Digital interface expansion circuit, electronic equipment and monitoring system

Abstract

A digital interface expansion circuit, an electronic device and a monitoring system belong to the technical field of alarm monitoring, the digital interface expansion circuit is connected with a host and a slave, and the slave is connected with the host through a digital bus; the digital bus comprises a serial communication bus and a data line, and the host is used for outputting a data signal to the slave through the data line, so that the slave executes a corresponding action according to the data signal; the digital interface expansion circuit comprises a master control circuit, at least one sensing circuit interface and at least one execution circuit interface. The sensing circuit interface accesses a sensing signal; the main control circuit outputs a first serial communication signal from the serial communication bus according to the at least one sensing signal, and is communicated with the at least one dry contact according to a second serial communication signal; the execution circuit interface is configured as a dry contact. The display data transmission and alarm functions can be simultaneously realized through one digital interface without an independent alarm controller, so that the alarm function is realized at low cost.

Description

Technical Field

[0001] The present application belongs to the technical field of alarm monitoring, and in particular relates to a digital interface expansion circuit, electronic equipment and a monitoring system. Background Art

[0002] In the network video recorder market, alarm input and output interfaces are usually only available on high-end models, and entry-level models are basically not equipped with them. However, a small number of users do have such a demand: they want both entry-level economical models and alarm control needs. Currently, there are usually two types of products that implement the alarm function of network video recorders: one is a high-end network video recorder, and the other is to add an independent alarm controller. Both solutions have the problem of high cost.

[0003] Therefore, there is an urgent need to provide a digital interface expansion circuit that can realize the alarm function at low cost. Utility Model Content

[0004] The purpose of the present application is to provide a digital interface expansion circuit, an electronic device and a monitoring system, aiming to solve the problem of high cost existing in existing network video recorder products with alarm functions.

[0005] The embodiment of the present application provides a digital interface expansion circuit, which is connected to a host and a slave, wherein the slave is connected to the host through a digital bus; the digital bus includes a serial communication bus and a data line, and the host is used to output a data signal to the slave through the data line, so that the slave performs a corresponding action according to the data signal; the digital interface expansion circuit includes a main control circuit, at least one sensor circuit interface and at least one execution circuit interface;

[0006] The sensor circuit interface is configured to receive a sensor signal;

[0007] The main control circuit is connected to at least one of the sensor circuit interfaces, the host and the slave, and is configured to output a first serial communication signal from the serial communication bus according to at least one of the sensor signals, and to connect at least one dry contact according to a second serial communication signal;

[0008] The execution circuit interface is connected to the main control circuit and configured as the dry contact;

[0009] The host is further configured to output the second serial communication signal according to the first serial communication signal.

[0010] In one embodiment, the digital interface expansion circuit is connected to at least one sensing circuit and at least one execution circuit;

[0011] The sensing circuit is connected to the sensing circuit interface and is configured to collect parameters of the surrounding environment and output a sensing signal according to the parameters;

[0012] The execution circuit is connected to the execution circuit interface and is configured to execute corresponding actions according to the connectivity of the dry contact.

[0013] In one of the embodiments, the main control circuit includes at least one level conversion circuit, at least one switch circuit and a control circuit;

[0014] The level conversion circuit is connected to the sensor circuit interface in a one-to-one correspondence and is configured to perform level conversion on the sensor signal;

[0015] The control circuit is connected to at least one level conversion circuit, the host and the slave, and is configured to output a first serial communication signal from the serial communication bus according to at least one level-converted sensing signal, and output at least one control signal according to a second serial communication signal;

[0016] The switch circuit is connected to the execution circuit interface in a one-to-one correspondence and to the control circuit, and is configured to connect the dry contact according to the control signal.

[0017] In one embodiment, the level conversion circuit includes a transient voltage suppression tube, a first switch tube, a first capacitor, a first resistor, a second resistor, a third resistor and a fourth resistor;

[0018] The first end of the transient voltage suppression tube and the first end of the first resistor are jointly used as the sensing signal input end of the level conversion circuit, and are connected to the sensing circuit to input the sensing signal; the second end of the first resistor, the first end of the second resistor, the first end of the first capacitor, and the control end of the first switch tube are connected, and the second end of the second resistor and the first end of the first switch tube are connected to the first power supply; the second end of the first switch tube is connected to the first end of the third resistor, and the second end of the third resistor and the first end of the fourth resistor are jointly used as the sensing signal output end after level conversion of the level conversion circuit, and are connected to the control circuit to output the sensing signal after level conversion; the second end of the transient voltage suppression tube, the second end of the first capacitor, and the second end of the fourth resistor are connected to the power ground.

