Indoor harmful gas detection circuit

Abstract

The utility model provides an indoor harmful gas detection circuit which has detection and prompt functions and can detect the concentration change degree of carbon monoxide, formaldehyde and methane in an indoor detected area. And when the collected signal exceeds the preset threshold limit, the concentration is obviously changed, so that the condition that the indoor air quality is relatively poor is prompted. The circuit comprises a detection circuit, a specification circuit, a processing comparison circuit and a prompt circuit, the output end of the detection circuit is connected with the first input end of the processing comparison circuit; the output end of the specification circuit is connected with the second input end of the processing comparison circuit; the output end of the processing comparison circuit is connected with the input end of the prompt circuit; and the prompt circuit receives and processes the signal of the comparison circuit and controls the LED lamp to flash and the buzzer to make a sound. The circuit adopts a chaos-like design to improve the measurement precision, reduces the dependence on a high-quality sensor, and effectively prevents potential health hazards through indoor air detection.

Description

Technical Field

[0001] This utility model relates to the field of detection circuits, and specifically provides an indoor harmful gas detection circuit. Background Technology

[0002] Carbon monoxide, formaldehyde, and methane are common indoor gases harmful to human health. These gases originate from various sources: incomplete combustion of fuels produces carbon monoxide, such as from improper use of gas water heaters or gas stoves; the combustion of tobacco during smoking can also lead to increased indoor carbon monoxide and formaldehyde concentrations; furthermore, formaldehyde-containing chemicals may be added during the production of indoor decoration materials, furniture, and household goods, and these items continue to release formaldehyde after use; and indoor gas leaks are a major cause of increased methane concentrations. Prolonged exposure to indoor environments with high concentrations of these gases can make vulnerable groups, such as children and the elderly, more susceptible to various diseases. It is worth noting that these three gases are usually colorless and odorless, and the indoor air pollution they cause is often insidious and persistent. Some pollutants may not show immediate and obvious effects on human health after short-term exposure; however, long-term exposure can lead to serious health problems. Although there are many types of air quality monitoring devices on the market, their data interpretation can be complex, and most gas-sensitive resistors require high temperatures to maintain their measurement accuracy. Therefore, it is particularly urgent and necessary to design a circuit device that can operate stably under low temperature requirements, has good responsiveness, and provides intuitive and easy-to-understand test result prompts.

[0003] Considering that conventional gas-sensitive resistors typically require high operating temperatures to ensure accuracy, and that such monitoring instruments are expensive, a mixed-signal circuit was designed to address the basic needs of indoor users for healthy air. This circuit eliminates the need for expensive monitoring instruments and high-precision sensors. The core of this circuit lies in the design of a quasi-chaotic circuit. By leveraging the high sensitivity of chaotic circuits, overall measurement accuracy is improved, significantly reducing reliance on high-quality sensors. Through indoor air quality monitoring, potential hazards can be detected and addressed promptly, effectively preventing long-term negative impacts on human health. Summary of the Invention

[0004] This invention addresses the aforementioned problems by providing an indoor hazardous gas detection circuit. The circuit includes a detection circuit, a standardization circuit, a processing and comparison circuit, and an alert circuit. This indoor hazardous gas detection circuit has the ability to flexibly select one or more detection targets, including carbon monoxide, formaldehyde, and methane. When the concentration of one or more selected gases in the indoor detection area exceeds a preset threshold indicating a significant change in concentration, the circuit triggers an LED to flash and activates a buzzer to sound an alarm, providing timely health risk alerts.

[0005] To achieve the above objectives, this utility model provides the following technical solution:

[0006] An indoor hazardous gas detection circuit includes:

[0007] The detection circuit (1) is connected to the first input terminal of the processing comparison circuit (3). After selecting the detection object, the control switch of the detection circuit (1) is adjusted to face the detection object. It can be used to collect changes in the concentration of carbon monoxide, formaldehyde and methane in indoor air, and transmit the collected change signal to the processing comparison circuit (3) for processing to achieve the function of signal acquisition.

[0008] The standard circuit (2) is connected to the second input terminal of the processing comparison circuit (3); after selecting the detection object, the standard resistor is adjusted to the standard resistance value corresponding to different detection conditions to ensure that the standard part circuit can play its role as a reference for the standard comparison value;

[0009] The comparison circuit (3) is configured such that its two input terminals are connected to the output terminals of the detection circuit (1) and the calibration circuit (2), respectively, and the output terminal of the comparison circuit (3) is connected to the input terminal of the prompting circuit (4). It can process and compare the signals generated by the detection circuit (1) and the calibration circuit (2), determine whether the degree of asynchrony between them exceeds a preset threshold, and output a high level to the prompting circuit (4) when the voltage after comparison processing is higher than the set threshold.

[0010] The prompting circuit (4) has its input terminal connected to the output terminal of the processing comparison circuit (3). It is used to collect the high-level signal output by the processing comparison circuit (3) and perform statistics in each cycle. When the statistical value in a certain cycle reaches the set value, it outputs a high level to control the LED light in the prompting circuit (4) to flash and the buzzer to make a sound, so as to achieve the reminder function.

[0011] The detection circuit (1) includes: a sampling module (101) consisting of a 555 timer chip U1, an MQ-7 gas-sensitive resistor R1, MQ-135 gas-sensitive resistors R2 and R3, control switches S1, S2 and S3, a resistor R9, a small DC power supply VCC2 and capacitors C1 and C2; and an adjustment module (102) consisting of inductors L1 and L2, resistors R5, R6, R7 and R8, operational amplifiers U3 and U4, a small DC power supply VCC1 and a small DC negative power supply VEE.

[0012] Furthermore, in the sampling module (101), the 555 time base chip U1, capacitors C1 and C2 and resistor R9 form the basic part of the 555 time base chip circuit; the MQ-7 gas-sensitive resistor R1 and the MQ-135 gas-sensitive resistors R2 and R3 are connected in series, and their connection is controlled by the control switches S1, S2 and S3 respectively. One end of them is connected to the 555 time base chip U1, and the other end is connected to the inductors L1 and L2 of the adjustment module (102) and the first input terminal of the processing comparison circuit (3); one end of the capacitor C1 is connected to the 555 time base chip U1, and the other end is connected to the resistor R6 of the adjustment module (102). Its function is to select the target sampling object and detect the voltage signal change caused by the concentration change of the object.

