A frequency signal generation circuit and a liquid level detection circuit

Abstract

The present invention discloses a frequency signal generating circuit and a liquid level detection circuit. The frequency signal generating circuit includes: a DC power supply VCC, a first switch circuit, a first resistor R1, a second resistor R2, and a second switch circuit connected in series in sequence, and the other end of the second switch is grounded; the first switch circuit and the second switch circuit are respectively connected to a control circuit for controlling their on / off states; a first capacitor C1, which is 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 present invention controls the charging and discharging of the first capacitor C1 by controlling the on / off period of the first switch circuit and the second switch circuit, thereby generating a high-frequency AC signal. It is possible to generate a high-frequency AC signal only by using a DC power supply, which simplifies the requirements for the power supply.

Description

Technical Field

[0001] The present invention relates to the field of electronic circuits, and in particular to a frequency signal generating circuit and a liquid level detecting circuit. Background Art

[0002] As living standards gradually improve, many intelligent household appliances are gaining popularity. Currently, electric kettles on the market feature intelligent steam-sensing temperature control, automatic power-off upon boiling, and dry-boiling protection. To meet the needs of everyday life, electric kettles are also increasingly becoming multifunctional, with features like leak-proofing, scalding protection, and water-locking capabilities. They offer advantages such as fast heating, excellent heat retention, robust filtration capabilities, and a wide variety of styles.

[0003] When a user uses an automatic water-filling electric kettle, the water level in the kettle will constantly change, so detecting the water level in the kettle is very important. Currently, the automatic water-filling electric kettles on the market basically use the water and the kettle body to form a capacitor structure to achieve this or use the water's conductivity.

[0004] However, during detection, electric kettles in the prior art require a high-frequency AC signal generated by positive and negative voltages as an excitation source. This is because a sine wave generally requires positive and negative voltages to be generated using the oscillation principle. If two outputs of positive and negative voltages are to be formed, the power supply requirements are relatively high. In addition, when generating a sine wave signal, an oscillation circuit needs to be formed using operational amplifier components, and the structure of the power supply circuit is also relatively complex. Summary of the Invention

[0005] Therefore, the technical problem to be solved by the present invention is to overcome the problem in the prior art that when detecting the water level of an electric kettle, a high-frequency AC signal generated by positive and negative voltages is required as an excitation source, which places high requirements on the power supply, thereby providing a frequency signal generating circuit and a liquid level detection circuit.

[0006] To achieve the above objectives, an embodiment of the present invention provides a frequency signal generating circuit, comprising: a DC power supply VCC, a first switch circuit, a first resistor R1, a second resistor R2, and a second switch circuit connected in series, with the other end of the second switch being grounded; the first switch circuit and the second switch circuit are respectively connected to a control circuit for controlling their on and off; a first capacitor C1 connected in parallel with the second resistor R2 and the second switch circuit; and a first connector X1 is connected between the first resistor R1 and the second resistor R2.

[0007] Optionally, the first switching circuit is a first transistor Q1, the base of the first transistor Q1 is connected to the first 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 first bias resistor R4 is connected to the output end of the control circuit.

[0008] Optionally, the second switching circuit is a second triode Q2. A second bias resistor R5 is connected to the base of the second triode Q2, the emitter is grounded, and the collector is connected to the second resistor R2; the other end of the second bias resistor R5 is connected to the output end of the control circuit.

[0009] Optionally, the first triode Q1 is a PNP type triode, and the second triode Q2 is an NPN type triode.

[0010] Optionally, when the control circuit outputs a low level, the first triode Q1 is saturated and conducting, and the second triode Q2 is cut off; when the control circuit outputs a high level, the first triode Q1 is cut off, and the second triode Q2 is saturated and conducting.

[0011] Optionally, the control circuit includes: a main control chip, a third bias resistor R6, a third triode Q3, a fourth bias resistor R7, and a fourth triode Q4; the third bias resistor R6 and the fourth 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 is connected to the other end of the third bias resistor R6, the emitter is grounded, and the collector is connected to the first switching circuit; the fourth triode Q4 is a PNP type triode, the base is connected to the other end of the fourth bias resistor R7, the emitter is connected to a positive voltage, and the collector is connected to the second switching circuit.

