Bipolar excitation voltage circuit for Wheatstone bridge

Abstract

The utility model discloses a bipolar excitation voltage circuit for a Wheatstone bridge in the field of power electronics, which comprises a positive voltage follower circuit connected with a reference voltage source, the positive voltage follower circuit is connected with a negative voltage follower circuit through a resistor R12, the positive voltage follower circuit is connected with a positive protection circuit, and the negative voltage follower circuit is connected with a negative protection circuit. The positive protection circuit is connected with the A point of the Wheatstone bridge, the negative voltage follower circuit is connected with the negative protection circuit, and the negative protection circuit is connected with the C point of the Wheatstone bridge. The positive and negative voltage following circuit outputs a voltage equal to a reference voltage of the reference voltage source, so that the voltage output to the Wheatstone bridges is ensured to be constant; the non-ideal factors can generate the same effect in the positive and negative directions through the alternate use of the positive and negative voltages, so that the non-ideal factors are mutually counteracted in the subsequent processing, and the measurement accuracy is improved.

Description

Technical Field

[0001] The utility model relates to a bipolar excitation voltage circuit in the field of power electronics. Background Art

[0002] A Wheatstone bridge is a bridge circuit composed of four resistors, which are respectively called the bridge arms of the bridge. The Wheatstone bridge uses the change of resistance to measure the change of physical quantity. The single-chip microcomputer collects the voltage across the variable resistor and then processes it, and then the change of the corresponding physical quantity can be calculated. It is a measurement method with high precision. In the prior art, the Wheatstone bridge usually uses a unipolar voltage. Due to the zero-point offset caused by the asymmetry of the bridge elements, temperature changes or other non-ideal factors in the circuit, this offset will only form a single change in the positive direction or the negative direction, which will affect the accuracy of the measurement result. Summary of the Utility Model

[0003] The purpose of the utility model is to provide a Wheatstone bridge using a bipolar excitation voltage circuit. The alternating use of positive and negative voltages can make these non-ideal factors produce the same effect in the positive and negative directions, so as to cancel each other out in the subsequent processing and improve the measurement accuracy.

[0004] To achieve the above purpose, the utility model provides a Wheatstone bridge using a bipolar excitation voltage circuit, which includes a positive voltage follower circuit connected to a reference voltage source. The positive voltage follower circuit is connected to a negative voltage follower circuit through a resistor R12. The positive voltage follower circuit is connected to a positive protection circuit, and the positive protection circuit is connected to point A of the Wheatstone bridge. The negative voltage follower circuit is connected to a negative protection circuit, and the negative protection circuit is connected to point C of the Wheatstone bridge.

[0005] Compared with the prior art, the beneficial effect of the utility model lies in that the positive and negative voltage follower circuits output voltages equal to the reference voltage of the reference voltage source, so as to ensure that the voltage output to the Wheatstone bridge is constant. The positive and negative protection circuits can interrupt the voltage output after the current in the circuit exceeds the limit value, so as to protect the circuit safety. Since the stable bipolar excitation voltage is applied to points A and C of the Wheatstone bridge, the alternating use of positive and negative voltages can make these non-ideal factors produce the same effect in the positive and negative directions, so as to cancel each other out in the subsequent processing and improve the measurement accuracy.

[0006] As a further improvement of the present utility model, the positive voltage follower circuit includes operational amplifiers U1A and U1B. Pin 1 of operational amplifier U1A is connected to pin 6 of operational amplifier U1B. Pin 5 of operational amplifier U1B is connected to a reference voltage source. Pins 8 and 4 of operational amplifier U1B are respectively connected to +3.3V and -3.3V. Pin 7 of operational amplifier U1B is connected to one end of resistor R9, and the other end of resistor R9 is connected to the positive protection circuit. Pin 1 of operational amplifier U1A is connected to pin 2. Pins 8 and 4 of operational amplifier U1A are respectively connected to +3.3V and -3.3V. Pin 3 of operational amplifier U1A is connected to one end of resistor R23, and the other end of resistor R23 is connected to the positive protection circuit. The positive protection circuit is connected to the positive electrode of capacitor C27. The negative electrode of capacitor C27 is grounded. Capacitor C27 is connected in parallel with capacitor C28. The positive electrode of capacitor C27 is connected to point A of the Wheatstone bridge.

