Headphone structure of bone sensing external sound switch

Abstract

The utility model relates to the technical field of headphones, and particularly discloses a headphone structure of a bone sensing external sound switch, which comprises a headphone main body and a drive-by-wire box electrically connected with the headphone main body, a bone transmission external sound input module is arranged in a left ear shell of the headphone main body, and a bone transmission external sound output module is arranged in a right ear shell of the headphone main body. The bone-transmission external sound input module is mounted in the left ear shell, the bone-transmission external sound input module is mounted in the left ear shell, the bone-transmission external sound input module is mounted in the bone-transmission external sound input module, the bone-transmission external sound input module is mounted in the bone-transmission external sound input module, the bone-transmission external sound input module is mounted in the bone-transmission external sound input module, and the bone-transmission external sound input module is mounted in the bone-transmission external sound input module. According to the utility model, two special functions of mute noise reduction and bone sensing audio frequency can be easily switched by slightly pressing the change-over switch on the drive-by-wire box, so that the earphone can clearly hear the external sound without any change, and the scene of occasionally listening to the external sound in a mute mode is omitted; the practicability of the earphone is improved.

Description

Technical Field

[0001] The utility model relates to the technical field of head-mounted headphones, in particular to a head-mounted headphone structure with a bone-sensing external sound switch. Background Art

[0002] With the continuous development of headphones, more practical function keys and operating experiences are brought to game players, office workers, students, and music listeners.

[0003] For example, the patent document application number is 202311129557.0, which discloses a headset, including a headband assembly and two earphone heads, one of which is provided with a microphone assembly for receiving sound, a regulator for adjusting the volume, and a USB connector, the headband assembly includes a head beam frame, two groups of arms slidably arranged at the two ends of the head beam frame, a sheath sleeved outside the head beam frame, and two groups of sheath boxes respectively arranged at the two ends of the sheath, the head beam frame is made of metal steel bars, the top of the head beam frame is provided with a plurality of hollow holes, the sheath box is provided with a locking piece for locking the position of the arm, the earphone head includes an ear shell with a cavity, a speaker seat arranged in the ear shell, a dynamic coil arranged on the side of the speaker seat close to the cavity, and a vibrator arranged on the side of the dynamic coil away from the speaker seat, and there is a space between the dynamic coil and the vibrator. This application has the effect of improving the overall wearing comfort of the headset.

[0004] However, the existing headphones generally have the problem of single function and cannot be used for multiple purposes, that is, they either have only the mute noise reduction function or only the bone sensing audio function. When users use such headphones, if they want both the mute noise reduction and bone sensing audio functions, they need to buy another headphone with the other function, and the headphone may not be suitable for the head shape they are used to. Therefore, we need to propose a headphone structure with a bone sensing external sound switch to solve the above-mentioned problems, so that it can easily realize the switching of the two dedicated functions of mute noise reduction and bone sensing audio, thereby improving the practicality of the headphones. Utility Model Content

[0005] The purpose of the utility model is to provide a headphone structure with a bone sensing external sound switch, which can easily realize the switching of two special functions of silent noise reduction and bone sensing audio, improve the practicality of the headphone, and solve the problems raised in the background technology.

[0006] To achieve the above-mentioned purpose, the utility model provides the following technical solutions: a headset structure with a bone-sensing external sound switch, comprising a headset body and a wire control box electrically connected to the headset body, a bone-transmitted external sound input module is installed in the left ear shell of the headset body, a conversion switch for external sound conversion is installed on the wire control box, and a control circuit electrically connected to the conversion switch is installed in the wire control box;

[0007] The control circuit includes a control unit for controlling audio conversion, a speaker unit and a call microphone unit, the conversion switch, the speaker unit and the call microphone unit are all electrically connected to the control unit, and the control unit is also electrically connected to a USB interface circuit for connecting to a DC power supply and an LED indication circuit for status indication;

[0008] The bone-transmitted sound input module includes a conductive microphone unit, a conductive vibrator unit and a power management unit. The conductive vibrator unit is electrically connected to the speaker unit, the conductive microphone unit is electrically connected to the conductive vibrator unit, and the power management unit is electrically connected to the conductive microphone unit and the conductive vibrator unit.

