Absolute humidity detection circuit and microwave oven

Abstract

The utility model provides an absolute humidity detection circuit and a microwave oven. The absolute humidity detection circuit comprises a sensor circuit, a PWM (Pulse Width Modulation)-analog voltage conversion circuit and an operational amplifier input and output circuit, the sensor circuit is connected with one end of the PWM-to-analog voltage circuit through the operational amplifier input and output circuit, and the other end of the PWM-to-analog voltage circuit is connected with the control chip through an IO port of the single-chip microcomputer. According to the absolute humidity detection circuit and the microwave oven, the structure of the detection circuit can be effectively simplified, occupation of IO ports of a single-chip microcomputer is reduced, resources are saved, and the single-chip microcomputer can have enough IO ports to achieve more functions. And the cost of the circuit can be reduced, the number of output voltage values of the circuit is increased, and the detection accuracy and reliability of the circuit are enhanced.

Description

TECHNICAL FIELD

[0001] The utility model relates to the technical field of microwave oven, concretely relates to a detection circuit of absolute humidity and microwave oven. BACKGROUND

[0002] At present, the microwave oven humidity sensor generally uses absolute humidity sensor, and the absolute humidity sensor usually adopts a pair of NTC thermistors with similar characteristics, one is placed in a cover with small air holes, and air can flow freely, and the other is placed in a safe seal and dry air.

[0003] In addition, the absolute humidity sensor usually uses a bridge circuit, and the bridge circuit has been calibrated to 0mV, 0g / m 3 If the atmospheric temperature and humidity change, the bridge will generate an output voltage. In the actual application circuit, the rear of the bridge output needs to be connected to an operational amplifier, and since different humidity sensors may have differences, in order to facilitate detection by the single-chip microcomputer, the initial state of the operational amplifier output needs to be set in a reasonable preset range, and too high or too low will affect the accuracy of the humidity detection. In order to meet the consistency of the initial state of the humidity detection, the traditional circuit design uses five channel resistors, which are connected to five IO ports of the single-chip microcomputer respectively, and the initial state is adjusted in a combined form.

[0004] Although the traditional scheme can meet the actual application requirements, it also has the following disadvantages:

[0005] 1. Too many IO ports are occupied, which increases the cost of the circuit or the IO ports of the single-chip microcomputer chip are occupied, resulting in insufficient IO ports of the single-chip microcomputer chip, and more functions cannot be realized.

[0006] 2. The voltage value that the circuit can output is small, and theoretically, 32 values (2 5 = 32) can be output at most by using five IO ports.

[0007] 3. The voltage drop of the diode changes with temperature, which affects the accuracy. Therefore, it is of great significance to study how to reduce the cost of the circuit and improve the accuracy of the circuit measurement.

[0008] In the patent CN109028180A, a kind of initialization control method of microwave oven absolute humidity sensor is presented, and the initial control circuit of its sensor includes the Wheatstone bridge circuit being arranged on humidity sensor, and five parallel resistors are arranged in Wheatstone bridge circuit.Different from prior art, the parallel resistor connected in output terminal is sequentially started and initialized according to certain order, which can easily make initialization time longer and affect initialization efficiency.The precision of initialization control can be improved by the patent, but due to the cooperation of Wheatstone bridge and five parallel resistors, the problems of too many IO ports occupied by single-chip microcomputer and complex circuit structure and high cost cannot be solved. Practical new type content

[0009] Therefore, the utility model aims at presenting a kind of absolute humidity detection circuit and microwave oven to solve the problems of complex structure of traditional detection circuit, more IO ports occupied, more functions of single-chip microcomputer cannot be realized due to insufficient IO ports, and rising circuit cost, less output voltage value and poor detection precision in prior art, so that the structure of detection circuit can be effectively simplified, the occupation of single-chip microcomputer IO port is reduced, resources are saved, and single-chip microcomputer can realize more functions with sufficient IO port.The cost of circuit can be reduced, the number of output voltage value of circuit is increased, and the detection precision and reliability of circuit are enhanced.