[0007] In this way, operational amplifiers U1A and U1B are used to form a voltage follower to copy and output the input voltage, achieving the effect of voltage following. In an ideal situation, the output voltage is equal to the input voltage. Therefore, the voltage at pin 6 of U1B is equivalent to the voltage at pin 5. Pin 6 is directly connected to pin 2 of U1A, and the voltages of both are equal. The voltage at pin 2 of U1A is equivalent to the voltage at pin 3, that is, the voltage at pin 3 is the voltage VREF at point A.

[0008] As a further improvement of the present utility model, the positive protection circuit includes triode Q3. Pin 2 of triode Q3 is respectively connected to pin 1 of triode Q2 and the other end of resistor R9. Pin 2 of triode Q2 is connected to +3.3V. Pin 3 of triode Q2 is respectively connected to pin 1 of triode Q3 and one end of resistor R24. The other end of resistor R24 is connected to pin 3 of triode Q3 and the positive electrode of capacitor C27.

[0009] In this way, pin 7 of U1B provides the base voltage and current for the triode to operate in the amplification state. The working current at point A comes from A3.3V, passes through pins 2 and 3 of triode Q3. The two ends of resistor R24 are connected to pins 1 and 3 of triode Q3. Pins 1 and 3 of triode Q2 are respectively connected to pins 2 and 1 of triode Q3. When the current in the circuit exceeds the voltage between pins 1 and 3 of triode Q3 (the theoretical value is 0.7V) / 2.5R, then Q2 does not have the conduction condition, thus playing a role in protecting the circuit.

[0010] As a further improvement of the present utility model, the negative voltage follower circuit includes an operational amplifier U2B. The 6th pin of the operational amplifier U2B is respectively connected to one end of a resistor R16 and one end of a resistor R12. The other end of the resistor R12 is connected to the 6th pin of the operational amplifier U1B. The other end of the resistor R16 is connected to one end of a resistor R17. The other end of the resistor R17 is connected to the negative protection circuit and the negative electrode of a capacitor C11. The negative protection circuit is connected to one end of a resistor R19. The other end of the resistor R19 is connected to the 7th pin of the operational amplifier U2B. The 5th pin of the operational amplifier U2B is grounded. The 8th and 4th pins of the operational amplifier U2B are respectively connected to +3.3V and -3.3V. The positive electrode of the capacitor C11 is grounded. The capacitor C11 is connected in parallel with a capacitor C12. The negative electrode of the capacitor C11 is connected to point C of the Wheatstone bridge.

[0011] In this way, the operational amplifier U2B is used to form a voltage follower to achieve the effect of voltage following. In an ideal situation, the output voltage is equal to the input voltage. Therefore, the voltage of the 5th pin of U2B is equivalent to the voltage of the 6th pin. The voltage of the 5th pin of U2B is GND, so the voltage of the 6th pin of U2B is 0V. Also, since the resistance value of the resistor R12 is equal to R16 + R17, assuming the voltage of point C of the Wheatstone bridge is Vc, then through the formula (VREF - 0) / R12 = (0 - Vc) / (R16 + R17), it can be obtained that Vc = -VREF, that is, the voltage of point C of the Wheatstone bridge is -VREF, which is equal in value and opposite in polarity to the voltage of point A of the Wheatstone bridge.

