Capacitance and resistance-responsive control circuits

[57] ABSTRACT

Control circuits for sensing and responding to impedance changes caused by a mammal in contact with or in proximity to an antenna or other sensor. Each circuit includes at least one tuned circuit which is periodically energized to cause it to “ring” at its natural frequency, i.e., to produce damped oscillations. Each tuned circuit includes an antenna or other sensor by which an external impedance is coupled to the tuned circuit. Thus, the oscillations in the tuned circuit are attenuated to a degree determined by the capacitive and resistive components of the external impedance. In the case of mammals, the resistive component is substantial and causes a marked change in the amplitude and duration of the damped oscillations in the tuned circuit, which are then enhanced and/or detected to produce a predetermined control signal.

Claims, 3 Drawing Figures

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PATENTED APR 21974

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PATENTEOAPR aim

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3,801,799

CAPACITANCE AND RESISTANCE-RESPONSIVE CONTROL CIRCUITS

CROSS REFERENCES TO RELATED APPLICATIONS

The present invention may advantageously incorporate the HIGH-DISCRIMINATION ANTENNA ARRAY FOR CAPACITANCE-RESPONSIVE CIRCUITS disclosed and claimed in U. S. Pat. No 3,740,567 issued June 19, 1973 upon copending application Ser. No. 245,799 filed on Apr. 20, 1972 in the name of Carl E. Atkins. The present invention advantageously incorporates a modified form of the circuits disclosed and claimed in copending application Ser.

^{255,155 entitIed} ELECTRONIC timing CIRCL'ITS filed on May 19, 1972 in the name of Paul A Carlson.

BACKGROUND OF THE INVENTION The present invention relates to capacitance and resistance responsive control circuitry. A wide variety of such condition-responsive circuits may be found in the prior art; see, for example, the following U.S. Pat. Nos.:

U.S. Pat. No. 3.200,304 3.200,305 3,275.897 Re 26,828 3,314,081 3,339,212 3.382,408 3,435,298 3,492,542 3,551,753 3,555,368 3,564,346 3,568,005 3,568,006 3.569,728

Inventor Atkins et al.

Atkins Atkins

Atkins et al.

Atkins et al.

Atkins et al.

Atkins

Atkins et al.

Atkins Atkins Atkins Atkins Atkins Atkins

Atkins

However, in certain applications such as detecting proper and improper usage of seat belts in automobiles, it is necessary to distinguish between mammalian and inanimate seat occupants. I have found that by coupling an occupant through an antenna associated with one or more selected seat surfaces to a tuned circuit, and detecting the degree of attenuation of oscillations in the tuned circuit by such coupling, a superior degree of discrimination may be achieved between humans and other mammals and inanimate objects (conductive or non-conductive) coming into proximity or contact with a conductive sensor positioned adjacent a selected seat surface. I have found further that this superior discrimination is due to the different degrees of degradation that humans and other mammals and inanimate objects have on the merit factor Q of a tuned circuit when coupled thereto. The Q of a tuned circuit represents the circuit’s ability to store energy as compared to the amount of energy it dissipates.

When the complex impedance formed by a human or other mammal or by an inanimate object is coupled to the tuned-circuit, the attenuation of the oscillations in the tuned circuit is thereby increased. Since the complex impedance of humans, and other mammals includes a substantial resistive or dissipative component which is not found in most inanimate objects, the Q of a tuned circuit will be more sharply reduced by loading from humans and other mammals than from inanimate objects. As a result of the decrease in Q· of the tuned circuit, there is a detectable decrease in the amplitude and/or duration of the damped oscillations or “ringing” of the tuned circuit when that circuit is loaded by humans and other mammals.

The circuits embodying the invention are readily adaptable to a wide variety of uses, e.g., in plumbing control systems. Because of the superior sensitivity of the tuned circuit to loading by humans, an antenna with an exposed surface area of only a few square inches may be used which is smaller than any previously employed antenna area.

SUMMARY OF THE INVENTION

The present invention is embodied in and carried out by a condition-responsive control circuit in which at least one tuned circuit is periodically energized by pulses from a pulse generator and permitted to “ring” (oscillate) at its natural frequency during each interpulse null, whereby the change in the amplitude and/or duration of oscillations of the tuned circuit caused by coupling of an external impedance having a substantial capacitive or resistive component to the tuned circuit is enhanced and/or detected to generate a control signal. The change in the amplitude of the damped oscillations may be enhanced before detection by providing an oscillator circuit which is shock excited into oscillation by the positive amplitude of the damped oscillations. In this way, the oscillator circuit will provide an oscillatory output when the positive amplitude of the damped oscillations in the tuned circuit is above a predetermined threshold, and no oscillatory output when the positive amplitude is below that predetermined threshold. The oscillating or non-oscillating output may then be detected to provide a control signal.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention may be better understood by reading the written description thereof in view of the accompanying drawings in which like numerals refer to like parts and:

