The microwave oven automatically stops heating when the rice is cooked

Abstract

The present invention discloses a microwave oven that automatically stops heating when rice is cooked. It is based on various existing microwave oven circuits, and adds a time-delay cut-off circuit 5 and a steam detection circuit 7. The humidity sensor of the steam detection circuit 7 is installed on the inner side of the moisture discharge hole of the microwave oven shell. When the heated food reaches 100 degrees and a large amount of water vapor is generated, the humidity switch 2 in the steam detection circuit 7 automatically connects to the working power of the time-delay cut-off circuit 5, and the time-delay cut-off switch 1 disconnects the microwave oven power supply and stops heating when the preset disconnection time is reached, thereby avoiding the drawbacks of overheating or underheating, time-consuming and power-consuming microwave ovens in the prior art. The present invention is used to improve the automation and use effect of the microwave oven, reduce power consumption, and save heating time.

Description

Technical Field

[0001] The invention relates to a food heating microwave oven, in particular to a microwave oven which automatically stops heating when rice is cooked. Background Art

[0002] According to the principles of physics, microwave ovens used for cooking and heating food use high-power microwaves generated by the magnetron of the microwave oven to penetrate deeply into the food to heat the food. The rapidly changing electric field component of the microwave electromagnetic wave in the cavity of the microwave oven drives the polar molecules or non-polar molecules that can be polarized in the food to swing violently and rapidly, which means that the temperature of the food has increased macroscopically. Since the microwave electromagnetic field can directly penetrate into the food, microwave oven heating has the advantages of heating the inside and outside of the food at the same time (while other heating methods rely on heat conduction to heat the food, which is slower) and fast heating speed. Therefore, microwave ovens have become a common household appliance in domestic and foreign families. However, the heating time for heating different types of food or the same type of food but different weights in the microwave oven should be different, otherwise the food will be dried or even burned due to a large amount of evaporation of moisture due to the heating time being too long, or the food will be undercooked due to the heating time being too short. Although the manufacturer has given some recipe heating times in the microwave oven manual, they are all for specific types of food and specific weights of food, and most users find it difficult to follow them in actual use. Because users cannot cook the types provided by the manufacturer, especially the specific weight of food, every day. Therefore, in most cases, users will overheat or underheat the food in the microwave oven. Overheating will cause the food to become dry and hard, or even burnt, and waste electricity, which is irreversible. Although underheating can be remedied by stopping the machine and then reheating for a period of time, it wastes time and may also overheat. Summary of the invention

[0003] The purpose of the present invention is to provide a microwave oven which can automatically detect whether the temperature of food has reached 100 degrees Celsius, and automatically continue to heat the food for a period of time after the food reaches 100 degrees Celsius, and automatically stop heating when the food is cooked. The microwave oven can effectively and automatically avoid overheating and underheating of food.

[0004] To achieve the above purpose, the present invention connects the upper plug core of the 220V plug 4 to the left end of the microwave oven timer 3, the middle plug core of the 220V plug 4 to the lower power input end of the microwave oven circuit 6, and the ground plug core of the 220V plug is connected to the microwave oven casing. It is characterized in that a delay switch 1 is also connected in series between the microwave oven timer 3 and the upper power input end of the microwave oven circuit 6, the right power input end of the delay circuit 5 is connected to the left contact of the delay switch 1 and the left contact of the humidity switch 2, the left power input end of the delay circuit 5 is connected to the lower power input end of the microwave oven circuit 6, the left power input end of the steam detection circuit 7 is connected to the connection line between the microwave oven timer 3 and the delay switch 1, the right power input end of the steam detection circuit 7 is connected to the lower power input end of the microwave oven circuit 6, the center point of the humidity switch 2 is connected to the center point of the delay switch 1 and then connected to the right end of the microwave oven timer 3, the humidity switch 2 is a relay automatic switch in the steam detection circuit 7, and the delay switch 1 is a relay automatic switch in the delay circuit 5.

