Digital display measuring tape sensor based on ADC and DAC

Abstract

The utility model provides a digital display measuring tape sensor based on ADC and DAC. The digital display measuring tape sensor comprises a circuit board, and a first photoelectric sensor, a second photoelectric sensor and a third photoelectric sensor which are connected with a displacement measuring circuit integrated on the circuit board. The displacement measurement circuit comprises a first comparator, a second comparator, an MCU, and DAC signal control 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. Each photoelectric sensor is connected with the input end of the MCU through ADC output, and the output end of the MCU is connected with each DAC signal control circuit; the first photoelectric sensor and the third photoelectric sensor are respectively connected with the input end of the first comparator, and 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. And the luminance of the three photoelectric sensors can be automatically adjusted.

Description

Technical Field

[0001] This utility model relates to the field of measuring instrument technology, and in particular to a sensor for digital display measuring tape based on ADC and DAC. 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] To measure the displacement of a digital measuring tape, a current sensor structure comprises three photoelectric sensors and corresponding VR adjustment circuits. The brightness of the light emitters in each photoelectric sensor is manually adjusted using VR resistors to ensure consistency among the three sensors. The outputs of the first and third photoelectric sensors are then connected to a first comparator, and the outputs of the second and third photoelectric sensors are connected to a second comparator. The outputs of both comparators are then connected to an MCU (Microcontroller Unit) to measure the displacement of the digital measuring tape. However, manually adjusting the photoelectric sensors using VR resistors is time-consuming, labor-intensive, costly, and makes it difficult to guarantee perfect consistency among the three sensors.

[0004] Therefore, there is an urgent need for an improved sensor for digital measuring tapes. Utility Model Content

[0005] In view of the above-mentioned shortcomings and deficiencies of the prior art, this utility model provides a digital display measuring tape sensor based on ADC and DAC, which can autonomously adjust the brightness of the three photoelectric sensors.

[0006] To achieve the above objectives, the main technical solutions adopted by this utility model include:

[0007] This utility model provides a sensor for digital display tape measure based on ADC and DAC, 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 displacement measurement circuit integrated on the circuit board.

[0008] The displacement measurement circuit includes a first comparator, a second comparator, an MCU, and a DAC signal control circuit connected to each photoelectric sensor to adjust the brightness of the photoelectric sensor. Each photoelectric sensor is connected to the input of the MCU via an ADC output. The output of the MCU is connected to each DAC signal control circuit. The DAC signal control circuit adjusts the brightness of the photoelectric sensor by changing the current of the photoelectric sensor according to the comparison result of the ADC signal in the MCU. The first and third photoelectric sensors are respectively connected to the input of the first comparator. 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 of the second comparator. The output signals of the second and third photoelectric sensors are compared to output a second square wave signal. The outputs of the first and second comparators are respectively connected to the input of the MCU. The MCU receives the first and second square wave signals and outputs the scale displacement.

[0009] Optionally, each photoelectric sensor has a first pin, a second pin, a third pin, and a fourth pin. The first pin and the second pin are used as two terminals for the light emitter inside the photoelectric sensor, and the third pin and the fourth pin are used as two terminals for the light receiver inside the photoelectric sensor.

[0010] The second pin of each photoelectric sensor is electrically connected to the power supply VDD. The first pin of the first photoelectric sensor is connected to the first ADC input pin of the MCU via the ADC output. The first DAC output pin of the MCU is connected to the input of the first DAC signal control circuit, and the output of the first DAC signal control circuit is connected to the first pin of the first photoelectric sensor. The first pin of the second photoelectric sensor is connected to the second ADC input pin of the MCU via the ADC output. The second DAC output pin of the MCU is connected to the input of the second DAC signal control circuit, and the output of the second DAC signal control circuit is connected to the first pin of the second photoelectric sensor. The first pin of the third photoelectric sensor is connected to the third ADC input pin of the MCU via the ADC output. The third DAC output pin of the MCU is connected to the input of the third DAC signal control circuit, and the output of the third DAC signal control circuit is connected to the first pin of the third photoelectric sensor.