[0012] As a further improvement of the present utility model, the negative protection circuit includes a triode Q4. The 2nd pin of the triode Q4 is respectively connected to the 1st pin of a triode Q5 and one end of a resistor R19. The 2nd pin of the triode Q5 is connected to -3.3V. The 3rd pin of the triode Q5 is respectively connected to the 1st pin of the triode Q4 and one end of a resistor R20. The other end of the resistor R20 is respectively connected to the 3rd pin of the triode Q4 and the negative electrode of the capacitor C11.

[0013] In this way, the 7th pin of U2B provides the base voltage and current for the triode to work in the amplification state. The working current at point C comes from A - 3.3V, passes through the 2nd and 3rd pins of the triode Q4. Both ends of the resistor R20 are connected to the 1st and 3rd pins of the triode Q4. The 1st and 3rd pins of the triode Q5 are respectively connected to the 2nd and 1st pins of the triode Q4. When the current in the circuit exceeds the voltage between the 1st and 3rd pins of the triode Q4 (the theoretical value is 0.7V) / 2.5R, then Q5 does not have the conduction condition, thus playing a role in protecting the circuit.

[0014] As a further improvement of the present utility model, the reference voltage source includes an electronic switch U21. The 5th pin of the electronic switch U21 is connected to +2.5V, the 4th pin of the electronic switch U21 is connected to the 2nd pin, the 3rd pin of the electronic switch U21 is respectively connected to +2.0V, one end of a resistor R11, and one end of a resistor R14. The 15th pin of the electronic switch U21 is connected to the 5th pin of an operational amplifier U1B. The 1st pin of the electronic switch U21 is respectively connected to +1.0V, the other end of the resistor R14, and one end of a resistor R58. The other end of the resistor R58 is grounded. The 12th, 13th, and 14th pins of the electronic switch U21 are grounded. The 6th pin of the electronic switch U21 is grounded. The 9th pin of the electronic switch U21 is connected to the VR2.5 / 2.0 pin of the single-chip microcomputer. The 10th pin of the electronic switch U21 is connected to the VR2.0 / 1.0 pin of the single-chip microcomputer. The 11th pin of the electronic switch U21 is grounded. The 16th pin of the electronic switch U21 is connected to +3.3V. The pin of the electronic switch U21 and the 7th pin are grounded.

[0015] In this way, U21 contains 3 single-pole double-throw analog switches. The 9th and 10th pins of U21 are controlled by the single-chip microcomputer. When the 9th pin is at low level and the 10th pin is at low level, the output VREF voltage is 2.5V. When the 9th pin is at high level and the 10th pin is at low level, the output VREF voltage is 2.0V. When both the 9th and 10th pins are at high level, the output VREF voltage is 1.0V. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a bipolar voltage circuit diagram of the present utility model.

[0017] Figure 2 It is a schematic diagram of a Wheatstone bridge circuit.

[0018] Figure 3 It is a gear voltage switching circuit of the present utility model. DETAILED DESCRIPTION OF THE INVENTION

[0019] The present utility model will be further described below with reference to the drawings:

[0020] As Figures 1-3 A Wheatstone bridge uses a bipolar excitation voltage circuit as shown. It includes a positive voltage follower circuit connected to a reference voltage source. The positive voltage follower circuit is connected to a negative voltage follower circuit via a resistor R12. The positive voltage follower circuit is connected to a positive protection circuit. The positive protection circuit is connected to point A of the Wheatstone bridge. The negative voltage follower circuit is connected to a negative protection circuit. The negative protection circuit is connected to point C of the Wheatstone bridge.

