PCB inductance induction type keyboard

Abstract

The utility model relates to the field of keyboards, and particularly provides a PCB inductance induction type keyboard which comprises a keycap, a connecting rod, a spring, a magnetic part, a base and a PCB, the connecting rod is connected with the keycap and the magnetic part, the spring is connected with the base and the connecting rod, the base is fixedly arranged above the PCB, and a through hole is formed in the middle of the base. A first inductance coil and a second inductance coil which are insulated from each other are arranged on the PCB, the first inductance coil and the second inductance coil are not overlapped, a magnetic part is arranged right above the first inductance coil, and no magnetic part is arranged right above the second inductance coil; when the key cap is knocked, the magnetic piece moves up and down right above the first inductance coil. The distances between the first inductance coil and the magnetic part and between the second inductance coil and the magnetic part are different, so that the inductance changes of the first inductance coil and the second inductance coil are different due to the movement of the magnetic part, and the position of the keyboard is determined through the inductance change difference; the interference of electromagnetic interference and noise on key signals is reduced, and the sensitivity of the keyboard is high.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of keyboards, in particular, to a PCB inductance sensing keyboard. BACKGROUND

[0002] The key of the traditional keyboard is a binary detection component, only having the function of sensing whether the key operation exists. However, with the development of VR, AR, e-sports and other technologies, people have higher requirements for the function of the keyboard, and expect to detect the strength, speed and other information of the key. Therefore, higher requirements are put forward for the sensitivity of the keyboard; the high-sensitivity keyboard can quickly capture and respond when the key action is small, fast or complex, thereby improving the input efficiency and user experience.

[0003] Taking the utility model patent with the name of "inductance keyboard device" and the authorization announcement number of "CN 221766602 U" as an example, the patent proposes a design of an inductance keyboard. The assembly area on the circuit board is provided with a hole for installing a ring-shaped inductor to form an axial sensing channel. The key assembly includes a key cap, a magnetic piece and a spring. The operation of the key drives the magnetic piece to move axially in the sensing channel, thereby changing the inductance value, and the detection of the key position is realized through the change. However, the hole must be opened on the circuit board as the assembly area of the ring-shaped inductor, which increases the manufacturing complexity and may affect the strength of the overall structure; more importantly, the magnetic piece needs to be deeply into the inductance sensing area to effectively produce inductance change, and the distribution of the magnetic field has low sensitivity to the position change of the magnetic piece. The sensing ability of a single inductor coil only depends on the change of the magnetic flux when the magnetic piece is close; when the key displacement is small, the magnetic field change caused by the magnetic piece is limited, resulting in a small change in inductance value; the sensitivity of the keyboard is low. SUMMARY

[0004] The utility model aims at the deficiency in the prior art, and provides a PCB inductance sensing keyboard to solve the problem of low sensitivity when the key displacement is small in the prior art.

[0005] To achieve the above-mentioned purpose, the utility model adopts the following technical scheme:

[0006] The present application provides a PCB inductance sensing keyboard, which includes a key cap, a connecting rod, a spring, a magnetic piece, a base and a PCB circuit board. The connecting rod connects the key cap and the magnetic piece, and the spring connects the base and the connecting rod. The base is fixedly arranged above the PCB circuit board, and a through hole is arranged in the middle of the base. The PCB circuit board is provided with a first inductor coil and a second inductor coil which are insulated from each other. The first inductor coil and the second inductor coil do not overlap. A magnetic piece is arranged directly above the first inductor coil, and no magnetic piece is arranged directly above the second inductor coil. When the key cap is struck, the magnetic piece moves up and down directly above the first inductor coil.

[0007] Further, the first inductor coil and the second inductor coil are the same in shape and size; the first inductor coil and the second inductor coil are both planar inductor coils.

[0008] Further, the first inductor coil and the second inductor coil are both two-layer coils connected by a via.

[0009] Further, the distance between the first inductor coil and the second inductor coil is greater than 0.1mm.

[0010] Further, the upper end of the connecting rod is connected with the key cap, and the lower end of the connecting rod is connected with the magnetic member.

[0011] Further, the lower end of the spring is connected with the base, and the upper end of the spring is connected with the connecting rod.

[0012] Further, the base is fixed on the support plate, and a plurality of bases are arranged on the support plate, and the positions of the bases on the support plate correspond to the positions of the planar inductor coils on the PCB circuit board one by one.

