Sensor for measuring displacement of tape band of digital display measuring tape

Abstract

The utility model provides a sensor for measuring the displacement of a tape band of a digital display measuring tape, which comprises a sensor shell, and a circuit board, a first photoelectric sensor, a second photoelectric sensor and a third photoelectric sensor which are accommodated in the sensor shell, the first photoelectric sensor, the second photoelectric sensor and the third photoelectric sensor are electrically connected with a sensor circuit integrated on the circuit board; the sensor circuit comprises a first comparator, a second comparator, an MCU, and resistance adjusting circuits which are connected with the photoelectric sensors in a one-to-one correspondence manner and are used for adjusting the brightness of the photoelectric sensors. The first photoelectric sensor and the third photoelectric sensor are respectively connected with the input end of the first comparator; the second photoelectric sensor and the third photoelectric sensor are respectively connected with the input end of the second comparator; the output end of the first comparator and the output end of the second comparator are respectively connected with the input end of the MCU. The sensor is simple in circuit structure and low in production cost.

Description

Technical Field

[0001] This utility model relates to the field of measuring instrument technology, and in particular to a sensor for measuring the displacement of a digital measuring tape. Background Technology

[0002] With the continuous development of science and technology, traditional measuring tapes that rely on tape strip readings are cumbersome and inefficient. To address these issues, measuring tape manufacturers have developed digital measuring tapes. See Chinese invention patent CN105486213B, filed on January 18, 2016, published on June 15, 2018. This digital measuring tape utilizes a photoelectric displacement sensor, a specially marked tape strip, and a display screen. During use, simply pulling the tape strip allows the photoelectric displacement sensor to quickly identify and calculate the tape strip's displacement distance based on the special markings, directly displaying the measured distance on the screen. This facilitates direct reading of measurement data, significantly improving the convenience and efficiency of the measuring tape.

[0003] However, the existing sensors used for measuring the displacement of digital tape measures have relatively complex circuit structures and high production costs, resulting in relatively large sensor sizes that cannot meet the needs of small, portable tape measures. Utility Model Content

[0004] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides a sensor for measuring the displacement of a digital measuring tape, which has a simple circuit structure, low production cost, and small sensor size.

[0005] To achieve the above objectives, the main technical solutions adopted by this utility model include:

[0006] This utility model provides a sensor for measuring the displacement of a digital tape measure, including a sensor housing and a circuit board, a first photoelectric sensor, a second photoelectric sensor and a third photoelectric sensor housed in the sensor housing. The first photoelectric sensor, the second photoelectric sensor and the third photoelectric sensor are arranged side by side at equal intervals along the extension direction of the tape and are all electrically connected to the sensor circuit integrated on the circuit board.

[0007] The sensor circuit includes a first comparator, a second comparator, an MCU, and resistor adjustment circuits connected one-to-one with the photoelectric sensors for adjusting the brightness of the photoelectric sensors. The first and third photoelectric sensors are respectively connected to the input terminals of the first comparator, and the output signals of the first and third photoelectric sensors are compared to output a first square wave signal. The second and third photoelectric sensors are respectively connected to the input terminals of the second comparator, and the output signals of the second and third photoelectric sensors are compared to output a second square wave signal. The output terminals of the first and second comparators are respectively connected to the input terminals of the MCU, and the MCU receives the first and second square wave signals and outputs the scale displacement.

[0008] Optionally, each photoelectric sensor has a first pin, a second pin, a third pin, and a fourth pin. The first pin serves as the output terminal of the light emitter within the photoelectric sensor, the second pin serves as the input terminal of the light emitter within the photoelectric sensor, the third pin serves as the signal output terminal of the light receiver within the photoelectric sensor, and the fourth pin serves as the ground terminal of the light receiver within the photoelectric sensor. The second pin of each photoelectric sensor is electrically connected to the power supply VDD, and the first pin of each photoelectric sensor is connected to the first terminal of its corresponding resistor adjustment circuit. The second terminal of each resistor adjustment circuit is grounded. The third pin of the first photoelectric sensor is connected to the first input pin of the first comparator, the third pin of the second photoelectric sensor is connected to the first input pin of the second comparator, and the second input pins of the first and second comparators are respectively connected to the third pin of the third photoelectric sensor. The output pins of the first and second comparators are respectively connected to two pins of the MCU.

[0009] Optionally, the resistance adjustment circuit is a VR resistance adjustment circuit.