[0011] 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, and the fourth pin of each photoelectric sensor is grounded; the output pins of the first and second comparators are respectively connected to two pins of the MCU.

[0012] Optionally, each DAC signal control circuit includes a MOSFET, the DAC output pin of the MCU is connected to the gate of the MOSFET, the source of the MOSFET is grounded, and the drain of the MOSFET is connected to the first pin of the photoelectric sensor; or, each DAC signal control circuit includes a transistor, the DAC output pin of the MCU is connected to the base of the transistor, the emitter of the transistor is grounded, and the collector of the transistor is connected to the first pin of the photoelectric sensor.

[0013] 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; the third pin of the second photoelectric sensor is connected to the first input pin of the second comparator through a fourth resistor, and the power supply VDD is connected to the first input pin of the second comparator in sequence through a fifth resistor and a fourth resistor, and the power supply VDD is grounded in sequence through a fifth resistor and a sixth resistor; 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 a seventh resistor, and the power supply VDD is connected to the second input pin of the first comparator and the second input pin of the second comparator in sequence through an eighth resistor and a seventh resistor.

[0014] Optionally, the displacement measurement circuit 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 displacement measurement circuit further 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 spacing between photoelectric sensors is 3 to 4 mm.

[0018] Optionally, it 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] Optionally, the MCU has a power supply pin and a ground pin, and the connector 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 are connected to the power supply VDD.

[0020] The beneficial effects of this utility model are:

[0021] The sensor provided by this utility model includes three photoelectric sensors arranged side by side and at equal intervals. All three photoelectric sensors are electrically connected to a displacement measurement circuit integrated on a circuit board. Each of the three photoelectric sensors is connected to a DAC signal control circuit for adjusting the brightness of the photoelectric sensors. Each photoelectric sensor is connected to the input terminal of an MCU through an ADC output. The output terminal of the MCU is connected to each DAC signal control circuit. The DAC signal control circuit changes the current of the photoelectric sensor according to the comparison result of the ADC signal in the MCU to adjust the brightness of the photoelectric sensor, and can autonomously adjust the brightness of the three photoelectric sensors to be consistent. The consistency of the three photoelectric sensors improves the accuracy of the comparator's signal conversion, thus making the measurement of the tape displacement more accurate. In the first comparator, the output signal of the first photoelectric sensor serves as the input signal, and the output signal of the third photoelectric sensor 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, the output signal of the second photoelectric sensor serves as the input signal, and the output signal of the third photoelectric sensor 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 basis for achieving autonomous adjustment of the consistency of the three photoelectric sensors. Furthermore, the circuit structure is simple, the production cost is low, and the sensor size is small, thus meeting the requirements for use with small, portable measuring tapes. Attached Figure Description

[0022] Figure 1This is a schematic diagram of the connection structure between the photoelectric sensor and the DAC signal control circuit according to an embodiment of the present invention;

[0023] Figure 2 This is a schematic diagram of the comparator circuit according to an embodiment of the present invention;

[0024] Figure 3 This is a schematic diagram of the circuit structure of the MCU according to an embodiment of the present invention;

[0025] Figure 4 This is a schematic diagram of the circuit structure of the connector according to an embodiment of the present utility model;

[0026] Figure 5 This is a schematic diagram of the circuit structure of the power supply VDD according to an embodiment of the present invention.

[0027] Explanation of reference numerals in the attached figures

[0028] Q1: First photoelectric sensor; Q2: Second photoelectric sensor; Q3: Third photoelectric sensor;

[0029] UI-A: First comparator; UI-B: Second comparator;

[0030] M: MOSFET (Metal-Oxide-Semiconductor);

[0031] 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;

[0032] C1: First capacitor; C2: Second capacitor; C3: Third capacitor; C4: Fourth capacitor; C5: Fifth capacitor; C6: Sixth capacitor; C7: Seventh capacitor; C8: Eighth capacitor;

[0033] CON: Connector. Detailed Implementation

[0034] 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.

[0035] Example 1

[0036] like Figures 1 to 5As shown, this utility model embodiment provides a sensor for a digital display measuring tape based on ADC and DAC, including a sensor housing and a circuit board housed in 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 extension direction of the measuring tape and are all electrically connected to a displacement measurement circuit integrated on the circuit board.

