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Original question:

ADS1115: Status of Ready Output in Single Cycle Mode

ADS1115: ADS1115 Resolution issue

Douglas Rodrigues
Prodigy 10 points
Part Number: ADS1115

Hi, We're designing an A/D converter using ADS1115 in a single-ended config, and we multiplex the analog informations before converting them by ADS1115.

A microcontroller is the master of the I2C bus, and there's a D/A in the same I2C bus. (A/D and D/A are slaves).

In the ADS1115 we have the Config register as follows:

- master sends a start bit;

- master sends 0x90 (Add pin is at GND);

- Master sends 0x01;

- master sends 0xC1;

- MAster send 0x83;

- Master sends a stop bit. (By thi moment, all bytes are acnowledged by ADS1115.

To read the Conversion register, we are proeeding as follows:

- Master sends a atart bit;

- Then sends a 0x90;

- Then sends 0x00

- Then a stop bit followed by a nes start bit;

- Then sends 0x91;

- ADS sends 0xC3;

- ADS sends a value between 0x00 and 0x64 (according to the analog value).

The problem is that this 0xC3 sent by ADS1115 is fixed, independent of the analog value. So we get bad resolution.

We tested different configurations and ICs.

Could you help us on this issue? If you have an example code for this Converter, could you send by email: douglas@dsrsolucoes.com.br ? It'll be very useful.

We have 6 equipments to deliver in January, 5th. So, if you could help us before Christmas, it'll be very nice!

Regards, Merry Christmas!

Douglas

  • 0
    TI__Mastermind 23275 points

    Hi Douglas,

    I am sorry to hear you are having issues with the ADS1115 while being on a tight schedule.

    I looked through your communication sequence and it looks okay to me. You may want to look at the SCL and SDA pins on a scope to double check the communication.
    Have you tried to read back the Config Register of ADS1115? This is usually a good sanity check for your communication.

    If I understand your description correctly, you are using an external Mux to feed in different signals into AIN0. Is that correct?
    Are all signals in front of the Mux single-ended signals referenced to GND?
    How are you synchronizing the Mux channel changes with the conversions on ADS1115?
    Have you tried to apply a constant voltage to the ADS1115 and to read back that voltage? Just to get the complication of the external Mux out of the way.

    Conversion results are provided in twos complement format. A conversion result of C3xxh would therefore indicate you measure a deferentially negative signal. I am not sure how that should happen when you have the ADS1115 configured to measure between AIN0 and GND.

    Regards,

  • 0 in reply to Joachim Wuerker
    TI__Mastermind 23275 points

    Hi Douglas,

    I wish you a Happy New Year.

    I wanted to check in to see if you resolved this issue already or if you need further support.

    Regards,