[0013] Furthermore, in the adjustment module (102), one end of inductor L2 is connected to the MQ-135 gas-sensitive resistor R3 and the positive input terminal of operational amplifier U3 of sampling module (101), and the other end of inductor L2 is connected to the output terminal of operational amplifier U3, resistor R5 and resistor R7; resistor R5 is connected to the inverting input terminal of operational amplifier U3 and resistor R6; resistor R7 is connected to the inverting input terminal of operational amplifier U4 and resistor R8; resistor R8 is connected to the output terminal of operational amplifier U4 and inductor L1; inductor L1 is connected to the positive input terminal of operational amplifier U4 and inductor L2, which plays a role in adjusting the sensitivity of the acquired signal to changes.

[0014] The positive power supply terminals of operational amplifiers U3 and U4 are connected to a small DC power supply VCC1; the negative power supply terminals of operational amplifiers U3 and U4 are connected to a small DC negative power supply VEE.

[0015] Furthermore, the working principle of the detection circuit (1) is as follows: The detection circuit (1) consists of a sampling module (101) and an adjustment module (102), and it can be regarded as a chaotic circuit as a whole. In the sampling module (101), the 555 timer chip U1 generates the oscillation signal required by the chaotic circuit. The MQ-7 gas-sensitive resistor R1 and the MQ-135 gas-sensitive resistors R2 and R3 are the main measuring resistors. The control switches S1, S2, and S3 are used to determine whether the MQ-7 gas-sensitive resistor R1 and the MQ-135 gas-sensitive resistors R2 and R3 are connected to the circuit. The change in the resistance value of the gas-sensitive resistor connected to the circuit will cause the chaotic state corresponding to the chaotic circuit to change. By controlling the on and off of the control switches S1, S2, and S3, the measurement object facing this circuit can be selected, and the voltage signal of the gas-sensitive resistor connected to the circuit is transmitted to the first input terminal of the processing comparison circuit (3) for further processing. The adjustment module (102) constitutes an analog inductor system. This part consists of inductors L1 and L2, resistors R5, R6, R7, and R8, and operational amplifiers U3 and U4. The formula for calculating the inductance of the system is as follows:

[0016]

[0017] in To correspond to the overall inductance value of the analog inductor system, These correspond to the inductance values ​​of inductors L1 and L2. The corresponding resistor values ​​are R5, R6, R7, and R8. By adjusting the value of resistor R6, the overall inductance of this part can be adjusted to change the chaotic characteristics of the designed chaotic circuit and achieve different levels of measurement sensitivity.

[0018] The specification circuit (2) includes: a comparison specification module (201) consisting of a 555 timer chip U2, specification resistor R4, resistor R14, small DC power supply VCC2 and capacitors C3 and C4; and an adjustment specification module (202) consisting of inductors L3 and L4, resistors R10, R11, R12 and R13, operational amplifiers U4 and U5 and small DC power supply VCC1.

[0019] Furthermore, in the comparison specification module (201), the 555 time base chip U2, capacitors C3 and C4 and resistor R14 form the basic part of the 555 time base chip circuit; one end of the specification resistor R4 is connected to the 555 time base chip U2, and the other end is connected to the second input terminal of the adjustment specification module (202) and the processing comparison circuit (3); one end of the capacitor C3 is connected to the 555 time base chip U2, and the other end is connected to the resistor R11 of the adjustment specification module (202), which serves to provide a standardized comparison reference.

[0020] Furthermore, in the adjustment specification module (202), one end of inductor L3 is connected to the specification resistor R4 of the comparison specification module (201) and the positive input terminal of operational amplifier U3, and the other end is connected to the output terminal of operational amplifier U5, one end of resistor R10 and one end of resistor R12; resistor R10 is connected to the inverting input terminal of operational amplifier U5 and resistor R11; resistor R12 is connected to the inverting input terminal of operational amplifier U6 and resistor R13; resistor R13 is connected to the output terminal of operational amplifier U6 and inductor L4; inductor L4 is connected to the positive input terminal of operational amplifier U6 and inductor L3, further ensuring the reference value of the comparison specification module (201).

[0021] The positive power supply terminals of operational amplifiers U5 and U6 are connected to a small DC power supply VCC1; the negative power supply terminals of operational amplifiers U5 and U6 are connected to a small DC negative power supply VEE.

[0022] Furthermore, the working principle of the standardization circuit (2) is as follows: The detection circuit (2) is composed of a standardization module (201) and an adjustment standardization module (202), and it can also be regarded as a chaotic circuit as a whole. In the standardization module (201), the 555 timer chip U2 generates the oscillation signal required by the chaotic circuit, and adjusts the corresponding standardization resistor R4 to the corresponding standardization resistor value in different measurement modes. At the same time, during the measurement process, the gas-sensitive resistor in the detection circuit (1) will change its resistance value due to the change in gas concentration. This change will cause the voltage signal on the gas-sensitive resistor to be different from the voltage signal on the standardization resistor in the standardization circuit (2). The voltage signals of the two are transmitted to the processing comparison circuit (3) for further analysis and processing. The adjustment standardization module (202) of the detection circuit (1) constitutes an analog inductor system. This part is composed of inductors L3 and L4, resistors R10, R11, R12, R13 and operational amplifiers U5 and U6. The formula for calculating the size of the inductor is as follows:

[0023]

[0024] in To correspond to the overall inductance value of the analog inductor system, These correspond to the inductance values ​​of inductors L3 and L4. The corresponding resistance values ​​are R10, R11, R12, and R13. The resistance value of R11 should match the adjusted resistance value of R6 in the acquisition circuit to ensure that the standard circuit (2) can meet the established standard.

[0025] The processing comparison circuit (3) includes: a processing module (301) consisting of resistors R15, R16, R17, R18, R19, R20, R21, R22, R23, operational amplifiers U7, U8, U9, diode D1, small DC power supply VCC1 and small DC negative power supply VEE; and a comparison module (302) consisting of comparator U10, adjusting resistor R21 and small DC power supply VCC3.