[0019] In one embodiment, the control circuit includes a microprocessor;

[0020] The power supply voltage input terminal of the microprocessor is connected to the second power supply; the ground terminal of the microprocessor is connected to the power ground; the multiple general input and output terminals of the microprocessor are respectively used as the multiple level-converted sensor signal input terminals of the control circuit, and are connected to the multiple level conversion circuits to respectively input the multiple level-converted sensor signals; the multiple general input and output terminals of the microprocessor are respectively used as the multiple control signal output terminals of the control circuit, and are connected to the multiple switch circuits to respectively output the multiple control signals; the first general input and output terminal of the microprocessor and the second general input and output terminal of the microprocessor are jointly used as the first serial communication signal output terminal of the control circuit and the second serial communication signal input terminal of the control circuit, and are connected to the host and the slave to output the first serial communication signal and input the second serial communication signal.

[0021] In one embodiment, the switch circuit includes a relay, a diode, a second switch tube, a second capacitor, a fifth resistor, a sixth resistor and a seventh resistor;

[0022] The first end of the fifth resistor serves as the control signal input end of the switch circuit and is connected to the control circuit to input the control signal; the second end of the fifth resistor is connected to the first end of the seventh resistor and the control end of the second switch tube, the first end of the second switch tube is connected to the positive electrode of the diode, the first end of the second capacitor and the first coil end of the relay, the second end of the second capacitor, the negative electrode of the diode, the first end of the sixth resistor and the second coil end of the relay are connected, and the second end of the sixth resistor is connected to the third power supply; the first common end of the relay, the second common end of the relay and the normally open end of the relay are collectively used as the dry contact and are connected to the execution circuit interface.

[0023] In one of the embodiments, the digital bus further includes a power line;

[0024] The host is also configured to output a supply voltage from the power line to power the slave and the main control circuit.

[0025] In one embodiment, the digital interface includes a high definition multimedia interface (HDMI) interface and a video graphics array (VGA) interface; the digital bus includes a HDMI bus and a VGA bus.

[0026] In one embodiment, the serial communication bus includes an inter-integrated circuit (I2C) bus.

[0027] An embodiment of the present application further provides an electronic device, which includes the above-mentioned digital interface expansion circuit.

[0028] An embodiment of the present application further provides a monitoring system, which includes a host, a slave, and the above-mentioned digital interface expansion circuit connected to a digital bus.

[0029] Compared with the prior art, the embodiments of the present application have the following beneficial effects: the digital interface expansion circuit is connected to the host and the slave, and the slave is connected to the host through a digital bus; the digital bus includes a serial communication bus and a data line, and the host is used to output a data signal to the slave through the data line, so that the slave performs a corresponding action according to the data signal; the digital interface expansion circuit includes a main control circuit, at least one sensor circuit interface, and at least one execution circuit interface; the sensor circuit interface accesses the sensor signal; the main control circuit outputs a first serial communication signal from the serial communication bus according to at least one sensor signal, and connects at least one dry contact according to the second serial communication signal; the execution circuit interface is configured as a dry contact. By adding a digital interface expansion circuit connected to the serial communication bus, the display data transmission and alarm function can be realized from one digital interface at the same time without an independent alarm controller, thereby realizing the alarm function at a low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical application in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0031] Figure 1 A schematic diagram of a structure of a digital interface expansion circuit provided in one embodiment of the present application;

[0032] Figure 2 Another structural schematic diagram of a digital interface expansion circuit provided in an embodiment of the present application;

[0033] Figure 3 Another structural schematic diagram of a digital interface expansion circuit provided in an embodiment of the present application;

[0034] Figure 4 A partial exemplary circuit schematic diagram of a digital interface expansion circuit provided in one embodiment of the present application. DETAILED DESCRIPTION

[0035] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0036] It should be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it can be directly on the other element or indirectly on the other element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or indirectly connected to the other element.