[0009] Preferably, the control unit includes an audio control chip U1 and a storage chip U2, pin 8 of the audio control chip U1 is connected to a filter circuit, pins 1 to 4 of the storage chip U2 are respectively connected to pins 5 to 2 of the audio control chip U1, a capacitor C20 is connected between pins 5 and 8 of the storage chip U2, and one end of the capacitor C20 is grounded.

[0010] Preferably, the conversion switch is configured as a conduction switch capable of switching the conduction mode on and off, the conduction switch comprising a switch SW1, a switch SW2, a switch SW3 and a switch SW4 which are arranged in parallel, one end of the switch SW1 being connected to pin 6 of the audio control chip U1, one end of the switch SW2 being connected to pin 10 of the audio control chip U1, one end of the switch SW3 being connected to pin 48 of the audio control chip U1, one end of the switch SW4 being connected to pin 39 of the audio control chip U1, and the connection ends of the switches SW1, SW2, SW3 and SW4 being grounded.

[0011] Preferably, the speaker unit includes a speaker SP1-R and a speaker SP2-L, pin 1 of the speaker SP1-R is connected to pin 32 of the audio control chip U1 through capacitor C10, pin 1 of the speaker SP2-L is connected to pin 30 of the audio control chip U1 through capacitor C11, pin 2 of the speaker SP1-R and pin 2 of the speaker SP2-L are both grounded, and one pin of the speaker SP2-L is also connected to the bone conduction sound input module.

[0012] Preferably, the call microphone unit includes a call microphone, one pin of the call microphone is connected to an inductor L5, one end of the inductor L5 is connected in parallel with a resistor R10 and a capacitor C12 arranged in series, and a resistor R14 and a resistor R13 arranged in series, one end of the capacitor C12 is connected to pin 27 of the audio control chip U1, and one end of the resistor R13 is connected to pin 25 of the audio control chip U1.

[0013] Preferably, the conductive microphone unit includes a conductive microphone MKR, one end of the conductive microphone MKR is connected to a capacitor AC1, a resistor AR2 and a resistor AR4 arranged in series, one end of the resistor AR4 is connected to an integrated chip AU2, pin 3 of the integrated chip AU2 is connected to a resistor AR18 and a ground resistor AR17, one end of the resistor AR18 is connected to a transistor AQ1, the emitter of the transistor AQ1 is connected to a power management unit, and a capacitor AF3, a capacitor AF1, and a resistor AR19 and a light-emitting diode AD1 arranged in series are connected in parallel between the connection end of the resistor AR18 and the transistor AQ1.

[0014] Preferably, the conductive vibrator unit includes a speaker SPR2 and a capacitor AC6 connected to pin 4 of the integrated chip AU2, one end of the capacitor AC6 is connected to a resistor AR13, one end of the resistor AR13 is connected to a capacitor AC10 and a resistor AR8, a resistor AR10 and a capacitor AC8 arranged in series and a resistor AR9 and a capacitor AC7 arranged in series are connected between the capacitor AC10 and the resistor AR8, and the connecting end of the resistor AR10 and the capacitor AC8 and the connecting end of the resistor AR9 and the capacitor AC7 are both grounded, the connecting end of the resistor AR8 and the resistor AR13 is connected to a capacitor AC11, and one end of the capacitor AC11 is connected to the positive terminal of the speaker SPR2 through a capacitor AC12.

[0015] Preferably, the power management unit includes a power management chip AU3, a resistor AR21 is connected between pins 4 and 5 of the power management chip AU3, a ground resistor AR22 is connected between the connection end of the resistor AR21 and pin 4 of the power management chip AU3, a capacitor AC14 is connected between the connection end of the resistor AR21 and pin 3 of the power management chip AU3, one pin of the power management chip AU3 is connected to a ground capacitor AC15, and the non-grounded end of the ground capacitor AC15 is connected to pin 35 of the audio control chip U1.

[0016] Compared with the prior art, the beneficial effects of the utility model are:

[0017] 1. The utility model adds a conversion switch and a control circuit to the wire control box, and installs the bone-transmitted external sound input module in the left ear shell, so that the two special functions of silent noise reduction and bone sensing audio can be easily switched by lightly pressing the conversion switch on the wire control box, so that the earphones can clearly hear the outside sounds without making any changes, eliminating the scene of occasionally needing to listen to external sounds in the silent mode, thereby improving the practicality of the earphones.