[0026] Furthermore, in the processing module (301), one end of resistor R15 is connected to the output of the detection circuit (1) as the first input of the processing comparison circuit (3); one end of resistor R16 is connected to the output of the standard circuit (2) as the second input of the processing comparison circuit (3); resistors R15, R16, R17, and R18 together with operational amplifier U7 form the difference acquisition part; resistors R19, R20, diode D1 and operational amplifier U8 are connected to take the negative of the absolute value of the voltage processed in the preliminary stage; resistors R21 and R22 are connected to operational amplifier U9 to perform inversion processing; resistor R22 is connected to the output of operational amplifier U9 and the comparison module (302) to transmit the processed signal to the comparison module (302).

[0027] Furthermore, in the comparison module (302), one end of resistor R22 in the processing module (301) is connected to the non-inverting input terminal of comparator U10; the upper terminal of adjusting resistor R23 is grounded, the lower terminal of adjusting resistor R23 is connected to small DC power supply VCC3, and the sliding terminal of adjusting resistor R23 is connected to the inverting input terminal of comparator U10, which serves to compare the processed signal with the set voltage; the output terminal of comparator U10 is connected to the input terminal of prompting circuit (4), and the compared signal is transmitted to prompting circuit (4).

[0028] Among them, the positive power supply terminals of operational amplifiers U7, U8, U9 and comparator U10 are connected to a small DC power supply VCC1; the negative power supply terminals of operational amplifiers U7, U8, U9 are connected to a small DC negative power supply VEE.

[0029] Furthermore, the working principle of the processing comparison circuit (3) is as follows: the voltage difference output by the two comparison circuits is obtained by the operational amplifier U7 in the processing module (301), and then the opposite of the absolute value of the difference is obtained by the operational amplifier U8. Finally, the absolute value of the voltage difference output by the two comparison circuits is obtained by the operational amplifier U9. This absolute value is input to the comparator U10 and compared with a preset voltage threshold that can be considered as having a large degree of asynchrony. This voltage threshold can be adjusted by adjusting the resistor R23 to change the measurement sensitivity. If the degree of asynchrony between the two acquisition circuits is greater than the set value, a high level is output and transmitted to the prompting circuit (4).

[0030] The prompting circuit (4) includes: a display processing module (401) consisting of digital tubes U11 and U12, 74LS chips U13 and U14, 74160 chips U15 and U16, dual-input AND gate U17, dual-input NAND gate U18, small DC power supply VCC4 and periodic pulse signal source XFG1; and a processing warning module (402) consisting of dual-input AND gates U19, U20, U21, U27, U28, U29, U30, single-input NOT gates U22, U23, U24, U25, U26, warning light X1, and alarm LS1.

[0031] Furthermore, in the display processing module (401), the six pins A, B, C, D, E, F, and G of the digital tube U11 are respectively connected to the six pins OA, OB, OC, OD, OE, and OG of the 74LS chip U13; the six pins A, B, C, D, E, F, and G of the digital tube U12 are respectively connected to the six pins OA, OB, OC, OD, OE, and OG of the 74LS chip U14; the digital tubes U11 and U12 are used to display the number of times the acquired signals, which can be considered asynchronous, occur within a fixed period. The four pins A, B, C, and D of the 74LS chip U13 are connected to the corresponding four pins QA, QB, QC, and QD of the 74160 chip U17, respectively; the four pins A, B, C, and D of the 74LS chip U14 are connected to the corresponding four pins QA, QB, QC, and QD of the 74160 chip U15, respectively. The 74LS chips U13 and U14 process and transmit the acquired signals from the 74160 chips U15 and U16 to the digital tubes U11 and U12 for display. The 74LS chips U13 and U14 are used to expand the counting digits, improving the system's stability and reliability. The input terminal CLK of the 74160 chips U15 and U16 is connected to the output terminal of the processing and comparison circuit to receive and count the number of signals output by the processing and comparison circuit.

[0032] Furthermore, in the processing warning module (402), the dual-input AND gate U20 and the single-input NOT gates U22 and U23 are connected to the 74160 chip U15, and the dual-input AND gate U28 and the single-input NOT gates U24, U25, and U26 are connected to the 74160 chip U16 to collect the warning signal; the signals transmitted by them are transmitted to the dual-input AND gates U19, U21, U27, U28, U29, and U30 for further warning signal processing. When the collection conditions are met, a high level is output to the warning light X1 and the alarm LS1. The warning light X1 and the alarm LS1 receive the warning signal and light up and sound to remind the user.

[0033] Further, the working principle of the prompting circuit (4) is as follows: the input terminal CLK of the 74160 chips U15 and U16 is connected to the output terminal of the processing comparison circuit, the signal count output by the processing comparison circuit is received and counted, and the signal is transmitted to the 74LS chips U13 and U14. The 74LS chips U13 and U14 expand the counting result of the 74160 chips U15 and U16 to improve the stability and reliability of the system. The dual-input AND gate U17 and the dual-input NAND gate U18 are connected to the 74160 chips U15 and U16 to ensure that the counting process is decimal. The counting result of the 74160 chips U15 and U16 is passed through the dual-input AND gates U19, U20, U21, U27, U28, U29, U30 and the single-input NOT gates U22, U23, U24, U25, U26. When the output is high, the warning light X1 lights up and the alarm LS1 sounds.

[0034] The beneficial effects of this utility model are as follows:

[0035] This invention, taking into account the basic needs of indoor users for healthy air, designs an indoor harmful gas detection circuit that can flexibly select one or more detection targets, including carbon monoxide, formaldehyde, and methane. It detects changes in the concentration of these three gases in corresponding indoor areas, and when the changes exceed a certain concentration, it provides an alert indicating poor indoor air quality.

[0036] The core of this circuit lies in the design of a chaotic circuit-like circuit. By utilizing the high sensitivity of chaotic circuits, the overall measurement accuracy is improved, thereby greatly reducing the dependence on high-quality sensors. Through indoor air detection, these potential hazards can be detected and dealt with in a timely manner, effectively preventing the long-term negative impact of these hazards on human health. Attached Figure Description

[0037] Figure 1 This utility model provides a circuit diagram for detecting indoor harmful gases.