[0037] It should be understood that the orientation or position relationship indicated by terms such as "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside" and "outside" are based on the orientation or position relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0038] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of this application, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0039] Figure 1 The structure diagram of the digital interface expansion circuit 300 provided in one embodiment of the present application is shown. For the convenience of description, only the part related to the present embodiment is shown, which is described in detail as follows:

[0040] The above-mentioned digital interface expansion circuit 300 is connected to the host 10 and the slave 20, and the slave 20 is connected to the host 10 through a digital bus; the digital bus includes a serial communication bus and a data line, and the host 10 is used to output a data signal to the slave 20 through the data line so that the slave 20 performs a corresponding action according to the data signal; the digital interface expansion circuit 300 includes a main control circuit 320, at least one sensor circuit interface and at least one execution circuit interface.

[0041] The sensing circuit interface is configured to receive a sensing signal.

[0042] The main control circuit 320 is connected to at least one sensor circuit 310, the host 10 and the slave 20, and is configured to output a first serial communication signal from the serial communication bus according to at least one sensor signal, and connect at least one dry contact according to a second serial communication signal.

[0043] The execution circuit interface is connected to the main control circuit 320 and is configured as a dry contact.

[0044] The host 20 is further configured to output a second serial communication signal according to the first serial communication signal.

[0045] The above-mentioned digital interface may include an HDMI interface and a VGA interface; the digital bus includes an HDMI bus and a VGA bus.

[0046] The function of the digital interface is expanded by the digital interface expansion circuit 300 , and the digital interface expansion circuit 300 is applicable to a variety of digital interfaces, thereby improving the functionality and practicality of the product.

[0047] The serial communication bus may include an inter-integrated circuit (I2C) bus.

[0048] By way of example and not limitation, Figure 2 As shown, the digital interface expansion circuit 300 is connected to at least one sensing circuit 310 and at least one execution circuit 330 .

[0049] The sensor circuit 310 is connected to the sensor circuit interface and is configured to collect parameters of the surrounding environment and output a sensor signal according to the parameters.

[0050] The execution circuit 330 is connected to the execution circuit interface and is configured to execute corresponding actions according to the connectivity of the dry contact.

[0051] The microprocessor U1 in the main control circuit 320 sets a group of registers for input ports, for example, the registers with addresses 128 and 129 in the following table. Each bit of data in the registers for the input ports corresponds one-to-one to the sensing circuit 310. The microprocessor U1 in the main control circuit 320 also sets a group of registers for output ports, for example, the registers with addresses 130 and 131 in the following table. Each bit of data in the registers for the output ports corresponds one-to-one to the execution circuit 320.

[0052] address data describe 128 Bit0:7 Status of input port 0:7 129 Bit8:15 Input port 8:15 status 130 Bit0:7 Output port 0:7 status 131 Bit8:15 Output port 8:15 status

[0053] When the sensing signal output by the sensing circuit 310 changes, the microprocessor U1 records the state of the corresponding input port of the sensing circuit 310 to the corresponding bit in the register. When the host 10 polls through the serial communication bus, it reads the register of the group of input ports, that is, the state of the corresponding input port of each sensing circuit 310.

[0054] The host 10 obtains the status of the corresponding input ports of each sensor circuit 310 based on the data in the registers of the group of input ports, and determines the corresponding execution circuit 330 based on the status of the corresponding input port of each sensor circuit 310 and / or the received instruction. Finally, the host 10 obtains the data corresponding to the registers of the group of output ports based on all the determined execution circuits 330. The host 10 sends the data corresponding to the registers of the group of output ports to the microprocessor U1 in the main control circuit 320. The microprocessor U1 writes the corresponding data into the registers of the group of output ports and sets the status of each output port according to the data corresponding to the registers of the group of output ports, thereby controlling each execution circuit 330 to perform corresponding actions.

[0055] By way of example and not limitation, Figure 3 As shown, the main control circuit 320 includes at least one level conversion circuit 321 , at least one switch circuit and a control circuit 322 .

[0056] The level conversion circuit 321 is connected to the sensor circuit interface in a one-to-one correspondence and is configured to perform level conversion on the sensor signal.

