Telephone anti-monitoring system based on Hall sensor
By using a hardware control loop composed of a Hall sensor and an analog switch chip, and utilizing the existing on-hook detection sensor in the telephone, the microphone signal is automatically controlled to switch on and off, thus solving the security risks and cumbersome operation problems of wired telephones and achieving a highly efficient and low-cost anti-eavesdropping effect.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SHENZHEN ZHILIAN TECH CO LTD
- Filing Date
- 2026-01-22
- Publication Date
- 2026-04-28
AI Technical Summary
The existing structure of direct electrical connection between the microphone module and the main control CPU in wired telephones poses a security risk, making them vulnerable to hacking and eavesdropping. Existing anti-eavesdropping solutions are cumbersome to operate, prone to failure, and require additional space.
The hardware control loop, consisting of a Hall sensor module and an analog switch chip, automatically controls the microphone signal on/off via the handheld device's hang-up action. The software system, independent of the main control CPU, utilizes the telephone's existing hang-up detection sensor to achieve anti-eavesdropping.
It achieves automatic anti-eavesdropping without any additional operation, improves hardware-level security, reduces the risk of mechanical failure, is compatible with most telephones on the market, and is low-cost and in line with user habits.
Smart Images
Figure CN121940481A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of communication equipment security protection technology, and in particular to a telephone anti-eavesdropping system based on Hall effect sensors. Background Technology
[0002] Wired telephones are widely used in critical scenarios such as homes, hotels, offices, and government command systems due to their high call stability and reliable signal transmission. However, the microphone module and main control CPU of existing wired telephones generally use a direct electrical connection structure, which poses a serious security risk: criminals can use hacking techniques to infiltrate and control the main control CPU of the telephone, and force the microphone module to continuously pick up sound by modifying the software program, thereby listening to and recording conversations around the telephone, leading to the leakage of personal privacy, trade secrets, and official information.
[0003] Currently, anti-eavesdropping telephones on the market mainly employ a technical solution that adds a mechanical self-locking switch to the communication line between the main control CPU and the microphone module. Its working principle is as follows: when the telephone is not in use, the mechanical switch remains open, so even if the main control CPU is compromised, the microphone cannot establish a signal path with the main control; during a call, the user must manually press the switch to close the line. However, this solution has significant drawbacks: firstly, the manual operation is cumbersome, and users may easily forget to press the switch, leading to call abnormalities; secondly, long-term use of the mechanical switch is prone to contact wear, oxidation, and jamming, affecting the device's lifespan and reliability; thirdly, the installation of the mechanical switch requires additional internal space in the telephone, increasing the complexity of product design.
[0004] While existing technologies offer solutions for preventing eavesdropping on devices using analog switches, these solutions all require physical buttons or toggle switches to trigger control signals, thus failing to achieve automatic control. Summary of the Invention
[0005] To overcome the technical defects of the existing technology, the present invention provides a telephone anti-eavesdropping system based on a Hall sensor, including a main control CPU3, a microphone, and a handset hang-up detection circuit, as well as a permanent magnet installed inside the telephone handset. A Hall sensor module is installed at a corresponding position on the telephone body. An analog switch module is connected in series between the main control CPU3 and the microphone. The output terminal of the Hall sensor is directly connected to the control terminal of the analog switch module, forming a hardware control loop independent of the main control CPU. The output terminal of the Hall sensor module is also connected to the handset hang-up detection circuit.