[0021] The positive voltage follower circuit includes operational amplifiers U1A and U1B. Pin 1 of operational amplifier U1A is connected to pin 6 of operational amplifier U1B. Pin 5 of operational amplifier U1B is connected to the reference voltage source. Pins 8 and 4 of operational amplifier U1B are respectively connected to +3.3V and -3.3V. Pin 7 of operational amplifier U1B is connected to one end of resistor R9, and the other end of resistor R9 is connected to the positive protection circuit. Pin 1 of operational amplifier U1A is connected to pin 2. Pins 8 and 4 of operational amplifier U1A are respectively connected to +3.3V and -3.3V. Pin 3 of operational amplifier U1A is connected to one end of resistor R23, and the other end of resistor R23 is connected to the positive protection circuit. The positive protection circuit is connected to the positive electrode of capacitor C27. The negative electrode of capacitor C27 is grounded. Capacitor C27 is in parallel with capacitor C28. The positive electrode of capacitor C27 is connected to point A of the Wheatstone bridge.

[0022] The positive protection circuit includes transistor Q3. Pin 2 of transistor Q3 is respectively connected to pin 1 of transistor Q2 and the other end of resistor R9. Pin 2 of transistor Q2 is connected to +3.3V. Pin 3 of transistor Q2 is respectively connected to pin 1 of transistor Q3 and one end of resistor R24. The other end of resistor R24 is connected to pin 3 of transistor Q3 and the positive electrode of capacitor C27.

[0023] The negative voltage follower circuit includes operational amplifier U2B. Pin 6 of operational amplifier U2B is respectively connected to one end of resistor R16 and one end of resistor R12. The other end of resistor R12 is connected to pin 6 of operational amplifier U1B. The other end of resistor R16 is connected to one end of resistor R17. The other end of resistor R17 is connected to the negative protection circuit and the negative electrode of capacitor C11. The negative protection circuit is connected to one end of resistor R19. The other end of resistor R19 is connected to pin 7 of operational amplifier U2B. Pin 5 of operational amplifier U2B is grounded. Pins 8 and 4 of operational amplifier U2B are respectively connected to +3.3V and -3.3V. The positive electrode of capacitor C11 is grounded. Capacitor C11 is in parallel with capacitor C12. The negative electrode of capacitor C11 is connected to point C of the Wheatstone bridge.

[0024] The negative protection circuit includes transistor Q4. Pin 2 of transistor Q4 is respectively connected to pin 1 of transistor Q5 and one end of resistor R19. Pin 2 of transistor Q5 is connected to -3.3V. Pin 3 of transistor Q5 is respectively connected to pin 1 of transistor Q4 and one end of resistor R20. The other end of resistor R20 is respectively connected to pin 3 of transistor Q4 and the negative electrode of capacitor C11.

[0025] The reference voltage source includes an electronic switch U21. The 5th pin of the electronic switch U21 is connected to +2.5V, the 4th pin of the electronic switch U21 is connected to the 2nd pin, the 3rd pin of the electronic switch U21 is respectively connected to +2.0V, one end of a resistor R11, and one end of a resistor R14. The 15th pin of the electronic switch U21 is connected to the 5th pin of an operational amplifier U1B. The 1st pin of the electronic switch U21 is respectively connected to +1.0V, the other end of the resistor R14, and one end of a resistor R58. The other end of the resistor R58 is grounded. The 12th, 13th, and 14th pins of the electronic switch U21 are grounded. The 6th pin of the electronic switch U21 is grounded. The 9th pin of the electronic switch U21 is connected to the VR2.5 / 2.0 pin of a single-chip microcomputer. The 10th pin of the electronic switch U21 is connected to the VR2.0 / 1.0 pin of the single-chip microcomputer. The 11th pin of the electronic switch U21 is grounded. The 16th pin of the electronic switch U21 is connected to +3.3V. The pin of the electronic switch U21 and the 7th pin are grounded.

[0026] In the present utility model, an operational amplifier U1A and U1B form one path of voltage follower, and U2B forms another path of voltage follower. Its function is to copy and output the input voltage to achieve voltage following. Ideally, the output voltage is equal to the input voltage. A3.3V and A - 3.3V are the power supplies required for the operation of the operational amplifier. U1A, U1B, and U2B perform the voltage following function; VREF is the voltage value obtained by resistor voltage division and then switched by an electronic switch, and a stable equivalent output voltage is obtained through the operational amplifier.

