CN110617866A - Frequency signal generating circuit and liquid level detection circuit - Google Patents
Frequency signal generating circuit and liquid level detection circuit Download PDFInfo
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- CN110617866A CN110617866A CN201910882491.XA CN201910882491A CN110617866A CN 110617866 A CN110617866 A CN 110617866A CN 201910882491 A CN201910882491 A CN 201910882491A CN 110617866 A CN110617866 A CN 110617866A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
- G01F23/00—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm
- G01F23/22—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water
- G01F23/26—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water by measuring variations of capacity or inductance of capacitors or inductors arising from the presence of liquid or fluent solid material in the electric or electromagnetic fields
- G01F23/263—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water by measuring variations of capacity or inductance of capacitors or inductors arising from the presence of liquid or fluent solid material in the electric or electromagnetic fields by measuring variations in capacitance of capacitors
- G01F23/266—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water by measuring variations of capacity or inductance of capacitors or inductors arising from the presence of liquid or fluent solid material in the electric or electromagnetic fields by measuring variations in capacitance of capacitors measuring circuits therefor
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- G—PHYSICS
- G05—CONTROLLING; REGULATING
- G05F—SYSTEMS FOR REGULATING ELECTRIC OR MAGNETIC VARIABLES
- G05F1/00—Automatic systems in which deviations of an electric quantity from one or more predetermined values are detected at the output of the system and fed back to a device within the system to restore the detected quantity to its predetermined value or values, i.e. retroactive systems
- G05F1/10—Regulating voltage or current
- G05F1/46—Regulating voltage or current wherein the variable actually regulated by the final control device is dc
- G05F1/56—Regulating voltage or current wherein the variable actually regulated by the final control device is dc using semiconductor devices in series with the load as final control devices
- G05F1/561—Voltage to current converters
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- Measurement Of Levels Of Liquids Or Fluent Solid Materials (AREA)
Abstract
The invention discloses a frequency signal generating circuit and a liquid level detecting circuit, wherein the frequency signal generating circuit comprises: the direct current power supply VCC, the first switch circuit, the first resistor R1, the second resistor R2 and the second switch circuit are sequentially connected in series, and the other end of the second switch is grounded; the first switch circuit and the second switch circuit are respectively connected with a control circuit for controlling the on-off of the first switch circuit and the second switch circuit; a first capacitor C1 connected in parallel with the second resistor R2 and the second switch circuit; a first connector X1 is connected between the first resistor R1 and the second resistor R2. The invention controls the charging and discharging of the first capacitor C1 by controlling the open-close period of the first switch circuit and the second switch circuit, thereby generating a high-frequency alternating current signal. The requirement for power supply can be simplified by using only a dc power supply to generate the high frequency ac signal.
Description
Technical Field
The invention relates to the field of electronic circuits, in particular to a frequency signal generating circuit and a liquid level detection circuit.
Background
With the gradual improvement of the living standard of people, a plurality of intelligent household appliances are gradually favored by people. The electric kettle sold in the market at present adopts intelligent steam induction temperature control, and has the functions of automatic power off after water boiling and dry heating prevention power off. Along with the needs of life, the existing electric kettle is developing towards multifunctional directions, such as leakage prevention, scald prevention, water locking and the like. The electric kettle has the advantages of high heating speed, good heat preservation effect, strong filtering function, various styles and the like.
When a user uses the automatic water inlet electric kettle, the water level of the electric kettle can be continuously changed, so that the detection of the water level in the kettle is very important. The principle of the electric kettle capable of automatically feeding water in the market for judging water level information is that the electric conductivity of water is realized or utilized by utilizing a capacitor structure formed by water and a kettle body.
However, in the detection, the electric kettle in the prior art needs to have a high-frequency alternating current signal generated by positive voltage and negative voltage as an excitation source, because sine waves generally need positive and negative voltages generated by using an oscillation principle, if two paths of output of the positive and negative voltages are formed, the requirement on a power supply is high, and an operational amplifier element is needed to form an oscillation circuit when the sine waves are generated, so that the structure of the power supply circuit is complicated.