[0018] 2. The utility model installs the conversion switch and the control circuit on the wire control box, and the wire control box can naturally fall on the chest, which can be conveniently operated by both hands, thereby improving the convenience of operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic diagram of the structure of the utility model;

[0020] Figure 2 It is a circuit diagram of the control circuit of the utility model;

[0021] Figure 3 This is a circuit diagram of the conversion switch and storage chip U2 of the utility model;

[0022] Figure 4 This is a circuit diagram of the USB interface circuit of the utility model;

[0023] Figure 5 This is a circuit diagram of the LED indicator circuit of the utility model;

[0024] Figure 6 This is the circuit diagram of the bone conduction sound input module of the utility model;

[0025] Figure 7 The utility model is a circuit diagram of a power management unit.

[0026] In the figure: 1. Headphone body; 2. Control box; 3. Switch. DETAILED DESCRIPTION

[0027] The following will be combined with the drawings in the embodiments of the utility model to clearly and completely describe the technical solutions in the embodiments of the utility model. Obviously, the described embodiments are only part of the embodiments of the utility model, not all of the embodiments. Based on the embodiments in the utility model, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the utility model.

[0028] See also Figure 1-7 The utility model provides a technical solution: a headset structure with a bone sensing external sound switch, comprising a headset body 1 and a wire control box 2 electrically connected to the headset body 1, a bone transmission external sound input module is installed in the left ear shell of the headset body 1, a conversion switch 3 for external sound conversion is installed on the wire control box 2, and a control circuit electrically connected to the conversion switch 3 is installed in the wire control box 2;

[0029] The control circuit includes a control unit for controlling audio conversion, a speaker unit and a call microphone unit, and the conversion switch 3, the speaker unit and the call microphone unit are all electrically connected to the control unit;

[0030] The control unit includes an audio control chip U1 and a storage chip U2. Pin 8 of the audio control chip U1 is connected to a filter circuit. Pins 1 to 4 of the storage chip U2 are respectively connected to pins 5 to 2 of the audio control chip U1. A capacitor C20 is connected between pins 5 and 8 of the storage chip U2, and one end of the capacitor C20 is grounded. The storage chip U2 is used for data exchange and instruction transmission, so that the audio control chip U1 can directly read instructions and data from the storage chip, or write processing results back to the storage chip U2.

[0031] The filtering circuit includes a capacitor C8 connected to pin 8 of the audio control chip U1 and a capacitor C9 connected to pin 9 of the audio control chip U1. The connection end of the capacitor C8 and pin 8 of the audio control chip U1 is connected to a capacitor C17 to ground, and the connection end of the capacitor C9 and pin 9 of the audio control chip U1 is connected to a capacitor C18 to ground. The capacitors C8, C9, C17 and C18 are used to stabilize the power supply voltage to prevent noise on the power line from interfering with the operation of the audio control chip U1. The voltage fluctuation on the power line can also be smoothed, so that the control chip U1 can obtain a more stable power supply.

[0032] The conversion switch 3 is configured as a conduction switch capable of switching the conduction mode on and off. The conduction switch includes a switch SW1, a switch SW2, a switch SW3 and a switch SW4 which are arranged in parallel. One end of the switch SW1 is connected to pin 6 of the audio control chip U1, one end of the switch SW2 is connected to pin 10 of the audio control chip U1, one end of the switch SW3 is connected to pin 48 of the audio control chip U1, and one end of the switch SW4 is connected to pin 39 of the audio control chip U1. The connection ends of the switches SW1, SW2, SW3 and SW4 are grounded. The application of the conversion switch 3 as a conduction switch not only optimizes the working performance of the audio control chip U1, but also improves the operating efficiency and reliability of the entire audio system through its flexible on-off control.

