A circuit for mutually exclusive access to a USB storage medium with dual control sources

Abstract

The present invention belongs to the technical field of embedded computer systems, and particularly relates to a circuit for mutually exclusive access to a USB storage medium by dual control sources, which is used to achieve mutually exclusive access to the same USB storage medium by a processor unit in an embedded computer and an external device. The circuit includes a relay circuit, two delay control circuits, an opto-MOS type bidirectional electronic relay, and two USB signal electronic switches. The present invention does not require disassembly and assembly of the USB storage medium, is suitable for use in an environment with strong structural reinforcement requirements, solves the problem of mutually exclusive access by dual control sources, and can achieve mutually exclusive access by internal and external dual control sources for a structurally reinforced USB storage medium inside an embedded computer system.

Description

Technical Field

[0001] The present invention belongs to the technical field of embedded computer systems, and particularly relates to a circuit for mutually exclusive access to a USB storage medium by two control sources. Background Art

[0002] USB storage media have been widely used in people's daily lives due to their low cost, easy portability, and convenient use. Especially because of the advantage of convenient data exchange, in recent years, embedded computer systems have also begun to use USB storage media to achieve real-time storage of the data generated and required during operation, so as to facilitate data download and transfer storage after the system operation ends. When a USB storage is applied in an embedded computer system, during real-time operation, the read and write access to the USB storage medium is realized by the processor unit in the embedded computer system. However, after the system ends or stops running, there are two methods to consider for downloading data: 1. Take out the USB storage medium in the embedded computer system to complete data download, but in order to continue using it in the next operation, the USB storage medium needs to be reinstalled back into the system after downloading the data; 2. The embedded computer system has a built-in external USB interface, and the internal USB storage medium does not need to be taken out. The external device of the system directly connects to the USB interface through a USB cable to realize the download of the data in the internal USB storage medium. Method 1 involves multiple disassembly and assembly operations and is not suitable for application scenarios with strong structural reinforcement requirements for the embedded computer system. Method 2 does not require disassembly and assembly of the USB storage medium and is suitable for use in an environment with strong structural reinforcement requirements, but it is necessary to solve the problem of mutually exclusive access by two control sources, that is, to realize the mutually exclusive access of the processor unit inside the embedded computer and the external device to the same USB storage medium. Summary of the Invention

[0003] In view of this, the present invention proposes a circuit for mutually exclusive access to a USB storage medium by two control sources, which can achieve mutually exclusive access by two internal and external control sources for the structurally reinforced USB storage medium inside the embedded computer system.

[0004] In order to achieve the above technical objectives, the specific technical solutions adopted by the present invention are as follows:

[0005] A circuit for mutually exclusive access to a USB storage medium by two control sources, which is used to realize the mutually exclusive access of the processor unit inside the embedded computer and the external device to the same USB storage medium, and includes: a relay circuit, two delay control circuits, an opto-MOS type bidirectional electronic relay, and two USB signal electronic switches;

[0006] The relay circuit is used to control the power supply of the USB storage medium. When an external USB interface is connected to the storage circuit, the internal power supply of the USB storage medium is switched to the power supply of the external USB interface. When the external USB is disconnected, the power supply of the external USB interface of the USB storage medium is switched to the internal power supply;

[0007] Two of the delay control circuits are respectively connected to two input ends of an opto-MOS type bidirectional electronic relay. The opto-MOS type bidirectional electronic relay is used to mutually exclusive control the power supply of two USB signal electronic switches. When an external USB interface is connected to the storage circuit, it is ensured that the internal USB signal of the product where the circuit for mutually exclusive access to the USB storage medium by the USB storage medium and the dual-control source is first disconnected, and then the interface signal between the USB storage medium and the external USB is connected.