Disclosure of Invention
Therefore, the technical problem to be solved by the present invention is to overcome the problem that the requirement for a power supply is high due to the fact that a high-frequency ac signal generated by a positive voltage and a negative voltage is required as an excitation source when detecting the water level of an electric kettle in the prior art, so as to provide a frequency signal generating circuit and a liquid level detecting circuit.
To achieve the above object, an embodiment of the present invention provides a frequency signal generating circuit, including: the direct current power supply VCC, the first switch circuit, the first resistor R1, the second resistor R2 and the second switch circuit are sequentially connected in series, and the other end of the second switch is grounded; the first switch circuit and the second switch circuit are respectively connected with a control circuit for controlling the on-off of the first switch circuit and the second switch circuit; a first capacitor C1 connected in parallel with the second resistor R2 and the second switch circuit; a first connector X1 is connected between the first resistor R1 and the second resistor R2.
Optionally, the first switching circuit is a first transistor Q1, a base of the first transistor Q1 is connected to a bias resistor R4, a collector is connected to the first resistor R1, and an emitter is connected to the dc power VCC; the other end of the bias resistor R4 is connected with the output end of the control circuit.
Optionally, the second switching circuit is a second transistor Q2, a base of the second transistor Q2 is connected to a bias resistor R5, an emitter of the second transistor Q2 is grounded, and a collector of the second transistor Q2 is connected to the second resistor R2; the other end of the bias resistor R5 is connected with the output end of the control circuit.
Optionally, the first transistor Q1 is a PNP transistor, and the second transistor Q2 is an NPN transistor.
Alternatively, when the control circuit outputs a low level, the first transistor Q1 is saturated and turned on, and the second transistor Q2 is turned off; when the control circuit outputs a high level, the first transistor Q1 is turned off and the second transistor Q2 is turned on in saturation.
Optionally, the control circuit comprises: the main control chip, a bias resistor R6, a third triode Q3, a bias resistor R7 and a fourth triode Q4; the bias resistor R6 and the bias resistor R7 are connected in parallel to the output end of the main control chip; the third triode Q3 is an NPN type triode, the base electrode of the third triode Q3 is connected with the other end of the bias resistor R6, the emitting electrode of the third triode Q3 is grounded, and the collector electrode of the third triode Q3 is connected with the first switch circuit; the fourth triode Q4 is a PNP type triode, the base electrode of the fourth triode Q4 is connected with the other end of the bias resistor R7, the emitting electrode of the fourth triode Q4 is connected with positive voltage, and the collecting electrode of the fourth triode Q4 is connected with the second switch circuit.
The embodiment of the invention also provides a liquid level detection circuit, which comprises: the frequency signal generating circuit of any one of the above and signal detection circuits, wherein the control circuit comprises: the main control chip, a bias resistor R6, a third triode Q3, a bias resistor R7 and a fourth triode Q4; the bias resistor R6 and the bias resistor R7 are connected in parallel to the output end of the main control chip; the signal detection circuit comprises a second connector X2, a first diode D1, a second diode D2, a second capacitor C2 and the main control chip; the negative electrode of the first diode D1 is connected with the AD end of the main control chip, and the positive electrode of the first diode D1 is connected with the second joint X2; the cathode of the second diode D2 is connected with the anode of the first diode D1, and the anode is grounded; one end of the second capacitor C2 is connected to the cathode of the first diode D1, and the other end is grounded; the first connector X1 and the second connector X2 are used for contacting with a measured liquid to form an equivalent capacitance CP.
Optionally, the signal detection circuit further includes a third capacitor C3 and a voltage regulator resistor R3, and the third capacitor C3 and the voltage regulator resistor R3 are both connected in parallel with the second capacitor C2.
Optionally, the first connector X1 is a metal container containing the liquid to be detected, and the second connector X2 is a detection probe; or, the second joint X2 is the metal container containing the liquid to be detected, and the first joint X1 is the detection probe.
