ADC measurement issue

Discussion in 'Analog & Mixed-Signal Design' started by RenesasT1, Nov 2, 2017.

  1. ebeowulf17

    Well-Known Member

    Aug 12, 2014
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    If any of the pins got too hot for too long when you were moving the chip, that could do it. That's my best guess, but I really am just speculating at this point.

    The only other answer I can think of is if the AIN input went too far above your supply voltage.

    Hopefully someone else will have some insights - I'm afraid we've reached the limits of my knowledge here.
     
  2. RenesasT1

    Thread Starter Member

    Jul 6, 2017
    105
    1
    Please do not be panic and afraid. I am sure you are good and your knowledge is fabulous.

    I will check the same with other IC and will update the same here.

    I have ordered the IC's and will receive by tomorrow. I will update you the status.
     
  3. RenesasT1

    Thread Starter Member

    Jul 6, 2017
    105
    1
    Hello ebeowulf17,

    Does ADS1015 and ADS1115 are available in through hole. I am thinking I should order through hole. I was finding but not able to find.
     
  4. be80be

    AAC Fanatic!

    Jul 5, 2008
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    There data sheet don't show them through hole
     
  5. RenesasT1

    Thread Starter Member

    Jul 6, 2017
    105
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    Ok I am receiving SMD part by today evening. I will share you the results as soon as possible.
     
    ebeowulf17 likes this.
  6. ebeowulf17

    Well-Known Member

    Aug 12, 2014
    1,477
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    Any luck with the new parts?
     
  7. RenesasT1

    Thread Starter Member

    Jul 6, 2017
    105
    1
    Hi ebeowulf17,

    The parts were coming from USA and somthing happens and they are asking me to submit KYC to clear customs. I had cleared KYC docs and will receive the shipment by tomorrow morning. I will keep you updated.
     
  8. ebeowulf17

    Well-Known Member

    Aug 12, 2014
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    Sorry to hear that. Sounds like a pain. I sincerely hope they solve the problem when they show up, especially after having to work with customs to get them. Good luck!
     
  9. RenesasT1

    Thread Starter Member

    Jul 6, 2017
    105
    1
    Hi ebeowulf17,

    I have got new pieces for of 12 bit ADC. Part number is ADS1015.

    I had mount on the board. Each morning I am testing the same board on the same project. ADC is running and in between ADC is giving fluctuations.

    After touching up the ADC(just over soldering PADs of ADC ) the issue is getting resolved. Then ADC is working fine. But next morning the same issue is arising. Again just over soldering the PADs of ADC resolves the issue.

    Please help me to finalize the project.
     
  10. ebeowulf17

    Well-Known Member

    Aug 12, 2014
    1,477
    239
    How much fluctuation are we talking about?

    Are you doing over sampling in code? If not, have you incorporated some other smoothing, averaging, or filtering in the code, or perhaps analog filtering on the input?
     
    ericgibbs likes this.
  11. be80be

    AAC Fanatic!

    Jul 5, 2008
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    Your setup is like this
    Screenshot from 2018-01-13 04-05-13.png
     
  12. RenesasT1

    Thread Starter Member

    Jul 6, 2017
    105
    1
    Yes exactly the same.

    Pin 4,5,6 are unused and left open. I am using pin7 for the i/p.

    Also I am not using ALERT/RDY pin . Hence no pull up resistor for that pin. This pin is left open.

    SCL and SDA pins are pulled up with 10K resistor. VDD is 5V .
     
  13. ebeowulf17

    Well-Known Member

    Aug 12, 2014
    1,477
    239
    You haven't answered my earlier questions:

    How much noise (fluctuation) are we talking about? How does the noise level compare to signal level?

    Are you certain the noise is from the ADC conversion, and that it's not actual analog noise in your test signal source?

    Assuming the noise is significant and only on the ADC side (not present in the actual analog signal input,) have you tried over sampling yet?
     
  14. RenesasT1

    Thread Starter Member

    Jul 6, 2017
    105
    1
    Hi,

    Please find the ans below,

    1) the random values are coming from ADC o/p like 1043,1057,951,999,1069,1079 etc.
    2) Yes. Sometimes it is proper working for 1 day and after that next day, the issue arises. Just soldering the PAD's of ADC resolves the issue and works for the whole day. Again next days same issue arises and again soldering requires.
    3) There is no oversampling is required me in this ADC. I was getting steady o/p using this ADC only.
     
  15. ebeowulf17

    Well-Known Member

    Aug 12, 2014
    1,477
    239
    Those fluctuations are larger than I was expecting. Have you measured the voltage at the inputs while you were getting these bad readings? Better still would be an oscilloscope - if the signal is moving quickly, but averaging in the same range, a simple volt meter might be too slow to show it. How can you be sure the actual voltage isn't jumping around as indicated by the ADC? What is the source of the signal that you're reading anyway? Knowing that *might* provide a clue towards understanding the noise issue.

    I'll be honest - this isn't making much sense to me, but maybe it's just a problem that's beyond my level of experience.

    It's hard to believe that the solder joints are continuously failing every day (or every several days) unless the circuit is in a really harsh environment. Are you sure this isn't an intermittent problem that would come and go on its own? Maybe it has nothing to do with solder, but given time while you're reworking the solder, it just happens to be in a good, working state again?

    Honestly, if it's really the solder joints, then you've answered your own question, and you need to do a better, more reliable, longer lasting solder job.

    If not, I'd be double checking grounding, power supply decoupling, isolation from high current, high voltage lines, etc. Might also be worth experimenting with ferrites or caps on the ADC input, depending on your frequency response requirements.
     
  16. RenesasT1

    Thread Starter Member

    Jul 6, 2017
    105
    1
    Hi ebeowulf17,

    I am in big trouble. I am not getting what is happening with me. I dont understand what is happening with me.


    I have mounted another board and with new ADC. Its the same result. It is running for 6 mins and again fluctuation starts.

    I am using diode as a temperature sensor.

    Does the issue is with decoupling. Its hard to find the issue. I am not understanding what is happening.

    Please help me.
     
  17. ebeowulf17

    Well-Known Member

    Aug 12, 2014
    1,477
    239
    Please share a schematic of how you've wired the diode temperature sensor circuit. How much current are you running through the diode?

    Diode temperature sensing is something I haven't yet learned much about, so I looked up what appears to be a good application note and I'm saving this link here for future reference:

    http://www.ti.com/lit/an/sboa019/sboa019.pdf
     
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