Write on DAC with desired Frequency of a Sine Wave

Question

pallab choudhury 2018-6-12

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https://ww2.mathworks.cn/matlabcentral/answers/405212-write-on-dac-with-desired-frequency-of-a-sine-wave

评论： Walter Roberson 2018-6-16

Hi,

I am trying to write a sine wave for a DAC by using the MATLAB support package of Arduino. The code that I used is as below:

------------------------------

clear all

a = arduino('COM3', 'Uno');
dev = spidev(a,'D10','Mode',2,'BitOrder','msbfirst','Bitrate',1000000); 
fs = 1024;                    % Sampling frequency
dt = 1/fs;                    % seconds per sample
StopTime = 1;                 % Total time
F1 = 100;                      % Sine wave frequency (hertz)
for t=0:dt:StopTime-dt  
data1 = 32767+24576*sin(2*pi*F1*t);     % 32767 and 24576 are the bias and amplitude setting of Sine wave for 16 bit DAC 
writeRead(dev,[24,flip(typecast(uint16(data1),'uint8'))],'uint8'); % Command/Address bits and 16 bit Data
end

-----------------------------------

The DAC output shows a sine wave with frequency reduced to 10 Hz instead of 100 Hz....I checked with other sample rate and different frequency setting but the output frequency is always lower than the desired frequency. Could you please suggest how to avoid such delay or match the output frequency with the desired one. Thanks.

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Answer 1

Walter Roberson 2018-6-12

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https://ww2.mathworks.cn/matlabcentral/answers/405212-write-on-dac-with-desired-frequency-of-a-sine-wave#answer_324316

在 MATLAB Online 中打开

You need a sampling frequency that is at least twice the frequency of the sine wave you want to create.

By the way, for efficiency you should probably create the entire output matrix first.

t=0:dt:StopTime-dt;
data1 = swapbytes(uint16(32767+24576*sin(2*pi*F1*t)));
for K = 1 : length(data1)
  writeRead(dev, [uint8(24), typecast(data1(K),'uint8')], 'uint8');
end

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pallab choudhury 2018-6-14

Thanks again for your prompt answer.....however, I am little bit late!!!

To get more details, I tested the same write operation through Arduino IDE (please check the attachments for both Arduino and Matlab code), however, the situation is quite changed.

1. with arduino IDE, fs=1024, f=100 Hz, the 10 samples are within only 2 ms (i.e. DAC out is 500 Hz!!) for Single channel Operation (Note that AD5664R has 4 DACs)..With 4-channels, the frequency slightly dropped...but even higher than the desired frequency.

2. With Matlab and same setting, the situation is similar to my previous post i.e DAC output frequency dropped a lot and its even very low for 4 channels. This behavior is completely opposite to Arduino IDE.

The relevant Traces are as follows:

Also to look into the delay issue for Write Operation for both Arduino and matlab, I collected the traces for a single packet in Clock and Data samples...the packet time is almost 24 microsec for Arduino and 80 microsec for Matlab.

so after all of these details, I have some questions:

1.Using Arduino IDE, why the DAC output shows such a high frequency signal compare to the desired one?..is there any wrong in my code?

2. Using Matlab, is the low frequency signal in DAC output mainly due to the delay in Write operation? or there are something else.

3. If the Matlab code is uploaded to Arduino (i am not sure, how), is the situation solved?..

4. I do not want to use Arduino IDE for my project..then how to handle this signal frequency setup through Matlab?

Walter Roberson 2018-6-16

The single-channel Arduino code you show, appears to me to output only one point per millisecond, with you outputting two points each with a delay(1) which is one millisecond. That is within the same overall loop as the multi-channel code, so the multi-channel code is having to wait 2 millisecond (to do the single-ended things) every cycle. I see no evidence that you are outputting 10 samples in 2 millisecond for single channel in your code.

Walter Roberson 2018-6-16

The part of the Arduino code where you output 1024 samples to each of four channels has no built-in delays: it will output as quickly as the hardware permits the cycles to be run.

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