The embodiment of the invention also provides a liquid level detection device which comprises the liquid level detection circuit in any one of the embodiments.
Compared with the prior art, the technical scheme of the invention has the following advantages:
1. an embodiment of the present invention provides a frequency signal generating circuit, including: the direct current power supply VCC, the first switch circuit, the first resistor R1, the second resistor R2 and the second switch circuit are sequentially connected in series, and the other end of the second switch is grounded; the first switch circuit and the second switch circuit are respectively connected with a control circuit for controlling the on-off of the first switch circuit and the second switch circuit; a first capacitor C1 connected in parallel with the second resistor R2 and the second switch circuit; a first connector X1 is connected between the first resistor R1 and the second resistor R2. According to the invention, the direct-current power supply VCC, the first switch circuit and the second switch circuit are arranged to control the on-off period of the first switch circuit and the second switch circuit, so that the charging and discharging of the first capacitor C1 are controlled, and a high-frequency alternating-current signal is generated. The frequency signal generating circuit of the embodiment of the invention can generate high-frequency alternating current signals only by using a direct current power supply, and simplifies the requirements on the power supply, thereby solving the problem that the high-frequency alternating current signals generated by positive voltage and negative voltage are needed to be used as excitation sources in the prior art and have higher requirements on the power supply.
2. The embodiment of the invention also provides a liquid level detection circuit which comprises a signal detection circuit and the frequency signal generation circuit, and the detected water level voltage is stable because the chip is not influenced by the temperature and the equivalent capacitance of water is hardly influenced by the temperature. Therefore, the problem that when a sine wave signal is generated in the prior art, the operational amplifier is greatly influenced by temperature, the generated sine wave is easy to be unstable, and the water level detection is inaccurate is solved.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without creative efforts.
Fig. 1 is a circuit diagram of a frequency signal generating circuit according to embodiment 1 of the present invention;
FIG. 2 is a graph of voltage variation of the first capacitor in accordance with embodiment 1 of the present invention;
FIG. 3 is a graph of the voltage cycling of the first capacitor in accordance with embodiment 1 of the present invention;
fig. 4 is a circuit diagram of a frequency signal generating circuit according to embodiment 2 of the present invention;
fig. 5 is a circuit diagram of a frequency signal generating circuit according to embodiment 3 of the present invention;
FIG. 6 is a first circuit diagram of a liquid level detecting circuit according to embodiment 4 of the present invention;
FIG. 7 is a second circuit diagram of a liquid level detecting circuit according to embodiment 4 of the present invention;
FIG. 8 is a third circuit diagram of a liquid level detecting circuit according to embodiment 4 of the present invention;
FIG. 9 is a graph showing the voltage variation of the filtered AC signal according to embodiment 4 of the present invention;
fig. 10 is a circuit diagram of a preferred embodiment of a liquid level detection circuit in embodiment 4 of the present invention.
Detailed Description
The technical solutions of the present invention will be described clearly and completely with reference to the accompanying drawings, and it should be understood that the described embodiments are some, but not all embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, and are only for convenience of description and simplicity of description, but do not indicate or imply that the device or element being referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus, should not be construed as limiting the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.
In the description of the present invention, it should be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection; can be mechanically or electrically connected; the two elements may be directly connected or indirectly connected through an intermediate medium, or may be communicated with each other inside the two elements, or may be wirelessly connected or wired connected. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.
In addition, the technical features involved in the different embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
In the prior art, because the temperature of the electric kettle is high, an operational amplifier in the water level detection device is easily influenced by the temperature, and therefore the detection is inaccurate. The water level detection device needs alternating current signal detection, and the generated alternating current signal needs a positive power supply and a negative power supply, wherein the positive power supply and the negative power supply generally have more power supply devices, more transformer windings and higher requirements on the power supply. The liquid level detection circuit provided by the embodiment of the invention simplifies the power supply and simultaneously meets the requirement of alternating current signals by matching the conventional direct current power supply with the switching frequency of the two switches, avoids the influence of temperature by adopting the PWM signal output end of the main control chip to output, can be widely applied to electric kettles, electric teapots and various liquid level detection devices needing the liquid level detection circuit, and is exemplified by the electric kettles.
