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ADS1115: Data readings get unstable in all channels after 10 minutes of readings

Alessandra Navarro
Prodigy 10 points
Part Number: ADS1115
Other Parts Discussed in Thread: PCA9306

Dear all,

I am using an ADS1115 to read 4 analog sensors with a Raspberry pi. I am using the Adafruit ADS1115 library for python to read the data. After 10 minutes, the analogue readings get messed up and unstable unless I disconnect completely the I2C bus. I have checked the code and I am  sure the readings are NOT in differential mode and it is a single shot reading mode. Even if I add some time delay it still does not work. 

Hardware wise we have checked and the signals are stable even when the ADS is returning messed up values. All the channels are referenced to ground and we have added a high frequency filter to avoid signal noise.

Does anyone has an idea of what could be the problem?

I would much appreciate help! Thanks very much in advance

Many thanks

Alessandra

  • 0
    TI__Guru* 92715 points
    Alessandra,


    There are probably a few things that could cause problems, but I'd need more information to help debug this.

    First, can you report back a length of data? I'd like to see what results you get when the data is messed up or unstable. I would note that the device reports back data in a two's complement notation and even if the device is set up as a single ended measurement, the output could be negative, if there is a negative offset voltage.

    I could also use a description of the setup with some details about the connections to the input, microcontroller, and to ground.

    Make sure that the microcontroller digital voltage is compatibile with the ADS1115 voltage. For example, the I2C should be running at the same voltage. If they aren't you may need a level translator like a PCA9306.

    For the ADS1115, the input impedance isn't as high as some of the other precision ADCs in our portfolio. What is it that you're measuring and is the source impedance high? This could cause problems in the measurement.

    Are there multiple I2C devices on the bus that you are using? If there are, I would check for some sort of bus contention. Are you using multiple ADS1115 devices and are you sure that you have selected independent addresses?

    I would make sure that the entire system has a common ground. Make sure there is a low impedance path from the microcontroller ground to the ADC ground and to the measurement ground.

    Go through my comments and post back, I'm sure we can solve this problem.


    Joseph Wu
  • 0 in reply to Joseph Wu
    TI__Guru* 92715 points
    Alessandra,


    I haven't heard from you in a while. Have you been able to solve your problem with the ADS1115? I mentioned a few things to try in my last post to try. If you're still having problems, then go back through my post and report back your results.

    I'll close this post for now, but again post back if it's not working.


    Joseph Wu