[0008] Further, the connection method of the external control source of the circuit for mutually exclusive access to the USB storage medium by the dual-control source is as follows: The external USB power supply 5V of the USB storage medium is connected to capacitor C3, the coil control terminal pin 2 of electromagnetic relay K1, the normally open contact pin 4 of electromagnetic relay K1, resistor R1, resistor R2, resistor R5, and pin 8 of opto-MOS type bidirectional electronic relay N1;

[0009] The external USB_D- signal of the USB storage medium is connected to pin 1 of USB signal electronic switch N3, and the external USB_D+ signal of the USB storage medium is connected to pin 10 of USB signal electronic switch N3;

[0010] The other end of resistor R2 is connected to capacitor C1 and the input end of NOT gate D1. The output end of D1 is connected to resistor R3. The other end of R3 is connected to capacitor C2 and one end of resistor R4. The other end of resistor R4 is connected to pin 3 of opto-MOS type bidirectional electronic relay N1;

[0011] The other end of resistor R5 is connected to capacitor C5 and one end of resistor R6. The other end of resistor R6 is connected to pin 1 of opto-MOS type bidirectional electronic relay N1;

[0012] Pin 7 of opto-MOS type bidirectional electronic relay N1 is connected to capacitor C7, pin 9, and pin 5 of USB signal electronic switch N3. Pin 8 of USB signal electronic switch N3 is connected to resistor R9. The logic level of pin 8 of USB signal electronic switch N3 is low. Pin 5 of USB signal electronic switch N3 is normally powered. When the logic level of pin 9 of USB signal electronic switch N3 is high, the internal switch pin 6 of USB signal electronic switch N3 is connected to pin 1 and pin 7 is connected to pin 10.

[0013] Further, the internal control source connection mode of the circuit for dual-control source mutually exclusive access to the USB storage medium is as follows: The internal USB power supply of 5V of the USB storage medium is connected to the capacitor C4, the normally closed contact pin 5 of the electromagnetic relay K1, and the pin 6 of the opto-MOS type bidirectional electronic relay N1;

[0014] The internal USB_D- signal of the USB storage medium is connected to the pin 1 of the USB signal electronic switch N2, and the internal USB_D+ signal of the USB storage medium is connected to the pin 10 of the USB signal electronic switch N2;

[0015] The pin 5 of the opto-MOS type bidirectional electronic relay N1 is connected to the capacitor C6, the pin 9 and the pin 5 of the USB signal electronic switch N2. The pin 8 of the USB signal electronic switch N2 is connected to the resistor R8. The logic level of the pin 8 of the USB signal electronic switch N2 is low. The pin 5 of the USB signal electronic switch N2 is normally powered. When the logic level of the pin 9 of the USB signal electronic switch N2 is high, the internal switch pin 6 is connected to the pin 1 and the pin 7 is connected to the pin 10.

[0016] Further, the connection mode of the USB storage standard interface of the USB storage medium is as follows:

[0017] The pin 1 of the USB storage standard interface is connected to the capacitor C8 and the pin 1 of the electromagnetic relay K1;

[0018] The pin 2 of the USB storage standard interface is connected to the pin 6 of the USB signal electronic switch N2 and the pin 6 (switch output terminal) of the USB signal electronic switch N3;

[0019] The pin 3 of the USB storage standard interface is connected to the pin 7 of the USB signal electronic switch N2 and the pin 7 of the USB signal electronic switch N3;

[0020] The pin 4 of the USB storage standard interface is connected to the ground.

[0021] Further, the component grounding connection mode of the circuit for dual-control source mutually exclusive access to the USB storage medium is as follows:

[0022] The low end of the coil control of the electromagnetic relay K1 is connected to the ground. The pin 2 of the opto-MOS type bidirectional electronic relay N1 is grounded. The pin 4 of the opto-MOS type bidirectional electronic relay N1 is grounded. One end of the resistor R1 is connected to the ground. One end of the resistor R8 is connected to the ground. One end of the resistor R9 is connected to the ground. One end of the capacitor C1 is connected to the ground. One end of the capacitor C2 is connected to the ground. One end of the capacitor C3 is connected to the ground. One end of the capacitor C4 is connected to the ground. One end of the capacitor C5 is connected to the ground. One end of the capacitor C6 is connected to the ground. One end of the capacitor C7 is connected to the ground. One end of the capacitor C8 is connected to the ground. Description of the Drawings

[0023] To more clearly illustrate the technical solutions of the embodiments of the present disclosure, the following will briefly introduce the drawings required in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present disclosure. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0024] Figure 1 This is the circuit design diagram of the dual-control source mutually exclusive access USB storage medium in the specific embodiment of the present invention. Specific Embodiment

[0025] The following will describe the embodiments of the present disclosure in detail with reference to the drawings.