The embodiment of the invention provides a frequency signal generating circuit, which comprises a direct current power supply VCC, a first switch circuit, a first resistor R1, a second resistor R2, a second switch circuit, a first capacitor C1 and a control circuit which are sequentially connected in series. The other end of the second switch circuit is grounded, and the first switch circuit and the second switch circuit are respectively connected with a control circuit for controlling the on-off of the first switch circuit and the second switch circuit. The first capacitor is connected in parallel with the second resistor R2 and the second switch circuit, and a first joint X1 is connected between the first resistor R1 and the second resistor R2.
Example 1
The frequency signal generating circuit is used for controlling the charging and discharging of the first capacitor C1 to generate a pulsating direct current voltage signal. In the present embodiment, the first switch circuit is taken as the first switch S1, the second switch circuit is taken as the second switch S2, and the control circuit is taken as the controller for illustration. As shown in fig. 1, specifically, when the controller controls the first switch S1 to be closed and controls the second switch S2 to be opened, the dc power VCC charges the first capacitor C1 through the first resistor R1, and the voltage across the first capacitor C1 continuously increases; when the controller controls the first switch S1 to be opened and the second switch S2 to be closed, the first capacitor C1 and the second resistor R2 form a closed loop with the ground, the first capacitor C1 discharges, and the voltage across the first capacitor C1 continuously decreases. As shown in fig. 2, the voltage across the first capacitor C1 changes to be approximately triangular.
As shown in fig. 3, when the open and closed states of the first switch S1 and the second switch S2 are periodically controlled, the waveform of the change in voltage across the first capacitor C1 can be detected as a triangular wave. The controller reasonably controls the frequency of the open and close states of the first switch S1 and the second switch S2, and when the first capacitor C1 is charged and discharged, pulsating direct current voltage signals with certain frequency are formed at two ends of the first capacitor C1, so that the water level of the electric kettle can be detected through the pulsating direct current voltage signals.
So set up, only through the disconnection and the closed frequency of controller control first switch S1 and second switch S2, realize DC power supply VCC to first electric capacity C1' S charge-discharge to the pulsation direct current voltage signal of certain frequency has been produced, the partial structural component of power among the liquid level detection circuit has greatly been simplified, do not need additionally to design positive negative voltage output alone in the circuit, reduced the operation requirement to the power, the constitution of liquid level detection circuit has also been simplified. Therefore, the problems that in the prior art, high-frequency alternating-current signals are generated by positive and negative voltages, so that a plurality of power supply devices and a plurality of transformer windings are needed are solved.
Example 2
As shown in fig. 4, an embodiment of the present invention provides a frequency signal generating circuit, wherein the control circuit is a PWM signal output terminal of the main control chip, the first switch circuit includes a bias resistor R4 and a first transistor Q1, and the second switch circuit includes a bias resistor R5 and a second transistor Q2. The first transistor Q1 is a PNP transistor, and the second transistor Q2 is an NPN transistor.
In this embodiment, the high level of the PWM signal output terminal should not be higher than the dc power VCC, and those skilled in the art can set the high level according to actual situations, which is not limited in this embodiment.
The bias resistor R4 and the bias resistor R5 are connected in parallel to the PWM signal output end of the main control chip, the base of the first triode Q1 is connected with the other end of the bias resistor R4, the emitter is connected with the direct-current power supply VCC, the collector is connected with one end of the first resistor R1, and the first resistor R1 is connected with the second resistor R2 in series. The other end of the second resistor R2 is connected with the collector of the second triode Q2, the base of the second triode Q2 is connected with the other end of the bias resistor R5, and the emitter is grounded. One end of the first capacitor C1 is connected between the first resistor R1 and the second resistor R2, and the other end is grounded.