[0013] Further, the diameter of the columnar part of the magnetic member is smaller than the inner diameter of the spring.

[0014] Further, the key cap, the connecting rod, the spring, the magnetic member, and the base coincide with the central axis of the first inductor coil.

[0015] Further, a capacitor is further arranged on the PCB circuit board, the capacitor is connected with the planar inductor coil to form a resonance circuit, the capacitance value of the capacitor and the inductance value of the planar inductor coil satisfy a resonance condition; each planar inductor coil is connected with one capacitor.

[0016] Compared with the prior art, the utility model has the advantages of:

[0017] (1) The magnetic field change caused by the magnetic member is not uniform, the magnetic field change is larger in the near place, and the magnetic field change is smaller in the far place. As a detection inductor, the first inductor coil is directly below the magnetic member, and the inductance of the first inductor coil changes greatly with the movement of the magnetic member; as a reference inductor, the second inductor coil is not directly below the magnetic member, and the distance from the magnetic member is far, the magnetic field change is small, and the inductance change is small; and the first inductor coil and the second inductor coil are independently affected by the magnetic field, which can avoid the magnetic field coupling and mutual interference between the two coils, improve the system stability and sensitivity. The application judges the sensitivity of the keyboard through the difference between the inductance changes of the first inductor coil and the second inductor coil. Not only can the change of the first inductor coil be accurately perceived, but also the noise brought by the small change in the second inductor coil can be filtered out, the environmental electromagnetic interference is avoided, the influence of them on the signal is reduced, and the small key action can be captured, and the sensitivity of the keyboard is improved.

[0018] (2) The first inductor coil is designed in two layers, and a higher inductance is formed by connecting through holes, which can significantly enhance the response capability to the magnetic field change caused by the displacement of the magnetic part, thereby increasing the inductance change. The second inductor coil is designed in a single layer, and the inductance value is small and stable, which provides a reference as a benchmark. The first inductor coil designed in two layers is more sensitive to the induction of the magnetic part, and the inductance change amplitude is significantly higher than that of the second inductor coil designed in a single layer, which increases the difference between the inductance changes of the two. The increase in the difference not only improves the capture ability of small displacement, but also reduces the interference of noise on the detection accuracy, thereby effectively improving the sensitivity and reliability of the keyboard.

[0019] (3) The planar inductor coil of the present application is arranged in the PCB circuit board, and a through hole does not need to be arranged in the middle of the inductor coil of the PCB circuit board to pass through the magnetic block. This not only improves the mechanical pressure resistance of the PCB circuit board, so that the PCB circuit board is not easy to be damaged, but also reduces the number of punching, which can be realized on the circuit board by photoetching, etching and other technologies, simplifying the preparation process.

[0020] (4) The first inductor coil and the second inductor coil are both designed as planar inductor coils, which saves space to the greatest extent, so that the inductor assembly can be compactly integrated on the PCB circuit board, and the integration degree is high. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 A schematic diagram of a PCB inductance induction type keyboard provided by the present application (the structure schematic diagram of a single key in the figure);

[0022] Figure 2 A schematic diagram of an inverted T-shaped magnetic part in a PCB inductance induction type keyboard provided by the present application;

[0023] Figure 3 An exploded view schematic diagram of part components of a PCB inductance induction type keyboard provided by the present application;

[0024] Figure 4 A schematic diagram of the arrangement mode of planar inductor coils in a PCB inductance induction type keyboard provided by the present application;

[0025] Figure 5 A top view schematic diagram of a double-layer coil in another PCB inductance induction type keyboard provided by the present application.

[0026] Figure legend: 1-key cap; 2-link; 3-spring; 4-magnetic part; 5-base; 6-PCB circuit board; 7-first inductor coil; 8-second inductor coil. DETAILED DESCRIPTION

[0027] In order to make the implementation process of the utility model more clearly, the following will be combined with the drawings to make a detailed description.