[0012] An embodiment of the present invention further provides a liquid level detection circuit, including: a signal detection circuit and the frequency signal generation circuit according to any one of the above. Wherein, the control circuit includes: a main control chip, a third bias resistor R6, a third triode Q3, a fourth bias resistor R7, and a fourth triode Q4; the third bias resistor R6 and the fourth bias resistor R7 are connected in parallel to the output end of the main control chip; the signal detection circuit includes 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 to the AD terminal of the main control chip, and the positive electrode is connected to the second connector X2; the negative electrode of the second diode D2 is connected to the positive electrode of the first diode D1, and the positive electrode is grounded; one end of the second capacitor C2 is connected to the negative electrode of the first diode D1, and the other end is grounded; the first connector X1 and the second connector X2 are used to contact the liquid to be measured to form an equivalent capacitor CP.

[0013] Optionally, the signal detection circuit further includes 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.

[0014] Optionally, the first connector X1 is a metal container containing the liquid to be measured, and the second connector X2 is a detection probe; or, the second connector X2 is the metal container containing the liquid to be measured, and the first connector X1 is the detection probe.

[0015] An embodiment of the present invention further provides a liquid level detection device, including a liquid level detection circuit according to any one of the above embodiments.

[0016] Compared with the prior art, the technical solution of the present invention has the following advantages:

[0017] 1. An embodiment of the present invention provides a frequency signal generation circuit, including: a DC power supply VCC, a first switch circuit, a first resistor R1, a second resistor R2, and a second switch circuit connected in series in sequence, with the other end of the second switch grounded; the first switch circuit and the second switch circuit are respectively connected to a control circuit for controlling their on / off; 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. By setting the DC power supply VCC, the first switch circuit and the second switch circuit, the on / off period of the first switch circuit and the second switch circuit is controlled, and then the charging and discharging of the first capacitor C1 is controlled, thereby generating a high-frequency AC signal. The frequency signal generation circuit of the embodiment of the present invention can generate a high-frequency AC signal only using a DC power supply, simplifies the requirements for the power supply, and thus solves the problem in the prior art that a high-frequency AC signal generated by a positive voltage and a negative voltage is required as an excitation source, and the requirements for the power supply are relatively high.

[0018] 2. An embodiment of the present invention further provides a liquid level detection circuit, including a signal detection circuit and the above frequency signal generation circuit. Since the chip is not affected by temperature, and the equivalent capacitance of water is hardly affected by temperature, the detected water level voltage is stable. Thus, the problem in the prior art that when generating a sine wave signal, the operational amplifier is greatly affected by temperature, and the generated sine wave is prone to instability, resulting in inaccurate water level detection, is solved. Description of the Drawings

[0019] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the specific embodiments or the prior art. Obviously, the following drawings are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0020] Figure 1 It is a circuit diagram of a frequency signal generation circuit according to Embodiment 1 of the present invention;

[0021] Figure 2Voltage change diagram of the first capacitor in Embodiment 1 of the present invention;

[0022] Figure 3 Periodic voltage change diagram of the first capacitor in Embodiment 1 of the present invention;

[0023] Figure 4 Circuit diagram of a frequency signal generation circuit in Embodiment 2 of the present invention;

[0024] Figure 5 Circuit diagram of a frequency signal generation circuit in Embodiment 3 of the present invention;

[0025] Figure 6 First circuit diagram of a liquid level detection circuit in Embodiment 4 of the present invention;

[0026] Figure 7 Second circuit diagram of a liquid level detection circuit in Embodiment 4 of the present invention;

[0027] Figure 8 Third circuit diagram of a liquid level detection circuit in Embodiment 4 of the present invention;

[0028] Figure 9 Voltage change diagram of the filtered AC signal in Embodiment 4 of the present invention;

[0029] Figure 10 Circuit diagram of a preferred embodiment of a liquid level detection circuit in Embodiment 4 of the present invention. Detailed implementation manners

[0030] Next, the technical solutions of the present invention will be clearly and completely described in conjunction with the accompanying drawings. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0031] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. is based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. In addition, the terms "first", "second", and "third" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance.

[0032] In the description of the present invention, it should be noted that unless otherwise clearly specified and defined, the terms "installation", "connection", and "coupling" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, and it can also be the communication inside two components. It can be a wireless connection or a wired connection. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0033] In addition, the technical features involved in different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0034] In the prior art, since the temperature of the electric kettle is relatively high, the operational amplifier in the water level detection device is easily affected by temperature, so the detection is inaccurate. And the water level detection device needs to detect an AC signal, and generating an AC signal requires positive and negative power supplies. Usually, there are many power supply devices and many transformer windings for the positive and negative power supplies, and the requirements for the power supply are relatively high. The liquid level detection circuit provided by the embodiment of the present invention simplifies the power supply by means of the switching frequency of a conventional DC power supply and two switches while meeting the requirements of the AC signal. The output of the PWM signal output terminal of the main control chip is adopted to avoid the influence of temperature. It can be widely applied to electric kettles, electric teapots, and various liquid level detection devices that require a liquid level detection circuit. The embodiment of the present invention will take an electric kettle as an example for illustration.

