Four-digit digital display meter circuit and digital display meter

Abstract

The utility model provides a four-digit digital display meter circuit and a digital display meter. The circuit comprises a control unit, a current and voltage output unit, a display unit and an NPN signal output unit. The output end of the control unit is respectively connected with the input ends of the output unit, the display unit and the NPN signal output unit; the control unit collects current and voltage signals and sends the current and voltage signals to the current and voltage output unit, the display unit and the NPN signal output unit. The current and voltage output unit converts the current and voltage signals into analog signals and outputs the analog signals; the display unit receives the current and voltage signals to drive a nixie tube to display; and the NPN signal output unit receives the current and voltage signals and performs reverse conversion. A current sampling circuit and a voltage sampling circuit are integrated together, NPN signal output is added, the integration level of the circuit is improved, and therefore the number of needed components and the overall cost are reduced.

Description

Technical Field

[0001] The utility model relates to the field of electronic measuring instruments, in particular to a four-digit display meter circuit and a digital display meter. Background Art

[0002] In the fields of industrial automation and process control, digital display instruments are widely used to measure and display a variety of parameters. However, existing digital display instruments often have several limitations and shortcomings. First, many existing digital display instruments are large, making them difficult to adapt to space-constrained applications. This size restriction not only increases installation difficulties but also limits their use in small devices or compact control panels. Second, traditional digital display instruments often have a single function and can only display a single type of parameter, such as current or voltage. This limitation necessitates the use of multiple instruments when multiple parameters need to be monitored simultaneously, increasing system complexity and cost.

[0003] Furthermore, existing digital display instruments often lack flexible communication capabilities. Many instruments are unable to implement remote data transmission and control, which creates significant functional deficiencies in modern Industrial Internet of Things (IIoT) and remote monitoring systems. The display range and alarm thresholds of many digital display instruments are difficult to adjust. This fixed design limits the instrument's adaptability and makes it unable to meet the specific needs of different application scenarios. Finally, existing digital display instruments often use discrete current and voltage sampling circuits, which not only increases the number of components, but also increases production costs and failure rates.

[0004] These problems have led to the limitations of existing digital display instruments in practical applications, making it difficult to meet the demand for miniaturized, multifunctional, highly integrated and low-cost instruments in the fields of industrial automation and process control. Utility Model Content

[0005] The purpose of the utility model is to solve the problem that the existing digital display meter is large in size and cannot be turned on and off in time.

[0006] In order to achieve the above-mentioned object, in a first aspect, the utility model provides a four-digit display meter circuit, comprising a control unit, a current and voltage output unit, a display unit and an NPN signal output unit;

[0007] The output end of the control unit is connected to the input end of the output unit, the display unit and the NPN signal output unit respectively;

[0008] The control unit collects current and voltage signals and sends them to the current and voltage output unit, the display unit and the NPN signal output unit;

[0009] The current and voltage output unit converts the current and voltage signals into analog signals and outputs the analog signals; the display unit receives the current and voltage signals to drive the digital tube display; and the NPN signal output unit receives the current and voltage signals and performs reverse conversion.

[0010] Furthermore, the control unit includes a control chip, a first resistor, a second resistor, a third resistor, a first capacitor and a second capacitor;

[0011] The fourth pin of the control chip is respectively connected to one end of the first resistor and one end of the first capacitor, the other end of the first resistor is connected to the power supply terminal, and the other end of the first capacitor is grounded;

[0012] The seventh pin of the control chip is grounded;

[0013] The ninth pin is connected to the power supply terminal and one end of the second capacitor respectively, and the other end of the second capacitor is grounded;

[0014] One end of the second resistor is connected to the eleventh pin, and the other end is connected to the power supply terminal; one end of the third resistor is connected to the twelfth pin, and the other end is connected to the power supply terminal.

