Simple low-power-consumption salt concentration test circuit

Abstract

The utility model discloses a simple salt concentration test circuit with low power consumption, which comprises a salt concentration detection circuit, a singlechip control circuit, a power supply circuit, a water flow detection circuit and a nixie tube display circuit, and the power supply circuit is respectively connected with and supplies power to the salt concentration detection circuit, the singlechip control circuit and the nixie tube display circuit. The single-chip microcomputer control circuit is connected with the water flow detection circuit so as to detect the water inlet state. The single chip microcomputer control circuit is connected with the salt concentration detection circuit so as to realize detection operation on the salt concentration in water; and the singlechip control circuit is connected with the nixie tube display circuit so as to output and display the salt concentration detection result. According to the utility model, the operational amplifier form is adopted, so that the reliability and precision of measurement are further improved, and the accuracy of measurement results is ensured.

Description

Technical Field

[0001] This utility model relates to the field of water quality testing, and in particular to a simple, low-power salt concentration testing circuit. Background Technology

[0002] Salt concentration testing technology has shown broad application potential in many fields, particularly in water quality monitoring, industrial process control, and environmental monitoring. Salt concentration, as an important indicator for evaluating water quality, directly reflects the purity and safety of water. Water with high salt concentrations may contain impurities or pollutants, thus affecting its suitability as drinking water or industrial water. Therefore, the detection of salt concentration in water bodies is of great significance.

[0003] Patent No. ZL201110440535.7 discloses a precise testing method and dedicated equipment for the salt content of seawater desalination liquid based on ion concentration, which can realize the detection of salt concentration in seawater. However, current salt concentration detection methods usually use direct current to power the brine. Although this method is simple, it has the problem of probe polarization, which can easily lead to oxidation at one end of the probe after long-term use. On the other hand, in existing commercially available salt concentration detection circuits, the probe is generally directly connected to the VCC voltage for detection. This method may lead to excessive probe current under high salt concentration conditions, and may even pull down the VCC voltage, thereby seriously affecting the accuracy of the detection results. It is necessary to improve this method. Summary of the Invention

[0004] The purpose of this invention is to address the above-mentioned problems by providing a simple, low-power salt concentration testing circuit that is easy to use and has a simple structure.

[0005] To achieve the above objectives, the technical solution of this utility model is as follows:

[0006] A simple, low-power salt concentration testing circuit includes a salt concentration detection circuit, a microcontroller control circuit, a power supply circuit, a water flow detection circuit, and a digital tube display circuit. The power supply circuit is connected to the salt concentration detection circuit, the microcontroller control circuit, and the digital tube display circuit to supply power to them. The microcontroller control circuit is connected to the water flow detection circuit to detect the water inflow status. The microcontroller control circuit is connected to the salt concentration detection circuit to detect the salt concentration in the water. The microcontroller control circuit is connected to the digital tube display circuit to output and display the salt concentration detection results.

[0007] Furthermore, the salt concentration detection circuit includes a probe J4, operational amplifiers U5A and U5B, MOSFETs Q1 and Q2. The source of MOSFET Q1 is connected to the power supply circuit. The gate of MOSFET Q1 is connected to one end of resistor R12 and the drain of MOSFET Q2. The other end of resistor R12 is connected to the power supply circuit. The drain of MOSFET Q1 is connected to one end of electrolytic capacitor EC2 and one end of resistor R13. The gate of MOSFET Q2 is connected to one end of resistor R10 and one end of resistor R11. The other end of resistor R10... One end of the probe J4 is connected to the microcontroller control circuit. The other end of resistor R13, the source of MOSFET Q2, and the other end of resistor R11 are all grounded. The other end of electrolytic capacitor EC2 is connected to the first pin of probe J4 and one end of resistor R14. The other end of resistor R14 is connected to one end of resistor R18, one end of resistor R15, and one end of capacitor C11. The other end of resistor R18 is connected to the positive input terminal of operational amplifier U5B. The other ends of resistor R15 and capacitor C11 are both grounded. The second pin of probe J4 is connected to the operational amplifier U5B. The positive input terminal of operational amplifier U5A is connected to one end of resistor R16, and the other end of resistor R16 is grounded. The positive power supply terminal of operational amplifier U5A is connected to the power supply circuit and one end of capacitor C14, and the other end of capacitor C14 is grounded. The negative input terminal of operational amplifier U5A is connected to one end of resistor R17 and one end of capacitor C12. The other ends of resistor R17 and capacitor C12 are connected to the output terminal of operational amplifier U5A and one end of resistor R19. The other end of resistor R19 is connected to the microcontroller control circuit and one end of capacitor C13. The other end of capacitor C13 and the negative power supply terminal of operational amplifier U5A are both grounded; the positive power supply terminal of operational amplifier U5B is connected to the power supply circuit; the negative input terminal of operational amplifier U5B is connected to one end of resistor R20 and one end of capacitor C16 respectively; the other end of resistor R20 and the other end of capacitor C16 are connected to the output terminal of operational amplifier U5B and one end of resistor R21 respectively; the other end of resistor R21 is connected to the microcontroller control circuit and one end of capacitor C15 respectively; the other end of capacitor C15 and the negative power supply terminal of operational amplifier U5B are both grounded.