[0035] The embodiment of the present invention provides a frequency signal generation circuit, which includes a DC 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 connected in series in sequence. The other end of the second switch circuit is grounded, and the first switch circuit and the second switch circuit are respectively connected to a control circuit for controlling their on / off states. The first capacitor is connected in parallel with the second resistor R2 and the second switch circuit, and a first connector X1 is connected between the first resistor R1 and the second resistor R2.

[0036] Embodiment 1

[0037] The frequency signal generation circuit is used to control the charging and discharging of the first capacitor C1 to generate a pulsating DC voltage signal. In this 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 Figure 1As shown in the figure, specifically, when the controller controls the first switch S1 to close and the second switch S2 to open, the DC power supply 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 open and the second switch S2 to close, the first capacitor C1, the second resistor R2 and the ground form a closed loop, and the first capacitor C1 discharges, and the voltage across the first capacitor C1 continuously decreases. As Figure 2 shown, the voltage change across the first capacitor C1 is approximately triangular.

[0038] As Figure 3 shown, when the opening and closing states of the first switch S1 and the second switch S2 are periodically controlled, a triangular wave can be detected as the voltage change waveform across the first capacitor C1. By reasonably controlling the frequency of the opening and closing states of the first switch S1 and the second switch S2 by the controller, when the first capacitor C1 is charged and discharged, a pulsating DC voltage signal with a certain frequency will be formed across the first capacitor C1, so that the water level of the electric kettle can be detected through the pulsating DC voltage signal.

[0039] With such a setting, only by controlling the opening and closing frequencies of the first switch S1 and the second switch S2 by the controller, the charging and discharging of the first capacitor C1 by the DC power supply VCC is realized, thereby generating a pulsating DC voltage signal with a certain frequency, greatly simplifying the structural components of the power supply part in the liquid level detection circuit, eliminating the need to separately design positive and negative voltage outputs in the circuit, reducing the requirements for the power supply, and also simplifying the composition of the liquid level detection circuit. Thus, the problem in the prior art that positive and negative voltages are required to generate high-frequency AC signals, resulting in many power supply devices and many transformer windings, is solved.

[0040] Embodiment 2

[0041] As Figure 4 shown, the embodiment of the present invention provides a frequency signal generation circuit, wherein the control circuit is the PWM signal output end of the main control chip, the first switch circuit includes a first bias resistor R4 and a first triode Q1, and the second switch circuit includes a second bias resistor R5 and a second triode Q2. The first triode Q1 is a PNP type triode, and the second triode Q2 is an NPN type triode.

[0042] In this embodiment, the high level of the PWM signal output end should not be higher than the DC power supply VCC, which can be set by those skilled in the art according to the actual situation, and this embodiment does not impose any limitations.

[0043] The first bias resistor R4 and the second bias resistor R5 are connected in parallel to the PWM signal output terminal of the main control chip. The base of the first triode Q1 is connected to the other end of the first bias resistor R4, the emitter is connected to the DC power supply VCC, and the collector is connected to one end of the first resistor R1. The first resistor R1 and the second resistor R2 are connected in series. The other end of the second resistor R2 is connected to the collector of the second triode Q2. The base of the second triode Q2 is connected to the other end of the second 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.

[0044] In the embodiment of the present invention, the signal generation circuit controls the conduction and cut-off of the first triode Q1 and the second triode Q2 through the high and low level pulse signals output by the PWM output terminal.

[0045] Since the first triode Q1 is a PNP type triode and the second triode Q2 is an NPN type 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 the saturation conduction and cut-off of the triode, the first triode Q1 conducts and the second triode Q2 cuts off. At this time, the DC power supply VCC charges the first capacitor C1 through the first resistor R1, and the voltage across the first capacitor C1 increases. It can be measured that the voltage of the first capacitor C1 shows an upward trend;

[0046] When the pulse signal output by the PWM output terminal of the main control chip is at a high level, similarly, according to the characteristics of the saturation conduction and cut-off of the triode, the first triode Q1 cuts off and the second triode Q2 conducts. At this time, the first capacitor C1, the second resistor and the ground form a closed loop, and the first capacitor C1 discharges, and the voltage across the first capacitor C1 continuously decreases. It can be measured that the voltage of the first capacitor C1 shows a downward trend.

