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Original question:

LAUNCHXL-F28379D: The Sine wave that I sample using DAC-B and output from GPIO pin 70 disappears after ~100 seconds

LAUNCHXL-F28379D: DAC and ADC values are not same

FAHAD BIN MAZHAR
Intellectual 295 points
Part Number: LAUNCHXL-F28379D

Hello,

I am using F28379D LaunchPad Development Kit for a project. I am competely new with this microcontroller programming.

I am design a circuit in the MATLAB simulink and run the design in the F28379D LaunchPad Development Kit.

I have generated the signal put it in the DAC pin and receivinging the same signal from ADC pin, connecting the DAC and ADC pins with a jumper wire physically.

But the real time ADC output is not the same.
I want to receive the same signal in the ADC.

Where should I change the values? and how can I modify my design for that?
I am attaching some snapshots of my design for clear view.

Thanks in Advance.

In the Above figure, this is the signal (scope 2) at DAC pin. The signal is square wave with 0 to 4096 values oscillation. 

In the Above figure, this is the signal (scope 3) at ADC pin output. This shows 0(zero) Values.

In the Above figure, this is my ADC parameter settings.

In the Above figure, this is the signal generator parameters.

In the Above figure, this is the SCI_A baud rate.

In the Above figure, this is the external mode.

  • 0
    TI__Guru* 80250 points

    Fahad,

    Have you been able to confirm with a volt meter that the DAC value is indeed coming on the pin of the LaunchPad?  I'd like to make sure that this portion of the code is working correctly before we debug the ADC.

    Best,

    Matthew

  • 0 in reply to MatthewPate
    Intellectual 295 points

    Yes, the DAC output provides the same graph and same values.
    In the Oscilloscope , the maximum value is 3.3V shown as the corresponding value for the input of DAC is 4095.
    Shown in the figure below.

    I want to receive the same signal in ADC and see in the scope of the Simulink.
    I think, this portion of code is working correctly.
    please help me with the further portion of the code and the design.

    Thanks in advance.
    and sorry for the late reply.

  • 0 in reply to FAHAD BIN MAZHAR
    Mastermind 6460 points

    Hi,

    One of the reasons why we see ADC return zero is the sample time mismatch between DAC and ADC.

    While the DAC is generating the square wave at 50Hz the ADC is configured to read the same at 2Hz (0.5 being the sample time in the ADC block).

    Another reason is ADC block used in polling mode does not guarantee the perfect synchronization with the DAC signal.

    The ADC block sampling of the input voltage it is not guaranteed if the sample is taken when the signal is low/high.

    So 2 approaches - ensure the DAC and ADC are in sync or ensure the sample times are consistent between the same.

    If you know the DAC output pattern, you can use an ePWM to generate the same pattern to trigger the ADC for conversion.

    Hope this helps,

  • 0 in reply to venkatesh chilapur
    TI__Guru 50611 points

    Hi,

    Is your issue resolved? Can we close the issue?