[0008] Furthermore, the water flow detection circuit includes a transformer T1. One end of the input side of the transformer T1 is connected to one end of capacitor C19 and the first pin of electrode J5. The other end of the input side of the transformer T1 is connected to one end of capacitor C18. The other ends of capacitor C18 and capacitor C19 are both connected to the second pin of electrode J5. The lower end of the output side of the transformer T1 is connected to the anode of diode D3. The cathode of diode D3 is connected to one end of resistor R25, one end of capacitor C17, and one end of resistor R26. The other end of resistor R26 is connected to the microcontroller control circuit. The upper end of the output side of the transformer T1 is connected to the cathode of diode D2 and one end of resistor R24. The other end of resistor R24 ​​is connected to the microcontroller control circuit. The middle end of the output side of the transformer T1, the anode of diode D2, the other end of resistor R25, and the other end of capacitor C17 are all grounded.

[0009] Furthermore, the digital tube display circuit includes an LED scanning driver chip U4 and a digital tube display. The DIG1, ​​DIG2, DIG3, and DIG4 pins of the LED scanning driver chip U4 correspond to and are interconnected with the BIT1, BIT2, BIT3, and BIT4 pins of the digital tube display, respectively. The A, B, C, D, E, F, G, and DP pins of the LED scanning driver chip U4 correspond to and are interconnected with the A, B, C, D, E, F, G, and DP pins of the digital tube display, respectively. The VDD pin of the LED scanning driver chip U4 is connected to one end of capacitor C10, one end of capacitor EC1, and the power supply circuit, respectively. The other ends of capacitor C10 and EC1 are grounded. The SDA and SCL pins of the LED scanning driver chip U4 are both connected to the microcontroller control circuit, and the GND pin of the LED scanning driver chip U4 is grounded.

[0010] Furthermore, the microcontroller control circuit includes a microcontroller U2. Pin P05 of microcontroller U2 is connected to one end of push-button switch SW1, and the other end of push-button switch SW2 is grounded. Pins P04 and P24 of microcontroller U2 are both connected to the power supply circuit. Pin P16 of microcontroller U2 is connected to one end of resistor R10. Pin P15 of microcontroller U2 is connected to one end of resistor R19 and one end of capacitor C13, respectively. Pin P14 of microcontroller U2 is connected to one end of capacitor C15 and one end of resistor R21, respectively. Pin P23 of microcontroller U2 is connected to one end of resistor R24, and pin P22 of microcontroller U2 is connected to one end of resistor R26. Pin P21 of microcontroller U2 is connected to the CLK pin of programming port J3. Pin P35 of microcontroller U2 is connected to the SDA pin of programming port J3. Pin VCC of programming port J3 is connected to the power supply circuit. Pin GND of programming port J3 is grounded. Pin P32 of microcontroller U2 is connected to one end of external high-frequency crystal oscillator Y1 and one end of capacitor C6. Pin P31 of microcontroller U2 is connected to the other end of external high-frequency crystal oscillator Y1 and one end of capacitor C4. The other ends of capacitors C6 and C4 are both grounded. Pin VDD of microcontroller U2 is connected to the power supply circuit and one end of capacitor C9. The other end of capacitor C9 and pin VSS of microcontroller U2 are both grounded.

[0011] Furthermore, the power supply circuit includes a lithium battery charging circuit unit and a voltage regulator circuit unit, which are connected together. The lithium battery charging circuit unit includes a linear charging chip U1 and a TYPE C terminal. The VBUS pin of the TYPE C terminal is connected to the voltage regulator circuit unit, one end of the thermistor RT1, one end of the capacitor C1, one end of the resistor R29, and the VIN pin of the linear charging chip U1. The other end of the thermistor RT1 is connected to the IS pin of the linear charging chip U1 and one end of the resistor R2. The other end of the resistor R2, the other end of the capacitor C1, and the GNG pin of the linear charging chip U1 are all grounded. The other end of the resistor R29 is connected to the P04 pin of the microcontroller U2 and one end of the resistor R30. The other end of the resistor R30 is grounded. The CC1 pin of the TYPE C terminal is connected to one end of the resistor R4, and the CC2 pin of the TYPE C terminal is connected to one end of the resistor R3. The other end of the resistor R3, the other end of the resistor R4, and the TYPE C terminal are all grounded. The GND pins of terminal C are all grounded; the ISET pin of the linear charging chip U1 is connected to one end of resistor R1, and the other end of resistor R1 is grounded; the CHRG pin of the linear charging chip U1 is connected to one end of indicator LED1, the DONE pin of the linear charging chip U1 is connected to one end of indicator LED2, the other ends of indicator LED1 and indicator LED2 are both connected to one end of resistor R5, and the other end of resistor R5 is connected to the voltage regulator circuit unit; the VBAT pin of the linear charging chip U1 is connected to one end of capacitor C2, the voltage regulator circuit unit, one end of resistor R27, and the second pin of external interface J1, respectively; the other end of resistor R27 is connected to one end of resistor R28, one end of capacitor C21, and the P24 pin of microcontroller U2, respectively; the other ends of capacitor C21 and resistor R28 are both grounded; the first pin of external interface J1, the other end of capacitor C2, and the EPAD pin of linear charging chip U1 are all grounded.

