SAADC example unexpected results

[criznach]

I'm trying to use the SDK 15.0 saadc example with a potentiometer on AIN0, and I'm getting weird values.  Left pot pin connected to VDD, right pot pin to GND, center pin to P0.03(A0).  The output is reading anywhere from 42-45 if I don't touch the potentiometer - regardless of it's rotation.  If I turn it toward ground and leave it there, I'll see the values momentarily dip to into the 30s then return to the 42-45 range.  If I turn it toward VDD and leave it there, they jump up into the 50s, then return to 42-45.  Similarly, if I connect AIN0 directly to VDD or GND, I get a single reading in the 30s or 50s, then it returns to the 42-45 range.  I've tried setting up the board in the arduino IDE and the analog examples work fine there.  They'll read full range to reflect the potentiometer.  Am I misunderstanding what this example does?  I saw another question describing something similar, but it is unanswered.

[MartinBL]

Hi

1. I assume you are using the same pot meter in all the tests? So no chance of a broken pot meter?
2. Have you double and triple checked that you are using the correct pins? AIN0 is pin P0.02, but I have done the mistake myself and assumed AIN0 is on P0.03 since it is marked 'A0' on the nRF52 DK. 
3. Can you upload your code so I can test it?

[criznach]

#2 is exactly what happened.  Can the docs be updated to explain this?  As someone who's new to NRF, the A0 marking on the PCB was much more prominent and convincing than the "Pin assignments" document that I ultimately found through another DevZone post, after a few hours of head scratching.

[MartinBL]

It is sort of documented here. I agree with you though, and I have already discussed it with the kit designers once before, but their reasoning is that A0 refers to the pinout of the standard Arduino form factor:

[criznach]

That documents what the arduino-compatible pinouts are, but doesn't disambiguate how they are labelled in your APIs.  I would argue that the printed board is in the developer's hands and in front of their eyes, so like myself, that appears to be the truth.  I had to search for quite a while to see what's really happening.  It's not explained in the example code where I looked first being new to the platform.  The example documentation mentions GPIO pin 2, which I was unsure about because it doesn't match the p0.02 notation used everywhere else.  Thanks for looking into it!