15-Design of digital frequency meter based on 51 single chip microcomputer

Specific implementation functions

The system consists of STC89C52 single chip microcomputer + signal input + 74HC14 shaping circuit + 74HC390 frequency division circuit + LCD1602 display module + power supply.

Specific functions:

1. It can measure the frequency of waveforms such as sine wave, triangle wave or square wave;

2. The frequency measurement range is 1Hz-20MHz, and it can detect signals with a minimum amplitude of 1Vpp;

3. The detected instant frequency value (up to 8 digits, in Hz) is displayed on the LCD1602 liquid crystal display.

design background

In the field of electronic measurement, frequency measurement has the highest accuracy. Therefore, in the production process, many physical quantities, such as temperature, pressure, flow, liquid level, pH value, vibration, displacement, speed, acceleration, and even the percentage composition of various gases, are converted into signal frequencies by sensors and then measured by digital frequency meters to improve accuracy.

There are many classifications of digital frequency meters in the world. According to the function classification, because the counting frequency meter has many measurement functions and a wide range of uses. Therefore, according to the functions of the instrument, electronic counters are divided into general and special. 1. General counter: General counter is a universal counter with multiple measurement functions and multiple uses. It can measure frequency, period, multi-period average, time interval, cumulative counting, timing, etc.; if equipped with corresponding plug-ins, it can measure phase, voltage, current, power, resistance and other electrical quantities; with appropriate sensors, it can also measure non-electrical quantities such as length, weight, pressure, temperature, speed, etc. 2. Special counter: Special counter refers to a counter specifically used to measure a single function. For example, frequency counter can only be used to measure high frequency and microwave frequency; time counter is a counter based on measuring time, and its time measurement resolution and accuracy are very high, up to the order of ns; special counter, it has special functions, such as reversible counter, threshold counter, difference counter, countdown counter, etc., used in industry and automatic control technology. Digital frequency meters are classified by frequency band: ① low-speed counter: maximum counting frequency <10MHz; ② medium-speed counter: maximum counting frequency 10-100MHz; ③ high-speed counter: maximum counting frequency >100MHz; ④ microwave frequency counter: measurement frequency range 1-80GHz or higher.

Due to the combination of large-scale and ultra-large-scale digital integrated circuit technology, data communication technology and single-chip microcomputer technology, the development of digital frequency meters has entered a new stage of intelligence and miniaturization. Its functions have been further expanded. In addition to the basic functions of measuring frequency, frequency ratio, period, time, phase, phase difference, etc., it also has the functions of self-pickup, self-calibration, self-diagnosis, mathematical statistics, calculation of root mean square value, data storage and data communication. It can be seen that the frequency meter is of great industrial value. This work is a digital frequency meter based on a single-chip microcomputer. It divides the frequency through the 74HC390 chip, overcoming the difficulty of the single-chip microcomputer in processing high-frequency signals, and uses LCD1602 liquid crystal display for output, with an accuracy of 1/200,000.

Design ideas

Digital frequency meter is a basic measuring instrument. It is widely used in aerospace, electronics, measurement and control, and is also used in computers and various mathematical instruments. Generally, decimal numbers are used to display the frequency of the measured signal. The basic function is to measure sinusoidal signals, square wave signals, and other physical quantities that deteriorate per unit time. Because it uses decimal numbers for display, the measurement is fast and accurate, and the display is intuitive, it is often used.

This article mainly introduces the design and debugging of digital frequency meter. This work is based on 52 single-chip microcomputer as the platform. The basic principle is to collect and analyze the frequency through 52 single-chip microcomputer, and then display it on the LCD1602 liquid crystal display through the program. Through the LCD display, the user can intuitively see the current input frequency.

Since the frequency signal strength that the 52 single-chip microcomputer can process is limited, this time we first use the 74HC390 chip to divide the input signal, reducing it 100 times before sending it to the single-chip microcomputer for processing. In addition, in order to make the 1602 LCD display more compatible, we have performed three initializations in the program, which will be shown to you one by one below.

Schematic

The schematic diagram of this system was designed using Altium Designer19, as shown in the figure.

program

This design uses KEIL5 software to implement program design, as shown in the figure.

Simulation Implementation

This design uses protues8.7 software to implement simulation design, as shown in the figure.