Sinwave harmonics on STM32F4 discovery board

[mohit rai]

Posted on January 02, 2018 at 06:26

Hello,

I am generating digital sin wave sample using the below formula.

sin wave[numberOfSample]=2047*(sin(2*3.14*n/numberOfSample)+1)

I am generating sample for 200 hertz wave.

numberOfSample=40 when sampling frequency=8000 hertz.

In my case,numberOfSample is 40 for 200 hertz sin wave generation.

Problem is that, when I am playing sin wave using DAC, harmonics are also present in my output. 

How can I resolve this problem?

harmonics are present due to above formula that I am using for generating sin wave sample.

I need digital sin wave in  my application. This harmonics creating lot of noise. I have tried low pass  filter (1000 hertz both software and hardware)  but it is not working effectively.

Thanks in advance

Regards,

Mohit Rai

[S.Ma]

Posted on January 02, 2018 at 09:10

Take an excel spreadsheet, create the table of n samples, format it so it can be easily copy paste in a C source code and see if the result is the same. It could also be a problem of formatting, if the DAC is in 8 bit, 10 bit or 12 bit mode etc... a ramp as input table should give more debugging clues. Is the output buffer enabled, and the test is done without output load?

[mohit rai]

Posted on January 03, 2018 at 11:24

hello,

Harmonics was present due to step size in sin wave sample.

When I have changed  in the sin wave generation formula. harmonics are reduced.

sin wave[numberOfSample]=100*sin(2*3.14*n/numberOfSample)+2047.

Regards,

Mohit Rai