[0012] Furthermore, the voltage regulator circuit unit includes a MOSFET Q3 and a voltage regulator chip U3. The drain of the MOSFET Q3 is connected to the VBAT pin of the linear charging chip U1. The gate of the MOSFET Q3 is connected to one end of resistor R6 and one end of resistor R7. The other end of resistor R6 is grounded, and the other end of resistor R7 is connected to the anode of diode D1 and the TYPE pin. The VBUS pin of terminal C is connected to one end of resistor R5; the cathode of diode D1 is connected to the source of MOSFET Q3, one end of capacitor C7, and one end of inductor L1 respectively. The other end of capacitor C7 is grounded, and the other end of inductor L1 is connected to the LX pin of voltage regulator chip U3. The VOUT pin of voltage regulator chip U3 is connected to one end of capacitor C8, the VCC pin of programming port J3, one end of capacitor C9, the VDD pin of microcontroller U2, the VDD pin of LED scanning driver chip U4, one end of capacitor C10, one end of capacitor EC1, one end of resistor R12, the source of MOSFET Q1, the positive power supply terminal of operational amplifier U5A, one end of capacitor C14, and the positive power supply terminal of operational amplifier U5B; the other end of capacitor C8 and the GND pin of voltage regulator chip U3 are both grounded.

[0013] Furthermore, the low-power salt concentration test circuit also includes a water temperature detection circuit, which includes a water temperature sensor connected to a sensor interface J2. One end of the sensor interface J2 is connected to one end of resistor R22, one end of resistor R23, and one end of capacitor C20. The other end of resistor R22 is connected to the VOUT pin of the voltage regulator chip U3, and the other end of resistor R23 is connected to the P13 pin of the microcontroller U2. The other ends of capacitor C20 and sensor interface J2 are both grounded.

[0014] Compared with the prior art, the advantages and positive effects of this utility model are:

[0015] This invention employs a microcontroller-driven PWM wave to power an operational amplifier, which converts the current to AC via an electrolytic capacitor to obtain a voltage signal. This method of outputting a square wave using a PWM signal effectively reduces the amplitude of the input current, preventing excessive input current from affecting the accuracy of the detection results and improving the accuracy of salt concentration detection in wastewater. Simultaneously, by converting DC power to AC via a capacitor to power the probe, this invention effectively avoids polarization problems that may occur when the probe is directly connected to VCC voltage, thus preventing oxidation at the probe tip and extending the probe's lifespan. Its simple structure and convenient operation effectively improve the safety and reliability of the salt concentration testing circuit. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this utility model or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 A circuit diagram of a lithium battery charging circuit unit;

[0018] Figure 2 This is a circuit diagram of a voltage regulator circuit unit;

[0019] Figure 3 This is a circuit diagram of a microcontroller control circuit.

[0020] Figure 4 This is a circuit diagram of a digital tube display circuit;

[0021] Figure 5 This is a circuit diagram of a salt concentration detection circuit;

[0022] Figure 6 This is a circuit diagram of a water flow detection circuit;

[0023] Figure 7 This is a circuit diagram of a water temperature detection circuit. Detailed Implementation

[0024] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, any modifications, equivalent substitutions, improvements, etc., made by those skilled in the art to all other embodiments obtained without creative effort should be included within the protection scope of the present utility model.

[0025] like Figures 1 to 7 As shown, this embodiment discloses a simple low-power salt concentration testing circuit, including a salt concentration detection circuit, a microcontroller control circuit, a power supply circuit, a water flow detection circuit, a digital tube display circuit, and a water temperature detection circuit. The power supply circuit is connected to the salt concentration detection circuit, the microcontroller control circuit, the digital tube display circuit, and the water temperature detection circuit to supply power to them. The microcontroller control circuit is connected to the water flow detection circuit and the water temperature detection circuit to realize the detection operation of the inlet water status and the inlet water temperature. The microcontroller control circuit is connected to the salt concentration detection circuit to realize the detection operation of the salt concentration in the water. The microcontroller control circuit is connected to the digital tube display circuit to output and display the salt concentration detection result.

[0026] The power supply circuit includes a lithium battery charging circuit unit and a voltage regulator circuit unit, with the lithium battery charging circuit unit connected to the voltage regulator circuit unit. The lithium battery charging circuit unit includes a linear charging chip U1 and a TYPE C terminal. The VBUS pin of the TYPE C terminal is connected to the voltage regulator circuit unit, one end of the thermistor RT1, one end of the capacitor C1, one end of the resistor R29, and the VIN pin of the linear charging chip U1. The other end of the thermistor RT1 is connected to the IS pin of the linear charging chip U1 and one end of the resistor R2. The other end of the resistor R2, the other end of the capacitor C1, and the GNG pin of the linear charging chip U1 are all grounded. The other end of the resistor R29 is connected to the P04 pin of the microcontroller U2 and one end of the resistor R30. The other end of the resistor R30 is grounded. The CC1 pin of the TYPE C terminal is connected to one end of the resistor R4, and the CC2 pin of the TYPE C terminal is connected to one end of the resistor R3. The other ends of the resistor R3, the other end of the resistor R4, and the TYPE C terminal are all grounded. The GND pins of terminal C are all grounded; the ISET pin of the linear charging chip U1 is connected to one end of resistor R1, and the other end of resistor R1 is grounded; the CHRG pin of the linear charging chip U1 is connected to one end of indicator LED1, the DONE pin of the linear charging chip U1 is connected to one end of indicator LED2, the other ends of indicator LED1 and indicator LED2 are both connected to one end of resistor R5, and the other end of resistor R5 is connected to the voltage regulator circuit unit; the VBAT pin of the linear charging chip U1 is connected to one end of capacitor C2, the voltage regulator circuit unit, one end of resistor R27, and the second pin of external interface J1, respectively; the other end of resistor R27 is connected to one end of resistor R28, one end of capacitor C21, and the P24 pin of microcontroller U2, respectively; the other ends of capacitor C21 and resistor R28 are both grounded; the first pin of external interface J1, the other end of capacitor C2, and the EPAD pin of linear charging chip U1 are all grounded; external interface J1 is used to connect to the lithium battery.

