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ADS1258EVM-PDK: external signal conditioning circuit failure/ADCPro software malfunctioning

Ruoshi Zhang
Prodigy 160 points
Part Number: ADS1258EVM-PDK
Other Parts Discussed in Thread: ADCPRO, ADS1258

Hi there,

I have this ads1258evm as my data collection system to sample my sensor data, from a customized interfacing pcb that I designed. on my interfacing pcb, I have AD8429 as my instrument amplifier between MOP, MON and AINP; AINN connects to ground.

I would like to route the signal from mux through Instrument amplifier and then feed into ADC. after I uncheck the "External Multiplexer loop bypass" box from ADCPro, the reading shown from "Data Monitor" is not correct: wrong sign and wrong scale. any idea?

Edit: Or how can I bypass the internal MUX-ADC connection properly?

  • 0
    TI__Mastermind 44680 points
    Hi Roushi,

    Would you be able to share a schematic that shows how you have connected the ADS1258EVM and your interfacing PCB? Also, what are your input and reference voltages?

    Which MUX channels are you using and are they properly selected so that your reading from the correct MUX inputs? Have you tried measuring the voltage between ADCINP and ADCINN to ensure that the input voltage to the ADC is what you're expecting?

    It sounds like you've got the BYPAS bit configured correctly so that the ADC is reading the voltages from ADCINP & ADCINN.

    Best Regards,
    Chris
  • 0 in reply to Christopher Hall
    Prodigy 160 points
    Hi Chris,

    I think I sort of get why I got it wrong, my sensor signal after the external instrument amp saturate the ADC. but an other issue comes up: when I check the "External Multiplexer Loop Bypass" box, it seems the signal go through the external conditioning circuit, which shows amplified signal; when I uncheck the box, it shows original "un-amplified" signal.

    also an other bug I found is that under "MUX" tab, in "Auto Scan" tab, AN14 has been marked as AN6.

    Could you please verify the labview code you guys using to code this ADCPro interface?

    Thank you!
  • 0 in reply to Ruoshi Zhang
    TI__Mastermind 44680 points
    Hi Ruoshi,

    Sorry for the confusion...

    I see that AIN14 is labelled incorrectly. However, it should still select the AIN14 input.

    As far as I can tell, the LabVIEW code ought to correspond 1-to-1 to the BYPAS bit, as defined in the ADS1258 datasheet.
    BYPASS = 0 (unchecked) would connect to the MUX internally; therefore, you would get the unamplified signal (...sorry I got that backwards in my previous post). Therefore, this box needs to be checked to get the input from the ADCINP and ADCINN pins.

    Best Regards,
    Chris