[0026] The following illustrates the embodiments of the present disclosure through specific specific examples. Those skilled in the art can easily understand other advantages and effects of the present disclosure from the content disclosed in this specification. Obviously, the described embodiments are only part of the embodiments of the present disclosure, rather than all the embodiments. The present disclosure can also be implemented or applied through other different specific embodiments. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present disclosure. It should be noted that, without conflict, the following embodiments and the features in the embodiments can be combined with each other. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present disclosure without creative efforts belong to the scope of protection of the present disclosure.

[0027] It should be noted that the following describes various aspects of the embodiments within the scope of the appended claims. It should be obvious that the aspects described herein can be embodied in a wide variety of forms, and any specific structure and / or function described herein is only illustrative. Based on the present disclosure, those skilled in the art should understand that one aspect described herein can be implemented independently of any other aspect, and two or more of these aspects can be combined in various ways. For example, any number of aspects described herein can be used to implement the device and / or practice the method. Additionally, this device and / or this method can be implemented using other structures and / or functions in addition to one or more of the aspects described herein.

[0028] It should also be noted that the diagrams provided in the following embodiments only schematically illustrate the basic concept of the present disclosure. The diagrams only show the components related to the present disclosure and are not drawn according to the number, shape, and size of the components in actual implementation. The type, quantity, and ratio of each component in its actual implementation can be an arbitrary change, and the component layout type may also be more complex.

[0029] In addition, in the following description, specific details are provided to facilitate a thorough understanding of the examples. However, those skilled in the art will understand that the aspects described may be practiced without these specific details.

[0030] In one embodiment of the present invention, a circuit for mutually exclusive access to a USB storage medium with dual control sources is proposed, which is used to realize the mutually exclusive access of a processor unit in an embedded computer and an external device to the same USB storage medium. The circuit includes: a relay circuit, two delay control circuits, an opto-MOS bidirectional electronic relay, and two USB signal electronic switches.

[0031] The relay circuit is used to control the power supply of the USB storage medium. When the external USB interface is connected to the storage circuit, the internal power supply of the USB storage medium is switched to the power supply of the external USB interface. When the external USB is disconnected, the power supply of the external USB interface of the USB storage medium is switched to the internal power supply.

[0032] The two delay control circuits are respectively connected to two input terminals of the opto-MOS bidirectional electronic relay. The opto-MOS bidirectional electronic relay is used to mutually exclusively control the power supply of the two USB signal electronic switches. When the external USB interface is connected to the storage circuit, it is ensured that the internal USB signal of the product in which the USB storage medium and the circuit for mutually exclusive access to the USB storage medium with dual control sources are installed is first disconnected, and then the interface signal between the USB storage medium and the external USB is connected.

[0033] In this embodiment, the connection method of the external control source of the circuit for mutually exclusive access to the USB storage medium with dual control sources is as follows: The external USB power supply 5V of the USB storage medium is connected to the capacitor C3, the coil control terminal pin 2 of the electromagnetic relay K1, the normally open contact pin 4 of the electromagnetic relay K1, the resistor R1, the resistor R2, the resistor R5, and the pin 8 of the opto-MOS bidirectional electronic relay N1.

[0034] The external USB_D- signal of the USB storage medium is connected to the pin 1 of the USB signal electronic switch N3, and the external USB_D+ signal of the USB storage medium is connected to the pin 10 of the USB signal electronic switch N3.

[0035] The other end of the resistor R2 is connected to the capacitor C1 and the input terminal of the NOT gate D1. The output terminal of D1 is connected to the resistor R3. The other end of R3 is connected to the capacitor C2 and one end of the resistor R4. The other end of the resistor R4 is connected to the pin 3 of the opto-MOS bidirectional electronic relay N1.

[0036] The other end of the resistor R5 is connected to the capacitor C5 and one end of the resistor R6. The other end of the resistor R6 is connected to the pin 1 of the opto-MOS bidirectional electronic relay N1.

[0037] Pin 7 of the opto-MOS bidirectional electronic relay N1 is connected to capacitor C7, pin 9 and pin 5 of the USB signal electronic switch N3. Pin 8 of the USB signal electronic switch N3 is connected to resistor R9. When the logic level of pin 8 of the USB signal electronic switch N3 is low, pin 5 of the USB signal electronic switch N3 is normally powered, and when the logic level of pin 9 of the USB signal electronic switch N3 is high, the internal switch pin 6 of the USB signal electronic switch N3 is connected to pin 1 and pin 7 is connected to pin 10.

