Interface circuit

Abstract

The utility model relates to an interface circuit, which belongs to the technical field of circuits and comprises a first current-limiting resistor R1, a second current-limiting resistor R2, a photoelectric coupler IC1, a third current-limiting resistor R3, a fourth current-limiting resistor R4, a fifth resistor R5 and a triode V1. When the CKOUT end outputs a high level, the condition of an external circuit between the alarm and the gas meter can be judged by judging the voltage value of the VA node, and the voltage relation corresponding to the VA node is Vd (short circuit) gt; vz (normal) gt; vk (open circuit); therefore, monitoring of an external line is completed while the switch state information is sent, and when it is monitored that the external line is abnormal, a fault warning is given out to remind a user to pay attention to the abnormal external line so that the abnormal external line can be processed in time. The gas meter has the beneficial effect that the state of the connecting line of the gas alarm and the gas meter can be conveniently monitored.

Description

Technical Field

[0001] This application relates to the technical field of circuits, and in particular to an interface circuit. Background Technology

[0002] As metering devices, gas meters are increasingly equipped with remote monitoring capabilities, allowing data to be transmitted wirelessly to a remote monitoring terminal for intelligent management. With the widespread use of gas, gas leak detectors are also becoming more common. A key function of gas alarms is to issue an audible and visual alarm when a gas leak is detected and reaches a certain concentration, alerting people and outputting a control signal to cut off the gas supply to prevent further leakage. Gas alarms are general-purpose electronic devices installed in gas-using locations; gas shut-off devices are typically installed on gas pipelines, such as shut-off valves or gas meters with shut-off functions.

[0003] Due to technological and management limitations, gas meters and gas alarms are separate products. The main factors are the installation location of gas leak detection and technical issues such as the power consumption of the sensors, which necessitate independent installation and use.

[0004] The connection methods between gas alarms and gas meters can be divided into wired and wireless types. Wired technology is simple, feasible, and cost-effective, but it is susceptible to short circuits and open circuits. Wireless technology is complex, less cost-effective, and more easily affected by external factors.

[0005] Taking wired gas alarms as an example, the connection lines between gas alarms and gas meters vary and there is no unified technical standard. In actual use, due to aging of the wiring harness or other external stresses, the connection lines may experience open circuits or short circuits. Once this happens, when a gas leak alarm occurs, the gas supply cannot be cut off, which may lead to even greater disaster consequences. Utility Model Content

[0006] To facilitate monitoring the status of the connection line between the gas alarm and the gas meter, this application provides an interface circuit, employing the following technical solution:

[0007] An interface circuit, comprising:

[0008] The first current-limiting resistor R1 is connected at one end to the internal power supply of the alarm and at the other end to the output terminal JA of the alarm.

[0009] The second current-limiting resistor R2 is connected at one end to the gas meter input terminal JC, and the alarm output terminal JA is connected to the gas meter input terminal JC through a wire.

[0010] The optocoupler IC1 has its first input terminal connected to the other end of the second current-limiting resistor R2, and its first output terminal connected to the internal power supply of the gas meter.

[0011] The third current-limiting resistor R3 has one end connected to the second input terminal of the optocoupler IC1 and the other end connected to the output terminal JD of the gas meter. The second output terminal of the optocoupler IC1 is connected to the CK_IN terminal inside the gas meter. The CK_IN terminal is the MCU switch input terminal inside the gas meter.

[0012] The fourth current-limiting resistor R4 has one end connected to the alarm input terminal JB and the other end connected to the internal AD_IN terminal of the alarm. The AD_IN terminal is an analog input terminal connected to the internal MCU of the alarm, used to monitor the corresponding voltage of the line during signal transmission. The alarm input terminal JB is connected to the gas meter output terminal JD through a wire.

[0013] The fifth resistor R5 is connected at one end to the other end of the fourth current-limiting resistor R4, and the connection point is marked as node VA.

[0014] Transistor V1 has its base connected to the CK_OUT terminal inside the alarm, which is the internal signal transmitting terminal of the alarm. Its collector is connected to the other end of the fifth resistor R5, and the connection point is marked as node VB. Its emitter is grounded.