[0010] Optionally, the VR resistor adjustment circuit includes a VR resistor and a protection resistor. The first fixed terminal of the VR resistor is connected to the first pin of the photoelectric sensor, the movable terminal of the VR resistor is grounded, and the second fixed terminal of the VR resistor is connected to the movable terminal of the VR resistor through the protection resistor.

[0011] Optionally, the third pin of the first photoelectric sensor is connected to the first input pin of the first comparator through a first resistor, and the power supply VDD is connected to the first input pin of the first comparator in sequence through a second resistor and a first resistor.

[0012] The third pin of the second photoelectric sensor is connected to the first input pin of the second comparator through the fourth resistor. The power supply VDD is connected to the first input pin of the second comparator through the fifth resistor and the fourth resistor in sequence. The power supply VDD is grounded through the fifth resistor and the sixth resistor in sequence.

[0013] The third pin of the third photoelectric sensor is connected to the second input pin of the first comparator and the second input pin of the second comparator through the seventh resistor. The power supply VDD is connected to the second input pin of the first comparator and the second input pin of the second comparator through the eighth resistor and the seventh resistor, respectively.

[0014] Optionally, the sensor for measuring the displacement of the tape measure in a digital display further includes a first capacitor, a second capacitor, a third capacitor, and a fourth capacitor; the first terminal of the first capacitor is connected to the first input pin of the first comparator, and the second terminal of the first capacitor is grounded; the first terminal of the second capacitor is connected to the second input pin of the first comparator, and the second terminal of the second capacitor is grounded; the first terminal of the third capacitor is connected to the first input pin of the second comparator, and the second terminal of the third capacitor is grounded; the first terminal of the fourth capacitor is connected to the second input pin of the second comparator, and the second terminal of the fourth capacitor is grounded.

[0015] Optionally, the output pin of the first comparator is connected to the first input pin of the first comparator through a tenth resistor, and the output pin of the second comparator is connected to the first input pin of the second comparator through an eleventh resistor.

[0016] Optionally, the sensor for measuring the displacement of the tape measure in a digital display also includes a fifth capacitor and a sixth capacitor; the first terminal of the fifth capacitor is connected to the output pin of the first comparator, and the second terminal of the fifth capacitor is grounded; the first terminal of the sixth capacitor is connected to the output pin of the second comparator, and the second terminal of the sixth capacitor is grounded.

[0017] Optionally, the output pin of the first comparator is connected to the pin of the MCU through the twelfth resistor, and the power supply VDD is connected to the output pin of the first comparator through the thirteenth resistor; the output pin of the second comparator is connected to the pin of the MCU through the fourteenth resistor, and the power supply VDD is connected to the output pin of the second comparator through the fifteenth resistor.

[0018] Optionally, the sensor for measuring the displacement of the digital measuring tape also includes a connector for communicating with an external device of the digital measuring tape; the signal output pin of the MCU is connected to the signal input pin of the connector, and the signal output pin of the connector is connected to the signal input pin of the MCU.

[0019] The beneficial effects of this utility model are:

[0020] The sensor provided by this utility model includes three photoelectric sensors arranged side by side and at equal intervals. These three photoelectric sensors are electrically connected to a sensor circuit integrated on a circuit board. Through a resistor adjustment circuit, the brightness of the light emitter in each photoelectric sensor can be adjusted. When the brightness of the light emitters of the three photoelectric sensors is consistent, the output signals are consistent, which is beneficial to the accuracy of the comparator signal conversion, and thus to making the measurement of tape displacement more accurate. In the first comparator, the output signal of the first photoelectric sensor serves as the comparator input signal, and the output signal of the third photoelectric sensor serves as the reference level. Comparing the input signal and the reference level converts the sine wave signal into a stable square wave signal. In the second comparator, the output signal of the second photoelectric sensor serves as the comparator input signal, and the output signal of the third photoelectric sensor serves as the reference level. Comparing the input signal and the reference level converts the sine wave signal into a stable square wave signal. The square wave signals output from the two comparators are then input into the MCU to measure the tape displacement. Therefore, this utility model provides a sensor structure basis for realizing the measurement of tape displacement in digital display tape measures. The circuit structure is simple, the production cost is low, and the sensor size is small, thus meeting the requirements for small-volume portable tape measures. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the connection structure between the photoelectric sensor and the resistance adjustment circuit according to an embodiment of the present invention;

[0022] Figure 2 This is a schematic diagram of the comparator circuit according to an embodiment of the present invention;

[0023] Figure 3 This is a schematic diagram of the circuit structure of the MCU according to an embodiment of the present invention;

[0024] Figure 4 This is a schematic diagram of the circuit structure of the connector according to an embodiment of the present utility model;

[0025] Figure 5 This is a schematic diagram of the circuit structure of the power supply VDD according to an embodiment of the present invention.

