US3331012A

US3331012A - Volume stabilizer arrangement employing a photo-sensitive resistance element

Info

Publication number: US3331012A
Application number: US424774A
Authority: US
Inventors: William R Aiken
Original assignee: Individual
Current assignee: Individual
Priority date: 1965-01-11
Filing date: 1965-01-11
Publication date: 1967-07-11
Anticipated expiration: 1984-07-11

Description

July 11. 1967 w. R. AIKEN 3,331,012

VOLUME STABILIZER ARRANGEMENT EMPLOYING A PHOTO-SENSITIVE RESISTANCE ELEMENT Filed Jan. 11,.1965

INPUT VOUTPUT INVENTOR WILLIAM ROSS AIKEN By M United States Patent Ofifice 3,331,012 Patented July 11, 1967 3 331,012 VOLUME STABILIZER ARRANGEMENT EM- PLOYING A PHOTO-SENSITIVE RESIST- ANCE ELEMENT William R. Aiken, 10410 Magdalena Ave., Los Altos Hills, Calif. 94022 Filed Jan. 11, 1965, Ser. No. 424,774 4 Claims. (Cl. 323-21) voltage passed through the circuit. The changes in the degree of illumination produced in this manner change the resistance of the photosensitive element of the circuit in such a manner as to maintain the output voltage of the circuit stable.

' -The problem with arrangements of this type is that the response of the source of light to changes in the voltage of the signal passed through the circuit and the response of the photosensitive element to changes in the illumination is often too slow depending upon the quality and cost of the lamps and photosensitive resistor elements, and as a result thereof the level of the output voltage of such circuits may rise initially to a noticeable extent beyond the desired level whenever the size of the input voltage incr'eases,.,and thereafter may droptemporarily below the .desired level and may become scarcely audible due to overcompensation, before it supplies a steady output voltage of the desired magnitude.

Another difiiculty with voltage stabilizer circuit arrangements of the type here under discussion is that their release time is too short, i.e., they release control of the output signal too promptly whenever the signal drops below the desired level, Hence, when such arrangements are used in the transmission of human speech, for example, they may release control of the output signal during the dips between the peaks in the volume of the human voice. As a result thereof, the peaks in the volume of the speech are reduced while the dips between the peaks are left substantially unchanged, and the reproduced speech, therefore, becomes a monotonous slur that has lost all character and may even be difficult to understand.

The initial attack time of voltage stabilizer arrangements employing inexpensive lamps and inexpensive photosensitive resistors can be shortened by using an initial increase in the volume of the output signal beyond the desired level as a control means to overvoltage the lamp which governs the resistance of the photosensitive resistance element. In this manner the increase in brightness of illumination of the lamp and the rate of reduction of the resistance value of the photosensitive resistance element may be accelerated to such an extent that the initial increase in the volume of the output signal is only of the briefest duration and scarcely noticeable, and there will be no noticeable over-attenuation of the volume of the output signal.

To prevent immediate release in the control of the output signal whenever the signal drops briefly below the desired level, such as during the dips in the volume of the human speech, the line along which the control signal is applied to the element that .governs the current flow in the power circuit of the lamp may be provided with a temporary memory, such as a storage condenser. Said memory is charged by the control signal, and upon disappearance of the control signal, it releases slowly and extends the time of application of the control current at the control element in the power circuit of the lamp.

In systems of the type wherein an initial rise in the output volume beyond the desired level occurs, the presence of a memory connected to provide a predetermined release time presents a problem. It charges to the level of the initial surge of the control voltage and when said surge disappears, the memory maintains the control element in the power circuit of the lamp at the level of said surge for a longer period than necessary to raise the illumination of the lamp rapidly to the required level. Hence, the lamp becomes brighter than necessary and stays brighter for a longer time than required. As a result thereof the volume of the output signal is reduced to a lower level than desired and, in the case of human speech, may temporarily become inaudible.

It is an object of the present invention to provide a voltage stabilizer arrangement of the type described, which though constructed from inexpensive and therefore slowly responding components, becomes almost instantaneously effective, yet does not overcompensate.

Another object of my invention is to provide a voltage stabilizer arrangement of the type referred to, that limits the output level of an applied signal, such as the human voice, without destroying its character.

In accordance with the invention the memory is provided with means which delay activation of the memory ,as the control current is applied to the current flow control element in the power circuit of the source of light. In this manner any surge of the control current can be fully applied to the control element in the power circuit of the lamp, and an adequate control current may be maintained on said element for the time necessary to prevent premature release of the volume control mechanism, without causing overcompensation in the volume of the output signal. The delay means prevents the memory from being charged to the voltage level of undesirable control current surges. Therefore, when the memory releases upon disappearance of the control current surge, it delivers an appropriately lower control voltage to the control element in the power circuit of the lamp. This control voltage provides the desired delay in release time and yet maintains the lamp at only the brightness required to limit the volume of the output signal to the desired level.