[0006] Preferably, the analog switch module includes a connector CN1, analog switch chips U1 and U2; the first pin of connector CN1 is connected to one end of TVS diode T1, and the other end of TVS diode T1 is grounded; the first pin of connector CN1 is also connected to one end of capacitor C4; the other end of capacitor C4 is connected to the second pin of connector CN1; one end of capacitor C4 is connected to ceramic filter capacitor C10, and the other end of ceramic filter capacitor C10 is grounded; the other end of capacitor C4 is connected to ceramic filter capacitor C11, and the other end of ceramic filter capacitor C11 is grounded. One end of the ceramic filter capacitor C10 is also connected to one end of the ferrite bead FB1. The other end of the ferrite bead FB1 is connected to one end of the capacitor C5. The other end of the ferrite bead FB1 is connected to the resistor R2. The other end of the resistor R2 is connected to one end of the filter capacitor C2 and one end of the filter capacitor C1. The other ends of the filter capacitor C2 and the other ends of the filter capacitor C12 are grounded. The other end of the resistor R2 is connected to the resistor R1. The other end of the resistor R1 is connected to the power supply MIC_VDD voltage. The other end of the capacitor C5 is connected to the NC pin of the analog switch U1. The COM pin of analog switch chip U1 is connected to one end of ceramic filter capacitor C3, and the other end of capacitor C3 is connected to the microphone input of the main control CPU through MIC+ network identifier; the IN pin of analog switch chip U1 is connected to current limiting resistor R4, and the other end of current limiting resistor R4 is connected to the output of Hall sensor module through network identifier HALL_MIC. Pin 2 of connector CN1 is connected to one end of TVS diode T2, and the other end of TVS diode T2 is grounded. Pin 2 of connector CN1 is connected to one end of ferrite bead FB2, and the other end of ferrite bead FB2 is connected to one end of capacitor C8. The other end of capacitor C8 is connected to the NC pin of analog switch U1. The COM pin of analog switch chip U2 is connected to one end of ceramic filter capacitor C9, and the other end of capacitor C9 is connected to the microphone input of the main control CPU through MIC+ network identifier. The IN pin of analog switch chip U2 is connected to one end of current limiting resistor R4, and the other end of current limiting resistor R4 is connected to the output of Hall sensor module through network identifier HALL_MIC. At the same time, analog switch chip U2 is grounded through resistor R5.
[0007] Preferably, the VDD pin of the analog switch chip U1 is connected to one end of capacitor C6 and one end of capacitor C7, and the other ends of capacitor C6 and capacitor C7 are grounded.
[0008] Preferably, the VDD pin of the analog switch chip U1 is connected to one end of capacitor C12, and the other end of capacitor C12 is grounded.
[0009] Preferably, the Hall sensor module includes a Hall sensor U3. The first pin of the Hall sensor U3 is connected to one end of the filter capacitor C13 and one end of the ferrite bead FB3. The other end of the ferrite bead FB3 is connected to the DC_3V3 power supply voltage. The other end of the filter capacitor C13 is grounded. The OUT pin of the Hall sensor U3 is connected to one end of the filter capacitor C15 and one end of the resistor R6. The other end of the capacitor C15 is grounded. The other end of the resistor R6 is connected to one end of the resistor R7 and the anode of the diode D1. The other end of the resistor R6 is connected to the other end of the current-limiting resistor R4 through the network identifier HALL_MIC. The other end of the resistor R7 is grounded. The cathode of the diode D1 is connected to the handle hanging detection circuit.
[0010] Preferably, the analog switch chips U1 and U2 are audio-specific analog switch chips.
[0011] Preferably, the Hall sensor U3 reuses the original on-hook detection sensor of the telephone.
[0012] Preferably, when the controller is hung up, the Hall sensor module outputs a first-level signal to control the analog switch module to open, and simultaneously outputs a first-level signal to the controller detection circuit to inform the main control CPU that the controller has been placed; when the controller is picked up, the Hall sensor module outputs a second-level signal to control the analog switch module to close, and simultaneously outputs a second-level signal to the controller detection circuit to inform the main control CPU that the controller has been picked up.
[0013] The beneficial effects of this invention are: 1. This invention is entirely hardware-based, with a software system independent of the main control CPU, fundamentally eliminating the possibility of remotely enabling eavesdropping through software vulnerabilities; both the Hall sensor and the analog switch module are contactless components with a service life of ≥100,000 cycles, significantly reducing mechanical failures; it does not require modification of the original telephone software program, but is achieved only through hardware circuit modifications, and is compatible with most wired telephones with handsets on the market.
[0014] 2. This invention requires no new sensors or complex control modules; it only requires the addition of low-cost analog switch chips and a small number of standard resistors and capacitors. The extremely low cost of upgrading a single unit makes this solution feasible for large-scale application in homes, hotels, businesses, and for upgrading older equipment.
[0015] 3. This invention eliminates the need for additional manual operation of the switch. It achieves automatic circuit switching by relying on the natural action of the handle to pick up and hang up, which conforms to the user's original usage habits and solves the problems of cumbersome and easily forgotten operation of mechanical switches. Attached Figure Description
[0016] One or more embodiments are illustrated by way of example with reference numerals in the accompanying drawings. These illustrations do not constitute a limitation on the embodiments. Elements with the same reference numerals in the drawings are denoted as similar elements. Unless otherwise stated, the figures in the drawings are not to be limited by scale.
[0017] Figure 1 This is a schematic diagram of the system of the present invention; Figure 2 This is a partial circuit diagram of the present invention.
