Single-chip temperature automatic test system based on LabVIEW (1)

Single chip microcomputer STM32L151CCU6

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Kaixin micro test

1 Introduction

LabVIEW is a virtual instrumentation platform developed by National Instruments. It is a development tool that uses icon code instead of a text-based programming language to create applications. Lab-VIEW is powerful, providing a wealth of data acquisition, analysis and storage library functions and all the functional functions of various instrument communication bus standards including DAQ, GPIB, PXI, VXI, RS 232/485. The data acquisition system designed by LabVIEW can simulate and collect various signals, but it is more expensive to install the data acquisition board of NI company. In actual development, the small-chip single-chip system can be used to collect data.

Cold storage is the infrastructure for the development of the refrigeration industry and is also a group of buildings that store goods under low temperature conditions. Food preservation mainly focuses on food cold chain, and pre-cools, processes, stores and refrigerates perishable livestock, poultry, aquatic products, fruits and vegetables, and frozen foods to effectively maintain the appearance, color, nutrients and flavors of foods. The purpose of preserving quality and keeping fresh, extending the shelf life of food, plays a role in regulating the market in the light season and the peak season and reducing the economic loss in the production and sales process. In these practical applications, temperature is a very important indicator of cold storage. Therefore, this paper designs an automatic temperature test system for single-chip microcomputer based on LabVIEW, and gives a detailed description of its system composition and implementation.

2 system structure and working principle

The data acquisition system of this system consists of temperature sensor and AT89C51 single chip microcomputer and MAX232. The small system consists of single-chip microcomputer collects, adjusts and converts the temperature signal, and then sends the data to the computer through RS 232 serial communication. Under the LabVIEW development platform, the data is processed and analyzed, and the signal is stored and displayed. And printing, and finally the PC displays the temperature of the 8 freezer compartments of the real-time measured cold storage, thus realizing a single-chip temperature automatic test system in the Lab-VIEW environment.

2.1 hardware circuit design

The hardware circuit of the system is shown in Figure 1. The AT89C51 is used as the main chip. The temperature sensor uses the integrated circuit temperature sensor AD590 produced by American AD Company. The temperature sensor has small volume, high temperature measurement accuracy, good stability and fast response. Good linearity, long-distance transmission and low price. This temperature sensor is particularly easy to work with with a microcomputer to form an automatic temperature measurement system. The amplifier circuit uses AD627, converts the measured temperature to a range of 0 to 5 V, and then sends it to the input of the A/D converter. Since the temperature changes slowly, the sample/holder can be eliminated in the system. The analog-to-digital conversion circuit selects ADC0809 with internal latch and 8 analog switches. Its resolution is 1/256, which can fully meet the requirement of ±1°C resolution.

The working process of starting ADC0809 is: first send the channel number address to ADDA, ADDB, ADDC, the channel number address is latched by the ALE signal, then let START be valid, start A/D conversion, that is, execute a "MOVX@DPTR, A" instruction. Generate WR signal, make ALE, START valid, latch channel number and start A/D conversion. After the A/D conversion is completed, the EOC sends a positive pulse and the application is interrupted. In the interrupt service routine, "MOVX A, @DPTR" generates the RD signal to make the OE terminal valid, open the output latch tristate gate, and use the "MOVX A, @DPTR" command to read the 8-bit data to the CPU. in.

2.2 Software Design

System software design mainly includes main program, interrupt service subroutine and so on. The software flow chart is shown in Figure 2.

The function of the main program: Responsible for the management of the whole system, such as setting the external interrupt mode of 89C51, establishing the data pointer, setting the initial value of the channel, starting the A/D conversion and communicating with the host computer.

Function of the interrupt service program: read the A/D converted data, change the channel number and data memory address pointer and judge whether the 8 channels are collected. If not, continue to start the next channel; if 8 channels have been converted, then Reset the initial value of the channel number and start the IN0 channel again.