[0027] In the lithium battery charging circuit unit, connecting the TYPE C terminal provides a 5V DC voltage to the linear charging chip U1, which is specifically designed to charge lithium batteries. Adjusting the resistance value of R1 (grounded at pin 2) regulates the charging current of the lithium battery (maximum 1A). Connecting an NTC thermistor to pin 1 effectively ensures that the charging function is shut down in case of overheating. LED1 (red) and LED2 (green) serve as charging status indicators. When the battery is charging, the red light is on and the green light is off. When the battery is fully charged, the red light is off and the green light is on. Resistors R3 and R4 are connected to a 5.1K pull-down resistor to ensure that when a fast charging adapter is plugged in, the fast charging protocol is directly recognized, and the adapter outputs a fixed 5V voltage.

[0028] The voltage regulator circuit unit includes a MOSFET Q3 and a voltage regulator chip U3. The drain of the MOSFET Q3 is connected to the VBAT pin of the linear charging chip U1. The gate of the MOSFET Q3 is connected to one end of resistor R6 and one end of resistor R7. The other end of resistor R6 is grounded. The other end of resistor R7 is connected to the anode of diode D1 and the TYPE pin. The VBUS pin of terminal C is connected to one end of resistor R5; the cathode of diode D1 is connected to the source of MOSFET Q3, one end of capacitor C7, and one end of inductor L1 respectively. The other end of capacitor C7 is grounded, and the other end of inductor L1 is connected to the LX pin of voltage regulator chip U3. The VOUT pin of voltage regulator chip U3 is connected to one end of capacitor C8, the VCC pin of programming port J3, one end of capacitor C9, the VDD pin of microcontroller U2, the VDD pin of LED scanning driver chip U4, one end of capacitor C10, one end of capacitor EC1, one end of resistor R12, the source of MOSFET Q1, the positive power supply terminal of operational amplifier U5A, one end of capacitor C14, and the positive power supply terminal of operational amplifier U5B; the other end of capacitor C8 and the GND pin of voltage regulator chip U3 are both grounded.

[0029] When no 5V power is connected to the Type-C terminal, the lithium battery directly powers the voltage regulator chip U3 through the MOSFET Q3 (PMOS). U3 is a small SOT23 packaged step-up / step-down fixed 5V output chip, which can provide a maximum output current of 1A, ensuring a stable VCC (5V) output from the lithium battery between 2.7V and 4.2V. When a 5V power supply is connected to the Type-C terminal, the MOSFET Q3 is turned off, and the input 5V power supply directly powers the voltage regulator chip U3 through diode D1. U3 can then stably output the VCC voltage. The VCC voltage powers the subsequent microcontroller U2, the LED scanning driver chip U4, and the operational amplifier U5.

[0030] The microcontroller control circuit includes a microcontroller U2. Pin P05 of microcontroller U2 is connected to one end of push-button switch SW1, and the other end of push-button switch SW2 is grounded. Pins P04 and P24 of microcontroller U2 are both connected to the power supply circuit. Pin P16 of microcontroller U2 is connected to one end of resistor R10. Pin P15 of microcontroller U2 is connected to one end of resistor R19 and one end of capacitor C13, respectively. Pin P14 of microcontroller U2 is connected to one end of capacitor C15 and one end of resistor R21, respectively. Pin P23 of microcontroller U2 is connected to one end of resistor R24, and pin P22 of microcontroller U2 is connected to one end of resistor R26. Pin 21 is connected to the CLK pin of programming port J3. Pin P35 of microcontroller U2 is connected to the SDA pin of programming port J3. Pin VCC of programming port J3 is connected to the power supply circuit. Pin GND of programming port J3 is grounded. Pin P32 of microcontroller U2 is connected to one end of external high-frequency crystal oscillator Y1 and one end of capacitor C6. Pin P31 of microcontroller U2 is connected to the other end of external high-frequency crystal oscillator Y1 and one end of capacitor C4. The other ends of capacitor C6 and capacitor C4 are both grounded. Pin VDD of microcontroller U2 is connected to the power supply circuit and one end of capacitor C9. The other end of capacitor C9 and pin VSS of microcontroller U2 are both grounded.

[0031] In the microcontroller control circuit, J3 is the program programming port, facilitating debugging and programming; U2 is the main control microcontroller, outputting PWM1 and PWM2 waveforms for detecting salt concentration and water flow. The TX and RX pins are connected to the communication pins of the LED scanning driver chip U4, thereby controlling the display status of the 4-digit LED display; Y1 is an external high-frequency crystal oscillator, providing a reference time for the microcontroller; button SW1 controls the display and shutdown of the LED display, saving battery power. If a 5V power supply is plugged into the TYPE C terminal, the button function is disabled.

