive pulses from said pulse source.

2. The combination as set forth in claim 1 and including a second source of pulses having a predetermined minimum potential with respect to a reference potential, circuit means for applying pulses from said second source to the starter anode of said second device, said control means controlling said second device for rendering it conductive in response to the application of a pulse from said second source to its starter anode only when said bistable device is in the second of its bistable states, whereby said bistable device is set to a predetermined one of its stable states'in response to each pulse from said'second source.

3. The combination as set forth in claim 2 and including a third device similar to said first and second devices, circuit means for applying pulses from said second source to the starter anode of said third device, said control means controlling said third device for rendering it conductive in response to the application of a pulse from said second source to its starter anode only when said bistable device is in the second of its bistable states, and means coupled to said third device and a selected one of said output terminals for inhibiting the production of an output pulse on said selected terminal when said third device was rendered conductive.

4. The combination as set forth in claim 3 wherein any one of said first, second, and third devices which is rendered conductive in response to the application of a pulse from either of said pulse sources to their respective starter anodes is rendered non-conducting in response to the shifting of said bistable device from one of its stable states to the other of its stable states.

5. The combination as set forth in claim 4 wherein said bistable device comprises an electromechanical device.

6. In a pulse repeater, first and second devices each having an anode, a cathode, and a starter anode, a source of pulses having a predetermined minimum potential with respect-to a reference potential, a bistable device, first circuit means for applying the pulses from said source to the starter anodes of both of said first and second devices, said bistable device including control means for rendering said first device conductive in response to the application of a pulse to its starter anode only when said bistable device is in a first of its stable states and for rendering said second device conductivein response to an application of a pulse to its starter anode only when said bistable device is in a second of its bistable states, second circuit means coupled to said first and second devices for setting said bistable device to its first and second states when said second and first devices, respectively, are rendered conducting, a two-terminal source of potential, first and second output bus leads, and a selected one of said two terminals of said potential source connected to said control means for connecting said selected terminal to said first and second bus leads when said bistable device is set to its first and second states, respectively, whereby the potential of said one terminal is alternately connected to said buses in response to successive pulses from said pulse source.

7. The combination as set forth in claim 6 and including a second source of pulses having a predetermined minimum potential with respect to a reference potential, circuit means for applying pulses from said second source to the starter anode of said second device, said control means controlling said second device for rendering it conductive in response to the application of a pulse from said second source to its starter anode only when said bistable device is in the second of its bistable states, whereby said bistable device causes the selected one of said two terminals of said potential source to be connected to a predetermined one of said buses in response to a pulse from said second source.

8. The combination as set forth in claim 7 and including a third device similar to said first and second devices, circuit means for coupling pulses from said second source to the starter anode of said third device, said control means controlling said third device for rendering it conductive in response to the application of a pulse from said second source to its starter anode only when said bistable device is in the second of its bistable states, a pulse output lead, and means coupled to said third device and said pulse output lead for inhibiting an output pulse on said pulse output lead until said third device is rendered conductive.

9. The combination as set forth in claim 8 wherein any one of said first, second, and third devices which is ren dered conductive in response to the application of a pulse from either of said pulse sources to their respective starter anodes is rendered non-conducting in response to the shifting of said bistable device from one of'its stable states to the other of its stable states.

10. In a driver for controlling a counting circuit, first and second tubes having an anode, a cathode, and a control anode, a bistable device, a given potential, first circuit means for selectively applying said given potential between the cathode and anode of said f'n'st tube when said bistable device is in its first stable state and for selectively applying said given potential between the cathode and anode of said second tube when said bistable device is in its second stable state, a source of driving pulses, coupling means for coupling pulses from said source to both of said control anodes, said first tube being responsive to the coupling of a pulse to said control anodes for providing a current in the anode-cathode circuit of said first tube when said bistable device is in said first state, said second tube being responsive to the'coupling of a pulse to said control anodes for producing a current in the anode-cathode circuit of said second tube when said bistable device is in said second state, and second circuit means responsive to the current in the anode-cathode circult of said first and second tubes, respectively, for switching said bistable device to its second and first states, stable device is set to a predetermined one of its bistable respectively. states in response to each pulse from said second source.

11. The combination as set forth in claim 10 and including a second source of driving pulses, coupling means References Cited in the file of this patent for coupling pulses from said second source to the con- 5 1 UNITED STATES PATENTS trol anode of said second tube, said second tube being responsive to the coupling of a pulse from said second 2,059,562 Curtis 1936 source to its starter anode for producing a current in 2,837,701 June 3, 1958 the anode-cathode circuit of said second tube when said 29641587 Eakm 1960 bistable device is in said second state, whereby said bi- 1o

Claims

1. IN A PULSE REPEATER, FIRST AND SECOND DEVICES EACH HAVING AN ANODE, A CATHODE, AND A STARTER ANODE, A SOURCE OF PULSES HAVING A PREDETERMINED MINIMUM POTENTIAL WITH RESPECT TO A REFERENCE POTENTIAL, A BISTABLE DEVICE, FIRST CIRCUIT MEANS FOR APPLYING THE PULSES FROM SAID SOURCE TO THE STARTER ANODES OF BOTH OF SAID FIRST AND SECOND DEVICES, SAID BISTABLE DEVICE INCLUDING CONTROL MEANS FOR RENDERING SAID FIRST DEVICE CONDUCTIVE IN RESPONSE TO THE APPLICATION OF ONE OF SAID PULSES TO ITS STARTER ANODE ONLY WHEN SAID BISTABLE DEVICE IS IN A FIRST OF ITS STABLE STATES AND FOR RENDERING SAID SECOND DEVICE CONDUCTIVE IN RESPONSE TO AN APPLICATION OF ONE OF SAID PULSES TO ITS STARTER ANODE ONLY WHEN SAID BISTABLE DEVICE IS IN A SECOND OF ITS BISTABLE STATES, SECOND CIRCUIT MEANS COUPLED TO SAID FIRST AND SECOND DEVICES FOR SETTING SAID BISTABLE DEVICE TO ITS FIRST AND SECOND STATES WHEN SAID SECOND AND FIRST DEVICES, RESPECTIVELY, ARE RENDERED CONDUCTING, FIRST AND SECOND OUTPUT TERMINALS, AND MEANS FOR PRODUCING AN OUTPUT PULSE AT SAID FIRST AND SECOND TERMINALS IN RESPONSE TO THE SETTING OF SAID BISTABLE DEVICE TO ITS FIRST AND SECOND STATES, RESPECTIVELY, WHEREBY PULSES ARE ALTERNATELY APPLIED TO SAID FIRST AND SECOND TERMINALS IN RESPONSE TO SUCCESSIVE PULSES FROM SAID PULSE SOURCE.