[0027] The input impedance of the voltage follower is very high, approaching infinity. This means that the input signal source will not be affected by the load of the operational amplifier, maintaining the stability of the input signal source. The high input impedance enables the operational amplifier to well protect the upstream circuit and avoid the signal source being affected due to excessive load.

[0028] The output impedance of the voltage follower is very low, approaching zero. This enables the output voltage to drive a relatively large load resistor and provides a greater output current capacity. The low output impedance ensures the stability of the output voltage, and even when the load changes, the output voltage can remain unchanged.

[0029] The voltage follower has good stability and can keep the amplification ratio of the input signal unchanged. This is because the amplifier gain of the operational amplifier is very high, and its feedback loop corrects the difference between the input and the output, thus ensuring the stability of the output.

[0030] During operation, using the concepts of virtual short and virtual open of the operational amplifier, the voltage of the 6th pin of U1B is equivalent to the voltage of the 5th pin. The 5th pin is directly connected to the 2nd pin of U1A, and the voltages of both are equal. The voltage of the 2nd pin of U1A is equivalent to the voltage of the 3rd pin, that is, the voltage of the 3rd pin is the voltage VREF at point A.

[0031] The voltage at pin 5 of operational amplifier U2B is equal to the voltage at pin 6. Since the voltage at pin 5 of U2B is GND, the voltage at pin 6 of U2B is 0V. Also, since the resistance value of resistor R12 is equal to R16 + R17, let the voltage at point C of the Wheatstone bridge be Vc. Then, through the formula (VREF - 0) / R12 = (0 - Vc) / (R16 + R17), we can obtain Vc = -VREF, that is, the voltage at point C of the Wheatstone bridge is -VREF, which is equal in value and opposite in polarity to the voltage at point A of the Wheatstone bridge.

[0032] Therefore, VREF and -VREF are the input reference voltages and also the two voltages with opposite polarities finally output to the Wheatstone bridge.

[0033] Pin 7 of U1B provides the base voltage and current for the triode to operate in the amplification state. The working current at point A comes from A3.3V, passes through pins 2 and 3 of triode Q3, and both ends of resistor R24 are connected to pins 1 and 3 of triode Q3. Pins 1 and 3 of triode Q2 are respectively connected to pins 2 and 1 of triode Q3. When the current in the circuit exceeds the voltage between pins 1 and 3 of triode Q3, Q2 does not have the conduction condition, thus playing a role in protecting the circuit. The specific process is as follows:

[0034] After pins 1 and 3 of Q3 are conducting, the voltage at pin 1 of Q3 is 0.7V higher than that at pin 3. At this time, pins 2 and 3 of Q3 are conducting, the voltage at pin 2 of Q3 is approximately equal to the voltage at pin 3, and the voltage at pin 1 of Q3 is 0.7V higher than that at pin 2. Then Q2 does not have the conduction condition, and pins 2 and 3 of Q2 are disconnected. The entire loop (from A3.3V to Q2, then to R24, and finally to point A) is disconnected, and the voltage across R24 will also drop rapidly. When the voltage between pins 1 and 3 of Q3 drops below 0.7V, pins 2 and 3 of Q3 are disconnected, and then the entire loop supplies power to point A again.

[0035] Similarly, pin 7 of U2B provides the base voltage and current for the triode to operate in the amplification state. The working current at point C comes from A - 3.3V, passes through pins 2 and 3 of triode Q4, and both ends of resistor R20 are connected to pins 1 and 3 of triode Q4. Pins 1 and 3 of triode Q5 are respectively connected to pins 2 and 1 of triode Q4. When the current in the circuit exceeds the voltage between pins 1 and 3 of triode Q4 (the theoretical value is 0.7V) / 2.5R, Q5 does not have the conduction condition, thus playing a role in protecting the circuit.

