A liquid level sensor

Abstract

The utility model discloses a liquid level sensor relates to electronic sensing technical field. The sensor includes printed circuit board, touch control chip and anti -interference resistance. Printed circuit board adopts four layer board structure, and is in proper order for the top layer of setting element, as the first intermediate layer of wiring layer, as the second intermediate layer of response pad layer and as the bottom layer of insulating surface. Touch response pad is built -in in the second intermediate layer, and is connected to touch control chip through anti -interference resistance, and the medium layer between the second intermediate layer and bottom layer constitutes touch response isolation layer. This structure will response unit and outside environment effectively isolate, and the power supply circuit including step -down chip and the two -level inverting circuit of shaping and power amplification to control signal are combined, and constitute a highly integrated module. Through the core response structure is integrated in the inside of PCB, has improved the anti -interference ability, reliability and sensitivity of sensor significantly, especially applicable to intelligent bathroom and other complex humid environment under the liquid level detection.

Description

Technical Field

[0001] This utility model relates to the field of electronic sensing technology, and in particular to a capacitive liquid level sensor with strong anti-interference capability for liquid detection. Background Technology

[0002] Smart bathtubs, whirlpool bathtubs, and other similar devices have commonly added functions such as hydrotherapy and bubble massage. When these functions are activated, the water surface generates violent fluctuations and a large number of bubbles, which severely interfere with traditional liquid level sensors, causing them to malfunction or degrade in performance. In addition, residual water droplets or ambient moisture after bathing can also easily cause false triggering of the sensors.

[0003] Currently, to control costs, many liquid level sensors employ a simple single-channel signal detection scheme. This scheme has poor anti-interference capabilities in complex operating environments, and once the detection signal is interfered with, it can easily lead to the malfunction of the entire system. Therefore, the market urgently needs a liquid level sensor that combines high sensitivity, high reliability, and strong anti-interference capabilities. Utility Model Content

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a liquid level sensor with a compact structure, high sensitivity, and strong anti-interference ability, which is particularly suitable for complex and humid application environments such as smart bathrooms.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A liquid level sensor includes a printed circuit board, a touch control chip, and an anti-interference resistor; The printed circuit board is a four-layer board, consisting of a top layer, a first intermediate layer, a second intermediate layer, and a bottom layer. The top layer is etched with lines and pads, and the touch control chip and anti-interference resistor are disposed on the top layer; The first intermediate layer is a wiring layer, with lines etched on it; The second intermediate layer is a touch-sensitive pad layer, which is etched to form touch-sensitive pads; The bottom layer is copper-free and is entirely covered with a green oil insulating layer; The top layer, the first intermediate layer, the second intermediate layer, and the bottom layer are electrically connected by preset through holes. The touch-sensitive pad is electrically connected to the sensing pin of the touch control chip through the anti-interference resistor; The dielectric layer between the second intermediate layer and the bottom layer constitutes a touch-sensitive isolation layer.

[0006] Furthermore, the liquid level sensor also includes a step-down chip, a current-limiting resistor, and a filter capacitor; an external power supply is connected to the input terminal of the step-down chip, and the output terminal of the step-down chip outputs a DC voltage, which is connected to the power pin of the touch control chip via the current-limiting resistor and the filter capacitor in sequence, for powering the touch control chip.

[0007] Furthermore, the liquid level sensor also includes a two-stage inverting circuit; the two-stage inverting circuit includes a first switch and a second switch connected in series; the output pin of the touch control chip is connected to the control terminal of the first switch; the output signal of the first switch is connected to the control terminal of the second switch; the output terminal of the second switch serves as the final output terminal of the two-stage inverting circuit.

[0008] Furthermore, the first switching transistor and the second switching transistor are transistors or MOSFETs.

[0009] Furthermore, the liquid level sensor also includes an LED indicator circuit; the LED indicator circuit includes a current-limiting resistor and a light-emitting diode connected in series; one end of the LED indicator circuit is connected to the power supply terminal of the secondary inverting circuit, and the other end is connected to the output terminal of the second switching transistor.

[0010] Furthermore, the LED indicator circuit consists of two sets, and the two sets of LED indicator circuits are connected in parallel.

[0011] Furthermore, the operating voltage of the secondary inverter circuit is 12V.

[0012] Furthermore, the material of the dielectric layer is FR4.

