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ADS1115: ADS1115 last four LSB reporting 0s

Travis Alley
Prodigy 50 points
Other Parts Discussed in Thread: ADS1015, ADS1115

Travis, because we're working on this one, I split this thread off from the original here:

https://e2e.ti.com/support/data-converters/f/73/t/921116

I purchased this breakout: https://www.amazon.com/gp/product/B082QX1RDV/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1

The chip is behaving exactly as a ADS1015 and is displaying the same behavior as can be seen here: https://forums.adafruit.com/viewtopic.php?f=19&t=65880

I'm starting to suspect I have a counterfeit chip since the stamping on the chip is correct (BOGI).

  • 0
    TI__Guru* 97415 points

    Travis,

    It's possible that you did get a counterfeit device mounted on the board, but before giving up on it, I would definitely use an oscilloscope or logic analyzer to look at the I2C communications when you're reading the data. 

    I always find it helpful look at the communication directly and make sure the last four bits are wiggling.

    Joseph Wu

  • 0 in reply to Joseph Wu
    TI__Guru* 97415 points

    Travis,

    Are you able to look at the I2C communication with the device? If you're planning on doing this, I think it would be best to split this conversation in to a different thread. If you're not, then we should just close it.

    Joseph Wu

  • 0 in reply to Joseph Wu
    Prodigy 50 points

    I will hook it up to an o-scope Monday.

  • 0 in reply to Joseph Wu
    Prodigy 50 points

    Here is the output from the O-scope. Serial monitor says the output should be 14912.

  • 0 in reply to Travis Alley
    TI__Guru** 113765 points

    Hi Travis,

    Joseph is out of the office for a couple of days.  In the meantime I will try to help out.  What I see in the scope shots is a register write to the configuration register.  I do not see a read from the conversion register.  Can you send us the scope plots of the reading of the conversion register.  This would consist of addressing the device with a write with the second byte the value of the conversion register (0x00) followed by an addressing of the device with a read while reading the next two bytes as the conversion data value.  The sequence is shown in Figure 30 of the ADS1115 datasheet.

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    TI__Guru* 97415 points

    Travis,

    I don't see the scope shots that Bob described, but were you able to get some more scope shots showing the read from the conversion register? As Bob mentioned, a read from the conversion register is a five byte I2C transaction and it would help to see the whole bit stream from SDA and SCL.

    Hopefully, you've solved your problem. I'll leave this thread open for a little longer, if you're still having problems, you should be able to post back.

    Joseph Wu

  • 0 in reply to Joseph Wu
    TI__Guru* 97415 points

    Travis,

    If you tried to edit your post to put in new images, you need to use the picture icon above the text window. The posts don't work with a standard crtl-c/crtl-v for images.

    Joseph Wu

  • 0 in reply to Joseph Wu
    Prodigy 50 points

    For whatever reason my O-Scope can't zoom into the second half of my waveform. I ended up getting an ads1115 direct from adafruit and it worked flawlessly. My previous 1115 had to have been a fake one. Be careful ordering these from amazon and ebay.

  • 0 in reply to Travis Alley
    TI__Guru* 97415 points

    Travis,

    Thanks for letting us know!

    Joseph Wu