US3458771A - Coin operated electronic timer with quenching means - Google Patents

Description

July 29, 1969' J. R. JARVIS 3,453,771

COIN OPERATED ELECTRONIC TIMER WITH QUENCHING MEANS Filed March 1, 1967 JA R IN VENTOR.

ATTORNE K}:

United States Patent ce 3,458,771 Patented July 29, 1969 3,458,771 COIN OPERATED ELECTRONIC TIMER WITH QUENCHING MEANS JohnR. Jarvis, 2020 Gaisford, Dallas, Tex. 75210 Filed Mar. 1, 1967, Ser. No. 619,665 Int. Cl. H0111 47/18 US. Cl. 317-142 7 Claims ABSTRACT OF THE DISCLOSURE A coin-actuated electronic timer controlling an exter* nal load over a long duration timing cycle. A switching control means including a relay and a control transistor is actuated by the passage of a coin through a coin switch to connect an RC timing circuit to a direct current source, thus, starting a predetermined timing cycyle. The timing circuit includes a timing capacitor which is charged at a predetermined rate by the direct current and is discharged by a unijunction transistor which switches to a low-impedance state when the capacitor charge reaches a predetermined level. The discharge of the capacitor causes the control transistor to stop conducting and deactuates the relay. The unijunction transistor is connected to a low-level A.C. signal to reduce its peak point switching current. A quenching circuit prevents recycling when the coin switch is struck.

This invention relates to an electronic timer providing long-duration timing cycles. In one of its aspects, it relates to a coin-actuated timer which controls an external load for periods up to and in excess of one hour.

Timers with electronic timing circuits are used extensively to control the operating cycle or period of various automated machines. One important use of such a circuit is in conjunction with a coin switch whereby a customer receives a stated period of operation in response to his deposit of a coin of predetermined denomination. Automatic car washing machines, clothes washers, clothes dryers, and various vending machines are prime examples. With such automated machines, it is desirable to provide long operating periods, sometimes in excess of one hour. In order to insure that a customer receives a full operating period and also comply with various government regulations, care must be taken to insure that when a customer deposits a coin of a certain value in the machine, he receives a period of operation substantially as stated. Thus, if a washing machine states on its face that the customer will receive 45 minutes of washing for 25 for deposit, it is important that he receives almost precisely that.

Since such machines are generally left unattended for long periods of time, it is also desirable to provide a timing circuit which not only has a stable operating cycle and the ability to repeat these cycles, but one which will also remain stable for long period of time and require a minimum of maintenance. Thus, both long-term and short-term stability are extremely important in such a circuit.

Also, the power sources from which such machines perate are generally subject to varying loads when a number of such machines are used together. Since the supply voltages to a control circuit may vary considerably as the various loads are switched on or off, the timing circuit provided must be insensitive to these voltage changes within a reasonable range. It is also desirable that a reasonable range of temperature variations do not affect the timing of the circuits.

Heretofore, timing circuits employed to control automated machines, in order to be stable and precise during varying voltage source conditions while providing long timing periods, have been complex and employed expensive components. For example, the ordinary R-C control and timing circuit for periods of thirty minutes to one hour uses extremely large electrolytic capacitors. These capacitors are expensive, take up much space, and are not reliable for long, trouble-free operation because their efiective capacitance changes as a function of the voltage history of the capacitor. Even though such expensive components are employed in these circuits, the exact repetition of timing cycles is not easily obtained over long periods of time and maintenance requirements are generally high. By use of the present invention the timing circuit can utilize paper or Mylar capacitors, which are smaller, cheaper and more reliable than electrolytic capacitors, to provide long timing periods.

It is thus an object of this invention to provide an electronic timer which will provide operating periods up to and in excess of one hour and yet use relatively inexpensive and easily obtained components. It is another object to provide such a timer with long timing periods in which exact repetition of the timing cycle is assured over relatively long periods of time.

It is still another object to provide such a timer which employs an R-C timing circuit having a relatively small value timing capacitor.

It is a further object to provide such an electronic timer in which the timing periods are unaflfectcd by supply voltage and temperature changes over a Wide range.

It is still a further object to provide such a timer in which maintenance requirements are low as compared to heretofore known timing circuits.

