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CCS/TMDXRM46HDK: ADC values show spikes

NeilBerry_at_Parker
Expert 1995 points
Part Number: TMDXRM46HDK
Other Parts Discussed in Thread: HALCOGEN

Tool/software: Code Composer Studio

I am using HalCoGen to setup ADC points on the  RM46 HDK.  The points have a spike issue.  Is there an optimal HalCoGen configuration? or changes to reduce spikes?

  • 0
    TI__Guru 59540 points
    Hello Neil,

    The question is if the spikes are really misreading by the ADC or if there is noise on the line that the ADC is simply converting. The HDK does have some RC circuits where you can add external filtering to the ADC inputs to help suppress board noise. the default for the HDK is to populate the resistances with 0ohm resistors and the capacitors are left unpopulated. More details can be seen in the schematics for the HDK which is availabl at this link: www.ti.com/.../spnr032

    Note that the link is to a zip file containing the schematic and other HDK design files. Specific information circuit info for th RC filters are on page 2 of the schematic.
  • 0 in reply to Chuck Davenport
    Expert 1995 points
    As a test, we disabled the "capacitor discharge" feature for all blocks, and the spikes are not being seen for now. I will let it run over night.
    We added the discharge when we saw bleed through on the temp sensor when the light sensor value changed (no ADC IN circuit was present). Now that we have wiring on the ADC IN points, maybe the circuit is resolving bleed through. The IN circuit is about 120 impedance.
  • 0 in reply to NeilBerry_at_Parker
    Expert 1995 points
    Revised: Spiking did resume today, and was worse when there was sunshine at a nearby window (cause undetermined). I did restore the capacitor discharge, after I began to see bleed through on the temperature sensor to ADC generated waveforms.
  • 0 in reply to NeilBerry_at_Parker
    TI__Guru 59540 points
    Hello Neil,

    The key to resolving is to identify the source of the spikes. This could be as simple as interference from localized noise from fluorescent lighting nearby fans (AC) or some other AC device. Of course, these approaches assume the source is something external. There is also some possibility that they could result from board generated noise given your comment that direct sunlight exposure causes them to occur. Assuming the this means that the sunlight is causing localized heating on the board and thus increasing noise susceptibility.
  • 0 in reply to Chuck Davenport
    Expert 1995 points
    You have raised good points. Right now I am thinking that correlation does not always imply causation. If I look and see smooth data, I should not think the latest changes are the cause. The hours/times when the data was smooth might simply be times when equipment that arcs in neighborhood was not running. I am here during daylight hours, and the unknown machines run periodically during the day shift. The amount of sunlight at any given time might just be incidental.
  • 0 in reply to NeilBerry_at_Parker
    TI__Guru 59540 points
    Neil,

    I see that you have posted a thread about a similar issue at this location: e2e.ti.com/.../2323877

    Is the new post referencing a new issue or is it the continuation of the issue referenced in this thread? If it is the same, should we close this thread and continue the support on the other? I don't want to have 2 different conversations ongoing at the same time for the same topic.
  • 0 in reply to Chuck Davenport
    Expert 1995 points
    Yes, I marked this thread as resolved, it could be closed. I was directed to consider the behavior in further detail, so I opened the newest topic (which had a discovery today on the impact of multiple groups on the size of the ring/spike).
  • 0 in reply to NeilBerry_at_Parker
    TI__Guru 59540 points
    Good to hear. I will close this thread and we will continue supporting through the new post and new line of discussions.