[0057] The control circuit 322 is connected to at least one level conversion circuit 321, the host 10 and the slave 20, and is configured to output a first serial communication signal from the serial communication bus according to at least one level-converted sensing signal, and output at least one control signal according to the second serial communication signal.

[0058] The switch circuit is connected to the execution circuit interface in a one-to-one correspondence and is connected to the control circuit 322, and is configured to connect the dry contacts according to the control signal.

[0059] The execution circuit 330 is specifically configured to execute corresponding actions according to the connection of the dry contact.

[0060] The adaptability of the circuit is improved by the level conversion circuit 321 .

[0061] By way of example and not limitation, a digital bus also includes power lines.

[0062] The host 10 is further configured to output a power supply voltage from a power line to supply power to the slave 20 and the main control circuit 320 .

[0063] The slave device 20 and the main control circuit 320 are powered by the host 10 without the need for additional input voltage, thus simplifying wiring.

[0064] Figure 4 A partial exemplary circuit structure of the digital interface expansion circuit 300 provided in an embodiment of the present application is shown. For the sake of convenience, only the part related to the embodiment of the present application is shown, which is described in detail as follows:

[0065] The level conversion circuit 321 includes a transient voltage suppressor tube Z1 , a first switch tube Q1 , a first capacitor C1 , a first resistor R1 , a second resistor R2 , a third resistor R3 and a fourth resistor R4 .

[0066] The first end of the transient voltage suppression tube Z1 and the first end of the first resistor R1 are used together as the sensing signal input end of the level conversion circuit 321, and are connected to the sensing circuit interface to input the sensing signal; the second end of the first resistor R1, the first end of the second resistor R2, the first end of the first capacitor C1, and the control end of the first switch tube Q1 are connected, and the second end of the second resistor R2 and the first end of the first switch tube Q1 are connected to the first power supply VAA; the second end of the first switch tube Q1 is connected to the first end of the third resistor R3, and the second end of the third resistor R3 and the first end of the fourth resistor R4 are used together as the sensing signal output end after the level conversion of the level conversion circuit 321, and are connected to the control circuit 322 to output the sensing signal after the level conversion; the second end of the transient voltage suppression tube Z1, the second end of the first capacitor C1, and the second end of the fourth resistor R4 are connected to the power ground.

[0067] The first switch tube Q1 may be a PNP transistor.

[0068] The circuit components are readily available and the construction cost is low.

[0069] The control circuit 322 includes a microprocessor U1.

[0070] The power supply voltage input terminal VDD of the microprocessor U1 is connected to the second power supply VBB; the ground terminal VSS of the microprocessor U1 is connected to the power ground; the multiple general input and output terminals of the microprocessor U1 are respectively used as the multiple level-converted sensor signal input terminals of the control circuit 322, and are connected to the multiple level conversion circuits 321 to respectively input the multiple level-converted sensor signals; the multiple general input and output terminals of the microprocessor U1 are respectively used as the multiple control signal output terminals of the control circuit 322, and are connected to the multiple switch circuits to respectively output the multiple control signals; the first general input and output terminal P24 of the microprocessor U1 and the second general input and output terminal P25 of the microprocessor U1 are jointly used as the first serial communication signal output terminal of the control circuit 322 and the second serial communication signal input terminal of the control circuit 322, and are connected to the host 10 and the slave 20 to output the first serial communication signal and input the second serial communication signal.

[0071] In a specific implementation, the third general input / output terminal P23 of the microprocessor U1 serves as the first level-converted sensing signal input terminal of the control circuit 322, and is connected to the first level conversion circuit 321 to input the first level-converted sensing signal; the fourth general input / output terminal P22 of the microprocessor U1 serves as the second level-converted sensing signal input terminal of the control circuit 322, and is connected to the second level conversion circuit 321 to input the second level-converted sensing signal; the fifth general input / output terminal P26 of the microprocessor U1 serves as the first control signal output terminal of the control circuit 322, and is connected to the first switch circuit to output the first control signal; the sixth general input / output terminal P30 of the microprocessor U1 serves as the second control signal output terminal of the control circuit 322, and is connected to the second switch circuit to output the second control signal.

[0072] The circuit is simple and reliable.

[0073] The switch circuit includes a relay K, a diode, a second switch tube Q2, a second capacitor C2, a fifth resistor R5, a sixth resistor R6 and a seventh resistor R7.