[0015] Furthermore, one end of the input end of the current and voltage output unit is connected to the control unit, and the other end is respectively connected to the third capacitor, the fourth resistor, the fifth resistor, the sixth resistor, and one end of the diode group; the other end of the third capacitor is grounded; the other end of the fifth resistor is grounded; and the other end of the sixth resistor is connected in series with the fourth capacitor and then grounded;

[0016] A voltage output terminal of the current and voltage output unit is further provided between the sixth resistor and the fourth capacitor;

[0017] The other end of the fourth resistor is respectively connected to the current output end of the current and voltage output unit, one end of the fifth capacitor, and one end of the seventh resistor; the other end of the fourth capacitor is grounded, and the seventh resistor is connected in series with the eighth resistor and then grounded;

[0018] The diode group includes a first diode and a second diode connected in parallel, the anode of the first diode is connected to the cathode of the second diode, the cathode of the first diode is connected to the power supply terminal, and the anode of the second diode is grounded.

[0019] Furthermore, it also includes a communication unit, and the communication unit includes a communication chip;

[0020] The second pin of the communication chip is connected to the third pin, and the third pin is connected in series with a ninth resistor and then grounded;

[0021] The fifth pin is grounded; the sixth pin is connected in series with a tenth resistor and then connected to the first output terminal, the tenth resistor is further connected to one end of a first bidirectional breakdown diode and an eleventh resistor respectively, the other end of the first bidirectional breakdown diode is grounded, and one end of the eleventh resistor is connected to the power supply terminal;

[0022] The seventh pin is connected to the second output terminal after being connected in series with a twelfth resistor, and the twelfth resistor is further connected in series with a thirteenth resistor and a second bidirectional breakdown diode and is grounded;

[0023] The eighth pin is connected in series with the sixth capacitor and then grounded. A power supply terminal is also connected between the eighth pin and the sixth capacitor.

[0024] Furthermore, the display unit includes a digital tube and a driver chip;

[0025] The first pin of the digital tube is connected to the thirteenth pin of the driver chip, the second pin is connected to the twelfth pin of the driver chip, the third pin is connected to the sixteenth pin of the driver chip, the fourth pin is connected to the eleventh pin of the driver chip, the fifth pin is connected to the fifteenth pin of the driver chip, the sixth pin is connected to the seventh pin of the driver chip, the seventh pin is connected to the ninth pin of the driver chip, the eighth pin is connected to the sixth pin of the driver chip, the ninth pin is connected to the fifth pin of the driver chip, the tenth pin is connected to the fourteenth pin of the driver chip, the eleventh pin is connected to the eighth pin of the driver chip, and the twelfth pin is connected to the first pin of the driver chip.

[0026] Furthermore, the fourth pin of the driver chip is grounded, the tenth pin is connected in series with the seventh capacitor and then grounded, and the tenth pin is also connected to the power supply terminal.

[0027] Furthermore, it also includes a power supply unit, which is respectively connected to the control unit, the current and voltage output unit, the display unit and the NPN signal output unit to provide power.

[0028] Furthermore, the power supply unit includes a power supply chip;

[0029] The first pin of the power chip is connected in series with a fourteenth resistor and a third diode and then connected to a voltage source. The fourteenth resistor is also connected in series with an eighth capacitor and a first polarity capacitor and grounded. The third diode is also connected to a third bidirectional breakdown diode and grounded.

[0030] The second pin is connected in series with an inductor and then connected to the power supply terminal. The second pin is also connected in series with a fourth diode and then grounded. The inductor is connected in series with a ninth capacitor and a second polarity capacitor and then grounded.

[0031] The third pin is connected in series with a tenth capacitor and is grounded; the fourth pin is grounded;

[0032] The fifth pin is connected to one end of a fifteenth resistor and one end of a sixteenth resistor respectively, the other end of the fifteenth resistor is connected to the power supply terminal, and the other end of the sixteenth resistor is grounded;

[0033] The sixth pin is connected to the eighth capacitor; the seventh pin is connected to the eighth pin and the first pin respectively;

[0034] The eighth pin is connected in series with the seventeenth resistor and then connected in series with the eighth capacitor.

[0035] Furthermore, the NPN signal output unit comprises an eighteenth resistor, one end of the eighteenth resistor is connected to the power supply terminal, and the other end is connected to the third output terminal;

[0036] The other end of the eighteenth resistor is also connected to one end of a fourth bidirectional breakdown diode and the collector of the transistor respectively, and the other end of the fourth bidirectional breakdown diode is grounded;

[0037] The base of the transistor is connected to one end of a nineteenth resistor and one end of a twentieth resistor respectively, the other end of the nineteenth resistor is connected to the control unit, and the other end of the twentieth resistor is grounded;

[0038] The emitter of the transistor is connected to one end of the twenty-first resistor and the twenty-second resistor respectively, the other end of the twenty-first resistor is connected to the control unit, and the other end of the twenty-second resistor is grounded.