[0037] The displacement measurement circuit includes a first comparator UI-A, a second comparator UI-B, an MCU, and DAC signal control circuits connected one-to-one with the photoelectric sensors for adjusting the brightness of the photoelectric sensors, namely a first DAC signal control circuit, a second DAC signal control circuit, and a third DAC signal control circuit.

[0038] Each photoelectric sensor has a first pin, a second pin, a third pin, and a fourth pin. The first and second pins are used as two terminals for the light emitter inside the photoelectric sensor, and the third and fourth pins are used as two terminals for the light receiver inside the photoelectric sensor.

[0039] The second pin of each photoelectric sensor is electrically connected to the power supply VDD. The first pin of the first photoelectric sensor Q1 is connected to the first ADC input pin of the MCU via the ADC output. The first DAC output pin of the MCU is connected to the input of the first DAC signal control circuit, and the output of the first DAC signal control circuit is connected to the first pin of the first photoelectric sensor Q1. The first pin of the second photoelectric sensor Q2 is connected to the second ADC input pin of the MCU via the ADC output. The second DAC output pin of the MCU is connected to the input of the second DAC signal control circuit, and the output of the second DAC signal control circuit is connected to the first pin of the second photoelectric sensor Q2. The first pin of the third photoelectric sensor Q3 is connected to the third ADC input pin of the MCU via the ADC output. The third DAC output pin of the MCU is connected to the input of the third DAC signal control circuit, and the output of the third DAC signal control circuit is connected to the first pin of the third photoelectric sensor Q3.

[0040] 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, the second input pins of the first comparator UI-A and the second input pins of the second comparator UI-B are respectively connected to the third pin of the third photoelectric sensor Q3, and the fourth pin of each photoelectric sensor is grounded; the output pins of the first comparator UI-A and the second comparator UI-B are respectively connected to two pins of the MCU.

[0041] In this sensor configuration, the first pin of the photoelectric sensor is connected to the ADC input pin of the MCU via the ADC output. The MCU's DAC output pin is connected to the input of the DAC signal control circuit, and the output of the DAC signal control circuit is connected to the first pin of the photoelectric sensor. This provides the circuit structure basis for the DAC signal control circuit to change the voltage or current of the photoelectric sensor based on the comparison result of the ADC signal in the MCU, enabling autonomous adjustment to keep the three photoelectric sensors consistent. The consistency of the three photoelectric sensors improves the accuracy of the comparator's signal conversion, thus making the measurement of the scale displacement more accurate. 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 and 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 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 scale displacement. Therefore, this utility model provides a sensor structure basis for achieving autonomous adjustment of consistency among three photoelectric sensors. Furthermore, the circuit structure is simple and the production cost is low, resulting in a small sensor size, which in turn meets the requirements for use with small-sized portable measuring tapes.

[0042] Preferably, each DAC signal control circuit includes a MOSFET M, the DAC output pin of the MCU is connected to the gate of the MOSFET M, the source of the MOSFET M is grounded, and the drain of the MOSFET M is connected to the first pin of the photoelectric sensor.

[0043] 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.

[0044] 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.

[0045] Preferably, the sensor 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 the capacitors, the signal of each input pin of the input comparator is filtered, improving the signal stability.

[0046] 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.

[0047] Preferably, the sensor 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.

[0048] 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.

[0049] 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.

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

[0054] The working principle of this sensor is as follows: The DAC signal control circuit receives ADC signals from the three photoelectric sensors in the MCU. Based on the comparison results of the ADC signals, the MCU outputs a photoelectric sensor brightness adjustment signal to the DAC signal control circuit, thereby automatically adjusting the brightness of the light emitter in each photoelectric sensor 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 spaced alternating bright and dark stripes that cooperate with the sensors are provided on the tape measure. 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 uses 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 length measurement. Finally, the MCU transmits the measured distance data to the central controller of the digital measuring tape through the UART serial communication protocol and the transmission port TXD in ASCII code level data frame format. It can be seen that this utility model provides a sensor structure basis for realizing the tape displacement measurement of digital measuring tape. The circuit structure is simple, the production cost is low, and the sensor size is small, thus meeting the needs of small-volume portable measuring tapes.