[0074] The first end of the fifth resistor R5 serves as the control signal input end of the switch circuit and is connected to the control circuit 322 to input a control signal; the second end of the fifth resistor R5 is connected to the first end of the seventh resistor R7 and the control end of the second switch tube Q2, the first end of the second switch tube Q2 is connected to the positive electrode of the diode, the first end of the second capacitor C2 and the first coil end of the relay K, the second end of the second capacitor C2, the negative electrode of the diode, the first end of the sixth resistor R6 and the second coil end of the relay K are connected, and the second end of the sixth resistor R6 is connected to the third power supply VCC; the first common end of the relay K, the second common end of the relay K and the normally open end of the relay K are collectively used as dry contacts and are connected to the execution circuit interface.

[0075] The second switch tube may be an NPN transistor.

[0076] The first power source VAA, the second power source VBB and the third power source VCC may be the same power source.

[0077] Relay K has a fast response speed and can achieve fast switching action.

[0078] The digital interface expansion circuit 300 further includes a protection circuit.

[0079] The following is a combination of working principles Figure 4 As shown for further explanation:

[0080] Take two sensing circuits 310 and two execution circuits 330 as an example for explanation. When the first sensing circuit 310 collects parameters of the surrounding environment and outputs a first sensing signal according to the parameters, it is connected to a first level conversion circuit. In the first level conversion circuit, the first end of the first resistor R1 and the first end of the transient voltage suppression tube Z1 are connected to the first sensing signal, the first switch tube Q1 performs level conversion on the first sensing signal, and outputs the first sensing signal after level conversion from the second end of the third resistor R3 and the first end of the fourth resistor R4 to a universal input and output terminal P23 of the microprocessor U1; the microprocessor U1 outputs a first serial communication signal from the first universal input and output terminal P24 of the microprocessor U1 and the second universal input and output terminal P25 of the microprocessor U1 to the serial communication bus according to the first sensing signal after level conversion, so that the host is also configured to output a second serial communication signal according to the first serial communication signal.

[0081] The microprocessor U1 inputs a second serial communication signal from the serial communication bus through a first universal input / output terminal P24 of the microprocessor U1 and a second universal input / output terminal P25 of the microprocessor U1, and the microprocessor U1 outputs a control signal from a universal input / output terminal P30 of the microprocessor U1 to the second switch circuit 323. In the second switch circuit 323, the first end of the fifth resistor R5 is connected to the control signal, and the relay K is actuated according to the control signal, so that the normally open end of the second relay K is connected to the first common end of the second relay K and the second common end of the second relay K, and the second execution circuit 330 is actuated.

[0082] An embodiment of the present application further provides an electronic device, which includes the above-mentioned digital interface expansion circuit.

[0083] An embodiment of the present application further provides a monitoring system, which includes a host, a slave, and the above-mentioned digital interface expansion circuit connected to a digital bus.

[0084] It should be understood that the size of the serial numbers of the steps in the above embodiments does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0085] The embodiments described above are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, a person skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application, and should all be included in the protection scope of the present application.

Claims

1. A digital interface expansion circuit, connected to a host and a slave, wherein the slave is connected to the host via a digital bus; the digital bus includes a serial communication bus and a data line, and the host is used to output a data signal to the slave via the data line, so that the slave performs a corresponding action according to the data signal; characterized in that: The digital interface expansion circuit includes a main control circuit, at least one sensor circuit interface and at least one execution circuit interface; The sensor circuit interface is configured to receive a sensor signal; The main control circuit is connected to at least one of the sensor circuit interfaces, the host and the slave, and is configured to output a first serial communication signal from the serial communication bus according to at least one of the sensor signals, and to connect at least one dry contact according to a second serial communication signal; The execution circuit interface is connected to the main control circuit and configured as the dry contact; The host is further configured to output the second serial communication signal according to the first serial communication signal.

2. The digital interface expansion circuit according to claim 1, characterized in that: connected to at least one sensing circuit and at least one execution circuit; The sensing circuit is connected to the sensing circuit interface and is configured to collect parameters of the surrounding environment and output a sensing signal according to the parameters; The execution circuit is connected to the execution circuit interface and is configured to execute corresponding actions according to the connectivity of the dry contact.