Occasionally, a coin inserted into the coil switch of an automatic machine will become lodged across the poles of the switch and remain there after an operating cycle is complete. Such action will result in a continuous recycling of the machine until it is turned off. Protection against such a happening is extremely important where machines are left unattended for long periods of time, and it is thus another object of this invention to provide an electronic timer of the character described in which each deposit in a coin switch of the denomination of coin required to actuate the timer results in just one operating cycle, even though the coin may still be lodged across the poles of the coil switch after the completion of the operating cycle. Any additional coins which are deposited in the machine while a coin is so lodged will be rejected and returned to the depositor through a coin return slot.

In accordance with this invention, a coin-actuated electronic timer is provided which has a long-duration timing cycle for controlling an external load. A switching control means is utilized which is responsive to one impulse signal to switch the load and connect a timing circuit to a direct current source to start a predetermined timing cycle, and responsive to a second impulse signal upon completion of the timing cycle to again switch the load and disconnect the timing circuit from the direct current source. The first impulse signal may be provided by the passage of a coin through a coin switch. The timing circuit is a resistancecapacitance (R-C) circuit which includes a timing capac-' itor which is charged at a predetermined rate to a predetermined voltage level. The capacitor is caused to discharge when this voltage level is reached by the switching of a unijunction transistor from a high-impedance state to a low-impedance state. This capacitor discharge is utilized to generate the second impulse signal.

A means is provided to cause the unijunction transistor to switch from its high-impedance state to its low-imped ance state at a peak point current substantially less than the usual peak point current of the unijunction, and when this is done, the current capacity of the timing capacitor may be substantially lower than those used in other electronic timers of equally long duration. For this purpose, low-value negative pulses are transmitted to one of the bases of the transistor from a source of alternating current.

Also, in order to prevent recycling of the timer in the event of a stuck coin or coin switch, a quenching circuit may be provided to block the passage of the first impulse signal from the coin switch when this signal is longer than a certain duration. This circuit may include a parallel connected resistance-capacitance circuit having a time constant greater than the duration of the normal first impulse signal, but less than the shortest timing period of the timer, for this purpose.

Other objects and advantages of this invention will become apparent during the course of the following description and with reference to the attached drawing illustrating a preferred embodiment of this invention, and in which is shown a circuit diagram illustrating a preferred embodiment of the present invention.

Referring now to the drawing, a load 1, such as a dryer or other device which requires an operating period of long duration, is turned on (or oif) in response to the start of a timing cycle initiated by the insertion of a coin into a coin receptacle (not shown), remains on for a predetermined period of time, and is then turned off (or on) in response to the completion of the timing cycle. The predetermined timing cycle is provided by a novel electronic timer circuit which will be hereinafter described. The load 1 is turned on or off by an external load control means actuated in response to the start and stop of the timing cycle. As illustrated, the external load control means includes pole A and its associated terminals of relay RE-l. Relay RE-l also includes pole B and its associated terminals B-1 and B-2, the purpose of which will be explained subsequently. Relay RE-l is actuated by the flow of sufficient current through its coil 2. The relay RE-l is shown in the drawing in its actuated state, which is its state during the duration of the timing cycle. The coil 2 is connected in series with the collector of a transistor TR-l so that when the transistor TR-l is conducting sufiicient current flows through the coil 2 to actuate the relay RE-l and hold it in its actuated state.

Coil 2, pole B and its associated terminals and transistor TR-1 form a switching control means through which the timing circuit to be described is connected to and from a voltage source 3 to start and stop the timing cycle respectively. The pole B and the coil 2 of the relay RE-1 are connected to a source of direct current at terminal 5 by a coin switch 4, which is actuated by depositing a coin of predetermined denomination in a coin receptacle (not shown). The terminal B-2 is connected directly to the direct current source at the terminal 5. The direct current may be obtained by rectifying and filtering an alternating current source 6, which may be 60-cycle 115 v. A.C. house current, in a conventional manner. In the embodiment shown, the rectification is provided by diode DI-1 and the filtering is provided by condenser C-1 and resistor R-9. Resistors R-6, R-7 and R-8 .serve as voltage dividers.

Pole B of relay RE-l is also connected through resistor R-1 to the base of transistor TR-1. Thus, when a coin of the proper denomination passes through the poles of coin switch 4, a momentary connection is provided between the base of the transistor TR-l through relay coil 2 and the source of direct current. The momentary connection provides a first impulse signal and excites transistor TR-l causing current to flow through coil 2 thereby actuating relay RE-l which moves the poles A and B to the position shown in the drawing. For example, the pole B is switched from terminal B-1 to terminal B-2 and pole A is switched to the position shown whereby the load 1 is in the actuated condition. This momentary switching provides a self-latching effect because when pole B is switched to terminal B-2 the transistor TR-l is directly connected through the coil 2 to the direct current source,

and is thus excited to a state of conductionsufficient to hold the relay RE-l in its actuated state.