[0018] Explanation of reference numerals in the attached diagram: 1. Microphone; 2. Analog switch module; 3. Main control CPU; 4. Handheld device detection circuit; 5. Hall sensor module. Detailed Implementation
[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the various embodiments of this invention will be described in detail below with reference to the accompanying drawings. However, those skilled in the art will understand that many technical details have been provided in the various embodiments of this invention to facilitate a better understanding of this application. However, the technical solutions claimed in the claims of this application can be implemented even without these technical details and with various variations and modifications based on the following embodiments.
[0020] like Figures 1 to 2 As shown, this embodiment provides a telephone anti-eavesdropping system based on a Hall sensor, the core architecture of which includes: The main control CPU3 is the central processing unit of the telephone, responsible for various signal processing and telephone function control. Microphone module 1 is used to collect user voice signals and typically includes a microphone diaphragm and its preamplifier circuit. Handset on-hook detection circuit 4 detects whether the telephone handset is in the on-hook state and reports this status to the main control CPU3; it is a standard functional module of the telephone. Hall sensor module 5 is fixedly installed inside the telephone body, corresponding to the permanent magnet (such as a neodymium iron boron magnet) embedded in the handset. Its core function is to detect the magnetic field generated by the permanent magnet when the handset is placed (on-hook) and output a corresponding level signal. A key improvement is that this invention reuses this sensor, allowing its output signal to not only be used for traditional on-hook detection but also to add an anti-eavesdropping control function. Analog switch module 2 is connected in series in the audio signal path between the microphone input pin of the main control CPU3 and the output pin of microphone module 1. This module is directly controlled by the level signal output by Hall sensor module 5; its on / off state determines whether the microphone audio signal can be sent to the main control CPU3.
[0021] Its anti-eavesdropping principle is as follows: Through hardware connection, the output terminal of Hall sensor module 5 is simultaneously connected to the control terminal of analog switch module 2 and the input terminal of handset hang-up detection circuit 4, forming a pure hardware control loop independent of the main control CPU 3 software control. When the handset hangs up, Hall sensor module 5 detects the magnetic field and outputs a first-level signal (such as a high level). This signal physically disconnects analog switch module 2, cutting off the microphone path; it also notifies handset hang-up detection circuit 4. When the handset is picked up, the magnetic field disappears, and Hall sensor module 5 outputs a second-level signal (such as a low level). This signal closes analog switch module 2, restoring the call, and notifies handset hang-up detection circuit 4 of the off-hook status. Thus, automatic, hardware-level anti-eavesdropping is achieved by connecting when the handset is picked up and isolating when it is hung up.
[0022] The analog switch module 2 includes a connector CN1, analog switch chips U1 and U2; the first pin of connector CN1 is connected to one end of TVS diode T1, and the other end of TVS diode T1 is grounded; the first pin of connector CN1 is also connected to one end of capacitor C4, and the other end of capacitor C4 is connected to the second pin of connector CN1; one end of capacitor C4 is connected to ceramic filter capacitor C10, and the other end of ceramic filter capacitor C10 is grounded; the other end of capacitor C4 is connected to ceramic filter capacitor C11, and the other end of ceramic filter capacitor C11 is grounded. One end of the ceramic filter capacitor C10 is also connected to one end of the ferrite bead FB1. The other end of the ferrite bead FB1 is connected to one end of the capacitor C5. The other end of the ferrite bead FB1 is connected to the resistor R2. The other end of the resistor R2 is connected to one end of the filter capacitor C2 and one end of the filter capacitor C1. The other ends of the filter capacitor C2 and the other ends of the filter capacitor C12 are grounded. The other end of the resistor R2 is connected to the resistor R1. The other end of the resistor R1 is connected to the power supply MIC_VDD voltage. The other end of the capacitor C5 is connected to the NC pin of the analog switch U1. The COM pin of analog switch chip U1 is connected to one end of ceramic filter capacitor C3, and the other end of capacitor C3 is connected to the microphone input terminal of the main control CPU through MIC+ network identifier; the IN pin of analog switch chip U1 is connected to current limiting resistor R4, and the other end of current limiting resistor R4 is connected to the output terminal of Hall sensor module 5 through network identifier HALL_MIC. Pin 2 of connector CN1 is connected to one end of TVS diode T2, and the other end of TVS diode T2 is grounded. Pin 2 of connector CN1 is connected to one end of ferrite bead FB2, and the other end of ferrite bead FB2 is connected to one end of capacitor C8. The other end of capacitor C8 is connected to the NC pin of analog switch U1. The other end of ferrite bead FB2 is connected to one end of resistor R3, and the other end of resistor R3 is grounded. The COM pin of analog switch chip U2 is connected to one end of ceramic filter capacitor C9, and the other end of capacitor C9 is connected to the microphone input of the main control CPU through MIC+ network identifier. The IN pin of analog switch chip U2 is connected to one end of current limiting resistor R4, and the other end of current limiting resistor R4 is connected to the output of Hall sensor module 5 through network identifier HALL_MIC. At the same time, analog switch chip U2 is grounded through resistor R5.
