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ADS1118: Does not switching to Single Ended Mode

Muslim Afandiyev
Prodigy 10 points
Part Number: ADS1118
Other Parts Discussed in Thread: ADS1115

Hello!
Due new project I need to implement 4 independed channel voltage measuring lines. To realise that task I used ADS1118 chip and STM32F103 series controller. I set configuration senquentionaly for each channel to switch ADC in 4 channel Single Ended mode.

They are:

Ch0-> 0xC58A(config), 0xC588 (read);

Ch1-> 0xD58A(config), 0xD588(read);

Ch2-> 0xE58A(config), 0xE588(read);

Ch3-> 0xF58A(config), 0xF588(read);

But all probe and tries does not gives desired result. The ADS1118 remains stay in differential mode -> A0 and A1 make affect to each other, same as A2 and A3 inputs. Looks like internal AINn does not connected to GND(ground pin).
Would you please help me to resolve that situation with some code example or correct configuration parameters advise.
Thank you.

  • 0
    TI__Guru 52156 points

    Hi,

    Can you share a schematic of your system? Can you also share the voltages you have applied to the input channels?

    Also, if you have logic analyzer shots of your communication that would be helpful as well. Thanks!

    -Bryan

  • 0 in reply to Bryan Lizon86
    Prodigy 10 points

    ASD1118_RTU_MODBUS.pdf

    Hello Bryan

    I have not analyzer shots.

    In fact, I'm reading the chip datas, but they are comming like as configurated in to differential mode, not Single ended.

    Just tell me - does that ads1118 chip has ability to work in Single Ended Mode?

    If YES - help me to figure it out with configuration...

    Thank you...

  • 0 in reply to Muslim Afandiyev
    TI__Guru 52156 points

    Hi,

    As you can see from the Configuration register in the ADS1118, the ADC can measure between two channels e.g. AIN0 and AIN1, or it can measure between any analog input and ground e.g. AIN0 and GND. So the configuration you have in your schematic should work.

    You said that the ADC "did not give the desired result", but it would help to know what you expected to see and what the ADC gave you. Can you please provide a table of the input voltages you apply and the output code you get from the ADC? Since the ADC might be stuck in differential mode, it would help to know what voltages you have applied on all channels, which channel is selected, and what the output code is.

    If this becomes a digital communication issue, you will need either a logic analyzer or an oscilloscope for additional debug. We will have to see what is being sent to the ADC and how the ADC responds.

    -Bryan

  • 0 in reply to Bryan Lizon86
    Prodigy 10 points

    Dear Bryan,

    I understood.

    But I'm afraid, it it not possible take an analyzer shots fot now.

    I did some examples with ADS1115 chip, and it get works at first try!

    But here....?

    Maybe let us make it much faster and easier way.

    Let say, You are get a task to read out 4 analog  independed voltage levels 0-3V by ads1118.

    What is yours solution to achieves it?

    There are some code examples or libraries for STM32 family controllers?

    I just need a sample to get clear that situation.

    Does it possible?

    Thank you in advance!

  • 0 in reply to Muslim Afandiyev
    TI__Guru 52156 points

    Hi

    I am not aware of any specific code to work with the STM32. A google search might help you with that. However, we do have the ADS1118 Evaluation Module (EVM). There is software to run this board, but we also make the source code available. You can find the folder for the EVM here:

    www.ti.com/.../ads1118evm

    That might at least help you get started, and then you can modify the code to work with your specific microcontroller.

    -Bryan