[0015] By adopting the above technical solution, when the CK_OUT terminal outputs a high level, the voltage of the VA node can be monitored to determine whether the external line between the alarm and the gas meter is normal, or short-circuited or open-circuited; that is:

[0016] When the CK_OUT terminal outputs a high level, transistor V1 is turned on, and node VB is effectively grounded.

[0017] When the external line is normal, the internal power supply of the alarm is grounded through the first current limiting resistor R1, the second current limiting resistor R2, the optocoupler IC1, the third current limiting resistor R3, the fourth current limiting resistor R4, the fifth resistor R5 and the transistor V1. At this time, the voltage of the VA node (denoted as Vz) is the voltage of the fifth resistor R5 to ground.

[0018] When the external line is short-circuited, the internal power supply of the alarm is grounded through the first current-limiting resistor R1, the fourth current-limiting resistor R4, the fifth resistor R5 and the transistor V1. At this time, the voltage of node VA (denoted as Vd) is the voltage of R5 to ground.

[0019] When the external circuit is broken, the internal power supply of the alarm cannot form a loop, and the voltage at point VA (denoted as Vk) is 0V (the VA node is grounded through the fifth resistor R5).

[0020] Therefore, when the CK_OUT terminal outputs a high level, the status of the external line between the alarm and the gas meter can be determined by judging the voltage value of the VA node. The voltage relationship corresponding to the VA node is Vd>Vz>Vk. Thus, while sending the switch status information, the monitoring of the external line is also completed. When an abnormality in the external line is detected, a fault warning is issued to remind the user to pay attention and take timely action.

[0021] Optionally, the interface circuit further includes:

[0022] The sixth resistor R6 is connected at one end to node VA and at the other end to the AD_IN terminal.

[0023] By adopting the above technical solution, the sixth resistor can be used to improve the input impedance of the MCU analog signal and resist the influence of external instantaneous interference signals on the MCU.

[0024] Optionally, the interface circuit further includes:

[0025] The seventh resistor R7 is connected at one end to the base of the transistor V1 and at the other end to the CK_OUT terminal.

[0026] By adopting the above technical solution, the output current at the CK_OUT terminal is reduced, thereby further protecting the circuit.

[0027] Optionally, the interface circuit further includes:

[0028] The eighth resistor R8 has one end connected to the second output terminal of the optocoupler IC1, and the other end grounded.

[0029] By adopting the above technical solution, the high and low levels of the transmitting end CK_OUT can be accurately transmitted to the CK_IN end.

[0030] Optionally, the interface circuit further includes:

[0031] The positive terminal of the first diode D1 is connected to the other end of the first current-limiting resistor R1, and the negative terminal is connected to the output terminal JA of the alarm.

[0032] The positive terminal of the second diode D2 is connected to the input terminal JB of the alarm, and the negative terminal is connected to one end of the fourth current-limiting resistor R4.

[0033] By adopting the above technical solution, the backflow of external interference signals can be prevented.

[0034] In summary, this application has at least the following beneficial effects:

[0035] 1. The purpose of setting the first current-limiting resistor R1, the second current-limiting resistor R2, the optocoupler IC1, the third current-limiting resistor R3, the fourth current-limiting resistor R4, the fifth resistor R5, and the transistor V1 is that when the CK_OUT terminal outputs a high level, the condition of the external line between the alarm and the gas meter can be determined by judging the voltage value of the VA node. The voltage relationship corresponding to the VA node is Vd>Vz>Vk. Thus, while sending the switch status information, the monitoring of the external line is also completed. When an abnormality in the external line is detected, a fault warning is issued to remind the user to pay attention and deal with it in time.

[0036] 2. The purpose of setting up the first diode D1 and the second diode D2 is to prevent the backflow of external interference signals. Attached Figure Description

[0037] Figure 1 This is the circuit schematic diagram of the interface circuit in this application when it is functioning normally;

[0038] Figure 2 This is the circuit schematic diagram of the interface circuit in this application when it is short-circuited;

[0039] Figure 3 This is the circuit schematic diagram when the interface circuit of this application is open-circuited. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of the embodiments of this utility model clearer, the following will be described in conjunction with the appendices in the embodiments of this utility model. Figure 1 -Attached Figure 3 The technical solutions in the embodiments of this utility model are clearly and completely described herein. Obviously, the described embodiments are only some, not all, of the embodiments of this utility model. Based on the embodiments of this utility model, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this utility model.