[0039] In a second aspect, the present invention further provides a digital display meter, which adopts the four-digit digital display meter circuit as described in any one of the above items.

[0040] Compared to existing technologies, the present invention offers at least the following advantages: By integrating the current and voltage sampling circuits and adding an NPN signal output, the circuit's integration is improved, thereby reducing the number of required components and overall cost. The control unit accurately collects current and voltage signals, and the display unit drives the digital tube display, ensuring accurate and intuitive readings. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0042] Figure 1 This is a module diagram of a four-digit display tube in one embodiment of the present utility model;

[0043] Figure 2This is a module diagram of a four-digit display tube in another embodiment of the present utility model;

[0044] Figure 3 This is a circuit diagram of a control unit in one embodiment of the present invention;

[0045] Figure 4 This is a circuit diagram of a current and voltage output unit in one embodiment of the present utility model;

[0046] Figure 5 This is a circuit diagram of a digital display tube in a display unit in one embodiment of the present utility model;

[0047] Figure 6 This is a circuit diagram of a chip in a display unit in one embodiment of the present invention;

[0048] Figure 7 This is a circuit diagram of a serial communication unit in one embodiment of the present invention;

[0049] Figure 8 This is a circuit schematic diagram of an NPN signal output unit in one embodiment of the present utility model;

[0050] Figure 9 This is a circuit diagram of a power supply unit in one embodiment of the present invention;

[0051] Figure 10 This is a schematic diagram of the H4 terminal in one embodiment of the present utility model;

[0052] Figure 11 This is a schematic diagram of the H2 terminal in one embodiment of the present utility model;

[0053] Figure 12 This is a circuit diagram of a key unit in one embodiment of the present utility model;

[0054] Figure 13 This is a circuit diagram of an indicator light unit in one embodiment of the present invention.

[0055] Among them, R1 is the first resistor; R2 is the second resistor; R3 is the third resistor; R4 is the fourth resistor; R5 is the fifth resistor; R6 is the sixth resistor; R7 is the seventh resistor; R8 is the eighth resistor; R9 is the ninth resistor; R10 is the tenth resistor; R11 is the eleventh resistor; R12 is the twelfth resistor; R13 is the thirteenth resistor; R14 is the fourteenth resistor; R15 is the fifteenth resistor; R16 is the sixteenth resistor; R17 is the seventeenth resistor; R18 is the eighteenth resistor; R19 is the nineteenth resistor; R20 is the twentieth resistor; R21 is the twenty-first resistor Resistor; R22-22nd resistor; C1-1st capacitor; C2-2nd capacitor; C3-3rd capacitor; C14-4th capacitor; C5-5th capacitor; C6-6th capacitor; C7-7th capacitor; C8-8th capacitor; C9-9th capacitor; C10-10th capacitor; D11-1st diode; D12-2nd diode; D13-3rd diode; D14-4th diode; D1-1st bidirectional breakdown diode; D2-2nd bidirectional breakdown diode; D3-3rd bidirectional breakdown diode; D4-4th bidirectional breakdown diode; Q1-transistor. DETAILED DESCRIPTION

[0056] The following is a more detailed description of a four-digit digital display circuit and digital display of the present invention, with reference to schematic diagrams. These diagrams illustrate preferred embodiments of the present invention. It should be understood that those skilled in the art may modify the present invention as described herein while still achieving the beneficial effects of the present invention. Therefore, the following description should be understood as generally known to those skilled in the art and not as a limitation of the present invention.

[0057] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "includes," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus.

[0058] The following paragraphs describe the present invention in more detail by way of example with reference to the accompanying drawings. The advantages and features of the present invention will become more apparent from the following description. It should be noted that the drawings are greatly simplified and not to exact scale, and are intended solely to facilitate and clearly illustrate the embodiments of the present invention.