[0023] The VDD pin of the analog switch chip U1 is connected to one end of capacitor C12, and the other end of capacitor C12 is grounded.
[0024] The specific structure and connection relationship of analog switch module 2: Analog switch module 2 is the key to physical isolation. This embodiment adopts a dual-channel design, independently controlling the positive (MIC+) and negative (MIC-) lines of the microphone signal to ensure complete signal isolation. Core components: including analog switch chip U1 and analog switch chip U2. U1 and U2 are audio-specific analog switch chips (such as TS5A23157) to ensure low-loss, high-fidelity transmission of audio signals in the on state. The control terminals (IN pins) of U1 and U2 are connected in parallel.
[0025] Input Interface and Protection: Microphone module 1 is connected via connector CN1. Pin 1 (MIC+) of CN1 is connected to transient voltage suppression diode T1 to ground for protection against electrostatic discharge (ESD) and surge voltage. Similarly, pin 2 (MIC-) of CN1 is connected to TVS diode T2 to ground.
[0026] Signal conditioning circuit: Common-mode filtering: Capacitor C4 is connected between pins 1 and 2 of CN1 to filter out common-mode noise on the microphone signal line.
[0027] π-type filtering: For the MIC+ line, a π-type filter network is formed by ferrite bead FB1, capacitors C10 and C11; for the MIC- line, a similar filter network is formed by ferrite bead FB2 and capacitor C11. The ferrite bead is used to suppress high-frequency noise and electromagnetic interference (EMI), and the capacitor is used to filter out high-frequency noise on the DC bias, together providing a "clean" transmission path for the audio signal.
[0028] DC bias circuit: The power supply MIC_VDD provides the operating voltage to microphone module 1 through current-limiting resistor R1 and bias resistor R2. Filter capacitors C1 and C2 are used to stabilize this bias power supply. Resistor R3 provides ground bias to the MIC line.
[0029] Signal path and control: The MIC+ signal is coupled through FB1 and C5 and then sent to the normally open terminal (NC pin) of the first analog switch chip U1. The common terminal (COM pin) of U1 is connected to the MIC+ input terminal of the main control CPU3 through the coupling capacitor C3.
[0030] The MIC signal is coupled through FB2 and C8 and then sent to the normally open terminal (NC pin) of the second analog switch chip U2. The common terminal (COM pin) of U2 is connected to the MIC input terminal of the main control CPU (3) through the coupling capacitor C9.
[0031] Control signal input: The control terminals (IN pins) of analog switch chips U1 and U2 are connected in parallel and then connected to the control line labeled HALL_MIC through a current-limiting resistor R4. This control line is directly derived from the output of Hall sensor module 5. Resistor R5 is connected between the control terminal of U2 and ground as a pull-down resistor to prevent the control pin from floating and causing malfunctions, thus enhancing circuit stability.
[0032] Power supply: The power supply pins (VDD) of analog switch chips U1 and U2 are connected to MIC_VDD and decoupled through filter capacitors C6, C7 and C12 to ensure stable chip operation.
[0033] The Hall sensor module 5 is specifically configured and connected as follows: Hall sensor U3 is included. The first pin of Hall sensor U3 is connected to one end of filter capacitor C13 and one end of ferrite bead FB3. The other end of ferrite bead FB3 is connected to DC_3V3 power supply voltage. The other end of filter capacitor C13 is grounded. The OUT pin of Hall sensor U3 is connected to one end of filter capacitor C15 and one end of resistor R6. The other end of capacitor C15 is grounded. The other end of resistor R6 is connected to one end of R7 and the anode of diode D1. The other end of resistor R6 is connected to the other end of current limiting resistor R4 through the network identifier HALL_MIC. The other end of R7 is grounded. The cathode of diode D1 is connected to handle hanging detection circuit 4.
