nRF9160 ADC Reference Values

RE: nRF9160 ADC Reference Values

Gurkan — Thu, 09 May 2019 15:24:22 GMT

Another inconsistency that I have seen is about gain:

I'm measuring 577mV signal;

If I setup the gain as;

"ADC_GAIN_1" -> ADC Value 984, calculated voltage 577mV

"NRF_SAADC_GAIN1" - > Configuration error - Selected ADC gain is not valid

"ADC_GAIN_1_2" -> ADC Value 497. calculated voltage 582 mV

"NRF_SAADC_GAIN1_2" -> same as "ADC_GAIN_1_2"

"ADC_GAIN_1_3" -> ADC Value 333, calculated voltage 585 mV

"NRF_SAADC_GAIN1_3" -> same as "ADC_GAIN_1_3"

"ADC_GAIN_1_5" -> ADC Value 204, calculated voltage 595 mV

"NRF_SAADC_GAIN1_5" -> same as "ADC_GAIN_1_5"

"ADC_GAIN_1_6" -> ADC Value 171, calculated voltage 601 mV

"NRF_SAADC_GAIN1_6" -> same as "ADC_GAIN_1_6"

RE: nRF9160 ADC Reference Values

Gurkan — Thu, 09 May 2019 14:42:34 GMT

Hi.

As I have mentioned earlier I always read the EVENTS_CALIBRATEDONE as 0, before setting TASK_CALIBRATEOFFSET or after.

    printk("Calibration has started\n");
	NRF_SAADC_NS->EVENTS_CALIBRATEDONE = 0;
	NRF_SAADC_NS->TASKS_CALIBRATEOFFSET = 1;
	while (!NRF_SAADC_NS->EVENTS_CALIBRATEDONE)
		;

For example it never passes the above check.

RE: nRF9160 ADC Reference Values

Jared — Thu, 09 May 2019 14:03:22 GMT

Hi,

Are you experiencing wrong results even after the first result? Could you try clearing the the NRF_SAADC_NS->EVENTS_CALIBRATEDON field by setting it to 0 before writing NRF_SAADC_NS->TASKS_CALIBRATEOFFSET = 1 and see if the flag is set?

RE: nRF9160 ADC Reference Values

Gurkan — Wed, 08 May 2019 12:49:19 GMT

Hi Jared,

That sample was the first thing I have tried actually.

Btw, I'm getting better readings if comment out "NRF_SAADC_NS->TASKS_CALIBRATEOFFSET = 1;"

And when I don't comment out that line I'm trying to check if the calibration is finished with "NRF_SAADC_NS->EVENTS_CALIBRATEDONE" but this register returns always 0.

RE: nRF9160 ADC Reference Values

Jared — Fri, 03 May 2019 09:01:04 GMT

Hi,

Could you try this example and see if you get the expected output?

Jared

RE: nRF9160 ADC Reference Values

Gurkan — Thu, 25 Apr 2019 18:07:11 GMT

Hey Jared,

I've switched to 1.8V and my observations;

ADC Settings;

Resolution: 14 bit

Gain: ADC_GAIN_1

Reference: ADC_REF_INTERNAL

Oversampling: NRF_SAADC_OVERSAMPLE_256X

at 640mV I can get 16380 which is maximum, it does not go over 16380

##############################################################

Resolution: 14 bit

Gain: ADC_GAIN_1

Reference: ADC_REF_VDD_1_4

Oversampling: NRF_SAADC_OVERSAMPLE_256X

at 580mV(I think this supposed to be 450mV since our VDD 1.8V) can get 16380 which is maximum, it does not go over 16380

################################################################

Gain: ADC_GAIN_1_3

Reference: ADC_REF_INTERNAL

Oversampling: NRF_SAADC_OVERSAMPLE_256X

AN0 pin connected to VDD (1.8V)

Resolution 14 bit - > ADC value 16130

Resolution 12 bit - > ADC value 4030

Resolution 10 bit - > ADC value 1008

RE: nRF9160 ADC Reference Values

Jared — Thu, 25 Apr 2019 13:55:30 GMT

Could you try implementing the workaround and see if it works?

RE: nRF9160 ADC Reference Values

Gurkan — Wed, 24 Apr 2019 17:55:53 GMT

Apperantly, the fault at output value of ADC is known issue, It has been pointed out at Errata.
Errata link