[0059] In the first aspect, the utility model provides a four-digit display circuit, please refer to Figure 1, including a control unit, a current and voltage output unit, a display unit and an NPN signal output unit;

[0060] The output end of the control unit is connected to the input end of the output unit, the display unit and the NPN signal output unit respectively;

[0061] The control unit collects current and voltage signals and sends them to the current and voltage output unit, the display unit, and the NPN signal output unit;

[0062] The current and voltage output unit converts the current and voltage signals into analog signals and outputs the analog signals; the display unit receives the current and voltage signals to drive the digital tube display; and the NPN signal output unit receives the current and voltage signals and performs reverse conversion.

[0063] By integrating the control unit, current and voltage output unit, display unit, and NPN signal output unit, a single-chip circuit design is achieved, simplifying the system structure. The circuit can simultaneously handle current and voltage signal acquisition, analog signal output, digital tube display, and reverse conversion of NPN signals, meeting various application requirements. The control unit can simultaneously transmit the acquired current and voltage signals to multiple units, enabling diverse signal applications such as analog signal output and digital display.

[0064] The digital tube display unit provides intuitive digital readings, allowing users to quickly obtain measurement information.

[0065] The reverse conversion function of the NPN signal output unit enables the circuit to adapt to different control requirements, improving the adaptability of the system. Through integrated design, the number of circuit components and connections is reduced, reducing material and manufacturing costs while improving the stability and reliability of the circuit.

[0066] For further information, please refer to Figure 3 , the control unit includes a control chip, a first resistor R1, a second resistor R2, a third resistor R3, a first capacitor C1 and a second capacitor C2;

[0067] The fourth pin of the control chip is connected to one end of the first resistor R1 and one end of the first capacitor C1 respectively, the other end of the first resistor R1 is connected to the power supply terminal, and the other end of the first capacitor C1 is grounded;

[0068] The seventh pin of the control chip is grounded;

[0069] The ninth pin is connected to the power supply terminal and one end of the second capacitor C2 respectively, and the other end of the second capacitor C2 is grounded;

[0070] One end of the second resistor R2 is connected to the eleventh pin, and the other end is connected to the power supply terminal; one end of the third resistor R3 is connected to the twelfth pin, and the other end is connected to the power supply terminal.

[0071] Specifically, the fourth pin of the control chip is connected to the power supply end through the first resistor R1 and is also grounded through the first capacitor C1, which is used to provide a stable power supply for the control chip, wherein the first resistor R1 is used for current limiting and the first capacitor C1 is used for filtering.

[0072] Pin 9 is connected to the power supply and one end of a second capacitor C2, the other end of which is grounded. This capacitor C2 is used to provide decoupling capacitance for the control chip to stabilize the power supply and filter noise. A second resistor R2 is connected to pin 11 and the power supply, respectively, for configuring specific functions of the control chip or providing a pull-up resistor. A third resistor R3 is connected to pin 12 and the power supply, respectively, for providing a pull-up resistor or performing specific signal configuration.

[0073] In one possible embodiment of the present invention, the control unit consists of an MS51 series control chip, peripheral circuits, resistors R1, R2, and R3, and capacitors C1 and C2. This microcontroller is an enhanced 8-bit 8051 core microcontroller with Flash memory, operating in 1T mode. Its instruction set is fully compatible with the standard 80C51 series, while offering higher performance. This microcontroller has 18KB of built-in Flash memory and is equipped with a rich set of special function modules, including: 256 bytes of SRAM, 1KB of XRAM, two standard 16-bit timer / counters, a 16-bit timer with three-pin input capture mode, a watchdog timer (WDT), a wake-up timer (WKT), a timer with auto-reload function, two standard serial ports (UARTs), an SPI interface, an I2C interface, 6-channel enhanced PWM outputs, and 8-channel 12-bit ADCs. Furthermore, it features superior anti-interference capabilities, an ultra-low price, high-speed operation, and low power consumption, meeting most design requirements.