[0032] The digital tube display circuit includes an LED scanning driver chip U4 and a digital tube display. The DIG1, ​​DIG2, DIG3, and DIG4 pins of the LED scanning driver chip U4 correspond to and are connected to the BIT1, BIT2, BIT3, and BIT4 pins of the digital tube display, respectively. The A, B, C, D, E, F, G, and DP pins of the LED scanning driver chip U4 correspond to and are connected to the A, B, C, D, E, F, G, and DP pins of the digital tube display, respectively. The VDD pin of the LED scanning driver chip U4 is connected to one end of capacitor C10, one end of capacitor EC1, and the power supply circuit, respectively. The other ends of capacitors C10 and EC1 are grounded. The SDA and SCL pins of the LED scanning driver chip U4 are both connected to the microcontroller control circuit, and the GND pin of the LED scanning driver chip U4 is grounded.

[0033] The U4 is a dedicated LED scanning driver chip that can directly drive a 4-digit LED display. Using this chip can effectively save the microcontroller's I / O ports. The driven LED can be either common anode or common cathode.

[0034] The salt concentration detection circuit includes probe J4, operational amplifier U5A, operational amplifier U5B, MOSFET Q1, and MOSFET Q2. The source of MOSFET Q1 is connected to the power supply circuit. The gate of MOSFET Q1 is connected to one end of resistor R12 and the drain of MOSFET Q2. The other end of resistor R12 is connected to the power supply circuit. The drain of MOSFET Q1 is connected to one end of electrolytic capacitor EC2 and one end of resistor R13. The gate of MOSFET Q2 is connected to one end of resistor R10 and one end of resistor R11. The other end of resistor R10 is connected to... The microcontroller control circuit is connected, with the other end of resistor R13, the source of MOSFET Q2, and the other end of resistor R11 all grounded; the other end of electrolytic capacitor EC2 is connected to the first pin of probe J4 and one end of resistor R14, the other end of resistor R14 is connected to one end of resistor R18, one end of resistor R15, and one end of capacitor C11, the other end of resistor R18 is connected to the positive input terminal of operational amplifier U5B, and the other ends of resistor R15 and capacitor C11 are both grounded; the second pin of probe J4 is connected to operational amplifier U5A... The positive input terminal of the operational amplifier U5A is connected to one end of resistor R17 and one end of capacitor C12. The other end of resistor R17 and one end of capacitor C12 are connected to the output terminal of operational amplifier U5A and one end of resistor R19. The other end of resistor R19 is connected to the microcontroller control circuit and one end of capacitor C13. The other end of capacitor C13 and the negative power supply terminal of operational amplifier U5A are both grounded; the positive power supply terminal of operational amplifier U5B is connected to the power supply circuit; the negative input terminal of operational amplifier U5B is connected to one end of resistor R20 and one end of capacitor C16 respectively; the other end of resistor R20 and the other end of capacitor C16 are connected to the output terminal of operational amplifier U5B and one end of resistor R21 respectively; the other end of resistor R21 is connected to the microcontroller control circuit and one end of capacitor C15 respectively; the other end of capacitor C15 and the negative power supply terminal of operational amplifier U5B are both grounded.

[0035] The salt concentration detection circuit is the core of this technical solution. This utility model adopts a combination of microcontroller and operational amplifier, and realizes voltage sampling through PWM wave, which effectively reduces the cost of traditional detection circuit. The components used are all common materials that are easy to obtain. Compared with the traditional detection method, this solution significantly reduces the polarization problem of the probe by introducing PWM wave output, and avoids the defect that the probe end may rust due to oxidation after long-term use.

[0036] During salt concentration detection, one end of probe J4 is connected to the salt water, and then a closed circuit is formed between probe electrode immersed in the salt water through resistor R16. The principle of salt concentration testing is to calculate the corresponding salt concentration by using the equivalent impedance value measured by the test circuit. The higher the salt concentration, the lower the equivalent impedance value; conversely, the lower the salt concentration, the higher the equivalent impedance value.

[0037] This technical solution uses a microcontroller to output a PWM1 wave for detection. The specific process is as follows: Within 1 second, PWM1 outputs a 50ms high-level pulse; when PWM1 outputs a low level, MOSFET Q2 is not turned on, and consequently, MOSFET Q1 is also not turned on; when PWM1 outputs a high level, MOSFET Q2 turns on, thus turning on MOSFET Q1 as well; the output square wave signal is converted from DC to AC signal through electrolytic capacitor EC2; U5 is a rail-to-rail operational amplifier, the positive input voltage of operational amplifier U5B is half the voltage of the first pin of the probe, and after the output of the operational amplifier, it is connected to the sampling pin NACL_REF of the microcontroller; the positive input terminal of operational amplifier U5A samples the voltage of the second pin of the probe, and after the output of the operational amplifier, it reaches the AD_NACL pin of the microcontroller; the voltage of the AD_NACL pin is divided by the resistor R16 to obtain the current value between the two ends of the probe, the voltage of the NACL_REF pin is multiplied by 2 and then subtracted from the voltage of the AD_NACL pin, which is the voltage value between the two ends of the probe. The impedance value across the probe can be obtained by dividing the voltage by the current. By combining the impedance value with the salt concentration, the magnitude of the salt concentration can be determined.

