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Original question:

CCS/TMS320F28335: Sine input analog signal in ADC

TMS320F28335: TMS320F28335

Ricky Mutsvairo
Prodigy 10 points
Part Number: TMS320F28335
Other Parts Discussed in Thread: C2000WARE

Tool/software:

I'm using TMS320F28335 on an evaluation board. I'm having this issue when I want to read the amplitude of 5Vrms voltage on ADCA0 of the dsp I'm not getting a sine wave, I'm getting this wave which is not a sine wave as shown below.

I'm new to using this dsp and i haven't figured out the issue . my settings for the ADC are as shown below 

In the main function I read and process my  ADC as shown below.

The above are my settings on the graphs properties. Any help i would appreciate it.

  • 0
    TI__Mastermind 36526 points

    Hi,

    I will need a day or two to get back to you about this.

    Best Regards,

    Ben Collier

  • 0
    TI__Mastermind 36526 points

    Hi,

    I apologize for my delay in getting back to you.

    Ricky Mutsvairo said:
    I want to read the amplitude of 5Vrms voltage on ADCA0 of the dsp

    What is the magnitude of the sine wave at the ADC input? It must be scaled down since 5Vrms sine wave would be outside of ADC input range.

    Ricky Mutsvairo said:
    I'm new to using this dsp and i haven't figured out the issue . my settings for the ADC are as shown below 

    Did you start with one of the examples in [C2000WARE]/device_support/f2833x? 

    What is your sampling frequency (set by PWM in your code)? 

    Ricky Mutsvairo said:
    The above are my settings on the graphs properties. Any help i would appreciate it.

    The graph setting are a problem. The graph will automatically update at a very slow rate, you need to use a buffer to properly display your values. 

    This example will show you how to set up the graph with a buffer: https://dev.ti.com/tirex/explore/node?node=A__AX4u1JCujNz1VnDNN1Wl9g__C28X-ACADEMY__1sbHxUB__LATEST

    Best Regards,

    Ben Collier

  • 0 in reply to Benjamin Collier
    Prodigy 10 points

    The magnitude to the ADC input is reduced to within 0-3V with a signal conditioning circuit. When i test the output of the signal conditioning circuit that goes to the dsp28335 using an oscilloscope, the output is a sine wave. 

    I did start with a code i wrote myself but i referred to an online document for the code. My sampling frequency is 40KHz. 

    I did change the graph settings according to the link you gave me and i didn't see any change. What do you think might be the other issues in this. Using my code i can see the dsp values change , it's just that the waveform isn't sinusoidal

  • 0 in reply to Ricky Mutsvairo
    TI__Mastermind 36526 points

    Hi Ricky,

    I'm trying to understand if your issue is with ADC sampling or displaying the data. Let's make sure the ADC is sampling the voltage correctly.

    1. Have you tried sampling a DC value? Do you get the expected conversion value? 

    2. When you look at the buffer of ADC readings, do you ever see a value outside of this 120-140 range? 

    3. What is the sine wave frequency? 

    Thanks,

    Ben Collier

  • 0 in reply to Benjamin Collier
    Prodigy 10 points

    Hi Benjamin . 

    Thank you for your assistance.  I managed to solve the problem by using a buffer and an appropriate sampling frequency.

    Thanks 

    Ricky