[0074] For further information, please refer to Figure 4 One end of the input end of the current and voltage output unit is connected to the control unit, and the other end is respectively connected to the third capacitor C3, the fourth resistor R4, the fifth resistor R5, the sixth resistor R6, and one end of the diode group; the other end of the third capacitor C3 is grounded; the other end of the fifth resistor R5 is grounded; the other end of the sixth resistor R6 is connected in series with the fourth capacitor C14 and then grounded;

[0075] A voltage output terminal of the current and voltage output unit is further provided between the sixth resistor R6 and the fourth capacitor C14;

[0076] The other end of the fourth resistor R4 is respectively connected to the current output end of the current and voltage output unit, one end of the fifth capacitor C5, and one end of the seventh resistor R7; the other end of the fourth capacitor C14 is grounded, and the seventh resistor R7 is connected in series with the eighth resistor R8 and then grounded;

[0077] The diode group includes a first diode D11 and a second diode D12 connected in parallel, the anode of the first diode D11 is connected to the cathode of the second diode D12, the cathode of the first diode D11 is connected to the power supply terminal, and the anode of the second diode D12 is grounded.

[0078] Specifically, the core function of this unit is to collect current and voltage data using the analog-to-digital converter (ADC) built into the microcontroller unit (MCU). After processing, it outputs analog signals that reach preset thresholds. The P0.4 pin of the control chip controls the entire circuit. The current signal is output through the MA terminal, while the voltage signal is output through the AI ​​terminal.

[0079] To filter out noise, bypass capacitor C3 is included in the circuit. The current output signal at the MA terminal is formed by resistors R4, R5, R7, R8, and capacitor C5, while the voltage output signal at the AI ​​terminal is formed by resistor R6 and capacitor C14. Furthermore, diodes protect the MA and AI terminals, preventing damage to the signal terminals if the external circuit is incorrectly connected.

[0080] In a possible embodiment of the present invention, the current and voltage output unit further includes two terminals H4 and H2, respectively. Figure 10 and Figure 11 As shown, the current and voltage signals are finally transmitted to the H4 terminal.

[0081] For further information, please refer to Figure 7 , the communication unit includes a communication chip;

[0082] The second pin of the communication chip is connected to the third pin, and the third pin is connected in series with a ninth resistor R9 and then grounded;

[0083] The fifth pin is grounded; the sixth pin is connected in series with a tenth resistor R10 and then connected to the first output terminal, the tenth resistor R10 is further connected to one end of a first bidirectional breakdown diode D1 and an eleventh resistor R11, respectively, the other end of the first bidirectional breakdown diode D1 is grounded, and one end of the eleventh resistor R11 is connected to the power supply terminal;

[0084] The seventh pin is connected in series with a twelfth resistor R12 and then connected to the second output terminal. The twelfth resistor R12 is further connected in series with a thirteenth resistor R13 and a second bidirectional breakdown diode D2 and is grounded.

[0085] The eighth pin is connected in series to the sixth capacitor C6 and then grounded. A power supply terminal is also connected between the eighth pin and the sixth capacitor C6.

[0086] Specifically, the communication unit design includes a communication chip whose pins are connected through components such as resistors, capacitors, and diodes to implement communication functions. Components such as resistors, capacitors, and bidirectional breakdown diodes in the circuit provide a stable power supply, protect the circuit, set the operating point, and perform filtering, ensuring the reliability and stability of the communication unit.

[0087] In one possible embodiment of the present invention, the communication unit utilizes an RS-485 transceiver compliant with the TIA / EIA-485 standard, offering a wide power supply range of 3.0V to 5.5V. This transceiver features excellent bus port ESD protection, with a Human Body Model (HBM) ESD immunity exceeding 15kV, and a bus voltage withstand range of up to ±15V. It supports half-duplex communication mode and operates with low power consumption. The device integrates a driver and a receiver, both of which can be independently enabled or disabled. When both are disabled, both the driver and receiver assume a high-impedance state. The device supports 1 / 8 load, allowing up to 256 transceivers to be connected in parallel on the same communication bus, enabling error-free data transmission at up to 14Mbps. Furthermore, the device operates in a 3.0-5.5V operating voltage range and includes fail-safe, overtemperature protection, current limiting, and overvoltage protection.