[0041] This application discloses an interface circuit. (Refer to...) Figure 1 As one embodiment of the interface circuit, the interface circuit may include a first current-limiting resistor R1, a second current-limiting resistor R2, an optocoupler IC1, a third current-limiting resistor R3, a fourth current-limiting resistor R4, a fifth resistor R5, and a transistor V1.

[0042] In this circuit, one end of the first current-limiting resistor R1 is connected to the internal DC12V power supply of the alarm, and the other end is connected to the alarm output terminal JA. One end of the second current-limiting resistor R2 is connected to the gas meter input terminal JC, and the other end is connected to the first input terminal of the optocoupler IC1. The alarm output terminal JA is connected to the gas meter input terminal JC. The first output terminal of the optocoupler IC1 is connected to the gas meter internal power supply VCC, the second input terminal is connected to one end of the third current-limiting resistor R3, and the second output terminal is connected to the internal CK_IN terminal of the gas meter. The other end of the third current-limiting resistor R3 is connected to the gas meter output terminal JD. One end of the fourth current-limiting resistor R4 is connected to the alarm input terminal JB, and the other end can be connected to the internal AD_IN terminal of the alarm. The alarm input terminal JB is connected to the gas meter output terminal JD via a wire. One end of the fifth resistor R5 is connected to the other end of the fourth current-limiting resistor R4, and the connection point is marked as node VA. The base of transistor V1 can be connected to the CK_OUT terminal inside the alarm, the collector is connected to the other end of the fifth resistor R5, the connection point is marked as node VB, and the emitter is grounded; transistor V1 is an NPN type transistor.

[0043] The CK_OUT terminal is the signal transmitting terminal of the alarm, controlled by its internal MCU. It can transmit switch status or digital communication according to timing, switch state, PWM pulse width, or digital communication. The AD_IN terminal is the analog input terminal connected to the internal MCU of the alarm, used to monitor the corresponding voltage of the line during signal transmission to determine the line status, such as normal, short circuit, or open circuit. DC12V provides the power source for switch communication. Transistor V1 enhances the driving capability, switches the load, and isolates the CK_OUT signal from interference. The CK_IN terminal is the MCU switch input terminal connected to the gas meter, and its signal is controlled by the conduction or cutoff of optocoupler IC1. Optocoupler IC1 is used to isolate the electrical relationship between the alarm and the gas meter, enhancing the system's anti-interference capability.

[0044] Furthermore, in order to increase the input impedance of the MCU analog signal, the interface circuit also includes a sixth resistor R6, one end of which is connected to the VA node and the other end is connected to the AD_IN terminal.

[0045] Furthermore, the interface circuit also includes a seventh resistor R7 and an eighth resistor R8. One end of the seventh resistor R7 is connected to the base of transistor V1, and the other end is connected to the CK_OUT terminal. One end of the eighth resistor R8 is connected to the second output terminal of optocoupler IC1, and the other end is grounded.

[0046] Furthermore, to prevent backfeeding of external interference signals, the interface circuit also includes a first diode D1 and a second diode D2. The anode of the first diode D1 is connected to the other end of the first current-limiting resistor R1, and the cathode is connected to the alarm output terminal JA. The anode of the second diode D2 is connected to the alarm input terminal JB, and the cathode is connected to one end of the fourth current-limiting resistor R4.

[0047] The implementation principle of this embodiment is as follows:

[0048] (1) When the external circuit is normal, that is, the output terminal of the alarm JA is connected to the input terminal of the gas meter JC, and the output terminal of the alarm JB is connected to the output terminal of the gas meter JD.