[0036] VREF is the voltage value obtained by dividing the voltage through resistors R11, R14, and R58 and then switching it via an electronic switch. The electronic switch U21 contains 3 single-pole double-throw analog switches. The 9th and 10th pins of U21 are controlled by the microcontroller. When the 9th pin is at low level and the 10th pin is at low level, the output VREF voltage is 2.5V; when the 9th pin is at high level and the 10th pin is at low level, the output VREF voltage is 2.0V; when both the 9th and 10th pins are at high level, the output VREF voltage is 1.0V. In this way, different output voltages can be switched according to actual needs.

[0037] The present utility model uses positive and negative excitation voltages to eliminate zero-point offset caused by asymmetrical bridge elements, temperature changes, or other non-ideal factors in the circuit. The alternating use of positive and negative voltages can make these non-ideal factors produce the same effects in the positive and negative directions, so as to cancel each other out in subsequent processing and improve the measurement accuracy.

[0038] Compared with unipolar voltage, bipolar excitation voltage can provide a larger voltage range, thereby increasing the output signal strength of the bridge. A stronger signal means that in subsequent signal processing, it is easier to identify and distinguish useful signals from noise, thereby improving the measurement accuracy.

[0039] Reducing the influence of temperature drift: Temperature change is one of the common interference factors in resistance measurement. Using positive and negative excitation voltages can, to a certain extent, reduce the influence of temperature change on the measurement result. Because the alternating use of positive and negative voltages can make the resistance changes caused by temperature change cancel each other out in the positive and negative directions, thus maintaining the stability of the measurement result.

[0040] Improving the system robustness: The use of positive and negative excitation voltages can also enhance the robustness of the bridge system. When the system is subject to external interference or internal component aging, the bipolar excitation voltage can better maintain the stability and reliability of the system.

[0041] Adapting to different requirements: In some specific application scenarios, it may be necessary to use excitation voltages of different polarities. The Wheatstone bridge using positive and negative excitation voltages can flexibly meet these requirements and achieve measurements under different polarities without replacing the circuit or components.

[0042] Improving compatibility: When integrated with other measurement devices or sensors, the Wheatstone bridge using positive and negative excitation voltages can improve compatibility. Because many measurement devices support bipolar input, which makes the Wheatstone bridge easier to cooperate with other devices and achieve more extensive functions and applications.

[0043] Convenient zero calibration: The zero calibration can be conveniently carried out by using positive and negative excitation voltages. Measure the output of the bridge under positive and negative voltages respectively, and adjust the circuit parameters so that the two output values are equal (or approximately equal), then the accurate zero calibration can be achieved.

[0044] The present utility model is not limited to the above embodiments. Based on the technical solutions disclosed herein, those skilled in the art can make some substitutions and deformations to some of the technical features without creative labor according to the disclosed technical content, and these substitutions and deformations are all within the protection scope of the present utility model.

Claims

1. A Wheatstone bridge uses a bipolar excitation voltage circuit, characterized in that: It includes a positive voltage follower circuit connected to a reference voltage source. The positive voltage follower circuit is connected to a negative voltage follower circuit via a resistor R12. The positive voltage follower circuit is connected to a positive protection circuit, and the positive protection circuit is connected to point A of the Wheatstone bridge. The negative voltage follower circuit is connected to a negative protection circuit, and the negative protection circuit is connected to point C of the Wheatstone bridge.