Also connected to the terminal 13-2 of relay RE-l is a resistance-capacitance (R-C) timing circuit providing a predetermined constant timing period. When the relay RE-l is actuated, the timing circuit is connectedto the source of direct current through the terminal B-2 so that the timing cycle is initiatedAn important feature of this invention is that the timing capacitor which may be used in this circuit may be substantially smaller invalue and cost than similar capacitors used in other timing circuits having comparable timing periods.

Referring to the drawing, the R-C timing circuit includes a timing capacitor C-2 and resistors R-2 and R-3. Resistors R-1 and R12' serve as voltage dividers to supply appropriate values of voltage on each side of" the timing capacitor C-2. The values of capacitor C-2 and resistors R-2 and R-=3 are chosen so that the circuit has a timing period in the range of several minutes to several hours. Resistor R-3 is shown as a'potentiometer by which the duration of the timing cycle may be varied, however resistor R-3 may be of a fixed value where it is not de* sired to vary the timing period. Also, the resistor R-3 may be replaced by a number of resistors in series which could be added into the circuit bya stepping switch, as is well known in the art.

When the relay RE-l is actuated and the timing circuit is connected to the source of the direct current, the capacitor C-2 begins to charge at a rate'determined by the values of R-2 and R-3 toward the potential at the junction C between resistors R-12 and R-3. Capacitor C-2 is connected at its negative terminal to the base of TR-l and, since this transistor is conducting when the relay RE-l is actuated,the potential at this point reaches a steady low value during the charging of the capacitor C-2.

Connected to the positive terminal of the condenser C2 at the po'int'G is a unijunction transistor TR-2 which serves to interrupt the charge on capacitor C-Z when the charge has reached a predetermined level, which is the peak point voltage and current of the unijunction. Transistor TR-2 has bases b and b and a gate a. The base b is connected to the negative side of the direct current source through a limiting resistor R-5 and the base 12;, is connected to junction C through a resistor R4 so that current flows between the bases of the unijunction transistor TR-2 when the relay RE-l is actuated. The gate a is connected to the capacitor C-2 at the point G.

The unijunction transistor TR-2 has the characteristics of switching or firing from a high-impedance state to a low-impedance state between its gate a and base b when its gate current has reached its peakpoint current. Thu-s,

. when the charge on the capacitor 0-2 at the point G reaches the peak point current of theunijunction transistor TR-2, the unijunction fires and connects a lowimpedance load equal. to the gate-base b resistance plus R-5, across the capacitor C-2, causing" it-to rapidly discharge. The rapid discharge of capacitor C-Z causes; an impulse of negative ,voltage at the base of transistor TR-l dropping it below the bias voltage cut-off. Therefore, the

transistor TR-1 will stop conducting. When this occurs,v

length of the cycle. However, the unijunction-transistor TR-2 characteristically requires about 5-milliarnperes peak point current. at its gate 'for'firing, and, for this reason, the capacitance of the capacitor C-Z must be high and the value of the maximum leakage current of the capacitor C2 must be very low to allow this current to be drawn. When a timing cycle of an hour or so is desired, this would mean that the capacitor would usually have to be an electrolytic or its equivalent which, as stated, are expensive, bulky and unreliable.

In the present invention, the peak point current of the unijunction transistor TR-Z is reduced to a value which may be a hundred times less than its usual value. Accordingly, the value of capacitor C-2 and its current capability can be decreased and the value of resistor R-3 accordingly increased to provide the same timing cycle of an hour or so. Hence, a paper or mylar condenser may be used for the timing capacitor C-Z.

The reduction of peak point current is accomplished by pulsing the base b of the transistor TR-Z with a low value negative pulse, for example, .6 volt. For this purpose, a means is provided which is adapted to be connected to a source of alternating current, such as the source 6, for rectifying and clamping pulses of alternating current to the appropriate low value and transmitting them to the base k of the unijun'ction transistor TR-2. In the embodiment illustrated, the negative half of the 60- cycle A.C. source is picked up at the point D, divided to appropriate levels by resistors R-11 and R-10, and clamped to approximately .6 volt negative by diode DI-3. The resultant 60-cycle pulses are applied to the base b through resistor R4 throughout the timing period. However, only one pulse has any affect on the timing period as the unijunction is caused to switch when the capacitor C-Z has charged to a point .6 volt below its peak point voltage.