[0033] The speaker unit includes a speaker SP1-R and a speaker SP2-L. Pin 1 of the speaker SP1-R is connected to pin 32 of the audio control chip U1 through capacitor C10, and pin 1 of the speaker SP2-L is connected to pin 30 of the audio control chip U1 through capacitor C11. Pin 2 of the speaker SP1-R and pin 2 of the speaker SP2-L are both grounded, and one pin of the speaker SP2-L is also connected to a bone conduction sound input module. Pin 1 of the speaker SP1-R is connected to pin 32 of the audio control chip U1 through capacitor C10, and pin 1 of the speaker SP2-L is connected to pin 30 of the audio control chip U1 through capacitor C11. Capacitor C11 blocks DC signals and only allows audio AC signals to pass through, thereby protecting the speaker from the influence of DC voltage and improving the quality of audio signals.

[0034] The call microphone unit includes a call microphone, one pin of the call microphone is connected to an inductor L5, one end of the inductor L5 is connected in parallel with a resistor R10 and a capacitor C12 arranged in series, and a resistor R14 and a resistor R13 arranged in series, one end of the capacitor C12 is connected to pin 27 of the audio control chip U1, and one end of the resistor R13 is connected to pin 25 of the audio control chip U1. The inductor L5 is used to pass direct current and block alternating current, that is, to allow direct current to pass while blocking alternating current signals, thereby preventing the alternating current component in the electrical signal from affecting other circuit parts. The resistor R10, the capacitor C12, the resistor R14 and the resistor R13 are arranged in series to form a low-pass filter, which only allows low-frequency signals to pass, thereby eliminating high-frequency noise, ensuring that the electrical signal output from the microphone is relatively clean, improving the call quality, and enabling the audio signal to be efficiently and clearly converted, transmitted and processed.

[0035] The bone-transmitted sound input module includes a conductive microphone unit, a conductive vibrator unit and a power management unit. The conductive vibrator unit is electrically connected to the speaker unit, the conductive microphone unit is electrically connected to the conductive vibrator unit, and the power management unit is electrically connected to the conductive microphone unit and the conductive vibrator unit.

[0036] The conductive microphone unit includes a conductive microphone MKR, one end of which is connected to a capacitor AC1, a resistor AR2 and a resistor AR4 arranged in series, one end of the resistor AR4 is connected to an integrated chip AU2, pin 3 of the integrated chip AU2 is connected to a resistor AR18 and a ground resistor AR17, one end of the resistor AR18 is connected to a transistor AQ1, the emitter of the transistor AQ1 is connected to a power management unit, capacitors AF3, capacitors AF1, and resistors AR19 and light-emitting diodes AD1 arranged in series are connected in parallel between the resistor AR18 and the connecting end of the transistor AQ1, the capacitor AC1 is used to block direct current signals and only allow audio alternating current signals to pass through, thereby protecting subsequent circuits from the influence of direct current voltage and improving the quality of audio signals, and the resistors AR2 and AR4 play the role of current limiting and voltage dividing, adjusting the strength of the electrical signal to meet the needs of subsequent circuits.

[0037] The conductive vibrator unit includes a speaker SPR2 and a capacitor AC6 connected to pin 4 of the integrated chip AU2, one end of the capacitor AC6 is connected to a resistor AR13, one end of the resistor AR13 is connected to a capacitor AC10 and a resistor AR8, a resistor AR10 and a capacitor AC8 arranged in series and a resistor AR9 and a capacitor AC7 arranged in series are connected between the capacitor AC10 and the resistor AR8, and the connecting end of the resistor AR10 and the capacitor AC8 and the connecting end of the resistor AR9 and the capacitor AC7 are both grounded, the connecting end of the resistor AR8 and the resistor AR13 is connected to a capacitor AC11, and one end of the capacitor AC11 is connected to the positive terminal of the speaker SPR2 through a capacitor AC12.

[0038] The power management unit includes a power management chip AU3, a resistor AR21 is connected between pins 4 and 5 of the power management chip AU3, a ground resistor AR22 is connected to the connection end of the resistor AR21 and pin 4 of the power management chip AU3, a capacitor AC14 is connected to the connection end of the resistor AR21 and pin 3 of the power management chip AU3, one pin of the power management chip AU3 is connected to a ground capacitor AC15, and the non-grounded end of the ground capacitor AC15 is connected to pin 35 of the audio control chip U1.