[0010] To achieve the above object, the technical scheme of the utility model is as follows:

[0011] The utility model relates to a kind of absolute humidity detection circuit and microwave oven, a kind of absolute humidity detection circuit, including sensor circuit, PWM conversion analog voltage circuit and operational amplifier input-output circuit;Sensor circuit is connected with the one end of PWM conversion analog voltage circuit by operational amplifier input-output circuit, and the other end of PWM conversion analog voltage circuit is connected with control chip by the IO port of single-chip microcomputer.

[0012] Further, sensor circuit includes absolute humidity sensor CN1 and sensor power module;Pin 1,2 of absolute humidity sensor CN1 are connected with sensor power module, and pin 3 of absolute humidity sensor CN1 is connected with operational amplifier input-output circuit.

[0013] Further, sensor power module includes fourth capacitor C4 and third resistor R3, one end of third resistor R3 is connected with one end of fourth capacitor C4 and pin 2 of absolute humidity sensor CN1 respectively, and the other end of third resistor R3 is connected with second power supply VDD;After the other end of fourth capacitor C4 is connected with pin 1 of absolute humidity sensor CN1 in parallel, it is grounded.

[0014] Further, the PWM-to-analog voltage circuit comprises a first third resistor R13, a first fourth resistor R14 and an RC filter circuit; one end of the first third resistor R13 is connected with one end of the first fourth resistor R14 and an IO port of the single-chip microcomputer respectively, and the other end of the first third resistor R13 is connected with a first power supply VCC; the other end of the first fourth resistor R14 is connected with the RC filter circuit and an operational amplifier input-output circuit respectively.

[0015] Further, the RC filter circuit comprises a first fifth resistor R15 and a sixth capacitor C6; one end of the first fifth resistor R15 and the sixth capacitor C6 is connected with the other end of the first fourth resistor R14 away from the first third resistor R13, and the other end of the first fifth resistor R15 and the sixth capacitor C6 is connected with the ground in parallel.

[0016] Further, the operational amplifier input-output circuit comprises an operational amplifier adjustment circuit and a protection circuit; one end of the operational amplifier adjustment circuit is connected with other components in the microwave oven through the protection circuit; the other end of the operational amplifier adjustment circuit is connected with the absolute humidity sensor CN1 and the first fourth resistor R14 respectively.

[0017] Further, the operational amplifier adjustment circuit comprises a first capacitor C1, a second capacitor C2, a fifth capacitor C5, a first resistor R1, a second resistor R2 and an operational amplifier U1A; one end of the second capacitor C2 is connected with the first resistor R1, the second resistor R2, one end of the first capacitor C1 and a negative input terminal of the operational amplifier U1A respectively, and the other end of the second capacitor C2 is connected with the PWM-to-analog voltage circuit and a positive input terminal UIN+ of the operational amplifier U1A respectively. The other end of the first resistor R1 is connected with the absolute humidity sensor CN1, and the other ends of the second resistor R2 and the first capacitor C1 are connected with an output terminal of the operational amplifier U1A and the protection circuit respectively in parallel.

[0018] Further, a positive side power supply pin of the operational amplifier U1A is connected with a second power supply VDD and one end of the fifth capacitor C5 respectively, and the other end of the fifth capacitor C5 is connected with the ground.

[0019] Further, the protection circuit comprises a fourth resistor R4, a diode D1, a fifth resistor R5 and a third capacitor C3; one end of the fourth resistor R4 is connected with the operational amplifier adjustment circuit, the other end of the fourth resistor R4 is connected with a positive electrode of the diode D1 and one end of the fifth resistor R5 respectively, a negative electrode of the diode D1 is connected with the first power supply VCC, the other end of the fifth resistor R5 is connected with other components in the microwave oven and one end of the third capacitor C3 respectively, and the other end of the third capacitor C3 is connected with the ground.

