Doing a digital sampling oscilloscope has always been my long-cherished desire, but after all, this goal is relatively difficult and involves too many aspects, analog front-end circuit, high-speed ADC, microcontroller, CPLD/FPGA, communications, host computer program, data processing, etc. And so on, not all of a sudden can be achieved, slowly and step by step, huh, huh, huh, have a good goal, have been learning all aspects of knowledge, but also have the power :) Due to the high-speed ADC involves sampling data storage problems, a large amount of data Influx makes the one-chip computer can't bear, so usually need to cooperate with CPLD with external high-speed RAM, or use the FPGA of large-capacity to do data storage processing, etc., then notify the one-chip computer to send the data out. This part is actually more difficult, the circuit is very complicated, and it is a lack of ability. It has to accumulate slowly. . .
Just ST introduced the new STM32 with CORTEX-M3 as the core. It integrates two independent 1Msps 12bit ADCs, and the internal frequency of up to 72MHZ, up to 1.25DMIPS/MHZ processing speed, high-speed DMA transfer function, flexible The powerful four TIMERs, etc., these are really attractive, why not use it to achieve a low-frequency digital oscilloscope function, my goal is to temporarily as long as the quantitative analysis of low-frequency signals below 20KHZ on the line, the goal is not high With STM32 can be easily achieved, and so have some experience and then slowly use FPGA and high-speed ADC to engage in a 100Msps sampling oscilloscope!
1, ADC conversion: STM32 enhanced chip built-in 2 independent ADC, can have 16 channels, and 2 channels can be simultaneously synchronized sampling, triggering is very flexible, can be triggered by TIMER and external levels, parallel mode ADC2 is automatically synchronized to ADC1; ADC needs 1.5+12.5 ADC cycles at the highest sampling speed, and 1Msps speed at 14M ADC clock, because my main frequency is 72M, so after 4 frequency division is slightly higher, 18MHz. ADC clock, sampling speed should be higher than 1M. The ADC sampled two simultaneous sampling methods and used the TIM2 CC2 to generate the clock signal to trigger the ADC to achieve sampling at the specified frequency. ADC1/ADC2 sampling result is a word
2. Sampling Frequency Control: Since the 4 TIMERs inside the STM32 are very powerful, and each TIMER has 4 channels, plus an independent pre-distributor, virtually any frequency division can be achieved. Therefore, the TIM2 CC2 is used to generate the specified frequency. The clock is used to trigger continuous ADC1 sampling.
3. Sampling data transmission and depth control for each sampling: The conversion data generated by the ADC is transmitted through the high-speed DMA channel 1 to the designated internal RAM, and the DMA channel is set to the highest priority to ensure the accuracy of the data and DMA is used. The number of transmissions to control the depth of sampling, for example, I want to collect 100 points then set up DMA transfer 100 times, each time from the 32-bit ADC conversion register to transfer a word to RAM, after completing 100 transmissions , DMA channel automatically stops (in fact, the ADC is always sampling in accordance with the required sampling frequency in the background, but I just go to fetch the data only), the next time I set the number of sampling down to enable the DMA CHANNEL1 on the line.
4. Communication with the host computer: Communication is also a problem. To achieve the goal of quickly sending a large amount of data to the host computer, the transmission rate is definitely low. At the beginning I want to use the serial port first, but I quickly give up, even if I use an external USB to serial chip can only reach 1M speed, and the data will be lost; later still using the network transmission method, using the SPI interface of the ENC28J60 chip, this chip I have used in MEGA32 and AT91SAM7S64, The interface is simple and convenient, the speed can also be, in the SAM7S64 DMA usually use UDP protocol one-way transmission speed can reach 400KB/S or more, this time with the STM32 discovery speed greatly increased, after I use STM32 DMA transfer, the same The unidirectional transmission speed of the UDP protocol even reached 500KB/s or even up to 600KB/s. This is an unexpected achievement.