In the embodiment of the present invention, the signal generating circuit controls the first transistor Q1 and the second transistor Q2 to be turned on and off by the high-low level pulse signal output from the PWM output terminal.
Because the first triode Q1 is a PNP triode and the second triode Q2 is an NPN triode, when the pulse signal output by the PWM output terminal of the main control chip is at a low level, according to the characteristics of saturation turn-on and turn-off of the triodes, the first triode Q1 is turned on and the second triode Q2 is turned off, and at this time, the dc power VCC charges the first capacitor C1 through the first resistor R1, and the voltage at the two ends of the first capacitor C1 rises, so that it can be detected that the voltage of the first capacitor C1 is in a rising trend;
when the pulse signal output by the PWM output terminal of the main control chip is at a high level, similarly, according to the saturation turn-on and turn-off characteristics of the transistors, the first transistor Q1 is turned off, the second transistor Q2 is turned on, at this time, the first capacitor C1, the second resistor and the ground form a closed loop, the first capacitor C1 discharges, the voltage at the two ends of the first capacitor C1 continuously decreases, and it can be detected that the voltage of the first capacitor C1 is in a decreasing trend.
The main control chip reasonably controls the pulse signal output by the PWM output end to generate high and low level frequency, and when the first capacitor C1 is charged and discharged, pulsating direct current voltage signals with certain frequency are formed at two ends of the first capacitor C1. In this embodiment, the high level of the PWM signal output terminal should not be higher than the dc power VCC, and those skilled in the art can set the high level according to actual situations, which is not limited in this embodiment.
So set up, the characteristic of switching on and cutting off according to the saturation of triode realizes only through DC power VCC to the charge-discharge of first electric capacity C1, produces the pulsation direct current voltage signal of certain frequency, has greatly simplified the partial structural component of power in the liquid level detection circuit, need not additionally design positive negative voltage output alone in the circuit, has reduced the operation requirement to the power, has also simplified the constitution of liquid level detection circuit. Therefore, the problems that in the prior art, high-frequency alternating-current signals are generated by positive and negative voltages, so that a plurality of power supply devices and a plurality of transformer windings are needed are solved. Meanwhile, as the PWM signal output by the PWM signal output end of the main control chip is not influenced by temperature, the on and off of the circuit can be stably and accurately controlled, and the problems that in the prior art, when an alternating current signal is adopted as an excitation source, a required operational amplifier is greatly influenced by temperature, sine waves which are easy to appear are unstable, the voltage amplitude changes are generated, and finally the water level detection is inaccurate are solved.
Example 3
As shown in fig. 5, in the frequency signal generating circuit, the control circuit includes a main control chip, a bias resistor R6, a third transistor Q3, a bias resistor R7, and a fourth transistor Q4. The first switch circuit includes a bias resistor R4 and a first transistor Q1, and the second switch circuit includes a bias resistor R5 and a second transistor Q2. The first transistor Q1 is a PNP transistor, the second transistor Q2 is an NPN transistor, the third transistor Q3 is an NPN transistor, and the fourth transistor Q4 is a PNP transistor.
The PWM signal output end of the main control chip is connected with a bias resistor R6 and a bias resistor R7 in parallel, the base electrode of a third triode Q3 is connected with the other end of the bias resistor R6, the emitting electrode is grounded, and the collecting electrode is connected with one end of the bias resistor R4. The base of the fourth triode Q4 is connected to the other end of the bias resistor R7, the emitter is connected to a positive voltage of +5V, and the collector is connected to one end of the bias resistor R5. In this embodiment, the high level of the PWM signal output terminal should not be higher than the positive voltage of +5V, and those skilled in the art can set the high level according to practical situations, and the embodiment is not limited.