The invention will be better understood by reference to the accompanying drawing which shows a circuit diagram of a preferred embodiment thereof.

The stabilizer arrangement of my invention illustrated in the drawing comprises a variable volume changer of the type employing a photo-sensitive resistor element. Said volume changer is a variable attenuator 10 formed by a fixed resistor 12 connected into the input line 14 for the arangement and a photosensitive resistor element 16, such as a solid state photocell, connected in series with resistor 12 between the input line and ground. The voltage developed across the photosensitive element 16 is taken off at the junction point 18 of

resistors

12 and 16 and appears as the output signal in the output line 2t) of the arrangement. The size of the voltage appearing in the output line depends upon the relative values of the two series-connected

resistors

12 and 16. It will be large when the value of the resistor element 16 is large compared with that of resistor 12, or small when the value of resistor element 16 is small as compared with that of resistor 12. To vary the resistance value of the photosensitive resistor element 16, said element is exposed to illumination from an adjacently positioned source of light such as the incandescent lamp 22, in such a manner that the resistance value of said photo-sensitive resistor element is inversely proportional to the degree of illumination of the lamp. To stabilize the voltage output of volume changer irrespective of variations in the volume of the input signal, the degree of illumination of the lamp is controlled by the signal that passes through the volume changer such that the lamp burns brighter and therefore reduces the resistance value of the photosensitive resistance element 'when the signal delivered to the volume changer increases in volume; and vice versa, the lamp dims when the signal applied to the volume changer becomes weaker, which causes the value of the photosensitive resistor element to increase and the output voltage developed across said resistor element to increase correspondingly.

V In the embodiment of the invention illustrated in the accompanying drawing the power circuit of the lamp 22 includes a normally non-conductive transistor 24 with its emitter and collector electrodes connected into said circuit. The emitter to collector conductivity of said transistor may be regulated by application of a control voltage to its base. The transistor 24 is by-passed by a rheostat 26 which is set to effect such energization of the lamp when the transistor 24 is non-conductive (or in a predetermined state of conductivity) as will place it on the threshold of illumination. Hence, when the transistor 24- is rendered conductive or its conductivity is increased, the flow of current in the power circuit of the lamp increases and the lamp lights up immediately.

To control the conductivity of transistor 24 a portion of the output of volume changer 10 is tapped off along a line 28, a measured part thereof determined by adjustment of a potentiometer 30 is rectified in a power rectifier represented by the transistor 32 and the DC. voltage supplied by the emitter of said transistor is applied along a control line 33 as control signal to the base of transistor 24 across a grounded resistor 34. To avoid premature disappearance of the control current supplied by the emitter of transistor 32 a memory in the form of a relatively large capacitor 36 is connected between the control line 33 and ground.

A delay bias may be placed upon the emitter of the rectifier transistor 32 so that the emitter of the transistor will not supply a control current until the signal voltage applied to its base exceeds a predetermined level. As a result thereof the stabilizer arrangement of the invention does not respond to changes in the level of the output signal below a predetermined level, but any rise in the volume of the output signal beyond said limit causes the emitter of the transistor to supply an exaggerated control current. For instance, the arrangement may be such that a 10% increase in the level of the output signal may produce a 100% increase in the control current supplied by the emitter of transistor 32. In the particular embodiment of the invention illustrated in the accompanying drawing, the transistor 32 is in itself constructed to perform in this manner. When an exaggerated control current of the described magnitude is applied to the base of the transistor 24 in the power circuit of the lamp, a greatly amplified current'is passed through the lamp and causes the lamp to gain rapidly in brightness. This produces an immediate response of the stabilizer arrangement, that reduces the volume of the output signal. However, if the response of the stabilizer arrangement is not quick enough and an overshoot in the volume of the output signal occurs, the presence of the storage condenser 36 between the control line 33 and ground introduces the danger of holding the surge in D0. voltage at the base of transistor 24 for a longer period than necessary for the lamp to reach the degree of brightness required for proper attenuation, and the lamp may become too bright and/ or may retain its excessive brightness for too long so that the volume of the output signal is excessively attenuated.

In the embodiment of the invention illustrated in the accompanying drawing a delay means in the form of a resistor 40 of relatively small value is interposed between the control line 33 and the memory condenser 36. Said resistor has the effect of delaying the charging of the storage condenser and therefore prevents said condenser from charging to the full value of the surge of control signal produced as a result of the brief overshoot in the diitput volume of volume changer 10. Hence, when the condenser 40 discharges, it temporarily maintains a somewhat lower voltage at the base of transistor 24 than the surge of control current. In this manner continued excessive illumination of the lamp and momentary limitation of the output volume of the volume changer to levels below the desired level will not occur. The presence of resistor 40 between control line 33 and memory condenser 36 has the added effect of preventing said condenser from introducing any undesirable delay in the application of control signal surges to the base of transistor 24.