[0038] The water flow detection circuit includes a transformer T1. One end of the input side of the transformer T1 is connected to one end of capacitor C19 and the first pin of electrode J5. The other end of the input side of the transformer T1 is connected to one end of capacitor C18. The other ends of capacitor C18 and capacitor C19 are both connected to the second pin of electrode J5. The lower end of the output side of the transformer T1 is connected to the anode of diode D3. The cathode of diode D3 is connected to one end of resistor R25, one end of capacitor C17, and one end of resistor R26. The other end of resistor R26 is connected to the microcontroller control circuit. The upper end of the output side of the transformer T1 is connected to the cathode of diode D2 and one end of resistor R24. The other end of resistor R24 ​​is connected to the microcontroller control circuit. The middle end of the output side of the transformer T1, the anode of diode D2, the other end of resistor R25, and the other end of capacitor C17 are all grounded.

[0039] The water temperature detection circuit includes a water temperature sensor, which is connected to a sensor interface J2. One end of the sensor interface J2 is connected to one end of resistor R22, one end of resistor R23, and one end of capacitor C20. The other end of resistor R22 is connected to the VOUT pin of the voltage regulator chip U3, and the other end of resistor R23 is connected to the P13 pin of the microcontroller U2. The other ends of capacitor C20 and sensor interface J2 are both grounded.

[0040] This technical solution employs a combination of a probe and electrode J5, utilizing a transformer to achieve voltage isolation, effectively avoiding ground current backflow and thus improving the accuracy of salt concentration detection. Specifically, electrode J5 acts as an electrode inserted into the water to detect the presence of water. In the absence of water, the detection circuit does not require further salt concentration testing; if water is detected, salt concentration detection is necessary. This solution uses a PWM2 signal for duty cycle control. When the water is in a pure water state, the voltage at the AD-FLOW terminal reaches its maximum value; once the water contains a certain concentration of salt, the AD-FLOW voltage will increase. In the program design, it is only necessary to determine whether the AD-FLOW voltage is below its maximum value to confirm the presence of water. This detection method outputs a square wave via a PWM signal, effectively avoiding probe polarization and effectively eliminating ground current backflow interference, thereby improving the accuracy of salt concentration detection. Furthermore, there is a certain relationship between salt concentration and water temperature. Within a certain range of salt concentration, temperature has a relatively small impact on the salt concentration value; however, when the salt concentration is high, the influence of temperature will increase accordingly. Therefore, sensor interface J2 is connected to a water temperature sensor for real-time monitoring of water temperature. Based on actual test data, a temperature compensation coefficient K can be calculated to calibrate the salt concentration measurement results, thereby obtaining more accurate salt concentration measurement results.

[0041] This solution uses a microcontroller to output a PWM wave to drive an operational amplifier, which then converts the DC current to AC through an electrolytic capacitor to obtain a voltage signal. This method of outputting a square wave using a PWM signal effectively reduces the amplitude of the input current. Simultaneously, by converting DC to AC through a capacitor to power the probe, the polarization problem that might occur when the probe is directly connected to VCC voltage can be effectively avoided. During detection, one end of the probe measures the current through the resistor R16; the other end measures the voltage through the probe. Using the resistance formula R = U / I, the equivalent impedance between the probes can be calculated, thus indirectly determining the salt concentration. Employing PWM for signal output not only effectively reduces the input current but also avoids polarization problems, improving the safety and reliability of the detection circuit.

[0042] Furthermore, this solution uses a 4-digit LED display to make the salt concentration value more intuitive and improve product readability. However, when the salt concentration exceeds a certain value, the LED display may not be intuitive enough. Using an LCD screen to directly display the salt concentration value would significantly improve the display effect, allowing operators to observe changes in salt concentration more directly.

[0043] This solution employs a single operational amplifier (op-amp) for voltage sampling, significantly reducing design costs. Furthermore, the components used are common and readily available. The op-amp operates at 5V; selecting an op-amp with a higher bias voltage could further improve test accuracy. Additionally, probe stability is affected, especially under water wave interference, making it difficult to maintain stable sampling voltage. Therefore, adding a filter circuit at the probe's front end can effectively improve voltage sampling stability. Simultaneously, selecting a low-bias op-amp also contributes to improving voltage sampling accuracy.

[0044] This solution uses a combination of microcontroller and operational amplifier to achieve voltage sampling through PWM waves, which significantly reduces the cost of traditional detection circuits. At the same time, the components used are all common materials that are easy to obtain.

[0045] Traditional detection methods have a significant drawback: when the salt concentration in water is high, the sampling signal is prone to distortion, thus affecting the detection accuracy. This solution perfectly solves this problem by introducing a transformer isolation circuit. Compared with traditional detection methods, this solution maintains detection accuracy even under high concentration conditions.

[0046] In practical applications, the circuit has a built-in rechargeable lithium battery, eliminating the need for external power supply. This reduces hardware costs, improves device portability, and enhances product safety and durability. Meanwhile, the button control enables a low-power operation mode, allowing the circuit to be used for about six months on a single charge, greatly improving the device's battery life.

[0047] Compared to other salt concentration detection circuits, this solution uses standard, readily available materials, resulting in lower costs. Furthermore, compared to professional salt concentration testers, this solution offers greater flexibility and scalability in its circuit structure, and the use of operational amplifiers further enhances measurement reliability and accuracy, ensuring the precision of the results.