The base of the first triode Q1 is connected with the other end of the bias resistor R4, the emitter is connected with the direct-current power supply VCC, the collector is connected with one end of the first resistor R1, and the first resistor R1 is connected with the second resistor R2 in series. The other end of the second resistor R2 is connected with the collector of the second triode Q2, the base of the second triode Q2 is connected with the other end of the bias resistor R5, and the emitter is grounded. One end of the first capacitor C1 is connected between the first resistor R1 and the second resistor R2, and the other end is grounded.
In this embodiment, the control circuit controls the third transistor Q3 and the fourth transistor Q4 to be turned on and off according to the PWM signal output by the PWM controller. Since the third transistor Q3 is an NPN transistor and the fourth transistor Q4 is a PNP transistor, when the PWM signal output by the PWM controller is at a high level, according to the saturation on-off characteristic of the transistors, the third transistor Q3 is turned on and the fourth transistor Q4 is turned off, at this time, the bias resistor R4 is grounded, and the bias resistor R5 has no base current; according to the saturation on and off characteristics of the transistors, the first transistor Q1 is turned on and the second transistor Q2 is turned off. At this time, the dc power VCC charges the first capacitor C1 through the first resistor R1, and the voltage across the first capacitor C1 continuously increases.
When the PWM signal output by the PWM controller is at a low level, the third transistor Q3 is turned off and the fourth transistor Q4 is turned on according to the saturation turn-on and turn-off characteristics of the transistors; at this time, there is no base current in the bias resistor R4, and the bias resistor R5 has base current due to the connection of 5V positive voltage; according to the saturation on and off characteristics of the transistors, the first transistor Q1 is turned off, and the second transistor Q2 is turned on. At this time, the first capacitor C1, the second resistor and the ground form a closed loop, the first capacitor C1 discharges, and the voltage across the first capacitor C1 decreases.
The PWM controller reasonably controls the PWM signal to generate high and low level frequency, and when the first capacitor C1 is charged and discharged, a pulsating direct current voltage signal with certain frequency is formed at two ends of the first capacitor C1.
Example 4
The embodiment of the invention also provides a liquid level detection circuit, as shown in fig. 6-8, the liquid level detection circuit comprises a signal detection circuit and any one of the frequency signal generation circuits in the above embodiments.
The signal detection circuit comprises a second connector X2, a first diode D1, a second diode D2, a second capacitor C2 and a main control chip. The negative electrode of the first diode D1 is connected with the AD end of the main control chip, and the positive electrode of the first diode D1 is connected with the other end of the equivalent capacitor CP. The cathode of the second diode D2 is connected with the anode of the first diode D1, and the anode is grounded. One end of the second capacitor C2 is connected to the cathode of the first diode D1, and the other end is grounded. The first joint X1 and the second joint X2 are in contact with the measured liquid to form an equivalent capacitance CP. The first joint X1 is a metal container filled with the liquid to be detected, and the second joint X2 is a detection probe; or the second joint X2 is a metal container containing the liquid to be detected, and the first joint X1 is a detection probe.
In the embodiment of the present invention, an electric kettle is exemplified. Thus, the first joint X1 is a metal kettle body of the electric kettle containing water, and the second joint X2 is a detection probe; or the second joint X2 is a metal kettle body of the electric kettle, and the first joint X1 is the detection probe.
When the first capacitor C1 of the frequency signal generating circuit generates the pulsating dc voltage signal, the pulsating dc voltage signal has an ac component, and therefore, only the ac signal remains after the pulsating dc signal passes through the equivalent capacitor CP. So, through setting up in water level detection probe, can detect alternating current signal after signal detection circuit inputs main control chip when alternating current signal to the voltage size through alternating current signal realizes the detection to the water level.
After the pulsating dc signal passes through the equivalent capacitor CP, only the ac signal remains. After the ac signal is input to the signal detection circuit, the second capacitor C2 may filter the ac signal. When the alternating current signal is in a positive half period, the first diode D1 is in a forward direction, the second diode D2 is in a reverse direction, and therefore the first diode D1 can rectify the alternating current signal; when the ac signal is in the negative half cycle, the first diode D1 is turned off in the reverse direction and the second diode D2 is turned on in the forward direction, so that the second diode D2 can rectify the ac signal.