[0020] A microwave oven comprises the absolute humidity detection circuit, the detection circuit is arranged in the microwave oven, and the detection circuit is connected with a single IO port of a control chip in the microwave oven.

[0021] Compared with the prior art, the absolute humidity detection circuit and the microwave oven have the following beneficial effects:

[0022] Through the setting of the detection circuit in the microwave oven, the structure of the detection circuit can be effectively simplified, the difficulty of PCB wiring is reduced, the area of the PCB board is saved, the occupation of the single-chip microcomputer IO port is reduced, resources are saved, the single-chip microcomputer can have enough IO ports to realize more functions, the cost of the circuit is reduced, the number of output voltage values of the circuit is increased, and the detection accuracy and reliability of the circuit are enhanced. BRIEF DESCRIPTION OF DRAWINGS

[0023] The accompanying drawings, which form a part of this application, are included to provide a further understanding of the application and are incorporated herein for reference. The illustrative embodiments of the present application and their description serve to explain the application and do not limit the application. In the drawings:

[0024] Figure 1 It is a whole structure principle diagram of the detection circuit;

[0025] Figure 2 It is a result schematic diagram of simulation of the PWM-to-analog voltage circuit with a first PWM duty ratio;

[0026] Figure 3 It is a result schematic diagram of simulation of the PWM-to-analog voltage circuit with a second PWM duty ratio;

[0027] Figure 4 It is a result schematic diagram of simulation of the PWM-to-analog voltage circuit with a third PWM duty ratio.

[0028] The accompanying drawings, which form a part of this application, are included to provide a further understanding of the application and are incorporated herein for reference. The illustrative embodiments of the present application and their description serve to explain the application and do not limit the application. In the drawings: DETAILED DESCRIPTION

[0029] The utility model concepts of the present disclosure will be described using terms generally used by those skilled in the art to convey the substance of their work to other skilled artisans in the art. However, these utility model concepts can be embodied in many different forms, and therefore should not be considered limited to the embodiments described herein.

[0030] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict.

[0031] The present application will be described in detail below with reference to the accompanying drawings and in conjunction with the embodiments.

[0032] The embodiment is directed to a microwave oven, and the overall structure of the microwave oven is composed of a baking tray, a baking rack and a high-frequency power conversion device, which is the same as a conventional microwave oven.

[0033] In order to solve the problems of the prior art, such as the complex structure of the conventional detection circuit, the large number of IO ports, the insufficient IO ports of the single-chip microcomputer, the high cost of the circuit, the small number of output voltage values, and the poor detection precision, the embodiment provides an absolute humidity detection circuit and a microwave oven.

[0034] The detection circuit can effectively simplify the structure of the detection circuit, reduce the difficulty of PCB wiring, save the area of the PCB, reduce the occupation of the IO port of the single-chip microcomputer, save resources, and facilitate the single-chip microcomputer to have sufficient IO ports to realize more functions.

[0035] The sensor circuit 1 includes an absolute humidity sensor CN1 and a sensor power-on module 11. The pins 1 and 2 of the absolute humidity sensor CN1 are connected to the sensor power-on module 11, and the pin 3 of the absolute humidity sensor CN1 is connected to the operational amplifier input-output circuit 3. The absolute humidity sensor CN1 is internally provided with two NTC thermistors. One end of the parallel connection of the two NTC thermistors is connected to the pin 3 of the absolute humidity sensor CN1, and the other end of the two NTC thermistors is connected to the pins 1 and 2 of the absolute humidity sensor CN1, respectively. In addition, the sensor power-on module 11 includes a fourth capacitor C4 and a third resistor R3. One end of the third resistor R3 is connected to one end of the fourth capacitor C4 and the pin 2 of the absolute humidity sensor CN1, respectively, and the other end of the third resistor R3 is connected to the second power supply VDD. The other end of the fourth capacitor C4 is connected to the pin 1 of the absolute humidity sensor CN1 in parallel connection, and grounded. In the embodiment, the voltage of the second power supply VDD is 15V or 12V.