[0038] In this embodiment, the internal control source connection method of the circuit for mutually exclusive access to the USB storage medium by dual control sources is as follows: The internal USB power supply 5V of the USB storage medium is connected to capacitor C4, the normally closed contact pin 5 of the electromagnetic relay K1, and pin 6 of the opto-MOS bidirectional electronic relay N1.

[0039] The internal USB_D- signal of the USB storage medium is connected to pin 1 of the USB signal electronic switch N2, and the internal USB_D+ signal of the USB storage medium is connected to pin 10 of the USB signal electronic switch N2.

[0040] Pin 5 of the opto-MOS bidirectional electronic relay N1 is connected to capacitor C6, pin 9 and pin 5 of the USB signal electronic switch N2. Pin 8 of the USB signal electronic switch N2 is connected to resistor R8. When the logic level of pin 8 of the USB signal electronic switch N2 is low, pin 5 of the USB signal electronic switch N2 is normally powered, and when the logic level of pin 9 of the USB signal electronic switch N2 is high, the internal switch pin 6 is connected to pin 1 and pin 7 is connected to pin 10.

[0041] The connection method of the USB storage standard interface of the USB storage medium is as follows:

[0042] Pin 1 of the USB storage standard interface is connected to capacitor C8 and pin 1 of the electromagnetic relay K1.

[0043] Pin 2 of the USB storage standard interface is connected to pin 6 of the USB signal electronic switch N2 and pin 6 (switch output terminal) of the USB signal electronic switch N3.

[0044] Pin 3 of the USB storage standard interface is connected to pin 7 of the USB signal electronic switch N2 and pin 7 of the USB signal electronic switch N3.

[0045] Pin 4 of the USB storage standard interface is connected to ground.

[0046] In this embodiment, the component grounding connection method of the circuit for mutually exclusive access to the USB storage medium by dual control sources is as follows:

[0047] The low - end connection of the coil of electromagnetic relay K1 is grounded. Pin 2 of opto - MOS bidirectional electronic relay N1 is grounded. Pin 4 of opto - MOS bidirectional electronic relay N1 is grounded. One end of resistor R1 is grounded. One end of resistor R8 is grounded. One end of resistor R9 is grounded. One end of capacitor C1 is grounded. One end of capacitor C2 is grounded. One end of capacitor C3 is grounded. One end of capacitor C4 is grounded. One end of capacitor C5 is grounded. One end of capacitor C6 is grounded. One end of capacitor C7 is grounded. One end of capacitor C8 is grounded.

[0048] Basic design rules of this embodiment:

[0049] 1. Each of the dual - control sources supports hot - plugging connection.

[0050] 2. The access priority of the external control source is higher than that of the internal control source.

[0051] 3. When the external control source is not connected to the circuit, it is defaulted to be accessed by the internal control source.

[0052] 4. For the control - source switching of the USB storage standard interface signals D - and D +, a mutually - exclusive design principle of disconnect - first - then - connect is adopted.

[0053] External control source connection:

[0054] As Figure 1 shown

[0055] 1. External USB power supply 5V is connected to capacitor C3, the coil control terminal pin 2 of electromagnetic relay K1, the normally - open contact pin 4 of electromagnetic relay K1, resistor R1, resistor R2, resistor R5, and pin 8 of opto - MOS bidirectional electronic relay N1 (i.e., the input terminal of the controlled switch signal).

[0056] 2. External USB_D - signal is connected to pin 1 of N3, and external USB_D + signal is connected to pin 10 of N3.

[0057] 3. The other end of resistor R2 is connected to capacitor C1 and the input terminal of NOT - gate D1. The output terminal of D1 is connected to resistor R3. The other end of R3 is connected to capacitor C2 and resistor R4. The other end of resistor R4 is connected to pin 3 of N1 (i.e., the input terminal of the light - emitting diode).

[0058] 4. The other end of resistor R5 is connected to capacitor C5 and resistor R6. The other end of resistor R6 is connected to pin 1 of N1 (i.e., the input terminal of the light - emitting diode).