[0047] By reasonably controlling the frequency of the high and low levels of the pulse signal output by the PWM output terminal of the main control chip, when the first capacitor C1 charges and discharges, a pulsating DC voltage signal with a certain frequency will be formed across the first capacitor C1. In this embodiment, the high level of the PWM signal output terminal should not be higher than the DC power supply VCC, which can be set by those skilled in the art according to the actual situation, and this embodiment does not impose any restrictions.

[0048] With such a setting, according to the characteristics of the saturation conduction and cut-off of the triode, the charging and discharging of the first capacitor C1 is realized only through the DC power supply VCC, generating a pulsating DC voltage signal with a certain frequency, greatly simplifying the structural components of the power supply part in the liquid level detection circuit, eliminating the need for separately designing positive and negative voltage outputs in the circuit, reducing the requirements for the power supply, and also simplifying the composition of the liquid level detection circuit. Thus, it solves the problem in the prior art that positive and negative voltages are required to generate high-frequency AC signals, resulting in a large number of power supply devices and transformer windings. At the same time, since the PWM signal output by the PWM signal output terminal of the main control chip is not affected by temperature, it can stably and accurately control the conduction and closing of the circuit, thereby solving the problem in the prior art that the operational amplifier required when using an AC signal as the excitation source is greatly affected by temperature, prone to unstable sine waves, generating changes in voltage amplitude, and ultimately leading to inaccurate water level detection.

[0049] Embodiment 3

[0050] As Figure 5 shown, the embodiment of the present invention provides a frequency signal generation circuit. In this frequency signal generation circuit, the control circuit includes a main control chip, a third bias resistor R6, a third triode Q3, a fourth bias resistor R7, and a fourth triode Q4. The first switch circuit includes a first bias resistor R4 and a first triode Q1, and the second switch circuit includes a second bias resistor R5 and a second triode Q2. The first triode Q1 is a PNP type triode, the second triode Q2 is an NPN type triode, the third triode Q3 is an NPN type triode, and the fourth triode Q4 is a PNP type triode.

[0051] The PWM signal output terminal of the main control chip is connected in parallel with the third bias resistor R6 and the fourth bias resistor R7 at the same time. The base of the third triode Q3 is connected to the other end of the third bias resistor R6, the emitter is grounded, and the collector is connected to one end of the first bias resistor R4. The base of the fourth triode Q4 is connected to the other end of the fourth bias resistor R7, the emitter is connected to the positive voltage of +5V, and the collector is connected to one end of the second 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, which can be set by those skilled in the art according to the actual situation, and this embodiment does not impose any limitations.

[0052] The base of the first triode Q1 is connected to the other end of the first bias resistor R4, the emitter is connected to the DC power supply VCC, and the collector is connected to one end of the first resistor R1. The first resistor R1 is connected in series with the second resistor R2. The other end of the second resistor R2 is connected to the collector of the second triode Q2. The base of the second triode Q2 is connected to the other end of the second 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.

[0053] In this embodiment, the control circuit controls the conduction and cut-off of the third triode Q3 and the fourth triode Q4 through the PWM signal output by the PWM controller. Since the third triode Q3 is an NPN-type triode and the fourth triode Q4 is a PNP-type triode, when the PWM signal output by the PWM controller is at a high level, according to the characteristics of the saturation conduction and cut-off of the triode, the third triode Q3 conducts and the fourth triode Q4 cuts off. At this time, the first bias resistor R4 is grounded, and the second bias resistor R5 has no base current. According to the characteristics of the saturation conduction and cut-off of the triode, the first triode Q1 is conducted and the second triode Q2 is cut off. At this time, the DC power supply VCC charges the first capacitor C1 through the first resistor R1, and the voltage across the first capacitor C1 continuously increases.

[0054] When the PWM signal output by the PWM controller is at a low level, according to the characteristics of the saturation conduction and cut-off of the triode, the third triode Q3 cuts off and the fourth triode Q4 conducts. At this time, there is no base current in the first bias resistor R4, and the second bias resistor R5 has a base current because it is connected to a 5V positive voltage. According to the characteristics of the saturation conduction and cut-off of the triode, the first triode Q1 is cut off and the second triode Q2 is conducted. At this time, the first capacitor C1, the second resistor and the ground form a closed loop, and the first capacitor C1 discharges, and the voltage across the first capacitor C1 continuously decreases.