[0038] Figure 2 This utility model provides a schematic diagram of an indoor harmful gas detection circuit;

[0039] Figure 3 This is a schematic diagram of the detection circuit for an indoor harmful gas detection circuit provided by this utility model;

[0040] Figure 4 This is a standard circuit diagram of an indoor harmful gas detection circuit provided by this utility model;

[0041] Figure 5 This is a schematic diagram of the processing and comparison circuit of an indoor harmful gas detection circuit provided by this utility model;

[0042] Figure 6 This utility model provides a schematic diagram of the prompting circuit for an indoor harmful gas detection circuit. Detailed Implementation Plan

[0043] To more clearly describe the technical solution, advantages, and working principle of this utility model, the following will provide a more complete and clear description of this utility model in conjunction with the accompanying drawings.

[0044] like Figure 1 As shown, an indoor harmful gas detection circuit includes:

[0045] The detection circuit (1) is connected to the first input terminal of the processing comparison circuit (3). After selecting the detection object, the control switch of the detection circuit (1) is adjusted to face the detection object. It can be used to collect changes in the concentration of carbon monoxide, formaldehyde and methane in the air, and transmit the collected change signals to the processing comparison circuit (3) for processing, so as to achieve the function of corresponding signal acquisition.

[0046] The standardization circuit (2) is connected to the second input terminal of the processing comparison circuit (3). After selecting the detection object, the standardization resistor is adjusted to the standardization resistance value corresponding to different detection conditions to ensure that the standardization circuit can play its role as a reference for the standardization comparison value.

[0047] A processing comparison circuit (3) is included, wherein the two input terminals of the processing comparison circuit (3) are connected to the two output terminals of the detection circuit (1) and the standardization circuit (2), and the output terminal of the processing comparison circuit (3) is connected to the input terminal of the prompting circuit (4). This is used to process the acquired signals.

[0048] The prompting circuit (4) is connected to the output of the processing comparison circuit (3). It collects the high-level signal output by the processing comparison circuit (3) and performs statistical analysis in each cycle. When the statistical value in a certain cycle reaches a set value, it outputs a high level to control the LED in the prompting circuit (4) to flash and the buzzer to sound, thus achieving an alarm function.

[0049] like Figure 2As shown, an indoor harmful gas detection circuit includes: a detection circuit (1), a standardization circuit (2), a processing and comparison circuit (3), and a prompting circuit (4). The output terminal of the detection circuit (1) is connected to the first input terminal of the processing and comparison circuit (3), and the output terminal of the standardization circuit (2) is connected to the second input terminal of the processing and comparison circuit (3). The processing and comparison circuit (3) processes the output electrical signals of the detection circuit (1) and the standardization circuit (2). The output terminal of the processing and comparison circuit (3) is connected to the input terminal of the prompting circuit (4), transmitting the processed signal to the prompting circuit (4). The prompting circuit (4) receives the signal from the processing and comparison circuit (3) and performs periodic statistics. When the statistics reach a set value, it outputs a control LED light to flash and a buzzer to sound as a reminder.

[0050] like Figure 3 As shown, the detection circuit (1) includes: a sampling module (101) consisting of a 555 timer chip U1, an MQ-7 gas-sensitive resistor R1, MQ-135 gas-sensitive resistors R2 and R3, control switches S1, S2 and S3, a resistor R9, a small DC power supply VCC2 and capacitors C1 and C2; and an adjustment module (102) consisting of inductors L1 and L2, resistors R5, R6, R7 and R8, operational amplifiers U3 and U4, a small DC power supply VCC1 and a small DC negative power supply VEE.

[0051] Furthermore, the working principle of the detection circuit (1) is as follows: The detection circuit (1) consists of a sampling module (101) and an adjustment module (102), and it can be regarded as a chaotic circuit as a whole. In the sampling module (101), the 555 timer chip U1 generates the oscillation signal required by the chaotic circuit. The MQ-7 gas-sensitive resistor R1 and the MQ-135 gas-sensitive resistors R2 and R3 are the main measuring resistors. The control switches S1, S2, and S3 are used to control whether the MQ-7 gas-sensitive resistor R1 and the MQ-135 gas-sensitive resistors R2 and R3 are connected to the circuit, respectively. The change in the resistance value of the gas-sensitive resistor connected to the circuit will cause the chaotic state corresponding to the chaotic circuit to change. The voltage of the gas-sensitive resistor connected to the circuit is transmitted to the input terminal of the processing comparison circuit (3) for further processing. The MQ-7 gas-sensitive resistor R1 is used to detect the concentration of carbon monoxide because it has high sensitivity and selectivity to carbon monoxide gas. Although the MQ-135 gas sensor is a multifunctional gas sensor capable of detecting various gases, including methane and formaldehyde, its sensitivity and accuracy may vary depending on the gas being detected, and its response range may also differ depending on the object being detected. Therefore, two MQ-135 gas sensors are used to distinguish different response ranges for formaldehyde and methane. The adjustment module (102) constitutes an analog inductor system, consisting of inductors L1 and L2, resistors R5, R6, R7, and R8, and operational amplifiers U3 and U4. The formula for calculating the inductance is as follows:

[0052]

[0053] in To correspond to the overall inductance value of the analog inductor system, These correspond to the inductance values ​​of inductors L1 and L2. The corresponding resistor values ​​are R5, R6, R7, and R8. By adjusting the value of resistor R6, the overall inductance of this part can be adjusted to change the chaotic characteristics of the designed chaotic circuit and achieve different levels of measurement sensitivity.