[0013] Furthermore, the overall thickness of the printed circuit board is 1.6 mm.

[0014] Compared with the prior art, the significant advantages of this utility model are: High integration and reliability: By integrating the key touch-sensing pads inside the PCB (second intermediate layer) and isolating them from the outside world through a dielectric layer, the sensor is modularized and miniaturized, fundamentally improving its resistance to environmental interference (such as water droplets and moisture) and long-term reliability.

[0015] Strong anti-interference capability: The unique four-layer PCB structure separates the sensing layer from the wiring layer and component layer, and combined with anti-interference resistors, it can effectively suppress signal interference caused by water surface fluctuations, bubbles or electromagnetic noise.

[0016] Strong driving capability: The control signal is shaped and amplified by a two-stage inverting circuit, and redundant LED indicators are designed, which not only improves the driving capability of the output signal, but also enhances the reliability of the system status indication. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the water level sensing circuit provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the signal processing and output circuit provided in an embodiment of the present invention; Figure 3 This is a schematic diagram of the PCB layer structure provided in an embodiment of the present invention. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this utility model clearer, the present utility model will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0019] The liquid level sensor described in this invention operates on the core principle of capacitive sensing. When liquid approaches the sensor, it changes the parasitic capacitance of the touch sensing pad. The touch control chip detects this change and outputs a corresponding control signal.

[0020] I. Circuit Structure like Figure 1 and Figure 2 As shown, the liquid level sensor circuit of this utility model mainly includes two parts: a water level sensing circuit and a signal processing output circuit.

[0021] Water level sensing circuit ( Figure 1 ): Responsible for the core function of liquid level detection.

[0022] Power supply module: An external power supply (e.g., 7-30V DC) is input from pin VDD7-30V, and after passing through a step-down chip U1 (e.g., 78L05), a stable DC operating voltage (e.g., 5V) is output. This voltage then passes through a π-type filter network composed of current-limiting resistor R1 and filter capacitors C9 and Cp to provide a clean and stable power supply for the touch control chip U2.

[0023] The sensing module, specifically the touch control chip U2 (in this embodiment, a dedicated capacitive sensing chip such as XW01K can be used), is the core. Its sensing pin KEY is connected to the touch sensing pad inside the PCB via an anti-interference resistor RX (preferably 2kΩ). This resistor suppresses transient pulse interference and improves the signal-to-noise ratio. Other configuration pins of the chip, such as the internal balancing capacitor interface C1, the reference capacitor interface C2, and the sensitivity adjustment pin CSEL, are connected to external resistors and capacitors according to the chip datasheet to optimize performance. The chip's output pin OUT is an open-drain output and needs to be connected to the power supply via a pull-up resistor R3.

[0024] Signal processing output circuit ( Figure 2 ): Conditioning, amplifying, and indicating sensor signals.

[0025] The two-stage inverting circuit consists of a first switching transistor Q1 and a second switching transistor Q2 (a bipolar transistor is used in this embodiment) connected in series. The Signal signal output from the touch control chip U2 directly drives the base of Q1. The collector output of Q1 drives the base of Q2, and finally the processed signal is output from the collector of Q2. This circuit structure inverts the original signal twice, so the final output signal (low-level output) is in phase with the Signal. More importantly, it plays a role in signal shaping and power amplification, enabling the output signal to directly drive loads such as relays and solenoid valves. This part of the circuit uses a relatively high operating voltage (e.g., 12V) to provide sufficient driving capability.

[0026] The LED indicator circuit employs a redundant design, comprising two parallel circuits, each consisting of a current-limiting resistor (R8, R9) and a series-connected LED (D1, D2). This circuit is connected between the power supply (12V) of the two-stage inverter circuit and the output of the second switching transistor Q2. When liquid is detected, Q2 conducts, its output is low, and the LED indicator circuit illuminates, providing a clear status indication.

[0027] II. Core Structural Design like Figure 3 As shown, the superior performance of this invention largely benefits from its innovative four-layer PCB structure: Top layer 1: Used for arranging the main surface mount devices (SMDs) and traces, including the touch control chip U2 and the noise immunity resistor RX.

[0028] First intermediate layer 2: As the main wiring layer, it is used to lay power and signal lines, avoiding excessively dense wiring on the top layer.