The diode DI-3 also serves as a voltage regulator so that the magnitude of the pulses obtained in this manner are constant. Also, since only one pulse is effective, the frequency of the pulses used has no affect on the timing cycle. Thus, reliable timing repeatability is insured.

Also, by pulsing the base b of the unijun'ction transistor TR-Z, the unijunction turns on or fires sharply without any mushiness.

Other means may also be employed to insure the stability and reliability of the circuit. For example, a Zener diode DI-Z may also be added to regulate the positive D.C. supply voltage and reduce ripple. The diode DI-2 is shown in the preferred embodiment as a l2-volt Zener connected across the points E and F for this purpose. The resistor R12 may also be used as a limiting resistor to aid in regulation and insure that the voltage across the diode DI-2 remains within the rating of the diode. By the proper selection of R-12, for example, voltage may vary from 60 volts to 160 volts without affecting the operation of the timing circuit since the diode DI-2 will hold the voltage at junction C at approximately 12 volts.

Regulation may be further aided and sensitivity to temperature changes can be decreased by the proper selection of the resistors R-4 and R-5. R-4 limits the current and voltage to base b of unijunction TR-Z and resistor R-S controls the firing or discharging current through the base b of unijunction T R-2. The unijunction transistor TR-Z has a negative temperature coeflicient such that its equivalent emitter diode and voltage decreases with an increase in temperature. To compensate for this, the resistors R-4 and R-S should have a positive temperature coefiicient such that the voltage across bases b and b is caused to increase with an increase of temperature. By proper selection of the resistors R-4 and R-5 the unijunction transistor TR-Z will fire at a stable voltage and current point on the gate a from temperature of 0 F. to 185 F.

A residual voltage level circuit also may be utilized to control the residual voltage on condenser C-2 during timer off periods in response to the opening of the relay RE-l contact. This control is provided by taking 011? voltage at point D from the alternating current supply. This voltage is rectified by the diode DI-3 and divided by the resistors R-11, R-10, R-4, R-14, R-2 and R-12 to provide the appropriate voltage levels, and is connected across the capacitor C2 by the terminal b of the relay RE-l. Such circuitry insures that at the start of each timing cycle the energy level in the condenser (3-2 will be the same and eliminates timing error due to various starting voltages in condenser C-Z.

Occasionally, a coin will stick in the coin switch 4 or the coin switch 4 may malfunction in a closed position and the timer would normally operate continuously through repeated cycles, since upon completion of a timing cycle the coin switch being in the closed position would initiate a new cycle and would continue to do so indefinitely. Thus, a means also may be added to provide a fail-safe circuit so that the timing circuit will be energized only once for each coin inserted in the coin switch 4. In the preferred embodiment shown, this means includes the resistor R-13 and the condenser C-3 connected parallel to each other and further connected in series with the voltage supply line between the coin switch 4 and the relay RE-l. When the coil switch 4 is closed other than is normal from the momentary passage of a coin, such as when a coin is struck across its contact, 06 will charge up and cause virtually an open circuit. When the coin switch 4 operates normally, C-3 may charge slightly but R-13 will bleed off the charge and operation will be normal.

In the preferred embodiment shown in the drawing, the following values for the components shown are preferred for operation with a volt A.C. supply source, but it is understood by those skilled in the art these values may be varled through a wide range without affecting the basic operation of this invention.

C1--1 00 m.f.d. v. condenser C-2250 m.f.d. 25 v, condenser C-310 m.f.d. 150 v. condenser R1-33K /2 watt resistor R24.7K /2 watt resistor R-33 MEG POT resistor R4330 ohms /2 watt resistor R5330 ohms /2 watt resistor R-6100 ohms 1 watt resistor R-75 10 ohms 2 watt resistor R8510 ohms 2 watt resistor R933K ohms 2 watt resistor R10-l0K ohms /2 watt resistor R1l-l00K ohms /2 watt resistor R12-1K ohm /2 watt resistor DI1-1N1693 rectifier DI-2-Zener diode Z4XL12 DI-3-Diode DHD80O TR12N3404 transistor TR-2-2N2646 transistor RE-l-Relay 42F-Sigma or RBM R-1333K ohms watt resistor R-1410K ohms /2 watt resistor From the foregoing it will be seen that this invention is one well adapted to attain all of the ends and objects heremabove set forth, together with other advantages which are obvious and which are inherent to the appara us.

It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of the claims.

