saadc value affects next values

[polyblank]

Hi, I'm developing custom board with nrf52832

The problem is that when saadc returns negative value, all values that saadc returns after are max possible values from config So the previous adc value affects all that goes after it. They stay at max until adc will return another negative value.

Things I tried that didn't help:

• Checking gnd/0
• Setting adc limits by nrf_drv_saadc_limits_set
• Pin in single-ended mode
• Calibrating adc  (different time intervals)
• Bitmask to adc returned value (adc is configured with 12 bit, so i zero 4 top bits)
• Different channel configs

Looking for help, I'm confused a lot

[polyblank]

Quickfix:

Board uses unipolar power supply, so there is no chance it can be wrong

[Jørgen Holmefjord]

Hi,

I'm not sure I understand what you mean by " max possible values from config". Can you give some examples of the values you are seeing? The samples from the SAADC are 16-bit signed integers.

Best regards,
Jørgen

[polyblank]

The values are close to 12 bit max value (3800-4096). 

Nvm, I just figured out what was wrong. The ble service value was unsigned int.  :D

But I faced another issue with saadc. My values now are not in the middle of 12 bit range (2048±), but it feels like they are shifted to the top (3200±), how can I solve this problem?

[Jørgen Holmefjord]

Are you using single-ended or differential mode?

What reference and gain settings are you using?

What is the supply voltage of the chip? 

What is the voltage level on the analog input that you are sampling?

[polyblank]

1.6V on adc (3.6V supply) discharged

0.4V on adc (4.3V supply) full charged

Internal and 1/6 gain

Single-ended, as i mentioned before