FIG. 1 is a schematic circuit diagram showing a first embodiment of the invention;

FIG. 2 is a schematic circuit diagram showing a second, preferred embodiment of the present inventionand ’

FIG. 3 is a schematic circuit diagram showing a third embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to FIG. 1, a pulse generator 10 of the type disclosed and claimed in cross-referenced application Ser. No. 255,155 provides periodic pulses of positive polarity between which the amplitude is substantially null, i.e., at approximately ground potential. These pulses are fed to bias circuit 12 which comprises resistance RI, capacitance Cl, and blocking diode DI. The positive-going pulses are passed through to tuned circuit 14, comprising inductance LI, capacitance C2, and the complex impedance of any external load (not shown) which may be coupled to the tuned circuit 14 by sensor 16. Detector 18 is connected to tuned circuit ' r ‘u ^dL^eteC- ^{variations in} the amplitude and/or duration of the damped oscillations which form the output of the tuned circuit 14.

The operation of the circuit shown in FIG. 1 is as follows. Pulse generator 10 supplies periodic pulses of positive polarity to bias circuit 12, preferably in the frequency range of 10-20 KHz with a duty cycle of 50%,

3,801,799

4 although other frequencies and duty cycles are acceptable. The value of capacitance Cl is selected to present nearly a short-circuit to the positive-going pulses. During each positive-going pulse capacitance Cl is charged with the polarity shown in FIG. 1, but the net bias on diode DI is forward. Thus, current flows through inductance LI of tuned circuit 14 thereby supplying energy to inductance LI which is stored in its magnetic field. The impedance presented by inductance LI is small, and consequently loads the output of pulse generator 10 to an extent which prevents generation of a control signal by detector 18 and also prevents charging of C2 to any significant degree. After its stored energy reaches a maximum value, LI presents a short circuit to the remainder of the generator output to limit the pulse amplitude to approximately ground potential during the remaining portion of the positive-going pulse. The energy thus stored in LI is not involved in the ringing of the tuned circuit 14. When the trailing edge of the positive-going pulse output of generator 10 is reached, the magnetic field of LI collapses, thereby inducing a current pulse through LI to ground that causes Cl to be charged to a higher level.

Because diode DI is a stored-charge diode, it stores more charge for a longer period of time and loses that charge faster than most semiconductor diodes. DI has a substantial diffusion capacitance at the time the trailing edge of the positive pulse occurs, and while this capacitance exists it prevents^ DI from isolating the bias circuit 12 from the tank circuit Ϊ4. Because Cl is charged by the positive pulse from generator 10 and the inductive pulse from LI, it acts as a small battery and causes current to flow from ground through LI, the diffusion capacitance of DI, Cl itself, and through pulse generator 10 to ground. Thus, energy is again electromagnetically stored in LI. The reverse current through DI causes the rapid elimination of the diffusion capacitance of DI, which is thus enabled to isolate the bias circuit 12 and the tuned circuit 14. Because diode DI is back-biased by the remaining charge on Cl, it presents a high impedance to the tuned circuit 14 so as not to load it. Similarly, detector 18 is designed so as not to load tuned circuit 14. With energy no longer being supplied to inductance LI, its magnetic field collapses, thereby producing ringing in the tuned circuit 14 at the natural frequency of that circuit. During the interpulse null, i.e., the time between successive positive-going pulses when the pulse amplitude is at approximately ground potential, capacitance Cl partially discharges through resistance Rl. The values of resistance R1 and capacitance Cl are chosen so that diode DI remains back-biased during the interpulse null. Resistance Rl and capacitance Cl may be replaced by a short circuit if the output of pulse generator 10 goes negative instead of being at approximately ground potential between positive-going pulses.

When no load is coupled to sensor 16, the amplitude, frequency, and duration of the damped oscillations of tuned circuit 14 are relatively fixed and detector 18 is designed not to respond. However, when a load with a complex impedance having a substantial resistive component is coupled to the tuned circuit 14 through sensor 16, the Q of tuned circuit 14 is reduced, thereby sharply reducing the amplitude and/or duration of oscillations of the tuned circuit 14. An inanimate object, which in most cases does not possess a substantial resistive component, has little or no effect upon the Q of the tuned circuit 14 and, consequently, little or no effect on the amplitude and/or duration of oscillations of the tuned circuit 14. In addition, a load having a complex impedance with a substantial capacitive component is 5 similarly capable of attenuating oscillations in the tuned circuit 14 when coupled thereto through sensor 16.