[0005] In order to remind the user in time when the rice is cooked, a rice cooked reminder 8 is connected in parallel between the right contact and the center contact of the time delay switch 1.

[0006] In order to simplify the circuit structure, reduce the cost and improve the reliability, the time delay circuit 5 and the steam detection circuit 7 are composed of a 555 circuit structure.

[0007] Since the present invention adds a steam detection circuit 7 and a delay circuit 5 to the microwave oven in the prior art, a delay switch 1 is connected in series in the power supply circuit of the microwave oven timer 3 and the microwave oven circuit 6, and the center point of the humidity switch 2 is connected to the center point of the delay switch 1, and the left contact of the humidity switch 2 is connected to the left contact of the delay switch 1 and then connected to the right power input end of the delay circuit 5, so that when the microwave oven heats food, it can automatically sense whether the heated food has reached 100 degrees Celsius (for simplicity, it will be called 100 degrees in the following), and automatically control to continue heating to the set time and stop heating, avoiding the defects of the microwave oven in the prior art that the moisture of the food is often overheated and evaporated excessively, and the food is dry and hard or even burnt and wastes electricity; at the same time, it also avoids the defect that the food is not cooked due to underheating caused by the food not reaching 100 degrees and needs to be heated again. In addition, the present invention can also remind the user that the rice is cooked through the sound of the rice cooked reminder 8. It can be seen that the present invention provides a more humane and convenient use experience for microwave oven users, making the microwave oven more time-saving and power-saving, achieving multiple goals at one stroke. In addition, the steam detection circuit 7 and the time-delay circuit 5 are constructed using 555 circuits, which simplifies the circuit structure, reduces costs, and improves reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 It is the overall principle circuit block diagram of the present invention;

[0009] Figure 2 is a circuit diagram of the steam detection circuit 7 of the present invention;

[0010] Figure 3 4 is a circuit diagram of the time-delay circuit 5 of the present invention. DETAILED DESCRIPTION

[0011] See Figure 1 . The upper plug of the 220V plug 4 is connected to the left end of the microwave oven timer 3 through a wire. The microwave oven timer 3 is not actually added by the present invention, but is originally in the microwave oven circuit in the prior art, except that the delay switch 1 is connected in series between the microwave oven timer 3 and the subsequent circuit of the microwave oven. The middle plug of the 220V plug 4 is connected to the lower power input end of the microwave oven circuit 6 through a wire. The ground plug of the 220V plug is connected to the microwave oven casing through a wire as grounding and electric shock protection. A delay switch 1 is also connected in series between the microwave oven timer 3 and the upper power input end of the microwave oven circuit 6. The right power input end of the delay circuit 5 is connected to the left contact of the delay switch 1 and the left contact of the humidity switch 2. The left power input end of the delay circuit 5 is connected to the connection line between the lower power input end of the microwave oven circuit 6 and the middle plug of the 220V plug 4. The left power input end of the steam detection circuit 7 is connected to the connection line between the microwave oven timer 3 and the center contact (referred to as the center point) of the delay switch 1. The right power input terminal of the steam detection circuit 7 is connected to the connection line between the lower power input terminal of the microwave oven circuit 6 and the middle plug core of the 220V plug 4. The center point of the humidity switch 2 is connected to the center point of the delay switch 1 and then connected to the right end of the microwave oven timer 3. The humidity switch 2 is a relay automatic switch in the steam detection circuit 7. When the relay electromagnet coil has no current, the humidity switch 2 is kept in Figure 1 The reset state of left-off and right-on shown in FIG. 1 is right-off and left-on when there is current. Similarly, the delay switch 1 is a relay automatic switch in the delay circuit 5. When there is no current in the relay solenoid coil, the delay switch 1 is kept in Figure 1 The reset state of left-off and right-on shown changes to right-off and left-on when current flows.