As explained above, an initial overshoot in the output volume of the volume changer may be used to apply an overly strong control signal of brief duration to the base of the transistor 24, to shorten the attack time of the stabilizer arrangement. The presence of the memory condenser 36 provides a predetermined release time which is sufficient to avoid conversion of the stabilized signal into a monotonous slur: and the presence of the delay resistor 40 between the control line 33 and the memory condenser 36 prevents any noticeable overcompensation in the volume of the output signal in spite of the presence of said storage condenser.

Recapitulating the performance of the stabilizer a1- rangement of my invention: when a signal applied to the input side of the stabilizer arrangement increases suddenly in volume as indicated at 42, the signal 44 appearing in the output line 20 of the arrangement will likewise increase and may briefly over shoot the desiredvolume level as indicated by the peak 45. The rise in the volume of the output signal above the desired level causes the emitter of the rectifier transistor 32 to supply a sudden surge of control current represented by the initial peak 46 of the graph indicated at 48. This sudden surge of the control current is applied direcly to the base of the control transistor 24 in the power circuit of the lamp and causes the flow of current in said power circuit to increase rapidly as indicated by the (negative) peak 50 in the graph 52 causing the brightness of the lamp to increase rapidly. The surge of control current will also charge the memory condenser 36, but due to the presence of the resistor 40, the charging will occur more gradually and the charge will not reach the magnitude of the initial control current surge as indicated by the graph 54 associated with the memory condenser 36. After the volume of the output signal has dropped to its desired level as indicated at 44, the initial surge of the control current supplied by the emitter of rectifier transistor 32 disappears before the lamp has reached an excessive degree of brightness. At this moment the condenser 36 discharges and maintains a somewhat lower and gradually decreasing control voltage at the base of the transistor 24 as indicated by the second part of graph 48. This decreasing control voltage maintains the flow of current in the power circuit of the lamp for a predetermined time at the level required to hol the volume of the output signal within the desired limits and prevents premature release of the control exercised upon the received signal by the stabilizer arrangement of my invention.

In a practical embodiment of the invention as represented by the accompanying drawing the components of the stabilizer arrangement were as follows:

Resistor 12 ohms 50K Resistor 16 CL703CL Rheostat 26 ohms 250 P-otentiometer 30 do 100K Resistor '34 do K Resistor 40 do 100 Capacitor 36 microfarads 250 Lamp 22 No. 48 Transistor 24 2N1304 Transistor 32 2N1304 Under certain conditions it is desirable to place a resistor of 3.3K ohms into the control line 33 as indicated at 56 in the drawing.

While I have explained my invention with the aid of a preferred embodiment thereof, it will be understood that the invention is not limited to the specific circuit components shown and described by way of example, which may be departed from without departing from the scope and spirit of the invention.

I claim:

1. A voltage stabilizer arrangement comprising a volume changer having an output line and including a variable resistance element and means for varying the resistance value of said element including a power circuit having a current flow control element therein adjustable by the application of control voltages thereto, circuit means connected between said output line and said current flow control element for applying upon a rise in the volume of the output of said volume changer in said output line thereof a first control voltage to said current flow control element in a manner effective to depress the volume of the output of said volume changer, and means for holding a second control voltage of lesser size at said current flow control element for a predetermined duration upon decline of said first control voltage.

2. A voltage stabilizer arrangement comprising a volume changer having an output line and including a photosensitive resistance element, means for illuminating said element to vary the resistance value thereof, a power circuit for said illuminating means including a current flow control element adjustable by the application of control voltages thereto, circuit means connected between said output line and said current flow control element for applying, upon a rise in the volume of the output of said volume changer in said output line thereof a first control voltage to said current flow control element to vary the brightness of said illuminating means and hence the resistance value of said resistance element in a manner effective to depress the volume of the output of said volume changer, and means for holding a second control voltage of lesser size at said curent flow control means for a predetermined duration upon decline of said first control voltage.

3. A voltage stabilizer arrangement according to claim 2 wherein said means for holding a second control voltage of lesser size for a predetermined duration at said current flow control means is a delay resistor and a memory capacitor connected in series to said circuit means.

4. A voltage stabilizer arrangement according to claim 2 including means for holding said current flow control element in a condition wherein said lamp is at the threshold of illumination.

References Cited UNITED STATES PATENTS 2,353,218 7/1944 Burnham et a1. 250205 X 3,171,032 2/1965 Holt 250-205 X 3,200,329 8/1965 Haisty 32321 X JOHN F. COUCH, Primary Examiner. A. D. PELLINEN, Assistant Examiner.