Detector 18 is preferably designed in known manner to respond to the reduction in amplitude and/or dura10 tion of the damped oscillations in the tuned circuit to thereby provide a control signal.

The change in amplitude and/or duration of the damped oscillation may advantageously be enhanced before detection. The preferred embodiment of the in15 vention shown in FIG. 2 includes enhancing means.

Referring now specifically to FIG. 2, the circuit shown comprises a pulse generator 20 of the type disclosed and claimed in cross-referenced application Ser. No. 255,155, bias circuits 22 and 24 of the type shown 20 in FIG. 1, tuned circuits 26 and 28, enhancing circuits 30 and 32, detector circuits 34 and 36, and controlled load circuits 38, 40 and 42. The two parallel control signal generating circuits formed by bias circuits 22 and 24, tuned circuits 26 and 28, enhancing circuits 30 and ²⁵ 32, and detecting circuits 34 and 36 are identical in structure and function. Therefore, detailed reference will be made to only one such circuit.

Bias circuit 22 is connected to receive the output of pulse generator 20 and channels it to tuned circuit 26 ³⁰ which comprises antenna Al and inductance L2, with the capacitance for the tuned circuit being formed by antenna Al and by capacitances C7 and C8 of enhancing circuit 30. Enhancing circuit 30 comprises transistor Q3, feedback capacitances C7 and C8, and bias re³³ sistances R8 and R9, and is connected to receive the output of tuned circuit 26 and to respond to providing an oscillatory input to detector 34.

Detector 34 comprises limiting resistances R12 and R13 and detecting transistor Q5, and operates to pro⁰ vide a control signal to load circuits 38 and 40 in response to a predetermined output signal from enhancing circuit 30.

The operation of the circuit shown in FIG. 2 is as follows. Pulse generator 20, bias circuit 22 and tuned circuit 26 operate as described in FIG. 1 wherein tuned circuit 26 periodically “rings”, i.e., produces damped oscillations at the natural frequency of the tuned circuit. When a complex impedance with a substantial re_5o sistive component is capacitively coupled to antenna Al, the Q of tuned circuit 26 is reduced to thereby reduce the amplitude and/or duration of the “ringing” in the tuned circuit 26 during the interpulse nulls in the output of pulse generator 20. In addition, a load having ₅₅ a complex impedance with a substantial capacitive component is similarly capable of attenuating oscillations in the tuned circuit 26 when coupled thereto through antenna Al.

Enhancing circuit 30 operates to accentuate the re₆₀ duction in the amplitude of the damped oscillations of the tuned circuit 26 caused by loading. In the absence of a positive output from the pulse generator, transistor Q3 is normally non-conductive since no base-emitter forward bias is provided. Capacitances C7 and C8, in ₆₅ conjunction with the requirements of the tuned circuit 26, are chosen to provide sufficient regeneration to force transistor Q3 to oscillate when Q3 is forwardbiased. Thus, when a positive pulse is provided to the

3,801,799 bias circuit 22 and tuned circuit 26 to induce ringing therein when the pulse output from the pulse generator 20 is at approximately ground potential or negative, transistor Q3 is shocked into oscillation by the increase in bias provided by the positive portions of the damped oscillations produced by the tuned circuit. Transistor Q3 is maintained in oscillation during the damped oscillations of the tuned circuit by the regeneration provided by capacitances C7 and C8. Resistances R8 and R9 are chosen to permit the damped oscillations to shock transistor Q3 into oscillation, thereby setting a threshold above which Q3 oscillates. Transistor Q3 is biased so that during oscillation, a positive DC component is provided at its emitter. As noted previously, the positive pulse from pulse generator 20 is of insufficient amplitude to bias transistor Q3 into oscillation.

Therefore, the output of transistor Q3 taken at its emitter oscillates with a positive DC component when tuned circuit 26 rings at sufficient amplitude, and is at approximately ground potential when the amplitude of the ringing is insufficient to cause oscillation and when the relatively small amplitude of positive pulse from pulse generator 20 is present. The amplitude of the ringing of tuned circuit 26 will be sufficiently reduced to prevent oscillation of transistor Q3 when a complex impedance load with a substantial capacitive or resistive component is capacitively coupled at antenna Al. As a result, the reduction in amplitude of the damped oscillations of tuned circuit 26 is enhanced at the emitter output of transistor Q3 to provide a change going from a periodic oscillatory output combined with a DC component to a non-oscillatory output at approximately ground potential.