[0054] Furthermore, such as Figure 3In the sampling module (101) shown, the VCC port of the 555 timer chip U1 is connected to the small DC power supply VCC2, and the RST NOT port of the 555 timer chip U1 is also connected to the small DC power supply VCC2. The left port of the MQ-7 gas-sensitive resistor R1 is connected to the OUT port of the 555 timer chip U1, and the right port of the MQ-7 gas-sensitive resistor R1 is connected to the left port of the MQ-135 gas-sensitive resistor R2. Control switch S1 is connected in parallel with the MQ-7 gas-sensitive resistor R1 to control whether the MQ-7 gas-sensitive resistor R1 is connected to the circuit. The right port of the MQ-135 gas-sensitive resistor R2 is connected to the left port of the MQ-135 gas-sensitive resistor R3. Control switch S2 is connected in parallel with the MQ-135 gas-sensitive resistor R2 to control whether the MQ-135 gas-sensitive resistor R2 is connected to the circuit. The circuit is connected to the right port of the MQ-135 gas-sensitive resistor R3 and the left port of the inductor L2 of the adjustment module (102). The control switch S3 is connected in parallel with the MQ-135 gas-sensitive resistor R3 to control whether the MQ-135 gas-sensitive resistor R3 is connected to the circuit. The output of the circuit is connected to the first input of the processing comparison circuit (3). The lower port of the resistor R9 is connected to the DIS port of the 555 timer chip U1 and the upper port of the resistor R9 is connected to the small DC power supply VCC2. The upper port of the capacitor C1 is connected to the THR and TRI NOT ports of the 555 timer chip U1 and the resistor R6 of the adjustment module (102). The lower port of the capacitor C1 is grounded. The upper port of the capacitor C2 is connected to the CON port of the 555 timer chip U1 and the lower port of the capacitor C2 is grounded.

[0055] Furthermore, such as Figure 3 In the adjustment module (102) shown, the left port of inductor L2 is connected to the right port of MQ-135 gas-sensitive resistor R3, the positive input terminal of operational amplifier U3, and the left port of inductor L1; the right port of inductor L2 is connected to the output terminal of operational amplifier U3, the right port of resistor R5, and the left port of resistor R7; the right port of resistor R5 is connected to the output terminal of operational amplifier U3, the left port of resistor R7, and the right port of inductor L2; the left port of resistor R5 is connected to the inverting input terminal of operational amplifier U3 and the right port of resistor R6; the left port of resistor R7... The left port is connected to the right port of inductor L2, the output of operational amplifier U3, and the right port of resistor R5. The right port of resistor R7 is connected to the inverting input of operational amplifier U4 and the left port of resistor R8. The right port of resistor R8 is connected to the output of operational amplifier U4 and the right port of inductor L1. The left port of inductor L1 is connected to the non-inverting input of operational amplifier U4, the left port of inductor L2, and the right port of MQ-135 gas-sensitive resistor R3. The right port of inductor L1 is connected to the output of operational amplifier U4 and the right port of resistor R8.

[0056] The positive power supply terminals of operational amplifiers U3 and U4 are connected to a small DC power supply VCC1; the negative power supply terminals of operational amplifiers U3 and U4 are connected to a small DC negative power supply VEE.

[0057] like Figure 4 As shown, the specification circuit (2) includes: a comparison specification module (201) consisting of a 555 timer chip U2, specification resistor R4, resistor R14, small DC power supply VCC2 and capacitors C3 and C4; and an adjustment specification module (202) consisting of inductors L3 and L4, resistors R10, R11, R12 and R13, operational amplifiers U4 and U5 and small DC power supply VCC1.

[0058] Furthermore, the working principle of the standardization circuit (2) is as follows: The detection circuit (2) is composed of a standardization module (201) and an adjustment standardization module (202), which can also be regarded as a chaotic circuit as a whole. In the standardization module (201), the 555 timer chip U2 generates the oscillation signal required by the chaotic circuit, and adjusts the corresponding standardization resistor R4 to the corresponding standardization resistor value in different measurement modes. At the same time, during the measurement process, the gas-sensitive resistor in the detection circuit (1) will change its resistance value due to the change in gas concentration. This change will cause the voltage signal on the gas-sensitive resistor to be different from the voltage signal on the standardization resistor in the standardization circuit (2). The voltage signals of the two are transmitted to the processing comparison circuit (3) for further analysis and processing. The adjustment standardization module (202) of the detection circuit (1) constitutes an analog inductor system. This part is composed of inductors L3 and L4, resistors R10, R11, R12, R13 and operational amplifiers U5 and U6. The formula for calculating the size of the inductor is as follows:

[0059]

[0060] in To correspond to the overall inductance value of the analog inductor system, These correspond to the inductance values ​​of inductors L3 and L4. The corresponding resistance values ​​are R10, R11, R12, and R13. The resistance value of R11 should match the adjusted resistance value of R6 in the acquisition circuit to ensure that the standard circuit (2) can meet the established standard.

[0061] Furthermore, such as Figure 4In the specification module (201) shown, the VCC port of the 555 timer chip U2 is connected to the small DC power supply VCC2, and the RST NOT port of the 555 timer chip U2 is connected to the small DC power supply VCC2; the left port of the specification resistor R4 is connected to the OUT port of the 555 timer chip U2, and the right port of the specification resistor R4 is connected to the left port of the inductor L3 of the adjustment specification module (202) and the second input terminal of the processing comparator circuit (3); the lower port of the resistor R14 is connected to the DIS port of the 555 timer chip U2, and the upper port of the resistor R14 is connected to the small DC power supply VCC2; the upper port of the capacitor C3 is connected to the THR and TRI NOT ports of the 555 timer chip U2 and the resistor R11 of the adjustment specification module (202), and the lower port of the capacitor C3 is grounded; the upper port of the capacitor C4 is connected to the CON port of the 555 timer chip U2, and the lower port of the capacitor C4 is grounded.

[0062] Furthermore, such as Figure 4 In the calibration module (202), the left port of inductor L3 is connected to the positive input terminal of operational amplifier U5, the left port of inductor L4, and the right port of calibration resistor R4 in the calibration module (201). The right port of inductor L3 is connected to the output terminal of operational amplifier U5, the right port of resistor R10, and the left port of resistor R12. The right port of resistor R10 is connected to the output terminal of operational amplifier U5, the left port of resistor R12, and the right port of inductor L3. The left port of resistor R10 is connected to the inverting input terminal of operational amplifier U5 and the right port of resistor R11. The left port of resistor R12 is connected to the positive input terminal of operational amplifier U5 and the right port of resistor R11. The left port is connected to the output of operational amplifier U5, the right port of resistor R10, and the right port of inductor L3. The right port of resistor R12 is connected to the inverting input of operational amplifier U6 and the left port of resistor R13. The left port of resistor R13 is connected to the right port of resistor R12 and the inverting input of operational amplifier U6. The right port of resistor R13 is connected to the output of operational amplifier U6 and the right port of inductor L4. The left port of inductor L4 is connected to the non-inverting input of operational amplifier U6, the left port of inductor L3, and the right port of the specification resistor R4 of the comparison specification module (201).