[0039] The control unit is also electrically connected to a USB interface circuit for connecting to a DC power supply and an LED indication circuit for status indication, wherein the USB interface circuit includes a USB terminal, pin 1 of the USB terminal is connected to a resistor R1, one end of the resistor R1 is connected in parallel to magnetic beads L2 and magnetic beads L3 connected to the audio control chip U1, pin 2 of the USB terminal is connected to a resistor R4 having one end connected to the audio control chip U1 and a capacitor C1 to ground, pin 3 of the USB terminal is connected to a capacitor C2 to ground and a resistor R5 having one end connected to the audio control chip U1, and pin 4 of the USB terminal is connected to a magnetic bead L1 having one end grounded, and anti-interference operation is performed through magnetic beads L1, magnetic beads L2 and magnetic beads L3 to improve the stability of signal transmission at the USB terminal.

[0040] The LED indication circuit includes a resistor R16 and a resistor R17 connected to the audio control chip U1, one end of the resistor R16 is connected to a light-emitting diode D5, one end of the resistor R17 is connected to a light-emitting diode D6, and one end of the light-emitting diode D5 and one end of the light-emitting diode D6 are both grounded. The status of the wearable headset is displayed through the light-emitting diode D6 and the light-emitting diode D5, so that personnel can confirm it in time.

[0041] When in use, the audio control chip U1 is responsible for processing the conversion, amplification and filtering of all audio signals. The storage chip U2 is used to store data and instructions so that the audio control chip U1 can quickly read and execute them. When the user presses the conversion switch 3 on the wire control box, this action will be recognized by the switch SW1, switch SW2 and switch SW3, and the signal will be sent to the audio control chip U1. The audio control chip U1 adjusts its internal circuit connection according to the received signal, thereby changing the way the audio signal is processed.

[0042] If the user selects the silent noise reduction mode, the audio control chip U1 will start the filter circuit, and stabilize the power supply voltage through capacitors C8, C9, C17 and C18 to prevent the noise on the power line from interfering with the chip's operation, and smooth the voltage fluctuation on the power line, so that the chip can obtain a more stable power supply. This can effectively eliminate background noise and provide clear audio output.

[0043] If the user selects the bone sensing audio mode, the audio control chip U1 will start the conduction microphone unit and the conduction vibrator unit. The conduction microphone unit performs preliminary processing on the sound signal through components such as capacitor AC1, resistor AR2 and resistor AR4, and then sends it to the integrated chip AU2 for further amplification and filtering. The conduction vibrator unit is responsible for converting the processed audio signal into vibration and transmitting it to the user's ear through the bones.

[0044] The utility model turns off the external sound mode by default, that is, there is only a silent noise reduction mode; after switching on, the external sound mode is added, that is, through quick switching, the headset can clearly hear the outside sound without any changes, eliminating the scene where you need to occasionally listen to the external sound in the silent mode, such as when the friend opposite you makes a hand gesture, or when the friends on the left and right sides touch you for prompts. By adding a conversion switch and a control circuit to the line control box, the bone-transmitted external sound input module is installed in the left ear shell, so that it can easily switch between the two special functions of silent noise reduction and bone sensing audio by lightly pressing the conversion switch on the line control box, so that the headset can clearly hear the outside sound without any changes, eliminating the scene where you need to occasionally listen to the external sound in the silent mode, and improving the practicality of the headset.

[0045] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A headphone structure with a bone sensing external sound switch, characterized in that: The invention comprises a headphone body (1) and a wire control box (2) electrically connected to the headphone body (1), a bone conduction external sound input module is installed in the left ear shell of the headphone body (1), a conversion switch (3) for external sound conversion is installed on the wire control box (2), and a control circuit electrically connected to the conversion switch (3) is installed in the wire control box (2); The control circuit comprises a control unit for controlling audio conversion, a speaker unit and a call microphone unit, the conversion switch (3), the speaker unit and the call microphone unit are all electrically connected to the control unit, and the control unit is also electrically connected to a USB interface circuit for connecting to a DC power supply and an LED indication circuit for status indication; The bone-transmitted sound input module includes a conductive microphone unit, a conductive vibrator unit and a power management unit. The conductive vibrator unit is electrically connected to the speaker unit, the conductive microphone unit is electrically connected to the conductive vibrator unit, and the power management unit is electrically connected to the conductive microphone unit and the conductive vibrator unit.