Detector 34, comprising resistances R12 and R13, and transistor Q5 detects the presence and absence of oscillations at the output of the enhancing circuit 30, and generates a corresponding control signal. Resistance R12 limits the base current and resistance R13 limits the collector current of transistor QS. During each period in which transistor Q3 is oscillatory, indicating no loading of tuned circuit 26, transistor QS is turned on by the DC component of the oscillation forcing the collector of transistor Q5 to approximately ground potential. When transistor Q3 ceases to oscillate, with its emitter going to approximately ground potential, indicating loading of tuned circuit 26, transistor Q5 is turned off and its collector rises to the supply voltage (approximately +10 volts DC).

Thus, when antenna Al is coupled to an impedance having either a substantial capacitive component, or a substantial resistive component such as is presented by humans and other mammals, a control signal of supply voltage is generated at the collector of transistor Q5; otherwise the control signal is at approximately the ground potential.

The control signals thus generated may be utilized either singly or in combination to control a variety of load circuits. For example, the output of detector 34 may control load circuit 38 or load circuit 40 or both. Similarly, the output of detector 36 may be used to control load circuit 42 or load circuit 40 or both. Alternatively, both control signals from detectors 34 and 36 may be employed independently or in combination to control a single load 40 which may include logic circuitry such as an OR circuit or an AND circuit.

In the second, preferred embodiment described follows:

above, the values of various circuit components are as max.)

Resistances R2 — IK ohms R3 — 30K ohms R4 — 330 ohms RS — 330 ohms R6 — 3.3K ohms R7 — 3.3K ohms R8 — 500 ohms ( R9 — 470 ohms R10 — 500 ohms (max.) R11 — 470 ohms R12 — 470K ohms R13- 33K ohms R14 — 470K ohms R15 — 33K ohms Transistors

QI — 2N4248 Q2 — 2N3567 Q3 - 2N5132 Q4 — 2N5132 QS — 2N5132 Q6 — 2N5132

Capacitances

C3 — 0.22 microfarads

C4 — 390 picofarads

C5 — 0.22 microfarads

C6 — 0.22 microfarads

C7 — 150 picofarads

C8 — 20 picofarads

C9 — 150 picofarads

CIO — 20 picofarads

Inductances

L2 — 39 microhenries

L3 — 39 microhenries

Diodes

DI — D2 — D3 — D4 —

1N4148

1N4148

1N4148

1N4148

Referring now to FIG. 3, another embodiment of a detector 44 is shown, a portion of which is peak detector 46. The output of the peak detector is taken at the junction of diode D4, capacitance C12 and resistance R18. The negative portions of the damped oscillation of the tuned circuit 14 turn off transistor Q7, causing a controlled quantity of charge to be supplied to capacitance C12 through resistance R17 and diode D4. The value of resistance R18 is chosen to prevent capacitance C12 from discharging between positive portions of the damped oscillation of tuned circuit 14. Thus, when tuned circuit 14 is ringing, diode D4, capacitance C12 and resistance R18 function as a peak detector maintaining a detector output voltage approximately equal to the supply voltage. When tuned circuit 14 is being energized by the positive-going pulse from pulse generator 10, transistor Q7 is biased off and its collector is at approximately the supply voltage and the detector output is again maintained at approximately the supply voltage. However, upon coupling the tuned circuit 14 through sensor 16 to an external impedance having either a substantial capacitive or resistive component the amplitude of the damped oscillations of tuned circuit 14 decreases and with it, the time that transistor Q7 is turned off also decreases. Consequently, the quantity of charge supplied to capacitance 012 during ringing is reduced and with it, the peak amplitude detected by the peak detector 46. In this way a detector output change of 2 to 1 is possible for smaller amplitude changes of the damped oscillations of tuned circuit 14.

The advantages of the present invention, as well as certain changes and modifications of the disclosed embodiments thereof, will be readily apparent to those skilled m the art. For example, variations in antenna loading could be effected by a miniaturized loading circuit including a plate adapted for selective coupling with either antennae Al and A2. Such a load circuit could be incorporated into an article worn by a person such as a ring or a watchband, and used as a key to cause a control circuit to open a lock, for example. The output of any or all of the detector circuits could be altered by the addition of a polarity inverter circuit In the case of the detector of FIG 3, a negative voltage could be provided by poling diode D4 in a manner opposite to that shown. Also, the resistive impedance for

3,801,799 loading the tuned circuit may be ohmically coupled to the sensor or antenna, rather than capacitively coupled. Other detecting schemes other than those disclosed and well-known in the art such as synchronous detection and time comparison detection may be used to detect the changes in amplitude and/or duration of the damped oscillations. Also, other pulse generator means other than that disclosed may be used to periodically energize the tuned circuit to cause it to ring. It is intended to cover all of those changes and modifications which could be made to the embodiments of the invention herein chosen for the purposes of the disclosure without departing from the spirit and scope of the invention.