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TMS320F28335-continuous slag.(ADC)

irfan rashed
Intellectual 270 points

Dear Sir,

Warm Greetings!

Recently when I was using ADC on the TMS320F28335-starter kit, I found lot of slag (continuously repeating digital values) as shown in the attached file.

The values repeat with some interval sometimes and sometimes wihout any gap. I wanted to know is this the noise or slag.? If so what is the possible solution for this as I know this is not the sign of noise as they cannot be repitative.

Can somebody help me with this problem?

Thanks a ton.

  • 0
    Guru 192875 points

    Hi Irfan,

    Are you using any kind of ADC input or is it floating ??? 

    Regards,

    Gautam

  • 0 in reply to Gautam Iyer
    Intellectual 270 points

    Hi Gautam,

    The problem is that the ADC (SoC) code is converted for four conversions. They are the readings obtained without any slave input attached,

    These are the noise readings only. the problem with these readings is that some values in this readings repeat continuously some times periodically and sometimes randomly which I don't think is noise. There is should be some error in my execution or something else.

    Regards,

    Irfan. 

  • 0 in reply to irfan rashed
    Guru 192875 points

    Hi Irfan,

    When you don't attach any input to ADCs, they deliver floating values. Please check with fixed voltages ranging from 1v to 3v from a DC supply and then check for variations.

    Regards,

    Gautam

  • 0 in reply to Gautam Iyer
    Intellectual 270 points

    Dear Gautam,

    Thank you so much. i will do it soon and let you know the result.

    Thanks a lot for the help.

    Regards,

    irfan.

  • 0 in reply to irfan rashed
    Intellectual 270 points

    Hi gautam,

    I tried doing what you said. Yes, the values change I connected the ADC pins to the power supply and checked the readings at different voltages (say 1,1.5,2,2.5,3) but the values were still repeating and not stable.

    I included the low-pass filter and repeated the experiment with it. The results were better offcourse but still repeating and not stable.

    I think the values which are repeating are due to constant voltage input and needs an average of it to compensate. I think so but not sure.

    Can you please help me with this problem?

    Also I have another problem, the configuration which I am setting is the one with (0x4,0x3,0x2,0x1-corresponding pins to be ADCINA4,ADCINA5,ADCINA6,ADCINA7).

    The corresponding registers which I allocated are ADCINA0,ADCINA1,ADCINA2,ADCINA3 respectively.

    But the reading which I observed were drastically repeating without the low-pass filter which is not the form of noise i think.

    When I changed the registers to different registers like ADCINA1,ADCINA5,ADCINA7,ADCINA3, the readings were not repeating and changing continuously which I felt like noise.

    But I did not understand the logic behind this that why the corresponding registers(0,1,2,3) are not showing the reading as with the non-corresponding registers (1,5,6,3).

    I tried for too many register options (permutations and combinations) and found that 1,5,7,3 register allocations shows reasonable readings which are understandable.

    When I apply a high standard low-pass filter to it, all the readings get stable and it is expected with or without corresponding registers.

    Please help me in this regard. Thanks a lot for all the help.

    Regards,

    Irfan.

     

  • 0 in reply to irfan rashed
    Guru 192875 points

    Hi Irfan,

    The ADC values do have a 2mV-3mV variation wrt fixed voltages. Yes by designing a good LPF you can reduce this variations. Averaging 10 ADC values would also be an option for accurate value but this increases the computation time and utilizes unnecessary cpu cycles. All ADC have same kind of variations please go through the ADCResults registers for details. Also please go through the ADC documentation "SPRU716D". 

    It is recommended that when some ADCs are ununsed , ground them.

    Regards,

    Gautam