SAADC reading problem?

RE: SAADC reading problem?

Jørgen Holmefjord — Tue, 20 Dec 2016 12:55:14 GMT

I tested the same scenario, conncted AIN0 of my nRF52 DK to an output pin of a nRF51 DK, and got the following results:

Can you try to read another source to see if you get normal results? You can also try another input on your IC. I have attached my example code, so you can test this with your board: saadc.zip.

RE: SAADC reading problem?

Ricardo Nunes — Mon, 19 Dec 2016 11:45:32 GMT

it's a digital output from m module. in this case it was changing between GND and VCC and it was stable on the oscilloscope, but very noisy when read by the SOC ADC.

RE: SAADC reading problem?

Jørgen Holmefjord — Mon, 19 Dec 2016 11:42:57 GMT

I have spoken to the designer, and the first and second image (VCC and GND) shows normal readings. Your third image does not show normal readings for the ADC. What are you reading in this image?

RE: SAADC reading problem?

Ricardo Nunes — Fri, 16 Dec 2016 14:51:09 GMT

Updated the post after testing with a USB power bank and the result is the same

RE: SAADC reading problem?

Jørgen Holmefjord — Thu, 15 Dec 2016 15:39:08 GMT

I'm getting similar readings to you for GND, a little better for VDD. As described here and here, you should expect some noise in the range of up to a few LSB. Notice that you should rund offset calibration regularly to correct for temperature drift. This is described in this post. What are you showing in the last picture?

RE: SAADC reading problem?

Ricardo Nunes — Thu, 15 Dec 2016 13:20:14 GMT

I tried it but it doesn't hide the problem and even if it does it's not normal that a stable line gets reading like those

RE: SAADC reading problem?

Jørgen Holmefjord — Thu, 15 Dec 2016 09:25:49 GMT

Hi, can you try enabling oversampling? This should improve the signal-to-noise ratio. Also, what source do you power your board with? If using USB, this can introduce a lot of noise.