[0059] 5. Pin 7 of N1 (i.e., the controlled switch signal output terminal) is connected to capacitor C7, pin 9 (switch selection terminal) and pin 5 (power supply terminal) of USB signal electronic switch N3. When the logic level of pin 8 of N3 is low, pin 5 is normally powered, and the logic level of pin 9 is high, the internal switch pin 6 of N3 is connected to pin 1, and pin 7 is connected to pin 10.

[0060] Internal control source connection:

[0061] As Figure 1 shown

[0062] 1. The internal USB power supply of 5V is connected to capacitor C4, the normally closed contact pin 5 of electromagnetic relay K1, and pin 6 of opto-MOS type bidirectional electronic relay N1 (i.e., the controlled switch signal input terminal);

[0063] 2. The internal USB_D- signal is connected to pin 1 of N2, and the internal USB_D+ signal is connected to pin 10 of N2;

[0064] 3. Pin 5 of N1 (i.e., the controlled switch signal output terminal) is connected to capacitor C6, pin 9 (switch selection terminal) and pin 5 (power supply terminal) of USB signal electronic switch N2. When the logic level of pin 8 of N2 is low, pin 5 is normally powered, and the logic level of pin 9 is high, the internal switch pin 6 of N2 is connected to pin 1, and pin 7 is connected to pin 10.

[0065] USB storage standard interface connection:

[0066] As Figure 1 shown

[0067] 1. Pin 1 (power supply terminal) of the USB storage standard interface is connected to capacitor C8 and pin 1 (switch output terminal) of electromagnetic relay K1;

[0068] 2. Pin 2 (signal D- of the serial data transmission line) of the USB storage standard interface is connected to pin 6 (switch output terminal) of N2 and pin 6 (switch output terminal) of N3;

[0069] 3. Pin 3 (signal D+ of the serial data transmission line) of the USB storage standard interface is connected to pin 7 (switch output terminal) of N2 and pin 7 (switch output terminal) of N3;

[0070] 4. Pin 4 of the USB storage standard interface is connected to ground.

[0071] Component ground connection:

[0072] As Figure 1 shown

[0073] The low - end connection of the coil control of the electromagnetic relay K1 is grounded. The pin 2 of the opto - MOS type bidirectional electronic relay N1 is grounded (i.e., the light - emitting diode output terminal is grounded), the pin 4 of the opto - MOS type bidirectional electronic relay N1 is grounded (i.e., the light - emitting diode output terminal is grounded), one end of the resistor R1 is grounded, one end of the resistor R8 is grounded, one end of the resistor R9 is grounded, one end of the capacitor C1 is grounded, one end of the capacitor C2 is grounded, one end of the capacitor C3 is grounded, one end of the capacitor C4 is grounded, one end of the capacitor C5 is grounded, one end of the capacitor C6 is grounded, one end of the capacitor C7 is grounded, and one end of the capacitor C8 is grounded.

[0074] As described above, it is only the specific implementation manner of the present disclosure, but the protection scope of the present disclosure is not limited thereto. Any change or replacement that can be easily thought of by those skilled in the art within the technical scope disclosed by the present disclosure should be covered within the protection scope of the present disclosure. Therefore, the protection scope of the present disclosure should be subject to the protection scope of the claims.

