ADS131E08S: Sample missing

Jignesh Gohil

Prodigy 50 points

Part Number: ADS131E08S
Other Parts Discussed in Thread: ADS131E08

Hi,

I am using ADS131E08S for 50Hz AC measurement.

ADC is used in bipoler mode (+2.5 to -2.5)

DRDY is connected to interrupt pin of micro-controller.

START pin in connected to GPIO pin of micro-controller.

ADC is running in internal clock mode.

ADC init sequence.

1. RESET command send over SPI

2. SDATAC command, stop continuos mode

3. Reading ADC ID register on SPI 0x20 0x00 0x00 ( Reading Id as 0xD2)

4. Send below configuration using WREG command

CONFIG1 = 0xD6 // Multiple data readback mode, Data Rate 1 KSPS

CONFIG2 = 0xE0 // Test signals are driven externally

CONFIG3 = 0xE0 // VREFP is set to 4 V

FAULT = 0x00 // 95% to 5 %

CHnSET = 0x10 // Gain 1, Nomral input

5. ADC offset calibration command

6. ADC Read continuos mode command

Once init is completed, I am making START pin high, which will be held high forever. On DRDY i am getting interrupts and storing the samples by reading 27 bytes over SPI.

Some time samples are getting missed, kindly refer the below plotted sine wave based on the samples from ADC.

What am i doing wrong? any suggestion.

Thanks

Jignesh Gohil

over 7 years ago

0 Tom Hendrick over 7 years ago

TI__Guru**** 180771 points

Hi Jignesh,

Welcome to the e2e forum!

Just looking at your plot, it seems like there are nine or so samples missing. I would suspect there is something going on in your software - perhaps in your interrupt service routine. If you have access to an oscilloscope, monitor the DRDY output and verify that there are no interruptions in getting data transferred to your micro controller.

0 Jignesh Gohil over 7 years ago in reply to Tom Hendrick

Prodigy 50 points

Hi Tom,

Thanks for reply and sorry for the delay.

I have tried to timestamp the samples using 1 ms external interrupt on the other pin on micro-controller, in that ISR i am increamenting counter to track mili-seconds.

When DRDY interrupt come i am reading sample from ADC along with i store the mili second count. When problem occurs i don't see any problem with time stamp.

every time i observed almost 8-9 samples are missing !!,

Best regards,

Jignesh

0 Tom Hendrick over 7 years ago in reply to Jignesh Gohil

TI__Guru**** 180771 points

Hi Jignesh,

How many good samples do you get between the missing samples? Is it consistent?

0 Jignesh Gohil over 7 years ago in reply to Tom Hendrick

Prodigy 50 points

I am taking 6000 samples, and this problem occur once and its randomly.

0 Tom Hendrick over 7 years ago in reply to Jignesh Gohil

TI__Guru**** 180771 points

Hi Jignesh,

There's nothing inside the ADS131E08 that would be causing this that I can think of. It would be helpful if your were to use an oscilloscope to probe DRDY, DOUT, SCLK and /CS to verify that you get all 27 bytes read out of the ADC before DRDY goes active again.

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ADS131E08S: Sample missing