[0036] The sensor power-on module 11 can provide working voltage for the absolute humidity sensor CN1 and protect the absolute humidity sensor CN1, thereby improving the stability and safety of the circuit.

[0037] The PWM-to-analog voltage circuit 2 comprises a first three-resistor R13, a first four-resistor R14 and an RC filter circuit 21. One end of the first three-resistor R13 is connected with one end of the first four-resistor R14 and an IO port of the single-chip microcomputer respectively, and the other end of the first three-resistor R13 is connected with a first power supply VCC; the other end of the first four-resistor R14 is connected with the RC filter circuit 21 and the operational amplifier input-output circuit 3 respectively. The RC filter circuit 21 comprises a first five-resistor R15 and a sixth capacitor C6. One end of the first five-resistor R15 and the sixth capacitor C6 is connected with the end of the first four-resistor R14 away from the first three-resistor R13, and the other end of the first five-resistor R15 and the sixth capacitor C6 is connected with the ground in parallel. In the embodiment, the voltage of the first power supply VCC is 5V or 3.3V.

[0038] By outputting a PWM signal with the IO port of the single-chip microcomputer and connecting an RC filter circuit 21, a simple PWM-to-analog voltage circuit 2 is formed. The detection circuit can adjust the voltage of the positive input end UIN+ of the operational amplifier input-output circuit 3 by adjusting the duty cycle of the PWM, and then adjust the initial state of the operational amplifier output. In addition, the use of the PWM-to-analog voltage circuit 2 is conducive to simplifying the structure of the detection circuit, and is also conducive to saving the number of IO ports of the single-chip microcomputer occupied by the detection circuit. Only one IO port is needed to adjust the positive input end UIN+, and the normal operation of the detection circuit can be realized, so that the single-chip microcomputer has sufficient IO ports to realize more functions. In addition, since an 8-bit PWM can output 256 values, the use of the PWM-to-analog voltage circuit 2 can accurately adjust the output voltage, which can simplify the circuit and reduce the difficulty of wiring and save the use of PCB area.

[0039] The operational amplifier input-output circuit 3 comprises an operational amplifier adjustment circuit 31 and a protection circuit 32. One end of the operational amplifier adjustment circuit 31 is connected with other components in the microwave oven through the protection circuit 32; the other end of the operational amplifier adjustment circuit 31 is connected with a pin 3 of the absolute humidity sensor CN1 of the sensor circuit 1 and the first four-resistor R14 of the PWM-to-analog voltage circuit 2 respectively.

[0040] The op-amp adjusting circuit 31 comprises a first capacitor C1, a second capacitor C2, a fifth capacitor C5, a first resistor R1, a second resistor R2 and an operational amplifier U1A. One end of the second capacitor C2 is connected with the first resistor R1, the second resistor R2, one end of the first capacitor C1 and the negative input end of the operational amplifier U1A respectively, and the other end of the second capacitor C2 is connected with the PWM-to-analog voltage circuit 2 and the positive input end UIN+ of the operational amplifier U1A respectively. The other end of the first resistor R1 is connected with the absolute humidity sensor CN1, and the other ends of the second resistor R2 and the first capacitor C1 are connected in parallel and then connected with the output end of the operational amplifier U1A and the protection circuit 32 respectively. The negative side power supply pin of the operational amplifier U1A is grounded, and the positive side power supply pin of the operational amplifier U1A is connected with the second power supply VDD and one end of the fifth capacitor C5 respectively, and the other end of the fifth capacitor C5 is grounded.