Claims

1. A circuit for mutually exclusive access to a USB storage medium with dual control sources, characterized in that It is used to realize the exclusive access of the processor unit and external devices in the embedded computer to the same USB storage medium, including: a relay circuit, two delay control circuits, an opto-MOS bidirectional electronic relay, and two USB signal electronic switches; The relay circuit is used to control the power supply of the USB storage medium. When an external USB interface is connected to the storage circuit, the internal power supply of the USB storage medium is switched to the power supply of the external USB interface. When the external USB is disconnected, the power supply of the external USB interface of the USB storage medium is switched to the internal power supply; The two delay control circuits are respectively connected to the two input ends of the opto-MOS bidirectional electronic relay. The opto-MOS bidirectional electronic relay is used to mutually control the power supply of the two USB signal electronic switches. When the external USB interface is connected to the storage circuit, it ensures that the internal USB signal of the product installed with the circuit for mutually exclusive access of the USB storage medium between the USB storage medium and the dual-control source is first disconnected, and then the interface signal between the USB storage medium and the external USB is connected; The connection method of the external control source of the circuit for mutually exclusive access of the USB storage medium by the dual-control source is: the external USB power supply 5V of the USB storage medium is connected to the capacitor C3, the coil control terminal pin 2 of the electromagnetic relay K1, the normally open contact pin 4 of the electromagnetic relay K1, the resistor R1, the resistor R2, the resistor R5, and the pin 8 of the opto-MOS bidirectional electronic relay N1; The external USB_D- signal of the USB storage medium is connected to pin 1 of the USB signal electronic switch N3, and the external USB_D+ signal of the USB storage medium is connected to pin 10 of the USB signal electronic switch N3; The other end of the resistor R2 is connected to the capacitor C1 and the input end of the NOT gate D1. The output end of D1 is connected to the resistor R3. The other end of R3 is connected to the capacitor C2 and one end of the resistor R4. The other end of the resistor R4 is connected to pin 3 of the opto-MOS bidirectional electronic relay N1; The other end of the resistor R5 is connected to the capacitor C5 and one end of the resistor R6. The other end of the resistor R6 is connected to pin 1 of the opto-MOS bidirectional electronic relay N1; Pin 7 of the opto-MOS bidirectional electronic relay N1 is connected to the capacitor C7, pin 9 and pin 5 of the USB signal electronic switch N3. Pin 8 of the USB signal electronic switch N3 is connected to the resistor R9; the logic level of pin 8 of the USB signal electronic switch N3 is low, pin 5 of the USB signal electronic switch N3 is normally powered, and when the logic level of pin 9 of the USB signal electronic switch N3 is high, the internal switch pin 6 of the USB signal electronic switch N3 is connected to pin 1 and pin 7 is connected to pin 10; The connection method of the internal control source of the circuit for mutually exclusive access of the USB storage medium by the dual-control source is: the internal USB power supply 5V of the USB storage medium is connected to the capacitor C4, the normally closed contact pin 5 of the electromagnetic relay K1, and pin 6 of the opto-MOS bidirectional electronic relay N1; The internal USB_D- signal of the USB storage medium is connected to pin 1 of the USB signal electronic switch N2, and the internal USB_D+ signal of the USB storage medium is connected to pin 10 of the USB signal electronic switch N2; Pin 5 of the opto-MOS bidirectional electronic relay N1 is connected to capacitor C6, pin 9 and pin 5 of the USB signal electronic switch N2. Pin 8 of the USB signal electronic switch N2 is connected to resistor R8. The logic level of pin 8 of the USB signal electronic switch N2 is low. Pin 5 of the USB signal electronic switch N2 is normally powered. When the logic level of pin 9 of the USB signal electronic switch N2 is high, the internal switch pin 6 is connected to pin 1 and pin 7 is connected to pin 10.

2. The circuit for dual-control source mutually exclusive access to a USB storage medium according to claim 1, characterized in that, The connection method of the USB storage standard interface of the USB storage medium is as follows: Pin 1 of the USB storage standard interface is connected to capacitor C8 and pin 1 of the electromagnetic relay K1; Pin 2 of the USB storage standard interface is connected to pin 6 of the USB signal electronic switch N2 and pin 6 of the USB signal electronic switch N3. Pin 6 is the switch output terminal; Pin 3 of the USB storage standard interface is connected to pin 7 of the USB signal electronic switch N2 and pin 7 of the USB signal electronic switch N3; Pin 4 of the USB storage standard interface is connected to ground.

3. The circuit for mutually exclusive access to a USB storage medium with dual control sources according to claim 2, wherein The grounding connection method of the components of the circuit for dual-control source mutually exclusive access to the USB storage medium is as follows: The low-end connection of the electromagnetic relay K1 coil is grounded. Pin 2 of the opto-MOS bidirectional electronic relay N1 is grounded. Pin 4 of the opto-MOS bidirectional electronic relay N1 is grounded. One end of resistor R1 is grounded. One end of resistor R8 is grounded. One end of resistor R9 is grounded. One end of capacitor C1 is grounded. One end of capacitor C2 is grounded. One end of capacitor C3 is grounded. One end of capacitor C4 is grounded. One end of capacitor C5 is grounded. One end of capacitor C6 is grounded. One end of capacitor C7 is grounded. One end of capacitor C8 is grounded.

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