[0012] In order to remind the user in time when the rice is cooked, a rice cooked reminder 8 is connected in parallel between the right contact and the center point of the time-delay switch 1. The rice cooked reminder 8 can be composed of a buzzer with a 220V working voltage in the prior art, or a music reminder circuit can be composed of an electronic circuit in the prior art instead.

[0013] The working principle of the overall principle circuit block diagram of the present invention is as follows: Figure 1The state of each switch in is the full reset state when the microwave oven is not powered on. When the user selects the microwave oven timer 3 for a certain heating time (for example, 20 minutes), the 220V mains power supply supplies power to the microwave oven circuit 6 through the 220V plug and its wires, the microwave oven timer 3, and the delay switch 1. The microwave oven circuit 6 starts to work, and the magnetron of the microwave oven is powered to generate high-power microwaves to heat the food. When the temperature in the food reaches 100 degrees, the moisture in the food will produce a large amount of water vapor due to boiling, and the water vapor will be discharged from the moisture discharge hole of the microwave oven. The humidity sensor in the steam detection circuit 7 is installed at the moisture discharge hole of the microwave oven. Therefore, the humidity sensor causes the humidity switch 2 driven by the steam detection circuit 7 to connect its left contact due to the increase in humidity, thereby connecting the power supply of the delay circuit 5. When the preset disconnection time of the delay circuit 5 (for example, 3 minutes) is reached, the center point of the delay switch 1 driven by the delay circuit 5 automatically connects to the left contact, thereby disconnecting the power supply circuit from the delay switch 1 to the microwave oven circuit 6. At this time, the microwave oven stops heating. At the same time, the cooked rice reminder 8 is powered (that is, it is not short-circuited) and makes a sound to remind the user to turn off the machine. At the same time, since the center point of the delay switch 1 is connected to the left contact, it continues to provide working power to the delay circuit 5 (once the microwave oven stops heating, the humidity will drop, causing the humidity switch 2 to reset to the right contact and disconnect the circuit to supply power to the delay circuit 5), thereby maintaining the state of the delay switch 1 disconnecting the microwave oven circuit 6 until the microwave oven timer 3 disconnects at the preset time, completely cutting off the power to the microwave oven. After that, all switches are reset to Figure 1 The state drawn, that is, the center point of the time-delay switch 1 is automatically connected to the right contact, the humidity switch 2 is reset to the right contact, and the microwave oven timer 3 is reset to the disconnected state, waiting for the next heating to start.

[0014] When the food is heated to 100 degrees, depending on the type of food, it will generally be cooked if it is heated for another 2-5 minutes. At this time, the microwave oven circuit 6 should be turned off to avoid the defects of food becoming dry and hard, wasting electricity, etc. caused by overheating. However, it is inconvenient for users to know whether the food has reached 100 degrees, so the microwave oven in the prior art often has the problem of overheating or underheating when in use. Obviously, the present invention can solve the above problem, can automatically sense whether the food has reached 100 degrees, and automatically delay heating for 2-5 minutes to make it cooked, avoiding the disadvantages of food becoming dry and hard, wasting electricity, or food not being cooked due to overheating.

[0015] Of course, the state of disconnecting the power supply of the microwave oven circuit 6 does not disconnect the power supply of the delay cut-off circuit 5, but the power consumption of the delay cut-off circuit 5 is only about 2 watts, which is negligible compared with the power consumption of about 1 kilowatt in the microwave oven circuit 6, and hardly increases the power consumption of the microwave oven. It can also be seen that it is not very meaningful to select the on time of the microwave oven timer 3, as long as it is longer than the expected microwave heating time, and even the longest heating time of 30 minutes of the microwave oven timer 3 can be selected, and it will not cause power consumption and overheating.

[0016] The present invention is effective for most foods (almost all foods have water), but is ineffective for pure fat and dry sugar. When heating pure fat and dry sugar, only the traditional heating method can be used.