[0026] Explanation of reference numerals in the attached figures

[0027] Q1: First photoelectric sensor; Q2: Second photoelectric sensor; Q3: Third photoelectric sensor;

[0028] UI-A: First comparator; UI-B: Second comparator;

[0029] Ro: Protective resistor;

[0030] R1: First resistor; R2: Second resistor; R3: Third resistor; R4: Fourth resistor; R5: Fifth resistor; R6: Sixth resistor; R7: Seventh resistor; R8: Eighth resistor; R9: Ninth resistor; R10: Tenth resistor; R11: Eleventh resistor; R12: Twelfth resistor; R13: Thirteenth resistor; R14: Fourteenth resistor; R15: Fifteenth resistor;

[0031] C1: First capacitor; C2: Second capacitor; C3: Third capacitor; C4: Fourth capacitor; C5: Fifth capacitor; C6: Sixth capacitor; C7: Seventh capacitor; C8: Eighth capacitor;

[0032] CON: Connector. Detailed Implementation

[0033] To better explain and facilitate understanding of this utility model, the present utility model will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0034] like Figures 1 to 5 As shown, this utility model embodiment provides a sensor for measuring the displacement of a digital measuring tape, including a sensor housing and a circuit board housed within the sensor housing, a first photoelectric sensor Q1, a second photoelectric sensor Q2, and a third photoelectric sensor Q3. The first photoelectric sensor Q1, the second photoelectric sensor Q2, and the third photoelectric sensor Q3 are arranged side by side at equal intervals along the tape extension direction and are all electrically connected to a sensor circuit integrated on the circuit board. The sensor circuit includes a first comparator UI-A, a second comparator UI-B, an MCU, and a resistor adjustment circuit that is connected to each photoelectric sensor in a corresponding manner.

[0035] Each photoelectric sensor has a first pin, a second pin, a third pin, and a fourth pin. The first pin is used as the output terminal of the light emitter inside the photoelectric sensor, the second pin is used as the input terminal of the light emitter inside the photoelectric sensor, the third pin is used as the signal output terminal of the light receiver inside the photoelectric sensor, and the fourth pin is used as the ground terminal of the light receiver inside the photoelectric sensor.

[0036] The second pin of each photoelectric sensor is electrically connected to the power supply VDD, and the first pin of each photoelectric sensor is connected to the first terminal of its corresponding resistor adjustment circuit. The second terminal of each resistor adjustment circuit is grounded. The third pin of the first photoelectric sensor Q1 is connected to the first input pin of the first comparator UI-A, the third pin of the second photoelectric sensor Q2 is connected to the first input pin of the second comparator UI-B, and the second input pins of the first comparator UI-A and the second comparator UI-B are respectively connected to the third pin of the third photoelectric sensor Q3. The output pins of the first comparator UI-A and the second comparator UI-B are respectively connected to two pins of the MCU.

[0037] This sensor configuration, through a resistor adjustment circuit, allows for the adjustment of the brightness of the light emitter in each photoelectric sensor. When the brightness of the light emitters in the three photoelectric sensors is consistent, the output signals are consistent, which improves the accuracy of the comparator's signal conversion and thus enhances the accuracy of the tape displacement measurement. In the first comparator UI-A, the output signal of the first photoelectric sensor Q1 serves as the comparator input signal, and the output signal of the third photoelectric sensor Q3 serves as the reference level. Comparing the input signal with the reference level converts the sine wave signal into a stable square wave signal. In the second comparator UI-B, the output signal of the second photoelectric sensor Q2 serves as the comparator input signal, and the output signal of the third photoelectric sensor Q3 serves as the reference level. Comparing the input signal with the reference level converts the sine wave signal into a stable square wave signal. The square wave signals output from the two comparators are then input into the MCU to measure the tape displacement. Therefore, this invention provides a sensor structure foundation for measuring the tape displacement of digital measuring tapes. The circuit structure is simple, the production cost is low, and the sensor size is small, thus meeting the requirements for small-sized portable measuring tapes.

[0038] Preferably, the resistance adjustment circuit corresponding to each photoelectric sensor is a VR resistance adjustment circuit. Using VR resistance adjustment offers advantages such as flexibility, accuracy, adaptability, reliability, and space saving.