[0055] By reasonably controlling the frequency of the high and low levels of the PWM signal by the PWM controller, when the first capacitor C1 charges and discharges, a pulsating DC voltage signal with a certain frequency will be formed across the first capacitor C1.

[0056] Embodiment 4

[0057] The embodiment of the present invention also provides a liquid level detection circuit, as Figures 6 - 8 shown, the liquid level detection circuit includes a signal detection circuit and any one of the frequency signal generation circuits in the above embodiments.

[0058] The signal detection circuit includes 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 to the AD terminal of the main control chip, and the positive electrode is connected to the other end of the equivalent capacitor CP. The negative electrode of the second diode D2 is connected to the positive electrode of the first diode D1, and the positive electrode is grounded. One end of the second capacitor C2 is connected to the negative electrode of the first diode D1, and the other end is grounded. The first connector X1 and the second connector X2 are in contact with the liquid to be measured, forming an equivalent capacitor CP. The first connector X1 is a metal container containing the liquid to be measured, and the second connector X2 is a detection probe; or, the second connector X2 is a metal container containing the liquid to be measured, and the first connector X1 is a detection probe.

[0059] In the embodiments of the present invention, an electric kettle is taken as an example for illustration. Thus, the first connector X1 is the metal kettle body of the electric kettle filled with water, and the second connector X2 is the detection probe; alternatively, the second connector X2 is the metal kettle body of the electric kettle, and the first connector X1 is the detection probe.

[0060] When the first capacitor C1 in the frequency signal generation circuit generates a pulsating DC voltage signal, since the pulsating DC voltage signal has an AC component, after the pulsating DC signal passes through the equivalent capacitor CP, only the AC signal remains. Thus, when the AC signal passes through the water level detection probe and is input into the main control chip through the signal detection circuit, the AC signal can be detected, and the water level can be detected by the voltage magnitude of the AC signal.

[0061] After the pulsating DC signal passes through the equivalent capacitor CP, only the AC signal remains. After the AC signal is input into the signal detection circuit, the second capacitor C2 can filter the AC signal. When the AC signal is in the positive half cycle, the first diode D1 conducts forward, and the second diode D2 cuts off reversely, so that the first diode D1 can rectify the AC signal; when the AC signal is in the negative half cycle, the first diode D1 cuts off reversely, and the second diode D2 conducts forward, so that the second diode D2 can rectify the AC signal.

[0062] As shown in Figure 9 After the rectified AC signal and the AC signal filtered by the second capacitor C2 are input into the main control chip AD, the main control chip can obtain the water level change in the electric kettle according to the voltage change of the AC signal.

[0063] Specifically, the reactance of the equivalent capacitor , where X C is the capacitive reactance, is the AC signal frequency, and CP is the capacitance value of the equivalent capacitor.

[0064] When the water level in the electric kettle becomes higher, the equivalent capacitor CP becomes larger, the capacitive reactance X C becomes smaller, and the amplitude of the AC signal coupled to the other end of the equivalent capacitor becomes larger, so the voltage value detected by the main control chip becomes larger; when the water level in the electric kettle becomes lower, the equivalent capacitor CP becomes smaller, the capacitive reactance X C becomes larger, and the amplitude of the AC signal coupled to the other end of the equivalent capacitor becomes smaller, so the voltage value detected by the main control chip becomes smaller, thus realizing the real-time detection of the water level in the electric kettle.

[0065] Meanwhile, since the PWM signal output by the PWM signal output terminal of the main control chip is not affected by temperature and can stably and accurately control the conduction and shutdown of the circuit, the problem in the prior art that the operational amplifier required when using an AC signal as the excitation source is greatly affected by temperature, resulting in unstable sine waves, voltage amplitude changes, and ultimately inaccurate water level detection, is solved.

[0066] As a preferred embodiment, as Figure 10 shown, 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 be an electrolytic capacitor with a relatively large capacitance, and the detected signal frequency can be lower, so that the AC signal of the pulsating DC voltage signal can be filtered. The voltage-stabilizing resistor R3 can make the voltage of the AC signal more stable. The settings of the third capacitor C3 and the voltage-stabilizing resistor R3 can make the liquid level detection circuit easier to detect and the detection effect better.

[0067] The embodiment of the present invention also provides a liquid level detection device, including the liquid level detection circuit described in any of the above embodiments.

[0068] Obviously, the above embodiments are merely examples for clear illustration and not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or variations can be made based on the above description. It is not necessary and impossible to list all the implementation manners here. And the obvious changes or variations derived therefrom are still within the protection scope of the present invention.