[0017] The left input terminal, right input terminal, upper input terminal and lower input terminal in the present invention are named for the convenience of analyzing the principle, wherein the upper, lower, left and right do not have absolute meanings, and descriptions using one input terminal and another input terminal are also acceptable, and any of the three module circuits (delay circuit 5, microwave oven circuit 6, steam detection circuit 7) can independently swap its two power input terminals.

[0018] The specific structure and working principle of the time-delay circuit 5:

[0019] exist Figure 3 In the circuit, the power transformer B steps down the 220V AC mains to 9V, and sends it to the bridge rectifier composed of diodes D1, D2, D3, and D4 to become pulsating DC power, which then passes through filter capacitors C3, C4, C5, and C6, three-terminal voltage regulator IC1, and boost diode D5 to become smooth 5.7V DC power. This DC power supply is the working power supply of the delay circuit 5. The second and sixth pins of the 555 time base integrated circuit IC are connected together to the timing capacitor C1, the timing potentiometer W1, and the discharge diode D7. The fourth and eighth pins of the 555 time base integrated circuit IC are connected together to the positive electrode of the 5.7V DC power supply, and one of the pins is grounded. The fifth pin is connected to capacitor C2, and the three pins of the output end are connected to the base of transistor T through protection resistor R2. The emitter of transistor T is grounded, and the collector is connected to the electromagnetic coil J of the relay. The electromagnetic coil J of the relay automatically controls the state of the delay switch 1 through electromagnetic force. The protection diode D6 protects the transistor T from being broken down by the reverse electromotive force of the relay electromagnetic coil J. If the relay J does not require a large driving current, the transistor T and the resistor R2 can be omitted. In this case, the relay electromagnetic coil J together with the protection diode D6 should be connected between the output terminal 3 and the ground (the positive pole of the diode D6 is grounded at this time).

[0020] Working principle of time-delay circuit 5: When the power is just turned on, the voltage on the timing capacitor C1 cannot suddenly change, so that the potential of the 2nd and 6th pins of the 555 timing integrated circuit IC is high, and there is no output voltage at the output terminal 3, so that the transistor T is cut off, and there is no current in the relay electromagnetic coil J, and the contact switch of the relay, that is, the time-delay switch 1, is in Figure 3 The reset state shown. However, when the preset delay time (for example, 3 minutes) is reached, the voltage on the timing capacitor C1 increases, causing the potential of the 2nd and 6th pins of the 555 time base integrated circuit IC to drop below 1 / 3 of the 5.7V DC power supply, and the output terminal pin 3 outputs a high voltage, causing the transistor T to be turned on, and there is current in the relay electromagnetic coil J, and the relay electromagnet is attracted to make the delay switch 1 in the state of the center point connected to the left contact (the dot-dash line in the figure indicates the mechanical connection between the two). This disconnects the power supply channel of the microwave oven circuit 6, the microwave oven stops heating, and at the same time connects the power supply channel of the delay circuit 5, and maintains this state until the microwave oven timer 3 is disconnected.

[0021] The parameters of each component are as follows: the resistance of the timing potentiometer W1 is 1 megohm, and the resistance of the resistor R2 is 3K. The capacitance values ​​of capacitors C1, C2, C3, C4, C5, and C6 are 1000, 0.01, 470, 0.1, 470, and 0.1 microfarads respectively. Diodes D1, D2, D3, D4, D5, D6, and D7 are all 1N4007, among which D5, D6, and D7 can also use switching diodes 1N4148. Transistor T can use C9013. Three-terminal regulator IC1 can use 7805. The rated working voltage of the electromagnetic coil J of relay J is 5-6V, and the rated current of its contact switch must be not less than 10A. The power transformer B can use an output voltage of 9V and a rated power of about 2W.

[0022] According to the above parameter settings, the longest delay of the delay circuit 5 is 16.67 minutes, and the potentiometer W1 should be turned to the maximum resistance of 1 megohm. The delay time scale can be marked on the knob of the timing potentiometer W1 (which can be calibrated through experiments) to facilitate the selection of the delay time.