As many possible embodiments may be made of the invention without departing from the scope thereof, it is to be understood that all matter herein set forth or shown in the accompanying drawings is to bt interpreted as illustrative and not in a limiting sense.

The invention having been described, what is claimed 1. A coin-actuated electronic timer having a timing cycle of long duration for controlling an external load,

comprising, in combination: a direct current source; a coin switch connected to said direct current source and producing a first impulse signal upon passage of a coin therethrough; a series-connected resistance-capacitance timing circuit having a timing period in the range of several minutes to several hours and including a timing capacitor which is charged when said timing circuit is connected to said direct current source at a predetermined voltage level at which point said capacitor is caused to produce a second impulse signal; switching control means responsive to said impulse signals and connected to said direct current source for connecting said timing circuit thereto in response to said first impulse signal whereby a timing cycle starts, and disconnecting said timing circuit from said direct current source in response to said second impulse signal whereby the timing cycle stops; a unijunction transistor having a gate element and two base elements and connected at its gate to said capacitor for interrupting the charging thereof, said transistor switching from a high-impedance state to low-impedance state at said predetermined voltage level to cause said capacitor to produce said second impulse signal; quenching means connected between said coin switch and said switching control means for passage of said first impulse signal and including a parallel-connected resistancecapacitance circuit having a time constant greater than the duration of said first impulse signal but less than the shortest timing period of said timer whereby signals from said coin switch of duration greater than said time constant are quenched; and means responsive to the starting and stopping of said timing cycle for controlling said load.

2. The timer of claim 1 in which said unijunction transistor switches from a high-impedance state to a lowimpedance state at a peak point current at its gate substantially higher than the peak point current at said predetermined voltage level and further provided with a means adapted to be connected to a source of alternating current for rectifying and clamping to a low negative value pulses therefrom and transmitting said pulses to one of the bases of said transistor whereby the peak point current requirement at said gate is reduced to the peak point current at said predetermined voltage level.

3. The timer of claim 1 further provided with a means including a resistor connected between said switching means and one of said bases and connected to said direct current source in response to said first impulse signal, and said resistor having a positive temperature coefficient so that the transistor switches to its low-impedance state at substantially the same point in time throughout a wide variation of temperatures.

4. The timer of claim 1 further including a residual voltage level circuit connected across said capacitor and adapted to be connected to a source of alternating current by said switching control means when said timing circuit is disconnected from said direct current source to provide a constant residual voltage across said capacitor.

5. A coin-actuated electronic timer having a timing cycle of long duration for controlling an external load, comprising in combination: a direct current source of voltage; a coin switch connected to said source and producing a first impulse signal upon passage of a coin therethrough; a series-connected resistance-capacitance timing circuit having a timing period in the range of several minutes to several hours and including a timing capacitor which is charged when said timing circuit is connected to said direct current source at a predetermined rate from a residual voltage level to a higher predetermind voltage level at which point said capacitor is caused to produce a second impulse signal; switching control means responsive to said impulse signals and connected to said coin switch and said direct current source and connecting said timing circuit to said direct current source in response to said first impulse signal whereby a timing cycle starts, and disconnecting said timing circuit from said direct current source in response to said second impulse signal whereby the timing cycle stops; a unijunction transistor having a gate element and two base elements and normally switching from a high-impedance state to low-impedance state at a peak point current at said gate substantially higher than the peak point current drawn at said predetermined voltage level, said transistor connected at its gate to said capacitor for interrupting the charging thereof upon said switching to cause said capacitor to produce said second impulse pulse signal; means adapated to be connected to a source of alternating current for rectifying and clamping to low negative value pulses therefrom and transmitting said pulses to one of said bases whereby the peak point current requirement at said gate is reduced to the peak point current drawn at said predetermined voltage level; and means responsive to the starting and stopping of said timing cycle for controlling said load.

6. The timer of claim 5 further provided with means including a resistor connected between said switching control means and one of said bases and connected across said direct current source in response to said first impulse signal, said resistor having positive temperature coefficient whereby said transistor switches to its low-impedance state at substantially the same point in time throughout a wide variation of temperatures.

7. The timer of claim 5 further including a residual voltage level circuit connected across said capacitor and adapted to be connected to a source of alternating current by said switching control means when said timing circuit is disconnected from said direct current source to provide a constant residual voltage across said capacitor;

References Cited UNITED STATES PATENTS 3,360,092 12/1967 McConnell 199-9 JOHN F. COUCH, Primary Examiner R. V. LUPO, Assistant Examiner U.S. Cl. X.R.

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