[0039] Preferably, the VR resistor adjustment circuit includes a VR resistor and a protection resistor Ro. The first fixed terminal of the VR resistor is connected to the first pin of the photoelectric sensor, the movable terminal of the VR resistor is grounded, and the second fixed terminal of the VR resistor is connected to the movable terminal of the VR resistor through the protection resistor Ro.

[0040] Preferably, the third pin of the first photoelectric sensor Q1 is connected to the first input pin of the first comparator UI-A through a first resistor R1, and the power supply VDD is connected to the first input pin of the first comparator UI-A in sequence through a second resistor R2 and a first resistor R1; the third pin of the second photoelectric sensor Q2 is connected to the first input pin of the second comparator UI-B through a fourth resistor R4, and the power supply VDD is connected to the first input pin of the second comparator UI-B in sequence through a fifth resistor R5 and a fourth resistor R4, and the power supply VDD is grounded in sequence through a fifth resistor R5 and a sixth resistor R6; the third pin of the third photoelectric sensor Q3 is connected to the second input pins of both the first comparator UI-A and the second comparator UI-B through a seventh resistor R7, and the power supply VDD is connected to the second input pins of both the first comparator UI-A and the second comparator UI-B in sequence through an eighth resistor R8 and a seventh resistor R7. This provides bias voltages to the input pins of the first comparator UI-A and the second comparator UI-B, making the signals input to the first comparator UI-A and the second comparator UI-B more stable.

[0041] Preferably, in this embodiment, the power supply VDD is connected to the second input pin of the first comparator UI-A in sequence through the eighth resistor R8, the seventh resistor R7, and the first ninth resistor R9; the power supply VDD is connected to the second input pin of the second comparator UI-B in sequence through the eighth resistor R8, the seventh resistor R7, and the second ninth resistor R9; the power supply VDD is connected to the terminal of the ninth resistor R9 in sequence through the second resistor R2, the third resistor R3, and the seventh resistor R7. This makes the circuit structure more stable.

[0042] Preferably, the sensor circuit further includes a first capacitor C1, a second capacitor C2, a third capacitor C3, and a fourth capacitor C4; the first terminal of the first capacitor C1 is connected to the first input pin of the first comparator UI-A, and the second terminal of the first capacitor C1 is grounded; the first terminal of the second capacitor C2 is connected to the second input pin of the first comparator UI-A, and the second terminal of the second capacitor C2 is grounded; the first terminal of the third capacitor C3 is connected to the first input pin of the second comparator UI-B, and the second terminal of the third capacitor C3 is grounded; the first terminal of the fourth capacitor C4 is connected to the second input pin of the second comparator UI-B, and the second terminal of the fourth capacitor C4 is grounded. In this way, by setting capacitors, the signal of each input pin of the input comparator is filtered, improving signal stability.

[0043] Preferably, the output pin of the first comparator UI-A is connected to the first input pin of the first comparator UI-A through the tenth resistor R10, and the output pin of the second comparator UI-B is connected to the first input pin of the second comparator UI-B through the eleventh resistor R11. This makes the circuit structure more stable.

[0044] Preferably, the sensor circuit further includes a fifth capacitor C5 and a sixth capacitor C6; the first terminal of the fifth capacitor C5 is connected to the output pin of the first comparator UI-A, and the second terminal of the fifth capacitor C5 is grounded; the first terminal of the sixth capacitor C6 is connected to the output pin of the second comparator UI-B, and the second terminal of the sixth capacitor C6 is grounded. Thus, by setting the capacitors, the signal output from the comparator output pins is filtered, improving signal stability.

[0045] Preferably, the output pin of the first comparator UI-A is connected to the MCU pin through the twelfth resistor R12, and the power supply VDD is connected to the output pin of the first comparator UI-A through the thirteenth resistor R13; the output pin of the second comparator UI-B is connected to the MCU pin through the fourteenth resistor R14, and the power supply VDD is connected to the output pin of the second comparator UI-B through the fifteenth resistor R15. This provides bias voltages to the output pins of the first comparator UI-A and the second comparator UI-B, making the signals output by the first comparator UI-A and the second comparator UI-B more stable.

[0046] Specifically, the first comparator UI-A also has a power supply pin and a ground pin, and the second comparator UI-B also has a power supply pin and a ground pin. The power supply pins of the first comparator UI-A and the second comparator UI-B are respectively connected to the power supply VDD.

[0047] Preferably, the spacing between the photoelectric sensors is 3-4 mm. More preferably, the spacing between the photoelectric sensors is 3.6 mm.