2. The headphone structure of the bone sensing external sound switch according to claim 1, characterized in that: The control unit includes an audio control chip U1 and a storage chip U2, wherein pin 8 of the audio control chip U1 is connected to a filter circuit, pins 1 to 4 of the storage chip U2 are respectively connected to pins 5 to 2 of the audio control chip U1, a capacitor C20 is connected between pins 5 and 8 of the storage chip U2, and one end of the capacitor C20 is grounded.

3. The headphone structure of the bone sensing external sound switch according to claim 2, characterized in that: The conversion switch (3) is configured as a conduction switch capable of switching the conduction mode on and off. The conduction switch comprises a switch SW1, a switch SW2, a switch SW3 and a switch SW4 which are arranged in parallel. One end of the switch SW1 is connected to pin 6 of the audio control chip U1, one end of the switch SW2 is connected to pin 10 of the audio control chip U1, one end of the switch SW3 is connected to pin 48 of the audio control chip U1, and one end of the switch SW4 is connected to pin 39 of the audio control chip U1. The connection ends of the switches SW1, SW2, SW3 and SW4 are grounded.

4. The headphone structure of the bone sensor external sound switch according to claim 3, characterized in that: The speaker unit includes a speaker SP1-R and a speaker SP2-L. Pin 1 of the speaker SP1-R is connected to pin 32 of the audio control chip U1 through capacitor C10, and pin 1 of the speaker SP2-L is connected to pin 30 of the audio control chip U1 through capacitor C11. Pin 2 of the speaker SP1-R and pin 2 of the speaker SP2-L are both grounded, and one pin of the speaker SP2-L is also connected to the bone conduction sound input module.

5. The headphone structure of the bone sensor external sound switch according to claim 4, characterized in that: The call microphone unit includes a call microphone, one pin of the call microphone is connected to an inductor L5, one end of the inductor L5 is connected in parallel with a resistor R10 and a capacitor C12 arranged in series, and a resistor R14 and a resistor R13 arranged in series, one end of the capacitor C12 is connected to pin 27 of the audio control chip U1, and one end of the resistor R13 is connected to pin 25 of the audio control chip U1.

6. The headphone structure of the bone sensor external sound switch according to claim 5, characterized in that: The conductive microphone unit includes a conductive microphone MKR, one end of the conductive microphone MKR is connected to a capacitor AC1, a resistor AR2 and a resistor AR4 arranged in series, one end of the resistor AR4 is connected to an integrated chip AU2, pin 3 of the integrated chip AU2 is connected to a resistor AR18 and a ground resistor AR17, one end of the resistor AR18 is connected to a transistor AQ1, the emitter of the transistor AQ1 is connected to a power management unit, and a capacitor AF3, a capacitor AF1, and a resistor AR19 and a light-emitting diode AD1 arranged in series are connected in parallel between the connection end of the resistor AR18 and the transistor AQ1.

7. The headphone structure of the bone sensor external sound switch according to claim 6, characterized in that: The conductive vibrator unit includes a speaker SPR2 and a capacitor AC6 connected to pin 4 of the integrated chip AU2, one end of the capacitor AC6 is connected to a resistor AR13, one end of the resistor AR13 is connected to a capacitor AC10 and a resistor AR8, a resistor AR10 and a capacitor AC8 arranged in series and a resistor AR9 and a capacitor AC7 arranged in series are connected between the capacitor AC10 and the resistor AR8, and the connecting end of the resistor AR10 and the capacitor AC8 and the connecting end of the resistor AR9 and the capacitor AC7 are both grounded, the connecting end of the resistor AR8 and the resistor AR13 is connected to a capacitor AC11, and one end of the capacitor AC11 is connected to the positive terminal of the speaker SPR2 through a capacitor AC12.

8. The headphone structure of the bone sensor external sound switch according to claim 7, characterized in that: The power management unit includes a power management chip AU3, a resistor AR21 is connected between pins 4 and 5 of the power management chip AU3, a ground resistor AR22 is connected to the connection end of the resistor AR21 and pin 4 of the power management chip AU3, a capacitor AC14 is connected to the connection end of the resistor AR21 and pin 3 of the power management chip AU3, one pin of the power management chip AU3 is connected to a ground capacitor AC15, and the non-grounded end of the ground capacitor AC15 is connected to pin 35 of the audio control chip U1.

Images