Tiva C EK-TM4C123GXL energia ADC accuracy issue

Francesco Cencioni

Hi all,

I have a problem using the Tiva C's ADC.

in order to discover the issue, I have connectecd my Analog Pin (PE_1) directly to GND and I perform a Serial.print( analogRead(PE_1) );

The result (with 1000ms delay between each measure), are

0 ; 0 ; 0 ; 0 ; 15 ; 0 ; 3 ; 0 ; 47 ; 0 ; 7; 0 ; 15 ; 0 ; 23 ; 0 ; 0 ; 0; ......

It seems strange...

I hope to solve this problem fast, because i need this for a project in the next 4 days.

Best regards,

Francesco

over 9 years ago

0 Amit Ashara over 9 years ago

TI__Guru**** 244400 points

Hello Francesco,

There is a known errata for PE3 (ADC#13). Can you check if the same in true in your case?

Regards
Amit

0 Francesco Cencioni over 9 years ago in reply to Amit Ashara

Prodigy 40 points

Hi,
I tried PE_2 and the result was the same.
I have done a test on PE_3 according to your request. It seem more stable, i get a [0;3] range in about 30 reads.
Applying an external fixed voltage on PE_3, i get a bad range [2395;2500] in about 30 reads.

Regards
Francesco

0 Amit Ashara over 9 years ago in reply to Francesco Cencioni

TI__Guru**** 244400 points

Hello Francesco

Then it seems that the issue is because of the errata ADC#13.

Do note that as cb1 did mention in the other posts, the accuracy of the ADC is tested under strict lab conditions and there can be a variation of readings as well in real time sampling.

Regards
Amit

0 Robert Adsett72 over 9 years ago in reply to Francesco Cencioni

Guru 10570 points

Definitely take note of cb1's suggestions regarding lead length and input capacitance, RF pickup could give you interesting results.

Also check your analog supply. Ensure it is free of noise and of sufficiently low impedance. Noise or high impedance, particularly on the return, could give you spurious results as well.

Robert

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Tiva C EK-TM4C123GXL energia ADC accuracy issue