As shown in fig. 9, after the rectified ac signal is input into the main control chip AD and filtered by the second capacitor C2, the main control chip can obtain the water level change in the electric kettle according to the voltage change of the ac signal.
In particular, the equivalent capacitance capacitive reactanceWherein, XCIs capacitance capacitive reactance, f is alternating signal frequency, and CP is capacitance value of the equivalent capacitance.
When the water level in the electric kettle becomes high, the equivalent capacitance CP becomes large, and the capacitance reactance XCReduced AC signal to which the other end of the equivalent capacitor is coupledThe amplitude value becomes larger, so that the voltage value detected by the main control chip becomes larger; when the water level in the electric kettle becomes low, the equivalent capacitance CP becomes small, and the capacitance reactance X becomes smallCThe grow, the alternating current signal amplitude that the equivalent capacitance other end couples to diminishes, so the voltage value that main control chip detected diminishes to the realization is to the real-time detection of insulating pot water level.
Meanwhile, as the PWM signal output by the PWM signal output end of the main control chip is not influenced by temperature, the on and off of the circuit can be stably and accurately controlled, and the problems that in the prior art, when an alternating current signal is adopted as an excitation source, a required operational amplifier is greatly influenced by temperature, sine waves which are easy to appear are unstable, the voltage amplitude changes are generated, and finally the water level detection is inaccurate are solved.
As a preferred embodiment, as shown in fig. 10, the signal detection circuit further includes a current limiting resistor R8, and a third capacitor C3 and a voltage stabilizing resistor R3 connected in parallel with the second capacitor C2. The third capacitor C3 can adopt an electrolytic capacitor, the capacity of the capacitor is large, and the detected signal frequency can be lower, so that the alternating current signal of the pulsating direct current voltage signal can be filtered, and the voltage stabilizing resistor R3 can enable the voltage of the alternating current signal to be more stable. The third capacitor C3 and the voltage stabilizing resistor R3 can enable the liquid level detection circuit to detect more easily, and the detection effect is better.
The embodiment of the invention also provides a liquid level detection device which comprises the liquid level detection circuit in any one of the embodiments.
It should be understood that the above examples are only for clarity of illustration and are not intended to limit the embodiments. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. And obvious variations or modifications therefrom are within the scope of the invention.
Claims (10)
1. A frequency signal generating circuit, comprising:
the circuit comprises a direct current power supply (VCC), a first switch circuit, a first resistor (R1), a second resistor (R2) and a second switch circuit which are sequentially connected in series, wherein the other end of the second switch circuit is grounded; the first switch circuit and the second switch circuit are respectively connected with a control circuit for controlling the on-off of the first switch circuit and the second switch circuit;
a first capacitor (C1) connected in parallel with the second resistor (R2) and the second switch circuit;
a first connector (X1) is connected between the first resistor (R1) and the second resistor (R2).
2. The frequency signal generating circuit according to claim 1, wherein the first switching circuit is a first transistor (Q1) and a bias resistor (R4), the base of the first transistor (Q1) is connected to the bias resistor (R4), the collector is connected to the first resistor (R1), and the emitter is connected to the dc power supply (VCC); the other end of the bias resistor (R4) is connected with the output end of the control circuit.
3. The frequency signal generating circuit of claim 2, wherein the second switching circuit is a second transistor (Q2) and a bias resistor (R5), the base of the second transistor (Q2) is connected to the bias resistor (R5), the emitter is connected to ground, and the collector is connected to the second resistor (R2); the other end of the bias resistor (R5) is connected with the output end of the control circuit.
4. The frequency signal generating circuit of claim 3, wherein the first transistor (Q1) is a PNP transistor and the second transistor (Q2) is an NPN transistor.