[0034] Core component: Hall sensor chip U3. Crucially, this invention preferably reuses the existing Hall sensor used for handset hang-up detection in the original telephone design as U3, eliminating the need for a new sensor and significantly reducing cost and modification difficulty.
[0035] Power supply and filtering: U3 is powered by the DC 3V3 power supply of the telephone system. A ferrite bead FB3 is connected in series and a filter capacitor C13 is connected in parallel in the power path to suppress power supply noise and provide U3 with a clean and stable operating voltage.
[0036] Output signal conditioning and distribution: The output terminal (OUT pin) of U3 outputs a level signal corresponding to the magnetic field state.
[0037] Filtering and Current Limiting: The output signal first passes through an RC filter network consisting of capacitor C15 and resistors R6 and R7 to smooth the signal and prevent false triggering of the analog switch due to jitter. Resistor R6 also serves to limit the current.
[0038] Signal distribution: The conditioned control signal appears at node A.
[0039] The first path (anti-eavesdropping control): It is directly led out from node A to form the HALL_MIC control line, and sent to the control terminal of the analog switch module (2) through the current limiting resistor R4.
[0040] The second path (on-hook status reporting): From node A, a forward diode D1 is connected to the original handle on-hook detection circuit (4). Diode D1 acts as a unidirectional isolation, allowing only the output signal of Hall sensor U3 to flow to detection circuit 4, preventing reverse signals or interference that may be generated by the detection circuit from affecting the output stability of U3, and ensuring the independence of the control loop.
[0041] The system workflow is as follows: Hang-up mode (anti-eavesdropping mode): When the telephone handset is placed back on the base (hang-up), the permanent magnet inside the handset approaches the Hall sensor U3. U3 detects a stable magnetic field, and its OUT pin outputs a continuous first-level signal (e.g., 3.3V high level).
[0042] After the high-level signal is conditioned by R6, etc.: (a) The signal is sent to the IN pins of U1 and U2 via the HALL_MIC line and R4. The high-level control signal disconnects the internal switches of U1 and U2. At this time, the MIC+ and MIC- outputs of microphone module 1 are physically isolated from the corresponding inputs of the main control CPU 3. Even if the main control CPU 3 is controlled by malicious software and attempts to start recording, it cannot pick up any ambient sound because the audio path is broken, thus achieving hardware-level anti-eavesdropping.
[0043] (b) At the same time, the high-level signal is sent to the handset hang-up detection circuit 4 through diode D1. The circuit (4) recognizes it as a "handset has been hung up" status signal and reports it to the main control CPU 3, triggering the telephone to enter standby or hibernation and other corresponding logic.
[0044] Off-hook status (normal call mode): When the user picks up the handset (off-hook), the permanent magnet moves away from the Hall sensor U3, and U3 can no longer detect the magnetic field. Its OUT pin outputs a continuous second-level signal (e.g., 0V low level).
[0045] After conditioning, the low-level signal is: (a) The signal is sent to the IN pins of U1 and U2 via the HALL_MIC line and R4. A low-level control signal closes the internal switches of U1 and U2. At this time, the audio signal path from microphone module 1 to the main control CPU 3 is fully connected, and the user can make calls normally. The voice signal can be transmitted to the CPU for processing without loss.
[0046] (b) Simultaneously, the low-level signal is sent to the handset off-hook detection circuit 4 via diode D1. Circuit (4) identifies it as a "handset off-hook" status signal and reports it to the main control CPU 3, triggering the telephone to enter the corresponding logic such as off-hook, dialing, or talking.
[0047] Those skilled in the art will understand that the above embodiments are specific examples of implementing the present invention, and in practical applications, various changes in form and detail may be made without departing from the spirit and scope of the present invention.
Claims
1. A telephone anti-eavesdropping system based on a Hall sensor, comprising a main control CPU (3), a microphone (1), and a handset hang-up detection circuit (4), characterized in that: It also includes a permanent magnet installed inside the telephone handset, a Hall sensor module (5) is installed at the corresponding position of the body, an analog switch module (2) is connected in series between the main control CPU (3) and the microphone (1), the output end of the Hall sensor module (5) is directly connected to the control end of the analog switch module (2) to form a hardware control loop independent of the main control CPU; the output end of the Hall sensor module (5) is also connected to the handset hang-up detection circuit (4).
