Intelligent dual-channel digital signal source

　　 Commonly used signal sources in laboratories generally use analog circuits to generate the signals used. Analog circuits have some inevitable shortcomings, such as inconvenience to use, incomplete functions, low resolution, and high price. The digital signal source implemented with a single-chip microcomputer is easy to use, powerful, and cost-effective. This project is implemented using a single-chip microcomputer, which inherits the advantages of general digital signal sources, and especially provides dual output signals with the same frequency and phase difference to meet the actual needs of laboratories and factories.

1 Hardware circuit description　　This system adopts a bus structure. The CPU is 8031, with an external 2718 RAM. The keyboard is a 4×4 matrix keyboard. It is connected to the 8031 ​​through a 244 buffer. The 138 decoder is responsible for providing addresses to each terminal. Its output terminal Connected to the chip select terminal of each chip. The four light-emitting diodes represent power supply, sine wave, cosine wave, and ramp wave respectively, and are hung on the bus through a 373 latch. ICM7212AM is an LED display decoding driver chip with decoding driver and hold functions. It can drive 4 common anode 7-segment digital tubes, and the brightness can be adjusted. DAC0832 is an 8-bit D/A converter with a two-level latch function and can implement various buffering methods to facilitate dual simultaneous output. The filter circuit adopts bipolar two-stage amplification filtering, which can adjust the output waveform amplitude and average value steplessly. The hardware schematic is shown in Figure 1. 2 Software flow chart and function demonstration 2.1 Software flow chart　　Software programming strives for modular design, divided into main programs and several subprograms. Considering that assembly language has higher execution efficiency, all programs are written in assembly language. The main program is mainly responsible for accepting keyboard input control and storing and displaying it. Sine wave, square wave, and ramp wave subroutines are mainly used to solve the given frequency of various waveforms from small phases to obtain the initial value of the timer. Timing interrupt is used to control the output frequency and phase difference. The interrupt subroutine is mainly used to look up the table and output each voltage point. Output the voltage at each point of various waveforms. The flow chart of each part is shown in Figure 2 (the flow chart of square wave and ramp wave is similar to that of sine wave).
　　

2.2 Function Demonstration
　　
　　The function demonstration is shown in Figure 3.

3 Performance Introduction
　　
　　This intelligent dual-channel digital signal source can generate three types of signals: square wave, ramp wave and sine wave. The frequency range of each signal is 0.1~2 kHz, and the minimum scale is 0.1 Hz. The frequency is displayed by a digital tube, which is clear and beautiful. It can output two signals of the same frequency but with phase difference at the same time, or it can also output one signal.
　　
　　The phase difference between the two outputs can be set manually, and the phase shift range is 0°~360°. All settings are completed through the keyboard, making the operation simple and convenient.
　　
　　The output signal can be adjusted arbitrarily, with the average value between -12 and +12 V and the peak-to-peak value between 0 and 10 V. All adjustments are stepless. It has complete functions and is cheap. The mass production cost is about 80 yuan. It is suitable for use in laboratories and factories and has good market prospects.

[1] Li Hua. Practical interface technology of MCS-51 series microcontroller［M］. Beijing: Beihang University Press, 1993.
[2] Gan Dengdai, Li Guangdong, Xu Jianping. Practical Development Guide for Microcontroller［M］． Beijing: Science Press, 1994.