5. The frequency signal generating circuit of claim 4, wherein when the control circuit outputs a low level, the first transistor (Q1) is saturated and turned on, and the second transistor (Q2) is turned off; when the control circuit outputs a high level, the first transistor (Q1) is turned off, and the second transistor (Q2) is saturated and turned on.
6. The frequency signal generating circuit according to claim 1, wherein the control circuit comprises: the circuit comprises a main control chip, a bias resistor (R6), a third triode (Q3), a bias resistor (R7) and a fourth triode (Q4); the bias resistor (R6) and the bias resistor (R7) are connected to the output end of the main control chip in parallel;
the third triode (Q3) is an NPN type triode, the base electrode of the third triode is connected with the other end of the bias resistor (R6), the emitting electrode of the third triode is grounded, and the collecting electrode of the third triode is connected with the first switch circuit;
the fourth triode (Q4) is a PNP type triode, the base electrode of the fourth triode is connected with the other end of the bias resistor (R7), the emitting electrode of the fourth triode is connected with positive voltage, and the collecting electrode of the fourth triode is connected with the second switch circuit.
7. A liquid level detection circuit, comprising: a signal detection circuit and a frequency signal generation circuit according to any one of claims 1 to 6,
the control circuit includes: the circuit comprises a main control chip, a bias resistor (R6), a third triode (Q3), a bias resistor (R7) and a fourth triode (Q4); the bias resistor (R6) and the bias resistor (R7) are connected to the output end of the main control chip in parallel;
the signal detection circuit comprises a second connector (X2), a first diode (D1), a second diode (D2), a second capacitor (C2) and the main control chip;
the negative electrode of the first diode (D1) is connected with the AD end of the main control chip, and the positive electrode of the first diode is connected with the second joint (X2); the cathode of the second diode (D2) is connected with the anode of the first diode (D1), and the anode is grounded;
one end of the second capacitor (C2) is connected to the cathode of the first diode (D1), and the other end of the second capacitor is grounded;
the first connector (X1) and the second connector (X2) are used for contacting with a tested liquid to form an equivalent Capacitor (CP).
8. The liquid level detection circuit according to claim 7, wherein the signal detection circuit further comprises a third capacitor (C3) and a voltage stabilizing resistor (R3), and the third capacitor C3 and the voltage stabilizing resistor (R3) are both connected in parallel with the second capacitor (C2).
9. The liquid level detection circuit according to claim 8, wherein the first connector (X1) is a metal container containing the liquid to be detected, and the second connector (X2) is a detection probe; or, the second connector (X2) is the metal container containing the detected liquid, and the first connector (X1) is the detection probe.
10. A liquid level detection apparatus comprising the liquid level detection circuit according to any one of claims 7 to 9.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201910882491.XA CN110617866A (en) | 2019-09-18 | 2019-09-18 | Frequency signal generating circuit and liquid level detection circuit |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201910882491.XA CN110617866A (en) | 2019-09-18 | 2019-09-18 | Frequency signal generating circuit and liquid level detection circuit |
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| CN110617866A true CN110617866A (en) | 2019-12-27 |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113394969A (en) * | 2020-12-22 | 2021-09-14 | 青岛鼎信通讯股份有限公司 | Negative voltage generation circuit applied to acquisition terminal |
| CN115615515A (en) * | 2022-12-19 | 2023-01-17 | 河北卧牛净水设备有限公司 | Water dispenser control system and water dispenser |
-
2019
- 2019-09-18 CN CN201910882491.XA patent/CN110617866A/en active Pending
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113394969A (en) * | 2020-12-22 | 2021-09-14 | 青岛鼎信通讯股份有限公司 | Negative voltage generation circuit applied to acquisition terminal |
| CN115615515A (en) * | 2022-12-19 | 2023-01-17 | 河北卧牛净水设备有限公司 | Water dispenser control system and water dispenser |
| CN115615515B (en) * | 2022-12-19 | 2023-03-10 | 河北卧牛净水设备有限公司 | Water dispenser control system and water dispenser |
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