[0028] The utility model provides a kind of PCB inductance induction type keyboard, as shown in figure, Figure 1 Keyboard includes key cap 1, connecting rod 2, spring 3, magnetic piece 4, base 5, PCB circuit board 6, first inductance coil 7, second inductance coil 8;The specific shape of connecting rod 2, base 5 and other auxiliary components is not limited.Key cap 1 can be any shape, for example, trapezoidal block, circular and so on.The top surface of key cap 1 is used for user to strike, the lower side of key cap 1 is connected with connecting rod 2, for transmitting external force action.Connecting rod 2 is rigid structure, can be hard plastic, alloy and other materials.Magnetic piece 4 is magnetic disc or magnetic cylinder, can also be other any shape, the diameter of the cylindrical portion of magnetic piece 4 is less than the inner diameter of spring 3, so that it can move up and down inside spring 3 along spring 3 central axis, without contact with spring 3 around to generate friction force, so that the up and down movement of key cap 1 is more sensitive.

[0029] The shape of magnetic piece 4 can also be inverted T-shaped, the upper part is cylindrical, and the lower part is disc-shaped, as shown in Figure 2 The upper part of the cylindrical shape helps to ensure that the magnetic piece 4 can stably approach the inductance coil during key action, avoiding unstable magnetic field interference, while optimizing the concentration of the magnetic field.The disc-shaped lower part increases the effective approach area of the magnetic piece 4 and the inductance coil, making the magnetic field change more uniform and obvious, improving the response capability of the inductance coil to small magnetic field changes.The lower end of the magnetic piece 4 can also be hemispherical, protruding towards one side of the PCB circuit board 6.The hemispherical shape allows the magnetic piece 4 to produce more uniform magnetic field changes with the inductance coil during displacement, avoiding uneven magnetic field distribution that can be caused by sharp or irregular shapes, and maximizing the influence on the inductance magnetic field when approaching the inductance coil, ensuring a larger inductance change, thereby enhancing the response capability to small displacement.The shape also reduces the distance change between the magnetic piece 4 and the inductance coil, making the inductance coil more sensitive to magnetic field changes, further improving the sensitivity of the keyboard.The material of the magnetic piece 4 is a magnetic material, such as iron, cobalt, nickel, neodymium iron boron, aluminum nickel cobalt, etc., used to change the magnetic medium of the inductance coil.Base 5 plays a supporting and connecting role, and is made of rigid material.The first inductance coil 7 and the second inductance coil 8 are spiral planar inductance coils, arranged in the PCB circuit board 6, and are made of metal conductors such as copper.The center axis of the key cap 1, connecting rod 2, spring 3, magnetic piece 4, base 5 and corresponding first inductance coil 7 coincides, ensuring that the magnetic piece 4 always moves along the same axis during key action, reducing unnecessary deviation and error, thereby enabling the inductance coil to more accurately sense the displacement change of the magnetic piece 4, helping to improve the accuracy and stability of the keyboard.

[0030] The connecting rod 2 connects the key cap 1 and the magnetic piece 4, the upper end of the connecting rod 2 is connected with the key cap 1, and the lower end of the connecting rod 2 is connected with the magnetic piece 4; under the action of external force, the key cap 1 moves downward, drives the magnetic piece 4 to displace downward through the connecting connecting rod 2, so that the magnetic piece 4 gradually approaches the induction area where the first inductance coil 7 is located. The displacement of the magnetic piece 4 changes the magnetic field strength near the first inductance coil 7, significantly increases the inductance, and at the same time has little effect on the magnetic field of the second inductance coil 8 far away, so that the inductance changes little. Through the difference between the inductance changes of the two coils, the system can accurately capture the displacement amplitude of the magnetic piece 4, and realize sensitive detection of the key action. The spring 3 connects the base 5 and the connecting rod 2, the lower end of the spring 3 is connected with the base 5, and the upper end of the spring 3 is connected with the connecting rod 2; in the case that no external force is applied, the spring 3 remains in a natural length state, the key cap 1 is in an initial position, and the magnetic piece 4 keeps a certain distance from the PCB circuit board 6. When the external force is removed, the spring 3 pushes the key cap 1 back to the original position through the elastic restoring force of itself, and drives the magnetic piece 4 away from the PCB circuit board 6, and restores to the initial induction state. This design not only ensures the rapid resetting of the key cap 1, but also restores the magnetic field between the magnetic piece 4 and the inductance coil to the initial condition, providing an accurate inductance reference benchmark for the next knocking action.