5, the host computer program: still use VS2005, I still like to use C #, mainly Microsoft's C # is doing too comfortable, the editor of the degree of intelligence is really high, I just lose the beginning of the letter, immediately perceived A bunch of choices for you, even a knack for knocking on the characters, saves you from having to worry about spelling mistakes when you're looking for causes. Oh, the downside is that the CPU utilization is higher when the program is executed, and when its C++ editor is also At this level I will switch back to C++, haha. The waveform display is still implemented using NI's measurementStudio8. One is beautiful and convenient, and the other is that MeasurementStudio8 has a lot of data processing libraries, from simple RMS waveform calculations, frequency calculations, to a variety of function filters. Function, FFT frequency domain analysis, time domain analysis and so on, but there are all instrument-related processing to be used. In addition, I originally intended to add a phase-locked circuit to the analog front end to display the starting point of the waveform. Later, it was found that there is a Peak Detector class in Measurement Studio 8, and this can be used to achieve the locking of waveforms. This circuit can be saved. It is very convenient and accurate to use MeasurementStudio8 to achieve. It's just that I don't have information and I'm still exploring
The displayed interface and some photos:
After the data is sampled, the graph output to the PC is very accurate, including the small spikes on the top of the sine wave generated by the MAX038. It is also clear that the STM32's ADC accuracy is very stable. For the low-frequency signals in the audio range, the 1Msps sampling is also Basic enough. As long as sufficient points are collected for analysis by the functions provided by measuresudio, it can reach a very precise level. The resolution of 12BIT is equivalent to the effect of three and a half digits of the digital watch. It is used to test the frequency, true rms value, peak value and peak value of the signal. The peak and so on are very convenient and accurate, and the same as the frequency meter and true rms reading I use in hardware (this also shows that the hardware of the signal generator I made is accurate, haha, before it is always wrong with the digital meter It seems that the accuracy of the digital watch is poor. It can be used as a low-frequency oscilloscope, plus an analog front-end circuit, which can be practically used.
Sine wave:
Click to see picture
The host computer program:
The host computer program is still in the fumble for the measuremenStudio, only a preliminary understanding of several functions, use it to achieve data processing is really convenient, look public void DataReceived_Proc () / / UDP data reception, data processing, data display function
{
Try
{
While (bStates)
{
myudpcomm.Receive(ref CommReceiveBuffer);
Received_Command = Bytes2Struct(ref CommReceiveBuffer);
//textBox3.Text = Received_Command.SampleRate.ToString() + (acEstimate++).ToString();
dADC1_Result = new double[Received_Command.SampleDepth];
dADC2_Result = new double[Received_Command.SampleDepth];
/ / Data processing, the ADC data in the communication receiving area is passed to the array for drawing
For (int i = 0; i " (int)(Received_Command.SampleDepth); i++)
{
dADC1_Result = (BitConverter.ToUInt16(CommReceiveBuffer, 40 + 4 * (i + 0))) * (3.3 / 4096.0);
dADC2_Result = (BitConverter.ToUInt16(CommReceiveBuffer, 40 + 4 * (i + 0) + 2)) * (3.3 / 4096.0);
}
Str = "Channel A (green)";
// test true rms
Measurements.ACDCEstimator(dADC1_Result, out acEstimate, out dcEstimate);//AC (AC mode is equivalent to signal passing through a capacitor and measured after straight line) and DC (DC through mode measurement) RMS measurement
Str += "AC Mode Valid Values:" + ((int)(acEstimate * 1000)).ToString() + "mV" + "DC Mode Valid Values" + ((int)(dcEstimate * 1000)).ToString( ) + "mV";
// test signal frequency, amplitude Vp
mySingleToneInformationADC1 = new SingleToneInformation(dADC1_Result, Received_Command.SampleRate);
Str += "Frequency:" + ((int)(acEstimate * 1000)==0 ? 0int )mySingleToneInformationADC1.Frequency).ToString() + "Hz" + "Amplitude Vp:" + ((int)mySingleToneInformationADC1.Amplitude* 1000).ToString() + "mV";
Str += "Channel B (red)";
// test true rms
Measurements.ACDCEstimator(dADC2_Result, out acEstimate, out dcEstimate);//AC (AC mode is equivalent to signal passing through a capacitor and measured after straight line) and DC (DC through mode measurement) RMS measurement
Str += "AC Mode Valid Values:" + ((int)(acEstimate * 1000)).ToString() + "mV" + "DC Mode Valid Values" + ((int)(dcEstimate * 1000)).ToString( ) + "mV";
// test signal frequency, amplitude Vp
mySingleToneInformationADC2 = new SingleToneInformation(dADC2_Result, Received_Command.SampleRate);
Str += "Frequency:" + ((int)(acEstimate * 1000) == 0 ? 0: (int)mySingleToneInformationADC1.Frequency).ToString() + "Hz" + "Amplitude Vp:" + ((int)mySingleToneInformationADC1 .Amplitude * 1000).ToString() + "mV";