[0063] The positive power supply terminals of operational amplifiers U5 and U6 are connected to a small DC power supply VCC1; the negative power supply terminals of operational amplifiers U5 and U6 are connected to a small DC negative power supply VEE.

[0064] like Figure 5As shown, the processing comparator circuit (3) includes: a processing module (301) consisting of resistors R15, R16, R17, R18, R19, R20, R21, R22, R23, operational amplifiers U7, U8, U9, diode D1, small DC power supply VCC1 and small DC negative power supply VEE; and a comparator module (302) consisting of comparator U10, adjusting resistor R21 and small DC power supply VCC3.

[0065] Furthermore, the working principle of the processing comparison circuit (3) is as follows: the voltage difference output by the two comparison circuits is obtained by the operational amplifier U7 in the processing module (301), and then the opposite of the absolute value of the difference is obtained by the operational amplifier U8. Finally, the absolute value of the voltage difference output by the two comparison circuits is obtained by the operational amplifier U9. This absolute value is input to the comparator U10 and compared with a preset voltage threshold that can be considered as having a large degree of asynchrony. This voltage threshold can be adjusted by adjusting the resistor R23 to change the measurement sensitivity. If the degree of asynchrony between the two acquisition circuits is greater than the set value, a high level is output and transmitted to the prompting circuit (4).

[0066] Furthermore, such as Figure 5In the processing module (301) shown, the left port of resistor R15 is connected to the output of the detection circuit (1) as the first input of the processing comparator circuit (3); the right port of resistor R15 is connected to the inverting input of operational amplifier U7 and the left port of resistor R17; the left port of resistor R17 is connected to the inverting input of operational amplifier U7 and the right port of resistor R15, and the right port of resistor R17 is connected to the output of operational amplifier U7 and the left port of resistor R19; the left port of resistor R16 is connected to the output of the standard circuit (2) as the second input of the processing comparator circuit (3); the right port of resistor R16 is connected to the non-inverting input of operational amplifier U7 and the upper port of resistor R18; the upper port of resistor R18 is connected to the non-inverting input of operational amplifier U7 and the right port of resistor R16, and the lower port of resistor R18 is grounded; the left port of resistor R19 is connected to the right port of resistor R17 and the output of operational amplifier U7, and the left port of resistor R19 is connected to the right port of resistor R17 and the output of operational amplifier U7. The right port of R19 is connected to the inverting input of operational amplifier U8 and the left port of resistor R20; the non-inverting input of operational amplifier U8 is grounded; the left port of resistor R20 is connected to the inverting input of operational amplifier U8 and the right port of resistor R19, the right port of resistor R20 is connected to the anode of diode D1 and the left port of resistor R21; the anode of diode D1 is connected to the right port of resistor R20 and the left port of resistor R21, the cathode of diode D1 is connected to the output of operational amplifier U8; the left port of resistor R21 is connected to the anode of diode D1 and the right port of resistor R20, the right port of resistor R21 is connected to the inverting input of operational amplifier U9 and the left port of resistor R22; the non-inverting input of operational amplifier U9 is grounded; the left port of resistor R22 is connected to the right port of resistor R21 and the inverting input of operational amplifier U9, the right port of resistor R22 is connected to the output of operational amplifier U9 and the comparator module (302).

[0067] Furthermore, such as Figure 5 In the comparison module (302) shown, the right port of resistor R22 in the processing module (301) is connected to the non-inverting input of comparator U10; the upper terminal of adjusting resistor R23 is grounded; the lower terminal of adjusting resistor R23 is connected to the small DC power supply VCC3; the sliding terminal of adjusting resistor R23 is connected to the inverting input of comparator U10; and the output of comparator U10 is connected to the input of prompting circuit (4).

[0068] The positive power supply terminals of operational amplifiers U7, U8, U9 and comparator U10 are connected to a small DC power supply VCC1; the negative power supply terminals of operational amplifiers U7, U8, U9 are connected to a small DC negative power supply VEE.

[0069] like Figure 6As shown, the prompt circuit (4) includes: a display processing module (401) consisting of digital tubes U11 and U12, 74LS chips U13 and U14, 74160 chips U15 and U16, dual-input AND gate U17, dual-input NAND gate U18, small DC power supply VCC4 and periodic pulse signal source XFG1; and a processing warning module (402) consisting of dual-input AND gates U19, U20, U21, U27, U28, U29, U30, single-input NOT gates U22, U23, U24, U25, U26, warning light X1, and alarm LS1.

[0070] Furthermore, the working principle of the prompting circuit (4) is as follows: the input terminal CLK of the 74160 chips U15 and U16 is connected to the output terminal of the processing comparison circuit to receive and count the number of signals output by the circuit within each set time period. The signal is then transmitted to the 74LS chips U13 and U14. The 74LS chips U13 and U14 expand the counting result of the 74160 chips U15 and U16 to increase the number of counting bits, thereby improving the stability and reliability of the display. The 74LS chips U13 and U14 transmit the collected signals to the digital tubes U11 and U12. The digital tubes U11 and U12 are used to display the number of times the collected signals, which can be considered asynchronous, occur within a fixed period. The dual-input AND gate U17 and the dual-input NAND gate U18 process the collected digital signals to ensure that these signals can be accurately counted on the 74160 chips U15 and U16 after appropriate logical operations. The counting results from chips U15 and U16 of the 74160 series are processed through dual-input AND gates U19, U20, U21, U27, U28, U29, and U30 and single-input NOT gates U22, U23, U24, U25, and U26, forming the circuit for processing the alert signal. The threshold value is set to 15, but the specific threshold can be adjusted according to the gas detection sensitivity requirements in the actual application. When the output is high, the warning light X1 illuminates and the alarm LS1 sounds.