[0031] As shown in Figure 1 , the base 5 is fixedly arranged above the PCB circuit board 6, and a through hole is arranged in the middle of the base 5 to provide a channel for the magnetic piece 4 to move up and down. Specifically, the base 5 is not directly fixed on the PCB circuit board 6, and the adhesive will affect the electromagnetic induction process, and the action force of the knocking is transmitted to the PCB circuit board 6, which is easy to cause the PCB circuit board 6 to break; the base 5 is fixed on the support plate, a plurality of bases 5 are arranged on the support plate, the bases 5 on the support plate correspond one by one to the positions of the first inductance coils 7 on the PCB circuit board 6, the PCB circuit board 6 is arranged below the support plate, and the distance between the PCB circuit board 6 and the lowest part of the base 5 is 0.5-2mm, which reserves a buffer space to avoid the base 5 from being slightly deformed downward and damaging the PCB circuit board 6. If the magnetic piece 4 is a reverse T-shaped magnetic piece 4 as shown in Figure 2 , the distance between the PCB circuit board 6 and the base 5 can be appropriately increased, and the corresponding partial component explosion diagram is as shown in Figure 3The support plate and the PCB circuit board 6 can be arranged on the shell of the keyboard 1 by clamping, the shell protects the internal support plate and the PCB circuit board 6, and the shell is not specifically limited. As a simple keyboard, the PCB circuit board 6 can be first fixed on a plane, and then the support plate is arranged above the PCB circuit board 6, support surfaces are arranged on the edges of the support plate or on both sides, and the lower ends of the support surfaces are arranged on the plane and arranged on the same plane as the PCB circuit board 6. In this way, the support plate is fixed directly above the PCB circuit board 6, and then the spring 3, the connecting rod 2, the magnetic member 4 and the keycap 1 connected with the base 5 are all fixed on the support plate. The fixing mode of the base 5 is not unique, and the specific fixing mode is not the main content of the present application scheme, and those skilled in the art can fix according to the prior art.

[0032] The PCB 6 is provided with a first inductor coil 7 and a second inductor coil 8 which are insulated from each other, and the first inductor coil 7 and the second inductor coil 8 do not overlap and are not electromagnetically coupled, independent of each other and do not affect each other. The first inductor coil 7 is provided with a magnetic member 4 directly above, and the second inductor coil 8 is not provided with a magnetic member 4 directly above. The change of the inductance of the first inductor coil 7 is greatly affected by the up-down position movement of the magnetic member 4, and the change of the inductance of the second inductor coil 8 is less affected by the up-down position movement of the magnetic member 4, so that the difference in inductance change of the first inductor coil 7 and the second inductor coil 8 is greater, and the sensitivity of the keyboard is higher. The first inductor coil 7 and the second inductor coil 8 are both planar inductor coils, and are spiral planar inductor coils. By winding the wire on the plane, it has the advantages of compact structure and space saving, and is suitable for high integration circuit board design. The number of turns of the coil can be 10-20 turns, and the coil diameter is 0.5-2 cm, which is only an example and is not a limitation of the present application. The center axis of the spiral planar inductor coil is the geometric center of the spiral coil, which is perpendicular to the plane of the coil. The center axes of the first inductor coil 7 and the second inductor coil 8 are both parallel to the normal direction of the plane of the PCB 6. The magnetic field change generated by the magnetic member 4 has non-uniformity, and the magnetic field change is more significant near the magnetic member, while the magnetic field change is weaker away from the magnetic member. The first inductor coil 7 as a detection inductor is located directly below the magnetic member 4 and can fully sense the magnetic field change caused by the displacement of the magnetic member 4, so its inductance will change significantly. The second inductor coil 8 as a reference inductor is away from the magnetic member 4 and not directly below the magnetic member 4, so it is less affected by the magnetic field and its inductance change is small. This design ensures that the magnetic field effect on the first inductor coil 7 and the second inductor coil 8 is independent of each other, avoiding the magnetic field coupling and interference between the two coils, improving the stability and sensitivity of the system. By comparing the difference in inductance change of the two coils, not only can the significant change of the first inductor coil 7 be accurately captured, but also the reference signal provided by the second inductor coil 8 can be used to effectively filter the noise in the small change. In addition, this differential detection mechanism has a strong inhibitory effect on electromagnetic interference in the external environment, reducing the influence of noise on the signal, enabling the system to accurately detect the small action of the key, thereby significantly improving the sensitivity and reliability of the keyboard. The first inductor coil 7 and the second inductor coil 8 are insulated from each other and do not contact each other; avoiding electrical interference and current leakage between the first inductor coil 7 and the second inductor coil 8, ensuring that the inductance change of the two coils is only affected by the magnetic field change. It also ensures that the inductance change is independent and linear, avoiding nonlinear response, improving the system's ability to perceive subtle magnetic field changes, and ultimately improving the sensitivity of the keyboard.