[0041] The protection circuit 32 comprises a fourth resistor R4, a diode D1, a fifth resistor R5 and a third capacitor C3. One end of the fourth resistor R4 is connected with the output end of the operational amplifier U1A in the op-amp adjusting circuit 31, and the other end of the fourth resistor R4 is connected with the positive electrode of the diode D1 and one end of the fifth resistor R5 respectively, the negative electrode of the diode D1 is connected with the first power supply VCC, the other end of the fifth resistor R5 is connected with other components in the microwave oven and one end of the third capacitor C3 respectively, and the other end of the third capacitor C3 is grounded.

[0042] Through the cooperation of the op-amp adjusting circuit 31 and the protection circuit 32 in the op-amp input and output circuit 3, the reliability and safety of the detection circuit as a whole can be improved, and the amplification of the absolute humidity signal detected by the absolute humidity sensor CN1 and the PWM signal received by the PWM-to-analog voltage circuit 2 is also facilitated, so as to better realize the real-time and accurate control of the initial state AD of the circuit output, and improve the stability and safety of the detection circuit. In addition, the setting of the first resistor R1 is conducive to protecting the absolute humidity sensor CN1, preventing the absolute humidity sensor CN1 from being damaged due to excessive current in the circuit, and also facilitating the calibration function, which is conducive to improving the accuracy and measurement accuracy of the sensor.

[0043] Simulation experiment:

[0044] Usually, the PWM frequency is set to 1-10KHz, and the output voltage UIN+ of the PWM-to-analog voltage circuit 2 is adjusted in the range of 0-5V by adjusting the duty cycle, and then the initial state AD is adjusted according to the required output.

[0045] Specifically, the PWM-to-analog voltage circuit 2 is simulated, and the block part simulates the open-drain IO port of the single-chip microcomputer, which is specifically as follows: Figures 2-4The input voltage of the PWM-to-analog voltage conversion circuit 2 is constant at 5V, and the output voltage UIN+ of the PWM-to-analog voltage conversion circuit 2 is shown in the figure. By adjusting the duty cycle of the PWM signal input to the PWM-to-analog voltage conversion circuit 2 while ensuring that the frequency of the PWM signal input to the PWM-to-analog voltage conversion circuit 2 is 10KHZ, the output voltage UIN+ of the PWM-to-analog voltage conversion circuit 2 under the same PWM signal frequency and different PWM signal duty cycles is obtained. The specific simulation results are as follows:

[0046] Example 1: PWM frequency 10KHz, duty cycle 99%, output voltage 0.1V; as shown in Figure 2

[0047] Example 2: PWM frequency 10KHz, duty cycle 32%, output voltage 2.5V; as shown in Figure 3

[0048] Example 3: PWM frequency 10KHz, duty cycle 1%, output voltage 4.6V; as shown in Figure 4

[0049] Unlike the prior art, which requires multiple resistors to be connected in parallel and adjusts the initial state of the detection circuit by adjusting the combination of the multiple resistors, through simulation experiments, it is not difficult to see that by adjusting the duty cycle of the PWM signal, the initial state of the detection circuit can be adjusted, which is beneficial to reducing the cost of the circuit and improving the flexibility and accuracy of the circuit adjustment, and enhances the reliability of the detection circuit.

[0050] In the present application, for any microwave oven, it can include an absolute humidity detection circuit structure as described in the embodiment, and based on the related structures and assembly relationships of the filter device and control chip provided in the embodiment, the microwave oven further includes conventional components such as baking tray, baking rack, high-frequency power conversion device, etc. Since they are all prior art, they will not be described here.

[0051] The above is only a preferred embodiment of the present application, and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.​​​

Claims

1. An absolute humidity detection circuit, characterized by comprising: It includes sensor circuit (1), PWM to analog voltage circuit (2) and operational amplifier input and output circuit (3), sensor circuit (1) is connected with one end of PWM to analog voltage circuit (2) through operational amplifier input and output circuit (3), the other end of PWM to analog voltage circuit (2) is connected with control chip through IO port of single-chip microcomputer.