[0048] The working principle of the sensor provided by this utility model is as follows: First, the brightness of the light emitter in each photoelectric sensor is adjusted through a resistor adjustment circuit to ensure that the brightness of the three photoelectric sensors is consistent. After the sensor is packaged, it is installed on a digital display tape measure. Multiple evenly arranged alternating bright and dark stripes are provided on the tape measure to cooperate with the sensors. After power-on, pulling the tape measure causes the three photoelectric sensors to continuously sense the bright and dark stripes on the tape measure, thereby outputting a sine wave signal. In the first comparator, the output signal of the first photoelectric sensor serves as the comparator input signal, and the output signal of the third photoelectric sensor serves as the reference level. Comparing the input signal and the reference level converts the sine wave signal into a stable square wave signal and outputs a first square wave signal with a first phase. In the second comparator, the second photoelectric sensor... The output signal of the first photoelectric sensor is used as the input signal of the comparator, and the output signal of the third photoelectric sensor is used as the reference level. By comparing the input signal and the reference level, the sine wave signal can be converted into a stable square wave signal, and a second square wave signal with a second phase is output. The phase difference between the first square wave signal and the second square wave signal is 66° to 110°. Then, the first square wave signal and the second square wave signal output from the two comparators are input into the MCU. The MCU obtains the phase difference between the first square wave signal and the second square wave signal, and counts based on the rising and falling edges of the first square wave signal and the second square wave signal to realize the measurement of the tape displacement. Finally, the MCU transmits the measured distance data to the central controller of the digital tape measure through the UART serial communication protocol and the transmission port TXD in the form of ASCII code level data frames. It can be seen that this utility model provides a sensor structure basis for realizing the measurement of tape displacement of digital tape measures. The circuit structure is simple, the production cost is low, and the sensor size is small, thus meeting the needs of small-sized portable tape measures.

[0049] The measurement range of this sensor is -32767mm to +32767mm.

[0050] Preferably, the sensor further includes a connector CON for communication with an external device of the digital measuring tape; the signal output pin of the MCU is connected to the signal input pin of the connector CON, and the signal output pin of the connector CON is connected to the signal input pin of the MCU. Thus, by connecting to the connector CON, the external device can achieve data exchange with the MCU.

[0051] Specifically, the MCU has a power supply pin and a ground pin, and the connector CON has a power supply pin and a ground pin. Both the power supply pins of the MCU and the power supply pins of the connector CON are connected to the power supply VDD.

[0052] Specifically, the sensor also includes a seventh capacitor C7 and an eighth capacitor C8; the first terminal of the seventh capacitor C7 is connected to the power supply VDD, and the second terminal of the seventh capacitor C7 is grounded; the first terminal of the eighth capacitor C8 is connected to the power supply VDD, and the second terminal of the eighth capacitor C8 is grounded. This filters the power supply VDD, improving the stability of the circuit structure.

[0053] In the description of this utility model, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this utility model, "a plurality of" means two or more, unless otherwise explicitly specified.

[0054] In this utility model, unless otherwise explicitly specified and limited, the terms "installation," "connection," "joining," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in this utility model can be understood according to the specific circumstances.

[0055] In this utility model, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "on top of," and "over" the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "beneath" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0056] In the description of this specification, the terms "one embodiment," "some embodiments," "embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0057] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make modifications, alterations, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A sensor for measuring the displacement of a digital measuring tape, characterized in that, The sensor includes a sensor housing and a circuit board housed within the sensor housing, a first photoelectric sensor, a second photoelectric sensor, and a third photoelectric sensor. The first photoelectric sensor, the second photoelectric sensor, and the third photoelectric sensor, which are arranged side by side at equal intervals along the extension direction of the ruler, are all electrically connected to the sensor circuit integrated on the circuit board. The sensor circuit includes a first comparator, a second comparator, an MCU, and resistor adjustment circuits connected one-to-one with the photoelectric sensors for adjusting the brightness of the photoelectric sensors. The first and third photoelectric sensors are respectively connected to the input terminals of the first comparator, and the output signals of the first and third photoelectric sensors are compared to output a first square wave signal. The second and third photoelectric sensors are respectively connected to the input terminals of the second comparator, and the output signals of the second and third photoelectric sensors are compared to output a second square wave signal. The output terminals of the first and second comparators are respectively connected to the input terminals of the MCU, and the MCU receives the first and second square wave signals and outputs the scale displacement.