[0023] Figure 3 The arrows in the figure indicate the connection Figure 1 The corresponding parts in the figure, and the directions of the arrows are Figure 1 It matches.

[0024] The specific structure and working principle of the steam detection circuit 7 are as follows.

[0025] exist Figure 2 In the case of a voltage regulator 8 and Figure 3 The same as in the above, no further description is given. IC3 is a 555 integrated circuit. The 1.0 pin of IC3 (also known as the 1 pin or Figure 3The pin in the circuit is connected to the ground (this is to distinguish different circuits, and the subsequent pins are named similarly). The 5.0 pin of the integrated circuit IC3 is grounded through the capacitor C8. The 4.0 pin, 8.0 pin of the integrated circuit IC3, the upper ends of the potentiometers W2 and W3, the cathode of the diode D7, and the upper end of the relay (coil) J2 are connected and then connected to the +5.7V end of the voltage regulator 8. The 3.0 pin of the integrated circuit IC3 is connected to the base of the transistor T2 through the resistor R3. The emitter of the transistor T2, the cathode of the capacitor C7, and the lower end of the humidity sensor RS are all grounded. The collector of the transistor T2 is connected to the anode of the diode D7 and the lower end of the relay J2. The 2.0 pin of the integrated circuit IC3 is connected to the upper end of the humidity sensor RS and the lower end of the potentiometer W2. The 6.0 pin of the integrated circuit IC3 is connected to the 7.0 pin and then connected to the anode of the capacitor C7 and the lower end of the potentiometer W3. The humidity switch 2 is the contact switch on the relay J2.

[0026] Figure 2 The arrows in the figure indicate the connection Figure 1 The corresponding parts in the figure, and the directions of the arrows are Figure 1 It matches.

[0027] When the temperature in the food reaches 100 degrees, a large amount of water vapor will blow onto the humidity sensor RS located at the moisture outlet of the microwave oven. This significantly reduces the resistance of the humidity sensor RS. When the voltage on it is less than 1 / 3 of the power supply voltage, the output terminal 3.0 of the integrated circuit IC3 outputs a high level, driving the transistor T2 to conduct, thereby energizing the relay J2 and closing it, causing the center point of the humidity switch 2 to connect to the left contact, thus connecting the Figure 1 The working power supply of the delay cut-off circuit 5 is shown. In the above process, since the delay cut-off switch 1 is still connected to the microwave oven circuit 6, the water vapor continues to be discharged, so that the humidity sensor RS continues to maintain a low resistance, and the voltage on it is less than 1 / 3 of the power supply voltage. The output terminal 3.0 of the integrated circuit IC3 continues to output a high level, and the center point of the humidity switch 2 continues to be connected to the left position. Figure 1 When the delay circuit 5 shown in the figure reaches the set disconnection time, the center point of the delay switch 1 is connected to the left contact, which disconnects the power supply path of the microwave oven circuit 6 on the one hand, and provides another power supply line for the delay circuit 5 on the other hand (equivalent to supplying power to the humidity switch 2 in parallel). Since the power supply path of the microwave oven circuit 6 is disconnected at this time, the water vapor decreases sharply, causing the resistance value of the humidity sensor RS to increase, and the voltage on it also increases. When it increases to 1 / 3 voltage or above, the 3.0 pin outputs a low level, causing the humidity switch 2 to reset to Figure 2 or Figure 3 The state shown (the premise is that the voltage on capacitor C7 or 6.0 pin is greater than 2 / 3 of the power supply voltage). Obviously, the time constant of the transient process to be selected, 1.1W3C7, will not affect Figure 1In the working process, steam is always generated when the center point of the time-delay switch 1 is still connected to the right contact, so the center point of the humidity switch 2 is kept connected to the left position to supply power to the time-delay circuit 5; when the center point of the time-delay switch 1 is connected to the left contact, the power supply path of the microwave oven circuit 6 is disconnected and no water vapor is generated, which quickly causes the center point of the humidity switch 2 to connect to the right contact (the premise is that the time constant 1.1W3C7 is selected to be small, if it is selected to be large, it is slow), but the power supply of the time-delay circuit 5 is not disconnected, so the center point of the time-delay switch 1 has been connected to the left contact in advance (that is, the aforementioned is equivalent to being connected in parallel with the humidity switch 2 to supply power to it), so the time-delay circuit 5 continues to maintain the disconnected state of the microwave oven circuit 6 until the microwave oven timer 3 is disconnected and reset.