[0033] Further, the first inductor coil 7 and the second inductor coil 8 have the same shape and size, and good symmetry, which reduces the zero signal. The zero signal refers to the reference signal output by the system when no key operation is performed, which is usually caused by temperature fluctuations, manufacturing errors or electromagnetic interference. Good symmetry ensures that the first inductor coil 7 and the second inductor coil 8 work under the same conditions, reducing unnecessary zero signal fluctuations, so that the small inductance change caused by key displacement can be more accurately detected. Reducing the zero signal helps to improve the signal-to-noise ratio, making it easier to capture small magnetic field changes, thereby improving the sensitivity of the keyboard, especially when detecting slight key actions.

[0034] Preferably, the first inductor coil 7 and the second inductor coil 8 have opposite spiral directions, as shown in Figure 4 Figure 4 (a) is a schematic diagram of counterclockwise arrangement, Figure 4 (b) is a schematic diagram of clockwise arrangement. If the first inductor coil 7 is arranged counterclockwise, the second inductor coil 8 is arranged clockwise, and vice versa. In this way, the magnetic field directions generated by the first inductor coil 7 and the second inductor coil 8 are opposite, which can effectively amplify the difference in inductance change. Specifically, when the magnetic member 4 is close, the inductance of the first inductor coil 7 increases, and the inductance of the second inductor coil 8 decreases, making the inductance change difference between the first inductor coil 7 and the second inductor coil 8 larger, which can significantly improve the detection capability of small displacement. At the same time, since the first inductor coil 7 and the second inductor coil 8 with opposite spiral directions have opposite responses to the same interference source, external electromagnetic interference can be effectively suppressed, the influence of common mode noise can be reduced, and the sensitivity of the keyboard can be further enhanced.

[0035] More preferably, the first inductor coil 7 and the second inductor coil 8 in the present application can both be two-layer inductor coils, with an additional inductor coil stacked in the vertical direction, which can increase the inductance of the coil, making the inductor coil more sensitive to the displacement change of the magnetic member 4, thereby improving the response capability to small displacement. It can also effectively increase the inductance in a limited space, thereby achieving a higher inductance value without increasing the area of the circuit board. Especially in the case of limited keyboard space, the performance of the inductor coil can be improved, and the physical space can be reduced, thereby improving the sensitivity without increasing the size. The first inductor coil 7 and the second inductor coil 8 can both be multi-layer inductor coils, for example, two-layer inductor coils, to enhance the response strength of the inductance. Preferably, the first inductor coil 7 is arranged as a two-layer coil, and the second inductor coil 8 is arranged as a single-layer coil, as shown in Figure 5 ​The first inductance coil 7 is shown as a top view schematic diagram of two layers of coils; in this way, the first inductance coil 7 adopts a two-layer structure, and the inductance is effectively improved by connecting through holes, the magnetic field change caused by the displacement of the magnetic member 4 is more sensitive to the response, so that the inductance change amplitude is significantly increased. The second inductance coil 8 is a single-layer design, and the inductance value is small and the change amplitude is stable, which provides a reference signal as a reference. The first inductance coil 7 with two layers is compared with the second inductance coil 8 with a single layer, and the inductance change difference is more obvious, so that the system is more likely to capture the small key displacement signal. The increase of inductance change difference not only improves the sensing accuracy of small displacement, but also effectively suppresses the interference of noise and enhances the signal stability, thereby further improving the sensitivity of the keyboard and the reliability of the system.