[0049] When CK_OUT outputs a high level, transistor V1 is turned on, and node VB is effectively grounded. The DC12V power supply forms a loop through the first current-limiting resistor R1, the first diode D1, the second current-limiting resistor R2, the optocoupler IC1, the third current-limiting resistor R3, the second diode D2, the fourth current-limiting resistor R4, the fifth resistor R5, and transistor V1. At this time, the voltage at node VA is equal to the voltage of the fifth resistor R5 to ground. Current flows through optocoupler IC1, and its internal phototransistor is turned on, causing CK_IN to output a high level.

[0050] When CK_OUT outputs a low level, transistor V1 is cut off, and DC12V cannot form a circuit to ground. At this time, the voltage (VA1) at node VA is equal to DC12V. Optocoupler IC1 has no current, its internal phototransistor is cut off, and CK_IN outputs a low level.

[0051] (2) When the external line is short-circuited, that is, when the output terminal of the alarm JA and the input terminal of the alarm JB directly form a loop, you can refer to Figure 2 .

[0052] When CK_OUT outputs a high level, transistor V1 is turned on, and node VB is effectively grounded. The DC12V power supply forms a loop through the first current-limiting resistor R1, the first diode D1, the second diode D2, the fourth current-limiting resistor R4, the fifth resistor R5, and transistor V1; at this time, the voltage (VA2) at node VA is equal to the voltage of R5 to ground. No current flows through optocoupler IC1, its internal phototransistor is cut off, and CK_IN outputs a low level.

[0053] Note: Due to the short circuit, the circuit load is less and the circuit current increases. Therefore, the voltage to ground formed on the fifth resistor R5, VA2, is greater than VA1.

[0054] When CK_OUT outputs a low level, transistor V1 is cut off, and DC12V cannot form a circuit to ground. At this time, the voltage VA3 at node VA is equal to DC12V. Optocoupler IC1 has no current, its internal phototransistor is cut off, and CK_IN outputs a low level.

[0055] (3) When the external circuit is broken, whether the circuit between the alarm JA output terminal and the gas meter JC input terminal is broken, or the circuit between the alarm JB input terminal and the gas meter JD output terminal is broken, the circuit effect is the same. (Refer to...) Figure 3 .

[0056] When CK_OUT outputs a high level, transistor V1 is turned on, and node VB is effectively grounded. Because the circuit is open, DC12V is not looped. At this time, node VA is grounded through resistor R5, so the voltage VA3 at node VA is 0V. No current flows through optocoupler IC1, its internal phototransistor is cut off, and CK_IN outputs a low level.

[0057] When CK_OUT outputs a low level, transistor V1 is cut off. Because the circuit is open, DC12V cannot form a loop to ground. At this time, node VA is essentially floating, and its voltage cannot be determined. Optocoupler IC1 has no current, its internal phototransistor is cut off, and CK_IN outputs a low level.

[0058] In practical applications, PWM (Pulse Width Modulation) is the most common method for expressing status information, which uses continuous pulses to represent the current state. For example, a 1 / 8 duty cycle indicates normal operation, a 2 / 8 duty cycle indicates self-test, a 3 / 8 duty cycle indicates a fault, a 4 / 8 duty cycle indicates an alarm, and a 5 / 8 duty cycle indicates the alarm has reached the end of its lifespan, etc. The pulse period T can be calculated as 1ms, so the high-level time for a 1 / 8 duty cycle is 1 / 8ms, or 125us. During this period, the MCU inside the alarm can complete the voltage acquisition and judgment at the AD_IN terminal. This allows the alarm MCU to simultaneously output a signal through CK_OUT and check whether the signal is output correctly through AD_IN.

[0059] Note: In the examples above, when more state transmission is required, a 1 / 16 or 1 / 32 duty cycle can be used. The period can also be adjusted according to the MCU used, for example, 10ms, 20ms, or even longer. The minimum duty cycle should be based on meeting the signal response of the optocoupler and can be increased or decreased.

[0060] When more data needs to be sent, serial communication is generally used. CK_OUT can be the TXD pin of the alarm MCU's serial port, and CK_IN can be the RXD pin of the gas meter MCU's serial port, communicating directly using the standard serial protocol.