[0028] Figure 2 Most of the parameters of the components in Figure 3 The same as in the above are not described again. Only the differences are described: Potentiometers W2 and W3 can be selected to be about 2 megohms. Capacitor C7 can be 220 microfarads. Humidity sensor RS can be a resistive humidity sensor. Potentiometer W2 should be adjusted so that when water vapor is sprayed onto humidity sensor RS, humidity switch 2 can be activated (i.e. its center point is switched to the left contact). Potentiometer W3 should be adjusted so that the transient time is shorter, which can more or less reduce the power consumption.

[0029] The circuit structure of the microwave oven circuit 6 used in the present invention is the one in the prior art, that is, it can be a mechanically controlled microwave oven circuit or a microcomputer controlled microwave oven circuit, which will not be described again. The time-delay circuit 5 and the steam detection circuit 7 should be installed in the microwave oven shell. The 220V plug 4 is the original working power plug of the microwave oven, and the microwave oven timer 3 is also the original mechanical or electronic timer of the microwave oven. The humidity sensor RS should be installed in the moisture discharge hole channel area between the inner cavity and the outer shell of the microwave oven, and cannot be installed inside the inner cavity, otherwise the high-power microwave will burn the humidity sensor RS. It is best to install it on the inner side of the outer shell, and then cover it with a metal mesh with an aperture of less than 0.7 mm and ground it to further shield the microwave that may leak.

[0030] The present invention can be modified in many ways. For example, the time-delay circuit 5 and the steam detection circuit 7 can be configured in other circuit structures. However, these modifications do not deviate from the essence of the present invention.

Claims

1. A microwave oven that automatically stops heating when rice is cooked, comprising a microwave oven housing, an upper plug of a 220V plug (4) connected to the left end of a microwave oven timer (3), a middle plug of the 220V plug (4) connected to the lower power input end of a microwave oven circuit (6), and a ground plug of the 220V plug (4) connected to the microwave oven housing, wherein the microwave oven A time-delay switch (1) is also connected in series between the timer (3) and the upper power input terminal of the microwave oven circuit (6). The right power input terminal of the time-delay switch (5) is connected to the left contact of the time-delay switch (1) and the left contact of the humidity switch (2). The left power input terminal of the time-delay switch (5) is connected to the lower power input terminal of the microwave oven circuit (6). The left power input terminal of the steam detection circuit (7) is connected to the connection line between the microwave oven timer (3) and the time-delay switch (1). The right power input terminal of the steam detection circuit (7) is connected to the lower power input terminal of the microwave oven circuit (6). The center point of the humidity switch (2) is connected to the center point of the time-delay switch (1) and then connected to the right end of the microwave oven timer (3). The humidity switch (2) is a relay automatic switch in the steam detection circuit (7). The time-delay switch (1) is a relay automatic switch in the time-delay switch circuit (5).

2. The microwave oven according to claim 1, wherein the microwave oven automatically stops heating when the rice is cooked. Delayed off A rice-cooked reminder (8) is connected in parallel between the right contact and the center point of the switch (1).

3. The microwave oven according to claim 1, wherein the microwave oven automatically stops heating when the rice is cooked. The time-delay circuit (5) is composed of a 555 circuit structure.

4. The microwave oven according to claim 1, wherein the microwave oven automatically stops heating when the rice is cooked. The humidity sensor in the steam detection circuit (7) is installed inside the moisture discharge hole of the microwave oven housing.

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