2. A Wheatstone bridge using a bipolar excitation voltage circuit according to claim 1, characterized in that: The positive voltage follower circuit includes operational amplifiers U1A and U1B. Pin 1 of operational amplifier U1A is connected to pin 6 of operational amplifier U1B. Pin 5 of operational amplifier U1B is connected to the reference voltage source. Pins 8 and 4 of operational amplifier U1B are respectively connected to +3.3V and -3.3V. Pin 7 of operational amplifier U1B is connected to one end of a resistor R9, and the other end of resistor R9 is connected to the positive protection circuit. Pin 1 of operational amplifier U1A is connected to pin 2. Pins 8 and 4 of operational amplifier U1A are respectively connected to +3.3V and -3.3V. Pin 3 of operational amplifier U1A is connected to one end of a resistor R23, and the other end of resistor R23 is connected to the positive protection circuit. The positive protection circuit is connected to the positive electrode of a capacitor C27, the negative electrode of capacitor C27 is grounded, capacitor C27 is in parallel with capacitor C28, and the positive electrode of capacitor C27 is connected to point A of the Wheatstone bridge.

3. A Wheatstone bridge using a bipolar excitation voltage circuit according to claim 2, characterized in that: The positive protection circuit includes a triode Q3. Pin 2 of triode Q3 is respectively connected to pin 1 of triode Q2 and the other end of resistor R9. Pin 2 of triode Q2 is connected to +3.3V. Pin 3 of triode Q2 is respectively connected to pin 1 of triode Q3 and one end of a resistor R24. The other end of resistor R24 is connected to pin 3 of triode Q3 and the positive electrode of capacitor C27.

4. A Wheatstone bridge using a bipolar excitation voltage circuit according to claim 3, characterized in that: The negative voltage follower circuit includes an operational amplifier U2B. Pin 6 of operational amplifier U2B is respectively connected to one end of a resistor R16 and one end of a resistor R12. The other end of resistor R12 is connected to pin 6 of operational amplifier U1B. The other end of resistor R16 is connected to one end of a resistor R17. The other end of resistor R17 is connected to the negative protection circuit and the negative electrode of a capacitor C11. The negative protection circuit is connected to one end of a resistor R19, and the other end of resistor R19 is connected to pin 7 of operational amplifier U2B. Pin 5 of operational amplifier U2B is grounded. Pins 8 and 4 of operational amplifier U2B are respectively connected to +3.3V and -3.3V. The positive electrode of capacitor C11 is grounded, capacitor C11 is in parallel with capacitor C12, and the negative electrode of capacitor C11 is connected to point C of the Wheatstone bridge.

5. A Wheatstone bridge using a bipolar excitation voltage circuit according to claim 4, characterized in that: The negative protection circuit includes a triode Q4. Pin 2 of triode Q4 is respectively connected to pin 1 of triode Q5 and one end of a resistor R19. Pin 2 of triode Q5 is connected to -3.3V. Pin 3 of triode Q5 is respectively connected to pin 1 of triode Q4 and one end of a resistor R20. The other end of resistor R20 is respectively connected to pin 3 of triode Q4 and the negative electrode of capacitor C11.

6. A Wheatstone bridge using a bipolar excitation voltage circuit according to claim 5, characterized in that: The reference voltage source includes an electronic switch U21. The 5th pin of the electronic switch U21 is connected to +2.5V, the 4th pin of the electronic switch U21 is connected to the 2nd pin, the 3rd pin of the electronic switch U21 is respectively connected to +2.0V, one end of a resistor R11, and one end of a resistor R14. The 15th pin of the electronic switch U21 is connected to the 5th pin of an operational amplifier U1B. The 1st pin of the electronic switch U21 is respectively connected to +1.0V, the other end of the resistor R14, and one end of a resistor R58. The other end of the resistor R58 is grounded. The 12th, 13th, and 14th pins of the electronic switch U21 are grounded. The 6th pin of the electronic switch U21 is grounded. The 9th pin of the electronic switch U21 is connected to the VR2.5 / 2.0 pin of a single-chip microcomputer. The 10th pin of the electronic switch U21 is connected to the VR2.0 / 1.0 pin of the single-chip microcomputer. The 11th pin of the electronic switch U21 is grounded. The 16th pin of the electronic switch U21 is connected to +3.3V. The [missing pin number] of the electronic switch U21 and the 7th pin are grounded.

Images