textBox3.Text = str;
//ThresholdPeakDetector.Analyze is used to find the array number from the trough to the peak of the rising edge of the crest
/ / Can be used to fixedly display the waveform from a fixed point on the rising edge, quite synchronous with the hardware trigger circuit function
//b = ThresholdPeakDetector.Analyze(dADC2_Result, 2, 10);
//foreach (int k in b)
//{
//textBox3.Text += k.ToString() + " ";
//}
//for (int i = 0; i Received_Command.SampleDepth - b[1]; i++)
{
//dADC1_Result = dADC2_Result[i + b[1]];
}
//textBox3.Text += b[b.Length - 1].ToString();
//bIsUdpDataReceived = true;// indicates that UDP data was received and allowed to be sent again
bIsDataReadyForPlot = true;
myGraphPlotProc();//Plot output*/
//myD1 = new myMethodDelegate(h);
//myD1(1);
}
}
Catch (Exception e1)
{
timer1.Enabled = false;
MessageBox.Show(e1.ToString());
}
Finally
{
timer1.Enabled = false;
}
}
/************************************************* ***********************************
* Drawing output process function for the mygGraphPlotThread process call
* Always loop test bIsDataReadyForPlot, once it is true then drawing, after the completion of the drawing flag is false
* ************************************************* *********************************/
Public void myGraphPlotProc()// Drawing Output Function
{
//while (true )
{
If(bIsDataReadyForPlot)
{
waveformPlot1.PlotY(dADC1_Result);
waveformPlot2.PlotY(dADC2_Result);
bIsDataReadyForPlot = false;
}
}
}
Lower computer program:
The program of the lower computer is still improving. Now it only has the basic functions, it is still unstable, and the main problem is still on the transmission. This time, in order to transfer more data at one time, the UDP data packet is decomposed and divided into multiple parts. Less than 1518 bytes of frame transmission, it is found that when the data is sent quickly can easily cause the data to stop sending, before using MEGA32 and SAM7 did not pay attention when the processing speed was slow, not exposed, think about it may be Due to the conflict caused by the speed of continuous transmission, the ENC28J60 error hangs, or ENC28J60 is not fully understood. For the flow control and Ethernet collision detection, these need further study.
/******************** (C) COPYRIGHT 2007 STMicroelectronics ********************
*STM32F10*** Dual Channel ADC Data Acquisition and UDP Communication Transmission via ENC28J60
* Author: alien2006
* Environment: keil for arm mdk 3.15b
* Version: V0.2
*time
* Description: V0.2
* First, the network communication part
*1. First use the STM32 SPI polling mode for transmission test, ping 192.168.1.100 -l 1400 -n 10
* The SPI1_SendByte() function has not been improved in the polling mode (the internal function statement directly provided by ST) needs avg=9ms time
* Modify the four statements in the SPI1_SendByte() function to direct register access and avg to 7ms in polling mode
* Cancel SPI1_SendByte() under polling mode and replace it directly with function avg raised to 6ms.
* After the above-mentioned gradual modification, transmission of UDP 1400 characters in two-way transmission (receive 1400 bytes and then send the 1400 bytes) interval 4MS up to 210KB/S
*2,enc28j60.c modify to increase STM32 SPI transfer DMA and non-DMA compile options, DMA mode network maximum transfer speed test up to 350KB/S
*3. Improved ZYP_UDP.C implementation when UDP data to be sent exceeds the length of a single frame
* Automatically group and customize each packet length at compile time;
* Improved the ENC28J60.C has added ENC28J60DMA idle and network transmission judgement, solved when the sending speed is too fast
* Causes transmission errors. Test one-way sending speed exceeds 500KB/S;
* Second, STM32 data acquisition part
*1, ADC1/ADC2 achieve parallel simultaneous data acquisition, 12BIT up to 1MSPS sampling speed and put into memory through DMA transfer of STM32
*2, TIM2 CC2 to achieve the ADC sampling trigger, ADC_Sample_Frequency_Set function to achieve custom TIM2 OC2 frequency output,
*3. The sampling frequency and number of samples are specified by the received UDP control command
* The sampling frequency is 20HZ~1MHZ;
*Sampling depth is 1~4000 data (limited by 20KB capacity of STM32 memory, one data is read by two 12bit ADC channels, one word is required)
*4. A simple UDP control command structure is defined for communication with a PC and control of sampling frequency and sampling depth
* Third, other
*1. The problem to be solved by the program: The problem of sending UDP packets is not completely solved. It needs to be further solved.
*2. It is expected to increase the analog front-end circuit and achieve the magnification control. It can be set by the host computer program.
*
* V0.1: Initial program to implement simple fixed frequency and depth parallel ADC sampling and UDP communication, and to prepare a simple upper computer program,
* Can display the sample waveform
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