The theme of this paper is the waveform acquisition, storage and playback system. By designing and manufacturing a waveform acquisition, storage and playback system, the system can collect two periodic signal waveforms at the same time, and it is required that the collected signals can be continuously played back and displayed on the oscilloscope after the system is powered off.
The current waveform acquisition, storage and playback systems are generally based on the principle of digital storage oscilloscope, with single chip microcomputer (89s5 1) and FPGA (EP1c6q240c8) as the control cores. The signal is sampled in real time by high-speed AD and triggered at the rising edge. The waveform can be stored and displayed continuously in real time, and it has a latching function. It can be stored by operating the "move" key to display. With the development of electronic technology and integrated circuits, the update speed of electronic products is getting faster and faster, and the requirements of functions are getting bigger and bigger. Therefore, on the basis of previous research results, the function of the system should be further improved to meet the rapid application of society and the needs of the public. With the development of semiconductor devices and digital processing technology, digital oscilloscope has become the mainstream. Therefore, the waveform acquisition, storage and playback system should also develop into digitalization, which is an inevitable trend. The system is designed for better digitization.
The expected result is that the waveform can be collected and stored in the memory, and the frequency, background voltage, low-end voltage, peak voltage and waveform of the waveform we want to study can be given through operation, and the measured data can be displayed on the oscilloscope together with the waveform in digital form. In this way, people can see the characteristics of the measured waveform more intuitively in practical application, which is convenient for studying related problems.
2. Overall scheme design 2. 1 Scheme 1 With single chip microcomputer as the core, it controls the acquisition, storage and playback of waveforms. It needs to be stored in a certain storage device. The frequency of single chip microcomputer is not very high, and it has strong anti-interference performance, simple operation and low cost. The goal is to add an external AD/DA chip and an external memory chip for LCD display. To realize the functions of waveform acquisition, storage and playback, the circuit will automatically acquire the acquired waveform, store it in the memory chip and display it on the LCD, and the data will not be lost when the power is off. After pressing the store key, the system samples the corresponding waveform and stores the sampled data. After pressing the playback key, the system will play back the stored waveform circularly, and the amplitude can be changed during acquisition, and the data collected during playback will also change. During playback, pressing the store key will stop waveform playback and display a straight line. If the playback key is pressed, the current playback key will be terminated, the current waveform will be terminated and a new waveform will be acquired.
The system consists of the following parts: power supply circuit, signal input circuit, signal acquisition and preprocessing circuit, data storage circuit, data display circuit and waveform playback circuit. The system circuit framework is as follows:
single chip microcomputer
power network
digital to analog conversion
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analog-to-digital conversion
Waveform input
Figure 1 Scheme I System Circuit Block Diagram
The DAC0832 chip used in the data processing module is an 8-resolution D/A conversion integrated chip, which is completely compatible with the microprocessor. This kind of DA chip has the advantages of low interval, simple interface and easy conversion control, and is widely used in the field of single chip microcomputer. Another chip used is ADC0809, which is widely used in single chip microcomputer. It is an analog interface that accepts digital quantities and outputs current or voltage signals corresponding to the digital quantities. D/A converter is widely used in computer function generator, computer graphic display and control system matched with A/D converter. This chip is an 8-bit double-buffered D/A converter developed by American Data Corporation. The chip has a data latch which can be directly connected to the data bus. The circuit has excellent temperature tracking performance, and uses CMOS current switch and control logic to obtain low power consumption and low output leakage current error. The chip uses R-2RT resistor network to shunt reference current to complete D/A conversion. The conversion result is output through a set of differential currents IOUT 1 and IOUT2. In this scheme, 32K low-power static RAM memory 62C256 is selected as the storage module, and the three-terminal fixed regulator 7805 is used as the voltage stabilizing module. The voltage stabilizing module is a commonly used three-stage integrated regulator with a fixed negative output voltage. Three-terminal IC means that the integrated circuit for voltage stabilization has only three pins to output, namely, input terminal, grounding terminal and output terminal. The regulator requires few peripheral components, and there are protection circuits such as overcurrent, overheating and regulating tube in the circuit, so it is reliable to use.
The design idea of the single-channel input-output circuit selected in the first scheme: the signal is input to the analog-to-digital converter through the input circuit, and the analog signal is converted into a digital signal, and then the converted signal is sent to the storage display control device, and then sent to the digital-to-analog converter to convert the stored digital signal into an analog signal, and finally the collected waveform is output through the output circuit. The block diagram is as follows:
input circuit
Channel input
Analog-digital conversion
Storage, display and control equipment
output circuit
Channel output
Number (word)-module
Figure 2 Scheme 1 Single Channel I/O Circuit Block Diagram
2.2 Scheme 2 adopts FPGA chip as the core to control the acquisition, storage and playback of waveforms, and all kinds of memories can be realized in FPGA. Its hardware programmable characteristics allow developers to flexibly set the width of memory data, the size of memory, read-write control logic and so on. , especially suitable for various occasions with special storage requirements. The FPGA device can work at a frequency above100M, and the access speed of its constructed memory can also reach above100M/s, so the high-speed memory can be suitable for working occasions where the amount of stored data is not too large, but the speed requirement is high and the cost is high. Because A/D and D/A conversion can be realized in FPGA, external A/D and D/A conversion circuits are omitted, and the hardware part of the whole system is reduced a lot, which makes the circuit look less complicated and simple. System structure block diagram:
keyboard
Field programmable gate array
analog-to-digital conversion
digital to analog conversion
rescue
Waveform display
Waveform input
Fig. 3 System block diagram of Scheme 2
The working principle of FGPA FPGA adopts the concept of logic cell array (LCA), including configurable logic block (CLB), input-output block (IOB) and interconnection. Field programmable gate array (FPGA) is a programmable device. Compared with traditional logic circuits and gate arrays (such as PAL, GAL and CPLD devices), FPGA has different structures. FPGA uses small lookup table (16× 1RAM) to realize combinational logic. Each lookup table is connected to the input of a D flip-flop, which drives other logic circuits or drives I/O, thus forming a basic logic unit that can realize both combinational logic functions and sequential logic functions. The logic of FPGA is realized by loading programming data into internal static storage unit. The value stored in the storage unit determines the logical function of the logic unit and the connection mode between modules or between modules and I/O, and finally determines the function that FPGA can realize. FPGA allows unlimited programming. The characteristic of FPGA is to design ASIC circuit (application specific integrated circuit) with FPGA, so users can get a shared chip without production. FPGA can be used as a pilot sample for other fully customized or semi-customized ASIC circuits.
By comparing the two schemes: FGPA may have many advantages, but it is not suitable for circuit design because of its high cost and high speed, so I choose the first scheme, because it uses single chip microcomputer as the core control, and the circuit design is easy and the cost is low.