2. The telephone anti-eavesdropping system based on a Hall sensor according to claim 1, characterized in that: The analog switch module (2) includes a connector CN1, analog switch chips U1 and U2; the first pin of connector CN1 is connected to one end of TVS transistor T1, and the other end of TVS transistor T1 is grounded; the first pin of connector CN1 is also connected to one end of capacitor C4, and the other end of capacitor C4 is connected to the second pin of connector CN1; one end of capacitor C4 is connected to ceramic filter capacitor C10, and the other end of ceramic filter capacitor C10 is grounded; the other end of capacitor C4 is connected to ceramic filter capacitor C11, and the other end of ceramic filter capacitor C11 is grounded. One end of the ceramic filter capacitor C10 is also connected to one end of the ferrite bead FB1. The other end of the ferrite bead FB1 is connected to one end of the capacitor C5. The other end of the ferrite bead FB1 is connected to the resistor R2. The other end of the resistor R2 is connected to one end of the filter capacitor C2 and one end of the filter capacitor C1. The other ends of the filter capacitor C2 and the other ends of the filter capacitor C12 are grounded. The other end of the resistor R2 is connected to the resistor R1. The other end of the resistor R1 is connected to the power supply MIC_VDD voltage. The other end of the capacitor C5 is connected to the NC pin of the analog switch U1. The COM pin of the analog switch chip U1 is connected to one end of the ceramic filter capacitor C3, and the other end of the C3 capacitor is connected to the microphone input terminal of the main control CPU through the MIC+ network identifier; the IN pin of the analog switch chip U1 is connected to the current limiting resistor R4, and the other end of the current limiting resistor R4 is connected to the output terminal of the Hall sensor module (5) through the network identifier HALL_MIC. Pin 2 of connector CN1 is connected to one end of TVS transistor T2, and the other end of TVS transistor T2 is grounded. Pin 2 of connector CN1 is connected to one end of ferrite bead FB2, and the other end of ferrite bead FB2 is connected to one end of capacitor C8. The other end of capacitor C8 is connected to the NC pin of analog switch U1. The COM pin of analog switch chip U2 is connected to one end of ceramic filter capacitor C9, and the other end of capacitor C9 is connected to the microphone input of the main control CPU through MIC+ network identifier. The IN pin of analog switch chip U2 is connected to one end of current limiting resistor R4, and the other end of current limiting resistor R4 is connected to the output of Hall sensor module (5) through network identifier HALL_MIC. At the same time, analog switch chip U2 is grounded through resistor R5.
3. A telephone anti-eavesdropping system based on a Hall sensor according to claim 2, characterized in that: The VDD pin of the analog switch chip U1 is connected to one end of capacitor C6 and one end of capacitor C7, and the other ends of capacitor C6 and capacitor C7 are grounded.
4. A telephone anti-eavesdropping system based on a Hall sensor according to claim 2, characterized in that: The VDD pin of the analog switch chip U1 is connected to one end of capacitor C12, and the other end of capacitor C12 is grounded.
5. A telephone anti-eavesdropping system based on a Hall sensor according to claim 2, characterized in that: The Hall sensor module (5) includes a Hall sensor U3. The first pin of the Hall sensor U3 is connected to one end of the filter capacitor C13 and one end of the magnetic bead FB3. The other end of the magnetic bead FB3 is connected to the DC_3V3 power supply voltage. The other end of the filter capacitor C13 is grounded. The OUT pin of the Hall sensor U3 is connected to one end of the filter capacitor C15 and one end of the resistor R6. The other end of the capacitor C15 is grounded. The other end of the resistor R6 is connected to one end of R7 and the anode of the diode D1. The other end of the resistor R6 is connected to the other end of the current limiting resistor R4 through the network identifier HALL_MIC. The other end of R7 is grounded. The cathode of the diode D1 is connected to the handle hanging detection circuit (4).
6. A telephone anti-eavesdropping system based on a Hall sensor according to claim 2, characterized in that: The analog switch chips U1 and U2 are audio-specific analog switch chips.
7. A telephone anti-eavesdropping system based on a Hall sensor according to claim 4, characterized in that: The Hall sensor U3 reuses the original on-hook detection sensor of the telephone.
8. A telephone anti-eavesdropping system based on a Hall sensor according to any one of claims 1-7, characterized in that: When the handle is hung up, the Hall sensor module (5) outputs a first level signal to control the analog switch module (2) to open, and at the same time outputs a first level signal to the handle detection circuit (4) to tell the main control CPU (3) that the handle has been placed; when the handle is picked up, the Hall sensor module (5) outputs a second level signal to control the analog switch module (2) to close, and at the same time outputs a second level signal to the handle detection circuit (4) to tell the main control CPU (3) that the handle has been picked up.