[0029] The second intermediate layer 3 serves as the touch-sensitive pad layer, where the critical touch-sensitive pads are etched. Placing it inside the PCB protects it from surface contamination, oxidation, and mechanical damage.

[0030] Bottom layer 4: All copper foil is removed by etching, and the entire surface is covered with a green oil insulation layer to form a clean insulating surface.

[0031] The critical isolation layer: The dielectric layer 7, made of FR4, lies between the second intermediate layer 3 and the bottom layer 4, forming the touch-sensing isolation layer. It determines the distance between the sensor mounting surface (touch surface 8) and the sensing pads. This distance is carefully designed (controlled by a standard 1.6mm board thickness and lamination structure) to maximize isolation from the installation environment (such as a bathtub wall) and external interference while ensuring sensitivity. The vias 5 are responsible for enabling the necessary electrical connections between the layers.

[0032] Brief description of working principle In the dry state: the capacitance of the touch-sensitive pad is the reference value. The touch control chip U2 outputs a high-level signal. This high level turns on Q1 and turns off Q2. The final output is a high level, and the LED is not lit.

[0033] In the presence of water: When liquid approaches the sensor mounting surface, it increases the capacitance of the touch-sensitive pads. U2 detects this change, and its output signal goes low. This low level turns Q1 off and Q2 on. The final output goes low, and the LED circuit turns on, illuminating the indicator light.

[0034] This invention integrates the sensing structure and processing circuitry onto a specially designed four-layer PCB, forming a modular product with advantages such as small size, high sensitivity, strong anti-interference ability, easy installation, and high reliability.

[0035] The above description is merely a specific embodiment of this utility model, but the protection scope of this utility model is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this utility model should be included within the protection scope of this utility model. Therefore, the protection scope of this utility model should be determined by the scope of the claims.

Claims

1. A liquid level sensor, characterized in that, This includes printed circuit boards, touch control chips, and anti-interference resistors; The printed circuit board is a four-layer board, consisting of a top layer, a first intermediate layer, a second intermediate layer, and a bottom layer. The top layer is etched with lines and pads, and the touch control chip and anti-interference resistor are disposed on the top layer; The first intermediate layer is a wiring layer, with lines etched on it; The second intermediate layer is a touch-sensitive pad layer, which is etched to form touch-sensitive pads; The bottom layer is copper-free and is entirely covered with a green oil insulating layer; The top layer, the first intermediate layer, the second intermediate layer, and the bottom layer are electrically connected by preset through holes. The touch-sensitive pad is electrically connected to the sensing pin of the touch control chip through the anti-interference resistor; The dielectric layer between the second intermediate layer and the bottom layer constitutes a touch-sensitive isolation layer.

2. The liquid level sensor according to claim 1, characterized in that, It also includes a step-down chip, a current-limiting resistor, and a filter capacitor; An external power supply is connected to the input terminal of the step-down chip. The output terminal of the step-down chip outputs a DC voltage, which is then connected to the power pin of the touch control chip via the current-limiting resistor and the filter capacitor to power the touch control chip.

3. The liquid level sensor according to claim 1, characterized in that, It also includes a two-stage inverter circuit; The secondary inverting circuit includes a first switch and a second switch connected in series. The output pin of the touch control chip is connected to the control terminal of the first switching transistor; The output signal of the first switch is connected to the control terminal of the second switch; The output terminal of the second switch is used as the final output terminal of the second-stage inverting circuit.

4. The liquid level sensor according to claim 3, characterized in that, The first and second switching transistors are either transistors or MOSFETs.

5. The liquid level sensor according to claim 3, characterized in that, It also includes LED indicator circuitry; The LED indicator circuit includes a current-limiting resistor and a light-emitting diode connected in series. One end of the LED indicator circuit is connected to the power supply terminal of the secondary inverter circuit, and the other end is connected to the output terminal of the second switching transistor.

6. The liquid level sensor according to claim 5, characterized in that, The LED indicator circuit consists of two sets, which are connected in parallel.

7. The liquid level sensor according to claim 3, characterized in that, The operating voltage of the secondary inverter circuit is 12V.

8. The liquid level sensor according to claim 1, characterized in that, The material of the dielectric layer is FR4.

9. The liquid level sensor according to claim 1, characterized in that, The overall thickness of the printed circuit board is 1.6 mm.

Images