[0048] In summary, the salt concentration testing circuit of this invention has the following significant advantages: First, the circuit structure is simple and the equipment is readily available; second, it is highly portable and can be carried for testing at any time; third, the circuit has a built-in lithium battery, supporting long-term use; fourth, it features excellent low-power design, allowing for continuous use for more than six months after a full charge; and fifth, it is equipped with a 4-digit digital tube display function, facilitating intuitive display of the salt concentration value. These features make it an economical and practical salt concentration testing device with excellent market prospects.

Claims

1. A simple, low-power salt concentration testing circuit, characterized in that: The low-power salt concentration testing circuit includes a salt concentration detection circuit, a microcontroller control circuit, a power supply circuit, a water flow detection circuit, and a digital tube display circuit. The power supply circuit is connected to the salt concentration detection circuit, the microcontroller control circuit, and the digital tube display circuit to supply power to them. The microcontroller control circuit is connected to the water flow detection circuit to detect the water inflow status. The microcontroller control circuit is connected to the salt concentration detection circuit to detect the salt concentration in the water. The microcontroller control circuit is connected to the digital tube display circuit to output and display the salt concentration detection results.

2. The simple low-power salt concentration testing circuit as described in claim 1, characterized in that: The salt concentration detection circuit includes probe J4, operational amplifier U5A, operational amplifier U5B, MOSFET Q1, and MOSFET Q2. The source of MOSFET Q1 is connected to the power supply circuit. The gate of MOSFET Q1 is connected to one end of resistor R12 and the drain of MOSFET Q2. The other end of resistor R12 is connected to the power supply circuit. The drain of MOSFET Q1 is connected to one end of electrolytic capacitor EC2 and one end of resistor R13. The gate of MOSFET Q2 is connected to one end of resistor R10 and one end of resistor R11. The other end of resistor R10 is connected to... The microcontroller control circuit is connected, with the other end of resistor R13, the source of MOSFET Q2, and the other end of resistor R11 all grounded; the other end of electrolytic capacitor EC2 is connected to the first pin of probe J4 and one end of resistor R14, the other end of resistor R14 is connected to one end of resistor R18, one end of resistor R15, and one end of capacitor C11, the other end of resistor R18 is connected to the positive input terminal of operational amplifier U5B, and the other ends of resistor R15 and capacitor C11 are both grounded; the second pin of probe J4 is connected to operational amplifier U5A... The positive input terminal of the operational amplifier U5A is connected to one end of resistor R17 and one end of capacitor C12. The other end of resistor R17 and one end of capacitor C12 are connected to the output terminal of operational amplifier U5A and one end of resistor R19. The other end of resistor R19 is connected to the microcontroller control circuit and one end of capacitor C13. The other end of capacitor C13 and the negative power supply terminal of operational amplifier U5A are both grounded; the positive power supply terminal of operational amplifier U5B is connected to the power supply circuit; the negative input terminal of operational amplifier U5B is connected to one end of resistor R20 and one end of capacitor C16 respectively; the other end of resistor R20 and the other end of capacitor C16 are connected to the output terminal of operational amplifier U5B and one end of resistor R21 respectively; the other end of resistor R21 is connected to the microcontroller control circuit and one end of capacitor C15 respectively; the other end of capacitor C15 and the negative power supply terminal of operational amplifier U5B are both grounded.

3. The simple low-power salt concentration testing circuit as described in claim 2, characterized in that: The water flow detection circuit includes a transformer T1. One end of the input side of the transformer T1 is connected to one end of capacitor C19 and the first pin of electrode J5. The other end of the input side of the transformer T1 is connected to one end of capacitor C18. The other ends of capacitor C18 and capacitor C19 are both connected to the second pin of electrode J5. The lower end of the output side of the transformer T1 is connected to the anode of diode D3. The cathode of diode D3 is connected to one end of resistor R25, one end of capacitor C17, and one end of resistor R26. The other end of resistor R26 is connected to the microcontroller control circuit. The upper end of the output side of the transformer T1 is connected to the cathode of diode D2 and one end of resistor R24. The other end of resistor R24 ​​is connected to the microcontroller control circuit. The middle end of the output side of the transformer T1, the anode of diode D2, the other end of resistor R25, and the other end of capacitor C17 are all grounded.

4. The simple, low-power salt concentration testing circuit as described in claim 3, characterized in that: The digital tube display circuit includes an LED scanning driver chip U4 and a digital tube display. The DIG1, ​​DIG2, DIG3, and DIG4 pins of the LED scanning driver chip U4 correspond to and are connected to the BIT1, BIT2, BIT3, and BIT4 pins of the digital tube display, respectively. The A, B, C, D, E, F, G, and DP pins of the LED scanning driver chip U4 correspond to and are connected to the A, B, C, D, E, F, G, and DP pins of the digital tube display, respectively. The VDD pin of the LED scanning driver chip U4 is connected to one end of capacitor C10, one end of capacitor EC1, and the power supply circuit, respectively. The other ends of capacitors C10 and EC1 are grounded. The SDA and SCL pins of the LED scanning driver chip U4 are both connected to the microcontroller control circuit, and the GND pin of the LED scanning driver chip U4 is grounded.