[0055] The measurement range of this sensor is -32767mm to +32767mm.

[0056] Example 2

[0057] The main difference between this embodiment and Embodiment 1 is:

[0058] In the DAC signal control circuit, a transistor is used instead of a MOSFET. The DAC output pin of the MCU is connected to the base of the transistor, the emitter of the transistor is grounded, and the collector of the transistor is connected to the first pin of the photoelectric sensor.

[0059] The remaining contents are the same as in Example 1, and will not be repeated here.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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 digital display measuring tapes based on ADC and DAC, 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 displacement measurement circuit integrated on the circuit board. The displacement measurement circuit includes a first comparator, a second comparator, an MCU, and a DAC signal control circuit connected to each photoelectric sensor to adjust the brightness of the photoelectric sensor. Each photoelectric sensor is connected to the input of the MCU via an ADC output. The output of the MCU is connected to each DAC signal control circuit. The DAC signal control circuit adjusts the brightness of the photoelectric sensor by changing the current of the photoelectric sensor according to the comparison result of the ADC signal in the MCU. The first and third photoelectric sensors are respectively connected to the input of the first comparator. 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 of the second comparator. The output signals of the second and third photoelectric sensors are compared to output a second square wave signal. The outputs of the first and second comparators are respectively connected to the input of the MCU. The MCU receives the first and second square wave signals and outputs the scale displacement.

2. The sensor for digital display measuring tape based on ADC and DAC 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 and second pins are used as two terminals for the light emitter inside the photoelectric sensor, and the third and fourth pins are used as two terminals for 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 the first photoelectric sensor is connected to the first ADC input pin of the MCU via the ADC output. The first DAC output pin of the MCU is connected to the input of the first DAC signal control circuit, and the output of the first DAC signal control circuit is connected to the first pin of the first photoelectric sensor. The first pin of the second photoelectric sensor is connected to the second ADC input pin of the MCU via the ADC output. The second DAC output pin of the MCU is connected to the input of the second DAC signal control circuit, and the output of the second DAC signal control circuit is connected to the first pin of the second photoelectric sensor. The first pin of the third photoelectric sensor is connected to the third ADC input pin of the MCU via the ADC output. The third DAC output pin of the MCU is connected to the input of the third DAC signal control circuit, and the output of the third DAC signal control circuit is connected to the first pin of the third photoelectric sensor. 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, and the fourth pin of each photoelectric sensor is grounded; the output pins of the first and second comparators are respectively connected to two pins of the MCU.

3. The sensor for digital display measuring tape based on ADC and DAC according to claim 1, characterized in that, Each DAC signal control circuit includes a MOSFET. The MCU's DAC output pin is connected to the gate of the MOSFET, the source of the MOSFET is grounded, and the drain of the MOSFET is connected to the first pin of the photoelectric sensor; or, Each DAC signal control circuit includes a transistor. The DAC output pin of the MCU is connected to the base of the transistor, the emitter of the transistor is grounded, and the collector of the transistor is connected to the first pin of the photoelectric sensor.

4. The sensor for digital display measuring tape based on ADC and DAC according to claim 1, 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.

5. The sensor for digital display measuring tape based on ADC and DAC according to claim 1 or 4, characterized in that, It 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.

6. The sensor for digital display measuring tape based on ADC and DAC according to claim 5, 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.

7. The sensor for digital display measuring tape based on ADC and DAC according to claim 5, characterized in that, It also includes the fifth and sixth capacitors; 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.

8. The sensor for digital measuring tape based on ADC and DAC according to claim 1, characterized in that, The spacing between photoelectric sensors is 3~4mm.

9. The sensor for digital display measuring tape based on ADC and DAC 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.

10. The sensor for digital display measuring tape based on ADC and DAC according to claim 9, characterized in that, The MCU has power supply pins and ground pins, and the connector has power supply pins and ground pins. Both the MCU's power supply pins and the connector's power supply pins are connected to the power supply VDD.

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