[0071] Furthermore, such as Figure 6In the display processing module (401) shown, pin A of the digital tube U11 is connected to pin OA of the 74LS chip U13, pin B of the digital tube U11 is connected to pin OB of the 74LS chip U13, pin C of the digital tube U11 is connected to pin OC of the 74LS chip U13, pin D of the digital tube U11 is connected to pin OD of the 74LS chip U13, pin E of the digital tube U11 is connected to pin OE of the 74LS chip U13, pin F of the digital tube U11 is connected to pin OF of the 74LS chip U13, and pin G of the digital tube U11 is connected to pin OG of the 74LS chip U13.The CA port of digital tube U11 is connected in series with the CA port of digital tube U12 and then connected to the small DC power supply VCC1; the LT NOT port, RBI NOT port, and BI NOT port of 74LS chip U13 are connected to the small DC power supply VCC1; the A pin of digital tube U12 is connected to the OA pin of 74LS chip U14, the B pin of digital tube U12 is connected to the OB pin of 74LS chip U14, the C pin of digital tube U12 is connected to the OC pin of 74LS chip U14, the D pin of digital tube U12 is connected to the OD pin of 74LS chip U13, the E pin of digital tube U12 is connected to the OE pin of 74LS chip U13, and the F pin of digital tube U12 is connected to the 74LS chip U13. The OF pin of U14 is connected to the 74LS chip U14; the G pin of the digital tube U12 is connected to the OG pin of the 74LS chip U14; the LT NOT port, RBI NOT port, and BI NOT port of the 74LS chip U14 are connected to the small DC power supply VCC1; the A pin of the 74LS chip U13 is connected to the QA pin of the 74160 chip U16; the B pin of the 74LS chip U13 is connected to the QB pin of the 74160 chip U16; the C pin of the 74LS chip U13 is connected to the QC pin of the 74160 chip U16; the D pin of the 74LS chip U13 is connected to the QD pin of the 74160 chip U16; the A pin of the 74LS chip U14 is connected to the QA pin of the 74160 chip U15. The B pin of the 74LS chip U14 is connected to the QB pin of the 74160 chip U15, the C pin of the 74LS chip U14 is connected to the QC pin of the 74160 chip U15, and the D pin of the 74LS chip U14 is connected to the QD pin of the 74160 chip U15. The CLK ports of the 74160 chip U15 and 74160 chip U16 are connected in series and then connected to the output of the processing comparator circuit. To ensure decimal representation, one input of the dual-input AND gate U17 is connected to the QD port of the 74160 chip U15, the other input is connected to the QA port of the 74160 chip U15, and the output of the dual-input AND gate U17 is connected to the 74160 chip U15. The ENP and ENT ports of the 4160 chip U16 are connected; one input port of the dual-input NAND gate U18 is connected to the QA port of the 74160 chip U15, and the other input port of the dual-input NAND gate U18 is connected to the QD port of the 74160 chip U15; the output of the dual-input NAND gate U18 is connected to the LOAD NOT port of the 74160 chip U15; the ENP and ENT ports of the 74160 chip U15 and the LOAD NOT port of the 74160 chip U16 are connected in series to a small DC power supply VCC1; the periodic pulse signal XFG1 is connected to the CLR NOT ports of the 74160 chip U15 and the CLR NOT ports of the 74160 chip U16 to perform periodic clearing.

[0072] Furthermore, such as Figure 6In the alarm processing module (402) shown, the input terminal of the single-input NOT gate U22 is connected to the QB of the 74160 chip U15, and the output terminal of the single-input NOT gate U22 is connected to one input terminal of the dual-input AND gate U21; the input terminal of the single-input NOT gate U23 is connected to the QD of the 74160 chip U15, and the output terminal of the single-input NOT gate U22 is connected to the other input terminal of the dual-input AND gate U21; the output terminal of the dual-input AND gate U21 is connected to one input terminal of the dual-input AND gate U19. One input of dual-input AND gate U20 is connected to the QA terminal of 74160 chip U15, and the other input is connected to the QC terminal of 74160 chip U15. The output of dual-input AND gate U20 is connected to the other input of dual-input AND gate U19. The output of dual-input AND gate U19 is connected to one input of dual-input AND gate U30. The input of single-input NOT gate U24 is connected to the QD terminal of 74160 chip U16. The output of the single-input AND gate U24 is connected to one input of the dual-input AND gate U27; the input of the single-input NOT gate U25 is connected to the QC pin of the 74160 chip U16; the output of the single-input NOT gate U24 is connected to the other input of the dual-input AND gate U27; the output of the dual-input AND gate U27 is connected to one input of the dual-input AND gate U29; the input of the single-input NOT gate U26 is connected to the QB pin of the 74160 chip U16; and the output of the single-input NOT gate U26 is connected to one input of the dual-input AND gate U28. One input terminal is connected; the other input terminal of the dual-input AND gate U28 is connected to the QA port of the 74160 chip U16; the output terminal of the dual-input AND gate U28 is connected to the other input terminal of the dual-input AND gate U29; the output terminal of the dual-input AND gate U29 is connected to the other input terminal of the dual-input AND gate U30; the output terminal of the dual-input AND gate U30 is connected to the input terminal of LED lamp X1 and the input terminal of buzzer LS1; the output terminals of LED lamp X1 and buzzer LS1 are grounded.

Claims

1. An indoor harmful gas detection circuit, characterized in that, It includes detection circuits, standardization circuits, processing and comparison circuits, and prompting circuits; The output terminal of the detection circuit (1) is connected to the first input terminal of the processing comparison circuit (3); The output terminal of the standard circuit (2) is connected to the second input terminal of the processing comparison circuit (3); The two input terminals of the processing comparison circuit (3) are connected to the output terminals of the detection circuit (1) and the standard circuit (2), and the output terminal of the processing comparison circuit (3) is connected to the input terminal of the prompting circuit (4); The input terminal of the prompting circuit (4) is connected to the output terminal of the processing comparison circuit (3).

