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ADS1014

BB
Prodigy 30 points
Other Parts Discussed in Thread: LM35, ADS1014

Hi,

I am currently usign a ADS1014 in differential mode to monitor temperature which is given by a lm35 in single supply mode.

The problem is that the value I read from the conversion register is always 0xFF70 until I reach about 1 - 1.2V then the values I read are in the range of 0xC0A0 like I am in the negative range of value.

The thing I don't understand is why even if AIN0-AIN1 in positive the values I read are in negative and why at 240mV the ADC stick at 0xFF70 which is the absolute positive value.

 

Thanks 

 

Ben

 

 

  • 0
    TI__Genius 17905 points

    Hi Ben,

    Can you please attach a snippet of your schematic showing the ADS1014 connections?

    I want to make sure that there are no communication issues -- can you write to the Config Register and read back its contents to verify proper communication? That is, perform the 4-byte sequence to write to the Config Register, then the 2-byte write sequence to set the Pointer to the Config register (*this is just to be sure, though the pointer should still be pointing to the Config Register from the first write), and finally, the 3-byte read sequence. See the Quickstart Guide starting on p.8 which outlines what byte sequences are needed for reads and writes.

     

  • 0
    TI__Guru* 97465 points

    One other thing to try is to remove the LM35 and simply short the inputs together. That way you should expect to get a 0V input.

    If you have a multimeter, you can also measure the output of the LM35 directly just to make sure that the input at a voltage that you expect.

    Joseph Wu

     

  • 0 in reply to Joseph Wu
    Prodigy 30 points

    I measure the voltages like this:

    AIN0 to GND = positive value

    AIN1 to GND = positive value

    AIN0(+) AIN1(ref) = fit with the AIN0 - AIN1 and the range of the values is -55mA to 1.5V

    I try your suggestion and I will be back the results

    Thanks

  • 0 in reply to BB
    Prodigy 30 points

    I do the test and I read a 0 when I tie AIN0 to AIN1, so that part looks ok...

    I think the problem is on the lm35 configuration side... I took out the recommended pull-down from the differential positive pin and my problem was solved, I will isolate the ADC from the sensor.

    Sorry for my error.

    Thanks for your help.

    Ben