CN202256477U - A digital voltmeter with automatic range conversion - Google Patents

Abstract

The utility model relates to a range automatic switching digital voltmeter belongs to the electron and measures technical field. The voltmeter comprises an input circuit, a range conversion circuit, an A/D converter, a master control single chip microcomputer, an LED display module and a power module, wherein the input circuit, the range conversion circuit, the A/D converter, the master control single chip microcomputer and the LED display module are sequentially connected, and the input circuit, the range conversion circuit, the A/D converter, the master control single chip microcomputer and the LED display module are respectively connected with the power module. By adopting the voltmeter for measurement, the direct-current voltage of 0-400V can be accurately measured, the measuring range can be automatically converted, the performance is stable, and the response is sensitive.

Description

A digital voltmeter with automatic range conversion

technical field

The utility model relates to a range automatic conversion digital voltmeter, which belongs to the technical field of electronic measurement.

Background technique

Voltage is a basic physical quantity and one of the three basic parameters (voltage, current, power) that characterize the energy of electrical signals in lumped circuits. Voltage measurement is the basic content of electronic measurement. In electronic circuits, the working state of the circuit, such as resonance, balance, cut-off, saturation, and the dynamic range of the operating point, are usually expressed in the form of voltage. The control signal, feedback signal and other information of electronic equipment are mainly expressed as voltage. In the measurement of non-electric power, various sensor devices are also used to convert non-electric parameters into voltage parameters.

A digital voltmeter is an instrument that uses digital measurement technology to convert a continuous quantity (input voltage) into a discontinuous, discrete digital form and display it. As the most basic and core measuring instrument in modern electronic measurement, the requirements for its measurement accuracy and function are getting higher and higher. Since the voltage measurement is the most common and involves a wide range, especially in the case of micro voltage, high voltage and the great difference in the strength of the signal to be measured, it is necessary to ensure the measurement accuracy of the weak signal and take into account the measurement range of the strong signal. The voltmeter with manual range conversion has certain difficulties in measurement technology; at the same time, if the range is not selected properly, not only will the measurement accuracy be reduced, but even the instrument will be damaged. Voltage measurement is the basis of electronic measurement. In the measurement and debugging of electronic circuits and equipment, the test results are required to have high measurement accuracy and stable performance. A digital voltmeter with automatic range conversion The test results show that the voltmeter has the characteristics of high precision and stable performance, and is widely used in voltage measurement.

Utility model content

The utility model provides a digital voltmeter with automatic range conversion, which has 16-bit resolution, takes the single-chip microcomputer AT89S52 as the main controller for measurement, and uses the A/D conversion chip LTC1865 as the basis, combined with the automatic range conversion circuit. 0 ~ 400V DC voltage for accurate measurement of automatic range conversion.

The utility model adopts following technical scheme for solving its technical problem:

A digital voltmeter with automatic range conversion, comprising an input circuit, a range conversion circuit, an A/D converter, a main control microcontroller, an LED display module and a power supply module, wherein the input circuit, the range conversion circuit, the A/D converter, the main The control single-chip microcomputer and the LED display module are connected sequentially, and the input circuit, the range conversion circuit, the A/D converter, the main control single-chip microcomputer and the LED display module are all respectively connected with the power supply module.

The beneficial effects of the utility model are as follows:

1. It has the characteristics of fast conversion speed, high precision (keep within 0.025%), stable performance and simple circuit.

2. Automatic range conversion and high-definition digital display function.

3. The voltage measurement range is wide, and the DC voltage of 0-400V can be accurately measured.

4. It has a strong expansion function. An absolute value converter is added to the input end to convert the AC voltage amplitude into the corresponding DC voltage value to realize the measurement of the AC value.

5. Sensitive response and stable display.

Description of drawings:

Figure 1 is a structural block diagram of a digital voltmeter with automatic range conversion.

Figure 2 Schematic diagram of the digital voltmeter.

Figure 3 is the circuit diagram of automatic range conversion.

Figure 4 is the main program flow chart.

Figure 5 Flowchart of the range conversion program.

Detailed ways

The invention will be described in further detail below in conjunction with the accompanying drawings.

The digital voltmeter measures the DC voltage in the range of 0-400V, with a measurement accuracy of ≤0.025%, and can automatically perform range conversion (the design is divided into four ranges of 0-0.4V, 0.4-4V, 4V-40V, and 40V-400V). The structural block diagram of the digital voltmeter with automatic range conversion is shown in Figure 1. It is mainly composed of input circuit, range conversion circuit, A/D conversion, main control microcontroller, LED display and power module. The analog signal to be tested is processed by the input circuit, and the interference is filtered out to output the DC signal; the range conversion circuit automatically selects the signal processing method of attenuation or amplification according to the size of the previous DC signal to ensure that the signal voltage sent to the A/D converter is within 0.4 Between ~4V; the main control microcontroller controls the automatic realization of the range conversion circuit according to the A/D conversion result, and at the same time calculates and processes the conversion result and sends it to the LED display.