[0088] For further information, please refer to Figure 5 and Figure 6 , the display unit includes a digital tube and a driver chip;

[0089] The first pin of the digital tube is connected to the thirteenth pin of the driver chip, the second pin is connected to the twelfth pin of the driver chip, the third pin is connected to the sixteenth pin of the driver chip, the fourth pin is connected to the eleventh pin of the driver chip, the fifth pin is connected to the fifteenth pin of the driver chip, the sixth pin is connected to the seventh pin of the driver chip, the seventh pin is connected to the ninth pin of the driver chip, the eighth pin is connected to the sixth pin of the driver chip, the ninth pin is connected to the fifth pin of the driver chip, the tenth pin is connected to the fourteenth pin of the driver chip, the eleventh pin is connected to the eighth pin of the driver chip, and the twelfth pin is connected to the first pin of the driver chip.

[0090] Furthermore, the fourth pin of the driver chip is grounded, the tenth pin is connected in series with the seventh capacitor C7 and then grounded, and the tenth pin is also connected to a 5V power supply.

[0091] Specifically, the display unit design uses a driver chip to drive the digital tubes, achieving digital display functionality. The driver chip's pins are connected in a one-to-one correspondence with the digital tube pins to control the individual segments of the tubes. Furthermore, the driver chip's power pins are decoupled via capacitors, ensuring power supply stability and display clarity.

[0092] In one possible embodiment of the present invention, the system consists of a four-digit digital tube driver and a four-digit common-cathode digital tube. A control chip controls the digital tube driver chip, thereby managing the current and voltage of the digital tube display input and output. This design reduces I / O port usage, frees up resources, and reduces code redundancy.

[0093] Furthermore, it also includes a power supply unit, please refer to Figure 9 The power supply unit is respectively connected to the control unit, the current and voltage output unit, the display unit and the NPN signal output unit and supplies power.

[0094] Furthermore, the power supply unit includes a power supply chip;

[0095] The first pin of the power chip is connected in series with a fourteenth resistor R14 and a third diode D13 and then connected to a voltage source. The fourteenth resistor R14 is also connected in series with an eighth capacitor C8 and a first polarity capacitor and grounded. The third diode D13 is also connected to a third bidirectional breakdown diode D3 and grounded.

[0096] The second pin is connected in series with an inductor and then connected to the power supply terminal. The second pin is also connected in series with a fourth diode D14 and then grounded. The inductor is connected in series with a ninth capacitor C9 and a second polarity capacitor and then grounded.

[0097] The third pin is connected in series with the tenth capacitor C10 and is grounded; the fourth pin is grounded;

[0098] The fifth pin is connected to one end of a fifteenth resistor R15 and one end of a sixteenth resistor R16, respectively. The other end of the fifteenth resistor R15 is connected to the power supply terminal, and the other end of the sixteenth resistor R16 is grounded.

[0099] The sixth pin is connected to the eighth capacitor C8; the seventh pin is connected to the eighth pin and the first pin respectively;

[0100] The eighth pin is connected in series with the seventeenth resistor R17 and then connected in series with the eighth capacitor C8.

[0101] Specifically, the power supply unit design manages and regulates power through a power chip, ensuring stable and safe power for the control unit, current and voltage output unit, display unit, and NPN signal output unit. Components such as resistors, capacitors, diodes, and inductors within the circuit are used to rectify, filter, protect, and manage power to ensure the proper operation of the entire digital display circuit.

[0102] In one possible embodiment of the present invention, this unit utilizes a DC-DC power supply chip that integrates an internal temperature-compensated reference, a voltage comparator, an oscillator with adjustable duty cycle, and an active current-limiting circuit, providing both drive capability and high-current output switching functionality. This power supply unit provides a stable voltage output for other units in the system, and the D3 transient voltage suppression (TVS) diode further enhances circuit protection.

[0103] For further information, please refer to Figure 8 , the NPN signal output unit includes an eighteenth resistor R18, one end of the eighteenth resistor R18 is connected to the power supply end, and the other end is connected to the third output end;

[0104] The other end of the eighteenth resistor R18 is also connected to one end of the fourth bidirectional breakdown diode D4 and the collector of the first transistor Q1 respectively, and the other end of the fourth bidirectional breakdown diode D4 is grounded;

[0105] The base of the first transistor Q1 is connected to one end of a nineteenth resistor R19 and one end of a twentieth resistor R20, respectively. The other end of the nineteenth resistor R19 is connected to the control unit, and the other end of the twentieth resistor R20 is grounded.