2. The sensor for measuring the displacement of a digital measuring tape according to claim 1, characterized in that, Each photoelectric sensor has a first pin, a second pin, a third pin, and a fourth pin. The first pin is used as the output terminal of the light emitter inside the photoelectric sensor, the second pin is used as the input terminal of the light emitter inside the photoelectric sensor, the third pin is used as the signal output terminal of the light receiver inside the photoelectric sensor, and the fourth pin is used as the ground terminal of the light receiver inside the photoelectric sensor. The second pin of each photoelectric sensor is electrically connected to the power supply VDD. The first pin of each photoelectric sensor is connected to the first terminal of its corresponding resistor adjustment circuit. The second terminal of each resistor adjustment circuit is grounded. The third pin of the first photoelectric sensor is connected to the first input pin of the first comparator. The third pin of the second photoelectric sensor is connected to the first input pin of the second comparator. The second input pins of the first and second comparators are respectively connected to the third pin of the third photoelectric sensor. The output pins of the first and second comparators are respectively connected to two pins of the MCU.

3. The sensor for measuring the displacement of a digital measuring tape according to claim 2, characterized in that, The resistance adjustment circuit is a VR resistance adjustment circuit.

4. The sensor for measuring the displacement of a digital measuring tape according to claim 3, characterized in that, The VR resistor adjustment circuit includes a VR resistor and a protection resistor. The first fixed terminal of the VR resistor is connected to the first pin of the photoelectric sensor, the moving terminal of the VR resistor is grounded, and the second fixed terminal of the VR resistor is connected to the moving terminal of the VR resistor through the protection resistor.

5. The sensor for measuring the displacement of a digital measuring tape according to claim 2, characterized in that, The third pin of the first photoelectric sensor is connected to the first input pin of the first comparator through the first resistor, and the power supply VDD is connected to the first input pin of the first comparator in sequence through the second resistor and the first resistor. The third pin of the second photoelectric sensor is connected to the first input pin of the second comparator through the fourth resistor. The power supply VDD is connected to the first input pin of the second comparator through the fifth resistor and the fourth resistor in sequence. The power supply VDD is grounded through the fifth resistor and the sixth resistor in sequence. The third pin of the third photoelectric sensor is connected to the second input pin of the first comparator and the second input pin of the second comparator through the seventh resistor. The power supply VDD is connected to the second input pin of the first comparator and the second input pin of the second comparator through the eighth resistor and the seventh resistor, respectively.

6. The sensor for measuring the displacement of a digital measuring tape according to claim 2 or 5, characterized in that, The sensor circuit also includes a first capacitor, a second capacitor, a third capacitor, and a fourth capacitor; The first terminal of the first capacitor is connected to the first input pin of the first comparator, and the second terminal of the first capacitor is grounded; the first terminal of the second capacitor is connected to the second input pin of the first comparator, and the second terminal of the second capacitor is grounded; the first terminal of the third capacitor is connected to the first input pin of the second comparator, and the second terminal of the third capacitor is grounded; the first terminal of the fourth capacitor is connected to the second input pin of the second comparator, and the second terminal of the fourth capacitor is grounded.

7. The sensor for measuring the displacement of a digital measuring tape according to claim 6, characterized in that, The output pin of the first comparator is connected to the first input pin of the first comparator through the tenth resistor, and the output pin of the second comparator is connected to the first input pin of the second comparator through the eleventh resistor.

8. The sensor for measuring the displacement of a digital measuring tape according to claim 6, characterized in that, The sensor circuit also includes a fifth capacitor and a sixth capacitor; The first terminal of the fifth capacitor is connected to the output pin of the first comparator, and the second terminal of the fifth capacitor is grounded; the first terminal of the sixth capacitor is connected to the output pin of the second comparator, and the second terminal of the sixth capacitor is grounded.

9. The sensor for measuring the displacement of a digital measuring tape according to claim 6, characterized in that, The output pin of the first comparator is connected to the MCU pin through the twelfth resistor, and the power supply VDD is connected to the output pin of the first comparator through the thirteenth resistor; the output pin of the second comparator is connected to the MCU pin through the fourteenth resistor, and the power supply VDD is connected to the output pin of the second comparator through the fifteenth resistor.

10. The sensor for measuring the displacement of a digital measuring tape according to claim 1, characterized in that, It also includes a connector for communicating with external devices of the digital measuring tape; The MCU's signal output pins are connected to the connector's signal input pins, and the connector's signal output pins are connected to the MCU's signal input pins.

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