[0036] The PCB circuit board 6 is also provided with a capacitor (not shown in the figure) Figure 2 ), which is connected with the planar inductance coil to form a resonance circuit. The capacitance value of the capacitor and the inductance value of the planar inductance coil satisfy the resonance condition, that is, the following expression is satisfied:

[0037]

[0038] Where L represents the inductance value (unit: henry H); C represents the capacitance value of the corresponding capacitor (unit: farad F); f is the resonance frequency. Each planar inductance coil is connected with a capacitor. Each key on the keyboard is provided with two capacitors, a first inductance coil 7 and a second inductance coil 8 under the PCB circuit board 6, and the first inductance coil 7 and the second inductance coil 8 respectively form a resonance circuit with the capacitors, and are in a resonance state during operation. The resonance state is very sensitive to the change of inductance value, so that small changes in magnetic flux can also be detected. Specifically, when the resonance frequency of the inductance and the capacitor matches, the impedance of the circuit is minimum, and the response of the signal can be maximized. When in use, the inductance of the planar inductance coil is at the inductance corresponding to the resonance frequency, and when the magnetic member 4 moves up and down, the inductance value changes near the inductance value corresponding to the resonance frequency, and small displacement can cause large resonance frequency change, thereby causing large signal change and improving the sensitivity of the keyboard.

[0039] In use, the resonant circuit is connected to a differential amplifier for differential amplification, and the differential amplifier is connected to a microprocessor. The microprocessor can simultaneously monitor multiple key operations, multiple microprocessors work in parallel, and are connected to a host microprocessor in a multi-machine interface mode of a serial protocol (Uart, SPI, I2C, etc.). The host microprocessor aggregates the key information reported by each detection microprocessor and transmits the key information to a connected computer or other external device through an interface. The microprocessor uses an ADC to realize analog-to-digital conversion of the detection signal, analyzes the signal through an algorithm, determines the triggered key and the trigger strength, and generates corresponding codes and timing according to the analysis results, and reports the key operation in the form of a serial interface. Signal processing can also be performed in other ways as long as the inductance change difference of the first inductor coil 7 and the second inductor coil 8 can be detected. The innovation of the present application is to design the first inductor coil 7 and the second inductor coil 8 in the PCB circuit board, and to use the inductance change difference of the two to sensitively sense the position of the magnetic member 4, thereby improving the sensitivity of the keyboard.

[0040] The preferred embodiments of the present application are described above, but are not intended to limit the present application. Those skilled in the art can make various modifications and changes to the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A PCB inductive keyboard, the keyboard comprising keycaps, a connecting rod, a spring, a magnetic component, a base, and a PCB circuit board, wherein the connecting rod connects the keycaps and the magnetic component, the spring connects the base and the connecting rod, the base is fixedly disposed above the PCB circuit board, and a through hole is provided in the center of the base, characterized in that, The PCB circuit board is provided with a first inductor coil and a second inductor coil which are insulated from each other, the first inductor coil and the second inductor coil are not overlapped, the magnetic piece is arranged above the first inductor coil, and the second inductor coil is not provided with the magnetic piece above it; when the key cap is struck, the magnetic piece moves up and down above the first inductor coil.

2. The PCB inductive sensing keyboard of claim 1, wherein, The first inductor coil and the second inductor coil are the same in shape and size; the first inductor coil and the second inductor coil are both planar inductor coils.

3. The PCB inductive sensing keyboard of claim 2, wherein, The first inductor coil and the second inductor coil are both two-layer coils, and the two layers of coils are connected through a via hole.

4. The PCB inductive sensing keyboard of claim 3, wherein, The distance between the first inductor coil and the second inductor coil is greater than 0.1 mm.

5. The PCB inductive sensing keyboard of claim 4, wherein, The upper end of the connecting rod is connected with the key cap, and the lower end of the connecting rod is connected with the magnetic piece.

6. The PCB inductive sensing keyboard of claim 5, wherein, The lower end of the spring is connected with the base, and the upper end of the spring is connected with the connecting rod.

7. The PCB inductive sensing keyboard of claim 6, wherein, The base is fixed on the support plate, a plurality of bases are arranged on the support plate, and the positions of the bases on the support plate correspond one-to-one with the positions of the planar inductor coils on the PCB circuit board.

8. The PCB inductive sensing keyboard of claim 7, wherein, The diameter of the cylindrical part of the magnetic piece is smaller than the inner diameter of the spring.

9. The PCB inductive sensing keyboard of claim 8, wherein, The key cap, the connecting rod, the spring, the magnetic piece, the base, and the center axis of the first inductor coil coincide.

10. The PCB inductive sensing keyboard of claim 9, wherein, The PCB circuit board is further provided with a capacitor, the capacitor is connected with the planar inductor coil to form a resonance circuit, the capacitance value of the capacitor and the inductance value of the planar inductor coil satisfy the resonance condition, and each planar inductor coil is connected with one capacitor.

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