[0061] The MCU's serial port transmission is automatic. It maintains a high-level state before and after transmission, allowing the TXD pin to naturally reach a high level before or after transmission, thus detecting the voltage at the AD_IN pin to determine the line status. This offers several advantages: it doesn't affect the timing of serial communication; it ensures the integrity of a data frame; it facilitates increased communication speed; it provides sufficient time to check the external circuit status before or after a frame is sent; the interval between frames can be customized by the user; and the serial communication data stream can be customized, specifying the start bit, data bits, and end bit, so the MCU knows the transmission of each bit and can perform line status checks at any time when needed.

[0062] Since the alarm will always be in a fault alarm state when it is not connected to the gas meter in actual use, affecting the user's use, an equivalent load resistor can be plugged into the output terminal of the alarm to eliminate the fault, so that no changes are required to the alarm, which is simple and easy to do.

[0063] Replenish:

[0064] Adding filtering capacitors to this circuit, or changing the values ​​of components, changing the power supply voltage, adding / removing components or changing their equivalent positions, adding other anti-interference components, or replacing them with other components with equivalent functions, are all considered to be within the scope of protection of this patent.

[0065] This patent is not limited to the interface between gas alarms and gas meters; any place / equipment that uses this method is considered to be within the scope of patent protection.

[0066] The above are all preferred embodiments of this application and are not intended to limit the scope of protection of this application. Any feature disclosed in this specification (including the abstract and drawings) may be replaced by other equivalent or similar features unless specifically stated otherwise. That is, unless specifically stated otherwise, each feature is only one example of a series of equivalent or similar features.

Claims

1. An interface circuit, characterized in that, include: The first current-limiting resistor R1 is connected at one end to the internal power supply of the alarm and at the other end to the output terminal JA of the alarm. The second current-limiting resistor R2 is connected at one end to the gas meter input terminal JC, and the alarm output terminal JA is connected to the gas meter input terminal JC through a wire. The optocoupler IC1 has its first input terminal connected to the other end of the second current-limiting resistor R2, and its first output terminal connected to the internal power supply of the gas meter. The third current-limiting resistor R3 has one end connected to the second input terminal of the optocoupler IC1 and the other end connected to the output terminal JD of the gas meter. The second output terminal of the optocoupler IC1 is connected to the CK_IN terminal inside the gas meter. The CK_IN terminal is the MCU switch input terminal connected to the gas meter. The fourth current-limiting resistor R4 has one end connected to the alarm input terminal JB and the other end connected to the internal AD_IN terminal of the alarm. The AD_IN terminal is an analog input terminal connected to the alarm MCU and is used to monitor the corresponding voltage of the line during signal transmission. The alarm input terminal JB is connected to the gas meter output terminal JD through a wire. The fifth resistor R5 is connected at one end to the other end of the fourth current-limiting resistor R4, and the connection point is marked as node VA. Transistor V1 has its base connected to the CK_OUT terminal inside the alarm, which is the internal signal transmitting terminal of the alarm. Its collector is connected to the other end of the fifth resistor R5, and the connection point is marked as node VB. Its emitter is grounded. While transmitting switch quantity and pulse digital quantity information at the CK_OUT terminal, the AD_IN terminal can be used to determine whether there is an abnormality in the transmission line, and the optocoupler IC1 can achieve electrical isolation between the CK_OUT terminal and the CK_IN terminal for the transmitted information.

2. The interface circuit according to claim 1, characterized in that, The interface circuit also includes: The sixth resistor R6 is connected at one end to node VA and at the other end to the AD_IN terminal.

3. The interface circuit according to claim 1, characterized in that, The interface circuit also includes: The seventh resistor R7 is connected at one end to the base of the transistor V1 and at the other end to the CK_OUT terminal.

4. An interface circuit according to claim 1, characterized in that, The interface circuit also includes: The eighth resistor R8 has one end connected to the second output terminal of the optocoupler IC1, and the other end grounded.

5. An interface circuit according to claim 1, characterized in that, The interface circuit also includes: The positive terminal of the first diode D1 is connected to the other end of the first current-limiting resistor R1, and the negative terminal is connected to the output terminal JA of the alarm. The positive terminal of the second diode D2 is connected to the input terminal JB of the alarm, and the negative terminal is connected to one end of the fourth current-limiting resistor R4.

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