5. The simple, low-power salt concentration testing circuit as described in claim 4, characterized in that: The microcontroller control circuit includes a microcontroller U2. Pin P05 of microcontroller U2 is connected to one end of push-button switch SW1, and the other end of push-button switch SW2 is grounded. Pins P04 and P24 of microcontroller U2 are both connected to the power supply circuit. Pin P16 of microcontroller U2 is connected to one end of resistor R10. Pin P15 of microcontroller U2 is connected to one end of resistor R19 and one end of capacitor C13, respectively. Pin P14 of microcontroller U2 is connected to one end of capacitor C15 and one end of resistor R21, respectively. Pin P23 of microcontroller U2 is connected to one end of resistor R24, and pin P22 of microcontroller U2 is connected to one end of resistor R26. Pin 21 is connected to the CLK pin of programming port J3. Pin P35 of microcontroller U2 is connected to the SDA pin of programming port J3. Pin VCC of programming port J3 is connected to the power supply circuit. Pin GND of programming port J3 is grounded. Pin P32 of microcontroller U2 is connected to one end of external high-frequency crystal oscillator Y1 and one end of capacitor C6. Pin P31 of microcontroller U2 is connected to the other end of external high-frequency crystal oscillator Y1 and one end of capacitor C4. The other ends of capacitor C6 and capacitor C4 are both grounded. Pin VDD of microcontroller U2 is connected to the power supply circuit and one end of capacitor C9. The other end of capacitor C9 and pin VSS of microcontroller U2 are both grounded.

6. The simple low-power salt concentration testing circuit as described in claim 5, characterized in that: The power supply circuit includes a lithium battery charging circuit unit and a voltage regulator circuit unit, with the lithium battery charging circuit unit connected to the voltage regulator circuit unit. The lithium battery charging circuit unit includes a linear charging chip U1 and a TYPE C terminal. The VBUS pin of the TYPE C terminal is connected to the voltage regulator circuit unit, one end of the thermistor RT1, one end of the capacitor C1, one end of the resistor R29, and the VIN pin of the linear charging chip U1. The other end of the thermistor RT1 is connected to the IS pin of the linear charging chip U1 and one end of the resistor R2. The other end of the resistor R2, the other end of the capacitor C1, and the GNG pin of the linear charging chip U1 are all grounded. The other end of the resistor R29 is connected to the P04 pin of the microcontroller U2 and one end of the resistor R30. The other end of the resistor R30 is grounded. The CC1 pin of the TYPE C terminal is connected to one end of the resistor R4, and the CC2 pin of the TYPE C terminal is connected to one end of the resistor R3. The other ends of the resistor R3, the other end of the resistor R4, and the TYPE C terminal are all grounded. The GND pins of terminal C are all grounded; the ISET pin of the linear charging chip U1 is connected to one end of resistor R1, and the other end of resistor R1 is grounded; the CHRG pin of the linear charging chip U1 is connected to one end of indicator LED1, the DONE pin of the linear charging chip U1 is connected to one end of indicator LED2, the other ends of indicator LED1 and indicator LED2 are both connected to one end of resistor R5, and the other end of resistor R5 is connected to the voltage regulator circuit unit; the VBAT pin of the linear charging chip U1 is connected to one end of capacitor C2, the voltage regulator circuit unit, one end of resistor R27, and the second pin of external interface J1, respectively; the other end of resistor R27 is connected to one end of resistor R28, one end of capacitor C21, and the P24 pin of microcontroller U2, respectively; the other ends of capacitor C21 and resistor R28 are both grounded; the first pin of external interface J1, the other end of capacitor C2, and the EPAD pin of linear charging chip U1 are all grounded.

7. The simple low-power salt concentration testing circuit as described in claim 6, characterized in that: The voltage regulator circuit unit includes a MOSFET Q3 and a voltage regulator chip U3. The drain of the MOSFET Q3 is connected to the VBAT pin of the linear charging chip U1. The gate of the MOSFET Q3 is connected to one end of resistor R6 and one end of resistor R7. The other end of resistor R6 is grounded. The other end of resistor R7 is connected to the anode of diode D1 and the TYPE pin. The VBUS pin of terminal C is connected to one end of resistor R5; the cathode of diode D1 is connected to the source of MOSFET Q3, one end of capacitor C7, and one end of inductor L1 respectively. The other end of capacitor C7 is grounded, and the other end of inductor L1 is connected to the LX pin of voltage regulator chip U3. The VOUT pin of voltage regulator chip U3 is connected to one end of capacitor C8, the VCC pin of programming port J3, one end of capacitor C9, the VDD pin of microcontroller U2, the VDD pin of LED scanning driver chip U4, one end of capacitor C10, one end of capacitor EC1, one end of resistor R12, the source of MOSFET Q1, the positive power supply terminal of operational amplifier U5A, one end of capacitor C14, and the positive power supply terminal of operational amplifier U5B; the other end of capacitor C8 and the GND pin of voltage regulator chip U3 are both grounded.

8. The simple low-power salt concentration testing circuit as described in claim 7, characterized in that: The low-power salt concentration test circuit also includes a water temperature detection circuit, which includes a water temperature sensor connected to a sensor interface J2. One end of the sensor interface J2 is connected to one end of resistor R22, one end of resistor R23, and one end of capacitor C20. The other end of resistor R22 is connected to the VOUT pin of the voltage regulator chip U3, and the other end of resistor R23 is connected to the P13 pin of the microcontroller U2. The other ends of capacitor C20 and sensor interface J2 are both grounded.

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