The voltmeter uses AT89S52 as the main control microcontroller, which is a low-power, high-performance CMOS 8-bit microcontroller. AT89S52 is manufactured by ATMEL's high-density non-volatile storage technology, compatible with the standard MCS-51 command system and 80C52 pin structure, and its most notable feature is that the chip contains 8K bytes of ISP (In System Programmable) repeatedly The Flash program memory that can be written 1000 times makes it possible to rewrite the program in the memory without relying on special programming tools or removing the chip from the circuit board.

The A/D converter chooses Linear's 16-bit successive approximation converter LTC1865. It is a differential input, dual-channel 250ksps, single-supply serial analog-to-digital converter, which can work reliably in the temperature range of -40°C to +125°C, and has the characteristics of high speed, high precision, and low power consumption.

The data output interface of LTC1865 adopts SPI mode, because AT89S52 does not have a special SPI port, so it needs to use general I/O pins to simulate. Connect P2.0 with SCK of LTC1865, clear and set P2.0 regularly through software. Use P2.1 to connect the SDI port, and write the configuration word to LTC1865 to realize the selection of the input mode. Connect SDO with P2.2, responsible for reading in data. Use P2.3 as the chip selection signal. See Figure 2 for specific connections. The start of the LTC1865 conversion cycle is triggered by the rising edge of the CONV pin. After a period of conversion time, the CONV is pulled low. At this time, a clock pulse is output by controlling the high and low level changes of the P2.0 pin of the microcontroller through software. At the same time, the The data is read in bit by bit from the P2.2 port. In this process, the microcontroller can be regarded as a master device with an SPI interface, and the two pins P2.0 and P2.2 act as the SPI interface respectively. Two pins in SCLK and MISO. When the 16-bit data is read, stop the pulse output of port P2.0.

Realization and working process of automatic range conversion: use voltage attenuation input buffer, operational amplifier and 2-way electronic switch combined with single-chip software programming to realize automatic range conversion function. The hardware circuit diagram of its realization is shown in Figure 3, in which AD822BP is a single-supply, low-power consumption, rail-to-rail output (full voltage output) dual-precision operational amplifier produced by American Analog Devices, with an input impedance of 1013Ω and a total of The mode rejection ratio is 80dB; MAX4602 is a CMOS analog switch with an on-resistance of only 2.5Ω. There are four normally open switches inside, and each switch can handle rail-to-rail analog signals. It has low power consumption, small size, The advantages of high reliability.

The automatic conversion of the range starts from the initial range setting until the appropriate range is selected. The input signal range of the A/D conversion circuit is 0~5V, and the upper limit of the voltage to be tested is 400V. AT89S52 sets the initial values of the switch control signals RS_SWH_1 and RS_SWH_2 to 0, that is, both switches are in the off state. The voltage attenuation input buffer stage is determined by the voltage division of R1 and R2 to attenuate the input signal by 100 times, while the operational amplifier stage is in the voltage following state, and the amplification factor is 1, so as to ensure that the A/D conversion input signal is between 0 and 4V; the microcontroller according to The result of A/D conversion re-determines the state of RS_SWH_1 and RS_SWH_2, so that the measured signal is in the appropriate range. The relationship and setting of the parameters of the automatic range conversion circuit are shown in Table 1.

Table 1 Parameter relationship and setting table of automatic range conversion

Range RS_SWH_1 Attenuation coefficient RS_SWH_2 gain A/D input Initial value 0 100 0 1 0~4V 0～0.4V 1 1 1 10 0~4V 0.4～4V 1 1 0 1 0.4～4V 4V～40V 0 100 1 10 0.4～4V 40V～400V 0 100 0 1 0.4～4V

The program of automatic range conversion of high-precision digital voltmeter adopts modular design and is written in C language. The program consists of the main program, the range conversion subroutine, the A/D conversion subroutine, and the LED display subroutine.

When the MCU is powered on, the initialization work is performed first, and the initial value of the switch control signal is set, that is, RS_SWH_1 and RS_SWH_2 are both 0; then the A/D conversion is started for the signal to be measured; then the range conversion program is called to determine whether the range is suitable, if not, then Reset the value of the switch control signal, restart the A/D conversion until the range is appropriate; the output data is sent to the LED display. Its software design flowchart is shown in Figure 4.

The automatic range conversion subroutine is called by the main program after a measurement is completed. When the program is called, the latest measurement data is compared with the threshold value of the initial range (the highest range). If it exceeds the threshold value, it is overflow or double sampling If the signal to be measured suddenly becomes larger during the gap, and exceeds the range of the original suitable range, it is necessary to take corresponding measures according to the state of the switch control signal; if it is within the normal range, it needs to be further compared with other range thresholds; If the range is suitable, the display data can be output; otherwise, the most suitable range among the other three ranges is selected and sampled. The implementation process is shown in Figure 5. In order to avoid the sudden increase of the signal to be measured between the two sampling intervals and exceed the input signal range of LTC1865, the protection circuits of D1 and D2 in Figure 3 are adopted.

Claims (1)

1. a range automatically converts a digital voltmeter, is characterized in that comprising an input circuit, a range conversion circuit, an A/D converter, a main control microcontroller, an LED display module and a power module, wherein the input circuit, a range conversion circuit, A/D The D converter, the main control single-chip microcomputer and the LED display module are sequentially connected, and the input circuit, the range conversion circuit, the A/D converter, the main control single-chip microcomputer and the LED display module are respectively connected with the power supply module.

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