3. The digital interface expansion circuit according to claim 1, characterized in that The main control circuit includes at least one level conversion circuit, at least one switch circuit and a control circuit; The level conversion circuit is connected to the sensor circuit interface in a one-to-one correspondence and is configured to perform level conversion on the sensor signal; The control circuit is connected to at least one level conversion circuit, the host and the slave, and is configured to output a first serial communication signal from the serial communication bus according to at least one level-converted sensing signal, and output at least one control signal according to a second serial communication signal; The switch circuit is connected to the execution circuit interface in a one-to-one correspondence and to the control circuit, and is configured to connect the dry contact according to the control signal.

4. The digital interface expansion circuit according to claim 3, characterized in that: The level conversion circuit includes a transient voltage suppression tube, a first switch tube, a first capacitor, a first resistor, a second resistor, a third resistor and a fourth resistor; The first end of the transient voltage suppression tube and the first end of the first resistor are jointly used as the sensing signal input end of the level conversion circuit, and are connected to the sensing circuit interface to input the sensing signal; the second end of the first resistor, the first end of the second resistor, the first end of the first capacitor, and the control end of the first switch tube are connected, and the second end of the second resistor and the first end of the first switch tube are connected to the first power supply; the second end of the first switch tube is connected to the first end of the third resistor, and the first end of the fourth resistor and the second end of the third resistor are jointly used as the sensing signal output end after level conversion of the level conversion circuit, and are connected to the control circuit to output the sensing signal after level conversion; the second end of the transient voltage suppression tube, the second end of the first capacitor, and the second end of the fourth resistor are connected to the power ground.

5. The digital interface expansion circuit according to claim 3, characterized in that: The control circuit includes a microprocessor; The power supply voltage input terminal of the microprocessor is connected to the second power supply; the ground terminal of the microprocessor is connected to the power ground; the plurality of general input and output terminals of the microprocessor are respectively used as the plurality of level-converted sensor signal input terminals of the control circuit, and are connected to the plurality of level conversion circuits to respectively input the plurality of level-converted sensor signals; The plurality of general input and output terminals of the microprocessor are respectively used as the plurality of control signal output terminals of the control circuit, and are connected to the plurality of switch circuits to respectively output the plurality of control signals; The first general purpose input / output terminal of the microprocessor and the second general purpose input / output terminal of the microprocessor serve together as the first serial communication signal output terminal of the control circuit and the second serial communication signal input terminal of the control circuit, and are connected to the host and the slave to output the first serial communication signal and input the second serial communication signal.

6. The digital interface expansion circuit according to claim 3, characterized in that: The switch circuit includes a relay, a diode, a second switch tube, a second capacitor, a fifth resistor, a sixth resistor and a seventh resistor; The first end of the fifth resistor serves as the control signal input end of the switch circuit and is connected to the control circuit to input the control signal; the second end of the fifth resistor is connected to the first end of the seventh resistor and the control end of the second switch tube, the first end of the second switch tube is connected to the positive electrode of the diode, the first end of the second capacitor and the first coil end of the relay, the second end of the second capacitor, the negative electrode of the diode, the first end of the sixth resistor and the second coil end of the relay are connected, and the second end of the sixth resistor is connected to the third power supply; the first common end of the relay, the second common end of the relay and the normally open end of the relay are collectively used as the dry contact and are connected to the execution circuit interface.

7. The digital interface expansion circuit according to any one of claims 1 to 6, characterized in that: The digital bus also includes a power line; The host is also configured to output a power supply voltage from the power line to power the slave and the main control circuit.

8. The digital interface expansion circuit according to any one of claims 1 to 6, characterized in that: The digital interface includes an HDMI interface and a VGA interface; the digital bus includes an HDMI bus and a VGA bus.

9. The digital interface expansion circuit according to any one of claims 1 to 6, characterized in that: The serial communication bus includes an I2C bus.

10. An electronic device, characterized in that: The electronic device comprises the digital interface expansion circuit as claimed in any one of claims 1 to 9.

11. A monitoring system, characterized in that: The monitoring system comprises a host and a slave connected to a digital bus and a digital interface expansion circuit as claimed in any one of claims 1 to 9.

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