[0106] The emitter of the first transistor Q1 is connected to one end of a twenty-first resistor R21 and one end of a twenty-second resistor R22 respectively. The other end of the twenty-first resistor R21 is connected to the control unit, and the other end of the twenty-second resistor R22 is grounded.

[0107] Specifically, when the P1.1 pin of the control chip outputs a high level, the base of Q1 receives the high-level signal through the P1.1 pin. Due to the forward bias between the base and emitter, Q1 turns on. When Q1 turns on, the resistance between its collector and emitter decreases, forming a low-impedance path from the power supply to ground. As a result, the potential of the output terminal OUT_C ​​(i.e., the third output terminal) decreases, from the original high level to the low level.

[0108] When the controller chip's P1.1 pin outputs a low level, the base of Q1 receives the low signal through the P1.1 pin. Because there's insufficient forward bias between the base and emitter, Q1 turns off (doesn't conduct). When Q1 turns off, the resistance between its collector and emitter becomes very high, creating almost no path from the power supply to ground. Therefore, the output terminal OUT_C ​​remains high and is typically connected to the power supply via a pull-up resistor.

[0109] Therefore, the NPN signal output unit converts the digital output signal of the control chip into a switching signal, in which the Q1 transistor Q1 serves as a switching element, and the P1.1 pin controls its conduction and cutoff, thereby obtaining a corresponding low level or high level output at the OUT_C ​​terminal.

[0110] In another possible embodiment of the present invention, Figure 2 As shown, the four-digit display circuit may further include a key unit and an indicator light unit. The principle diagram of the key unit and the indicator light unit is shown in FIG. Figure 12 and Figure 13 shown.

[0111] In this key unit, four buttons are set to adjust the display range to meet different measurement needs. Upper and lower limit alarm lights are also set and connected to pins 10 and 19 of the control chip, respectively. When the measured value exceeds the set range, an alarm is issued through the LED indicator circuit.

[0112] In a second aspect, the present invention further provides a four-digit display meter, which adopts the four-digit display meter circuit as described in any one of the above items.

[0113] The above examples are used to illustrate the present invention, which are only used to help understand the present invention and are not intended to limit the present invention. Those skilled in the art of the present invention can make some simple deductions, modifications or substitutions based on the concept of the present invention.

Claims

1. A four-digit display circuit, characterized in that: It includes a control unit, a current and voltage output unit, a display unit and an NPN signal output unit; The output end of the control unit is connected to the input end of the output unit, the display unit and the NPN signal output unit respectively; The control unit collects current and voltage signals and sends them to the current and voltage output unit, the display unit, and the NPN signal output unit; The current and voltage output unit converts the current and voltage signals into analog signals and outputs the analog signals; the display unit receives the current and voltage signals to drive the digital tube display; and the NPN signal output unit receives the current and voltage signals and performs reverse conversion.

2. The four-digit display circuit according to claim 1, characterized in that: The control unit includes a control chip, a first resistor, a second resistor, a third resistor, a first capacitor and a second capacitor; The fourth pin of the control chip is respectively connected to one end of the first resistor and one end of the first capacitor, the other end of the first resistor is connected to the power supply terminal, and the other end of the first capacitor is grounded; The seventh pin of the control chip is grounded; The ninth pin is connected to the power supply terminal and one end of the second capacitor respectively, and the other end of the second capacitor is grounded; One end of the second resistor is connected to the eleventh pin, and the other end is connected to the power supply terminal; one end of the third resistor is connected to the twelfth pin, and the other end is connected to the power supply terminal.

3. The four-digit display circuit according to claim 1, characterized in that: One end of the input end of the current and voltage output unit is connected to the control unit, and the other end is respectively connected to the third capacitor, the fourth resistor, the fifth resistor, the sixth resistor and one end of the diode group; the other end of the third capacitor is grounded; the other end of the fifth resistor is grounded; the other end of the sixth resistor is connected in series with the fourth capacitor and then grounded; A voltage output terminal of the current and voltage output unit is further provided between the sixth resistor and the fourth capacitor; The other end of the fourth resistor is respectively connected to the current output end of the current and voltage output unit, one end of the fifth capacitor, and one end of the seventh resistor; the other end of the fourth capacitor is grounded, and the seventh resistor is connected in series with the eighth resistor and then grounded; The diode group includes a first diode and a second diode connected in parallel, the anode of the first diode is connected to the cathode of the second diode, the cathode of the first diode is connected to the power supply terminal, and the anode of the second diode is grounded.