2. The indoor harmful gas detection circuit according to claim 1, characterized in that, The detection circuit (1) includes: a sampling module (101) consisting of a 555 timer chip U1, an MQ-7 gas-sensitive resistor R1, MQ-135 gas-sensitive resistors R2 and R3, control switches S1, S2 and S3, a resistor R9, a small DC power supply VCC2, and capacitors C1 and C2; and an adjustment module (102) consisting of inductors L1 and L2, resistors R5, R6, R7 and R8, operational amplifiers U3 and U4, a small DC power supply VCC1, and a small DC negative power supply VEE. In the sampling module (101), the 555 timer chip U1, capacitors C1 and C2 and resistor R9 form the basic part of the 555 timer chip circuit; the MQ-7 gas-sensitive resistor R1 and the MQ-135 gas-sensitive resistors R2 and R3 are connected in series, and their connection is controlled by the control switches S1, S2 and S3 respectively. One end of them is connected to the 555 timer chip U1, and the other end is connected to the inductors L1 and L2 of the adjustment module (102) and the first input terminal of the processing comparison circuit (3); one end of the capacitor C1 is connected to the 555 timer chip U1, and the other end is connected to the resistor R6 of the adjustment module (102); In the adjustment module (102), one end of inductor L2 is connected to the MQ-135 gas-sensitive resistor R3 and the positive input terminal of operational amplifier U3 in the sampling module (101), and the other end is connected to the output terminal of operational amplifier U3, resistors R5 and R7; resistor R5 is connected to the inverting input terminal of operational amplifier U3 and resistor R6; resistor R7 is connected to the inverting input terminal of operational amplifier U4 and resistor R8; resistor R8 is connected to the output terminal of operational amplifier U4 and inductor L1; inductor L1 is connected to the positive input terminal of operational amplifier U4 and inductor L2. The positive power supply terminals of operational amplifiers U3 and U4 are connected to a small DC power supply VCC1; the negative power supply terminals of operational amplifiers U3 and U4 are connected to a small DC negative power supply VEE.

3. The indoor harmful gas detection circuit according to claim 1, characterized in that, The specification circuit (2) includes: a comparison specification module (201) consisting of a 555 timer chip U2, specification resistors R4 and R14, a small DC power supply VCC2 and capacitors C3 and C4; and an adjustment specification module (202) consisting of inductors L3 and L4, resistors R10, R11, R12 and R13, operational amplifiers U4 and U5 and a small DC power supply VCC1. In the comparison specification module (201), the 555 time base chip U2, capacitors C3 and C4 and resistor R14 form the basic part of the 555 time base chip circuit; one end of the specification resistor R4 is connected to the 555 time base chip U2, and the other end of the specification resistor R4 is connected to the second input terminal of the adjustment specification module (202) and the processing comparison circuit (3); one end of capacitor C3 is connected to the 555 time base chip U2, and the other end is connected to the resistor R11 of the adjustment specification module (202); In the adjustment specification module (202), one end of inductor L3 is connected to the specification resistor R4 of the comparison specification module (201) and the positive input terminal of operational amplifier U5; the other end of inductor L3 is connected to the output terminal of operational amplifier U5, resistor R10, and resistor R12; resistor R10 is connected to the inverting input terminal of operational amplifier U5 and resistor R11; resistor R12 is connected to the inverting input terminal of operational amplifier U6 and resistor R13; resistor R13 is connected to the output terminal of operational amplifier U6 and inductor L4; inductor L4 is connected to the positive input terminal of operational amplifier U6 and inductor L3. The positive power supply terminals of operational amplifiers U5 and U6 are connected to a small DC power supply VCC1; the negative power supply terminals of operational amplifiers U5 and U6 are connected to a small DC negative power supply VEE.

4. The indoor harmful gas detection circuit according to claim 1, characterized in that, The processing comparison circuit (3) includes: a processing module (301) consisting of resistors R15, R16, R17, R18, R19, R20, R21, R22, an adjusting resistor R23, operational amplifiers U7, U8, U9, diode D1, a small DC power supply VCC1, and a small DC negative power supply VEE; and a comparison module (302) consisting of comparator U10, adjusting resistor R21, and a small DC power supply VCC3. In the processing module (301), one end of resistor R15 is connected to the output of the detection circuit (1) as the first input of the processing comparison circuit (3); one end of resistor R16 is connected to the output of the standard circuit (2) as the second input of the processing comparison circuit (3); resistors R15, R16, R17, and R18 together with operational amplifier U7 form the difference acquisition part; resistors R19, R20, diode D1 and operational amplifier U8 are connected to take the negative of the absolute value of the voltage processed in the preliminary stage; resistors R21 and R22 are connected to operational amplifier U9 to perform inversion processing; resistor R22 is connected to the output of operational amplifier U9 and the comparison module (302); In the comparison module (302), resistor R22 in the processing module (301) is connected to the non-inverting input terminal of comparator U10; the adjusting resistor R23, comparator U10 and small DC power supply VCC3 constitute the comparison output section, and the output terminal of comparator U10 is connected to the input terminal of the prompting circuit (4). The positive power supply terminals of operational amplifiers U7, U8, U9 and comparator U10 are connected to a small DC power supply VCC1; the negative power supply terminals of operational amplifiers U7, U8, U9 are connected to a small DC negative power supply VEE.

5. The indoor harmful gas detection circuit according to claim 1, characterized in that, The prompting circuit (4) includes: a display processing module (401) composed of digital tubes U11 and U12, 74LS chips U13 and U14, 74160 chips U15 and U16, dual-input AND gate U17, dual-input NAND gate U18, small DC power supply VCC4 and periodic pulse signal source XFG1; and a processing warning module (402) composed of dual-input AND gates U19, U20, U21, U27, U28, U29, U30, single-input NOT gates U22, U23, U24, U25, U26, warning light X1, and alarm LS1. In the display processing module (401), the digital tubes U11 and U12, the 74LS chips U13 and U14, the small DC power supply VCC4, and the periodic pulse signal source XFG1 constitute the acquisition and display section; the input terminal CLK of the 74L160 chips U15 and U16 is connected to the output terminal of the processing comparison circuit; the dual-input AND gate U17 and the dual-input NAND gate U18 are connected to the 74L160 chips U15 and U16. In the warning processing module (402), dual-input AND gate U20 and single-input NOT gates U22 and U23 are connected to 74160 chip U15, and dual-input AND gate U28 and single-input NOT gates U24, U25, and U26 are connected to 74160 chip U16 to collect warning signals. The signals transmitted by these gates are then transmitted to dual-input AND gates U19, U21, U27, U28, U29, and U30 for further warning signal processing. When the collection conditions are met, a high level is output to warning light X1 and alarm LS1. Warning light X1 and alarm LS1 receive the warning signal and light up and sound to provide a warning.

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