2. The absolute humidity detection circuit according to claim 1, wherein The sensor circuit (1) includes an absolute humidity sensor CN1 and a sensor power-on module (11), the pins 1 and 2 of the absolute humidity sensor CN1 are connected with the sensor power-on module (11), and the pin 3 of the absolute humidity sensor CN1 is connected with the operational amplifier input and output circuit (3).

3. The absolute humidity detection circuit according to claim 2, wherein The sensor power-on module (11) includes a fourth capacitor C4 and a third resistor R3, one end of the third resistor R3 is connected with one end of the fourth capacitor C4 and the pin 2 of the absolute humidity sensor CN1 respectively, the other end of the third resistor R3 is connected with a second power supply VDD, and the other end of the fourth capacitor C4 is grounded in parallel with the pin 1 of the absolute humidity sensor CN1.

4. The absolute humidity detection circuit according to claim 2, wherein The PWM to analog voltage circuit (2) includes a first three resistor R13, a first four resistor R14 and an RC filter circuit (21), one end of the first three resistor R13 is connected with one end of the first four resistor R14 and an IO port of a single-chip microcomputer respectively, the other end of the first three resistor R13 is connected with a first power supply VCC, and the other end of the first four resistor R14 is connected with the RC filter circuit (21) and the operational amplifier input and output circuit (3) respectively.

5. The absolute humidity detection circuit according to claim 4, wherein The RC filter circuit (21) includes a first five resistor R15 and a sixth capacitor C6, one end of the first five resistor R15 and the sixth capacitor C6 is connected with the end of the first four resistor R14, away from the first three resistor R13, and the other end of the first five resistor R15 and the sixth capacitor C6 is grounded in parallel.

6. The absolute humidity detection circuit according to claim 4, wherein The operational amplifier input and output circuit (3) includes an operational amplifier adjusting circuit (31) and a protection circuit (32), one end of the operational amplifier adjusting circuit (31) is connected with other components in a microwave oven through the protection circuit (32), and the other end of the operational amplifier adjusting circuit (31) is connected with the absolute humidity sensor CN1 and the first four resistor R14 respectively.

7. The absolute humidity detection circuit according to claim 6, wherein The operational amplifier adjusting circuit (31) includes a first capacitor C1, a second capacitor C2, a fifth capacitor C5, a first resistor R1, a second resistor R2 and an operational amplifier U1A, one end of the second capacitor C2 is connected with the first resistor R1, the second resistor R2, one end of the first capacitor C1 and a negative input end of the operational amplifier U1A respectively, the other end of the second capacitor C2 is connected with the PWM to analog voltage circuit (2) and a positive input end UIN+ of the operational amplifier U1A respectively, the other end of the first resistor R1 is connected with the absolute humidity sensor CN1, and the other end of the second resistor R2 and the first capacitor C1 are grounded in parallel and connected with an output end of the operational amplifier U1A and the protection circuit (32) respectively.

8. The absolute humidity detection circuit according to claim 7, wherein The positive side power supply pin of the operational amplifier U1A is connected with the second power supply VDD and one end of the fifth capacitor C5 respectively, and the other end of the fifth capacitor C5 is grounded.

9. The absolute humidity detection circuit according to claim 6, wherein The protection circuit (32) comprises a fourth resistor R4, a diode D1, a fifth resistor R5 and a third capacitor C3; one end of the fourth resistor R4 is connected with the operational amplifier adjusting circuit (31), the other end of the fourth resistor R4 is connected with the anode of the diode D1 and one end of the fifth resistor R5 respectively, the cathode of the diode D1 is connected with the first power supply VCC, the other end of the fifth resistor R5 is connected with other components in the microwave oven and one end of the third capacitor C3 respectively, the other end of the third capacitor C3 is grounded.

10. A microwave oven characterized by comprising: The detection circuit comprises the absolute humidity detection circuit according to any one of claims 1-9, and the detection circuit is arranged in the microwave oven and connected with a single IO port of a control chip in the microwave oven.

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