Claims

1. A frequency signal generation circuit, characterized in that, Comprising: A DC power supply (VCC), a first switch circuit, a first resistor (R1), a second resistor (R2), and a second switch circuit connected in series in sequence, with the other end of the second switch circuit grounded; the first switch circuit and the second switch circuit are respectively connected to a control circuit for controlling their on / off states. A first capacitor (C1), which is 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). Control the on / off cycle of the first switch circuit and the second switch circuit, thereby controlling the charging and discharging of the first capacitor (C1) to generate a high-frequency AC signal.

2. A frequency signal generation circuit, characterized in that, Comprising: A DC power supply (VCC), a first switch circuit, a first resistor (R1), a second resistor (R2), and a second switch circuit connected in series in sequence, with the other end of the second switch circuit grounded; the first switch circuit and the second switch circuit are respectively connected to a control circuit for controlling their on / off states. A first capacitor (C1), which is 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 first switch circuit is a first triode (Q1) and a first bias resistor (R4). The base of the first triode (Q1) is connected to the first 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 first bias resistor (R4) is connected to the output terminal of the control circuit. Control the on / off cycle of the first switch circuit and the second switch circuit, thereby controlling the charging and discharging of the first capacitor (C1) to generate a high-frequency AC signal.

3. The frequency signal generation circuit according to claim 2, wherein The second switch circuit is a second triode (Q2) and a second bias resistor (R5). The base of the second triode (Q2) is connected to the second bias resistor (R5), the emitter is grounded, and the collector is connected to the second resistor (R2); the other end of the second bias resistor (R5) is connected to the output terminal of the control circuit.

4. The frequency signal generation circuit according to claim 3, wherein The first triode (Q1) is a PNP type triode, and the second triode (Q2) is an NPN type triode.

5. The frequency signal generation circuit according to claim 4, wherein When the control circuit outputs a low level, the first triode (Q1) is saturated and conducting, and the second triode (Q2) is cut off; when the control circuit outputs a high level, the first triode (Q1) is cut off, and the second triode (Q2) is saturated and conducting.

6. A frequency signal generation circuit, characterized in that, Comprising: A DC power supply (VCC), a first switch circuit, a first resistor (R1), a second resistor (R2), and a second switch circuit connected in series in sequence, with the other end of the second switch circuit grounded; the first switch circuit and the second switch circuit are respectively connected to a control circuit for controlling their on / off states. A first capacitor (C1), which is 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 control circuit includes: a main control chip, a third bias resistor (R6), a third triode (Q3), a fourth bias resistor (R7), and a fourth triode (Q4); the third bias resistor (R6) and the fourth bias resistor (R7) are connected in parallel to the output terminal of the main control chip; The third triode (Q3) is an NPN type triode, the base is connected to the other end of the third bias resistor (R6), the emitter is grounded, and the collector is connected to the first switch circuit; The fourth triode (Q4) is a PNP type triode, the base is connected to the other end of the fourth bias resistor (R7), the emitter is connected to the positive voltage, and the collector is connected to the second switch circuit; Control the on-off cycle of the first switch circuit and the second switch circuit, thereby controlling the charge and discharge of the first capacitor (C1) to generate a high-frequency alternating current signal.

7. A liquid level detection circuit, characterized in that, Comprising: A signal detection circuit and a frequency signal generation circuit according to any one of claims 1-6, wherein, The control circuit includes: a main control chip, a third bias resistor (R6), a third triode (Q3), a fourth bias resistor (R7), and a fourth triode (Q4); the third bias resistor (R6) and the fourth bias resistor (R7) are connected in parallel to the output terminal of the main control chip; The signal detection circuit includes 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 to the AD terminal of the main control chip, and the positive electrode is connected to the second connector (X2); the negative electrode of the second diode (D2) is connected to the positive electrode of the first diode (D1), and the positive electrode is grounded; One end of the second capacitor (C2) is connected to the negative electrode of the first diode (D1), and the other end is grounded; The first connector (X1) and the second connector (X2) are used to contact the liquid to be measured to form an equivalent capacitor (CP).

8. The liquid level detection circuit according to claim 7, wherein The signal detection circuit further includes 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 measured, and the second connector (X2) is a detection probe; or, the second connector (X2) is the metal container containing the liquid to be measured, and the first connector (X1) is the detection probe.

10. A liquid level detection device, characterized in that, Comprising a liquid level detection circuit according to any one of claims 7-9.

Images