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Original question:

ADS1115: How to get the right readings from ADS1115 for a voltage range -3 to 3 V?

ADS1115: ADS1115 least count or resolution issue

Shrikant Walvekar
Prodigy 50 points
Part Number: ADS1115
Other Parts Discussed in Thread: ADS1015

Dear sir,

I have interfaced the ADS1115 adc with ESP32. I am using it for single ended, FSR = +/- 2.048, Single shot mode. I operated the device all SPS.

My observation is that the counts that I get from the ADS1115 change by 16 and not by 1.

By this I mean that even that the resolution of the ADC is 16 bit, the lower 4 bits are always zero.

For example : if the conversion counts are say 28304(0x6E90) for 1.7647V than by varying the input (even if the least count is 62.5uV/count) by minimum +/-1mV I get the counts change to 28320(0x6EA0) or 28288(0x6E80).

I am confused  why is that so.

I tried using ready drivers for ADS and also wrote the driver myself. But even then I am facing the same problem.

Kindly, suggest whether  I am wrong somewhere or I am missing something.

Awaiting your reply.

  • 0
    TI__Guru* 97465 points

    Shrikant,


    Just to be clear, your ADC is reporting an output where the data is reporting codes only every 16 counts? From your explanation, it looks like the last four bits is reporting 0000b, which would have the same result.

    My first thought is that you have the wrong device in your system. While the ADS1115 is a 16-bit ADC, the ADS1015 is a similar 12-bit ADC. For that device, the communication is identical, with similar settings in the configuration register. However because the ADS1015 ADC is 12-bit, the conversion register outputs data for only 12-bits, leaving the last four bits as 0000b.

    Check the labeling on the ADC, and see what the package marking is on the device. There will be a 3 or 4 letter marking on the device, identifying the model. You can use that to check against the device marking listed in the datasheet for the ADS1115 and the ADS1015 (in the package option addendum section).

    If it isn't that, then I would start debugging by using an oscilloscope to check the I2C communications with the device. Make sure that the read of the conversion register gives all the bits for the conversion. You can post back the oscilloscope plot here for review.

    Check all these things and post back. Again, start with the package marking on the device to see if the device isn't an ADS1015. Then let me know what you find.


    Joseph Wu

  • 0 in reply to Joseph Wu
    Prodigy 50 points

    Dear Josheph Wu,

    The marking on the device is "BOGI" which is for ADS1115 as per the datasheet.

    The Device Marking for ADS1115 VSSOP package should be BRNI/BROI/BOGI  as per the datasheet &

    the device marking for ADS1015 VSSOP package should be BRMI/BRPI/BRQI as per the datasheet.

    Secondly, I had 2 devices wiith the same marking. After your reply I checked the second device also.

    The other device is working fine (same marking "BOGI").

    I will share the I2C output from the faulty device .shortly.

  • 0 in reply to Shrikant Walvekar
    TI__Guru* 97465 points

    Shrikant,

    Thanks for the information. When you can, post back with the I2C communication plots. One other thing you can try to do is read the configuration register. This register should be a known value, so you can read it back and compare what you get to the expected configuration or the default register value.

    Joseph Wu

  • 0 in reply to Joseph Wu
    TI__Guru* 97465 points

    Shrikant,


    I haven't heard from you for a little while, so I thought I'd check on your progress. In my original post, I'd suggested that you might have gotten and ADS1015, but with the package markings, I guess that's not the case. After that, I suggested that you get an oscilloscope shot of the I2C transaction and post it back for review. I thought you might be easily able to debug the problem just by looking at the I2C communication. I hope that's the case.

    I'll close this post for now. If you continues to have problems with this, post back and we can continue to work on this again.


    Joseph Wu

  • 0 in reply to Joseph Wu
    Prodigy 50 points

    I am experiencing this EXACT same issue.

  • 0 in reply to Travis Alley
    TI__Guru* 97465 points

    The previous post has been split into a different thread:

    https://e2e.ti.com/support/data-converters/f/73/t/925508

    Joseph Wu