4. The four-digit display circuit according to claim 1, wherein: Also included is a communication unit, the communication unit including a communication chip; The second pin of the communication chip is connected to the third pin, and the third pin is connected in series with a ninth resistor and then grounded; The fifth pin is grounded; the sixth pin is connected in series with a tenth resistor and then connected to the first output terminal, the tenth resistor is further connected to one end of a first bidirectional breakdown diode and an eleventh resistor respectively, the other end of the first bidirectional breakdown diode is grounded, and one end of the eleventh resistor is connected to the power supply terminal; The seventh pin is connected to the second output terminal after being connected in series with a twelfth resistor, and the twelfth resistor is further connected in series with a thirteenth resistor and a second bidirectional breakdown diode and is grounded; The eighth pin is connected in series with the sixth capacitor and then grounded. A power supply terminal is also connected between the eighth pin and the sixth capacitor.

5. The four-digit display circuit according to claim 1, wherein: The display unit includes a digital tube and a driving chip; The first pin of the digital tube is connected to the thirteenth pin of the driver chip, the second pin is connected to the twelfth pin of the driver chip, the third pin is connected to the sixteenth pin of the driver chip, the fourth pin is connected to the eleventh pin of the driver chip, the fifth pin is connected to the fifteenth pin of the driver chip, the sixth pin is connected to the seventh pin of the driver chip, the seventh pin is connected to the ninth pin of the driver chip, the eighth pin is connected to the sixth pin of the driver chip, the ninth pin is connected to the fifth pin of the driver chip, the tenth pin is connected to the fourteenth pin of the driver chip, the eleventh pin is connected to the eighth pin of the driver chip, and the twelfth pin is connected to the first pin of the driver chip.

6. The four-digit display circuit according to claim 5, characterized in that: The fourth pin of the driver chip is grounded, the tenth pin is connected in series with the seventh capacitor and then grounded, and the tenth pin is also connected to the power supply terminal.

7. The four-digit display circuit according to claim 1, wherein: It also includes a power supply unit, which is respectively connected to the control unit, the current and voltage output unit, the display unit and the NPN signal output unit to supply power.

8. The four-digit display circuit according to claim 7, wherein: The power supply unit includes a power chip; The first pin of the power chip is connected in series with a fourteenth resistor and a third diode and then connected to a voltage source. The fourteenth resistor is also connected in series with an eighth capacitor and a first polarity capacitor and grounded. The third diode is also connected to a third bidirectional breakdown diode and grounded. The second pin is connected in series with an inductor and then connected to the power supply terminal. The second pin is also connected in series with a fourth diode and then grounded. The inductor is connected in series with a ninth capacitor and a second polarity capacitor and then grounded. The third pin is connected in series with a tenth capacitor and is grounded; The fourth pin is grounded; The fifth pin is connected to one end of a fifteenth resistor and one end of a sixteenth resistor respectively, the other end of the fifteenth resistor is connected to the power supply terminal, and the other end of the sixteenth resistor is grounded; The sixth pin is connected to the eighth capacitor; The seventh pin is connected to the eighth pin and the first pin respectively; The eighth pin is connected in series with the seventeenth resistor and then connected in series with the eighth capacitor.

9. The four-digit display circuit according to claim 1, wherein: an eighteenth resistor of the NPN signal output unit, one end of the eighteenth resistor being connected to the power supply end, and the other end being connected to the third output end; The other end of the eighteenth resistor is also connected to one end of a fourth bidirectional breakdown diode and the collector of the transistor respectively, and the other end of the fourth bidirectional breakdown diode is grounded; The base of the transistor is connected to one end of a nineteenth resistor and one end of a twentieth resistor respectively, the other end of the nineteenth resistor is connected to the control unit, and the other end of the twentieth resistor is grounded; The emitter of the transistor is connected to one end of the twenty-first resistor and the twenty-second resistor respectively, the other end of the twenty-first resistor is connected to the control unit, and the other end of the twenty-second resistor is grounded.

10. A digital display meter, characterized in that: A four-digit display circuit as described in any one of claims 1 to 9 is used.

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