How can we find accurate voltage in ADC channel in nRF9160?

RE: How can we find accurate voltage in ADC channel in nRF9160?

Sigurd — Thu, 17 Oct 2019 14:21:45 GMT

There is some chip to chip variation, so on some DK’s you can have ~100mV accuracy for single-ended input measuring at these voltages. On other DK’s you might get a better result because of the chip to chip variation. Looking at the specification for the SAADC at this link, the error for the 1/6 gain is from -3 to 3%. You also have some temperature drift (typ 0.02 %/C), and maybe around 2-4 LSB single-ended offset error.

RE: How can we find accurate voltage in ADC channel in nRF9160?

jaydip kavaiya — Mon, 14 Oct 2019 09:02:42 GMT

Hi Sigurd

I checked with Multimeter from both sides like where are give supply and from the board, it's accurate e.g.

like if I provide 1202 so on multimeter showing exactly 1202 and board pins also same but the result is

not showing accurate like its 100 or 95 mV is less.

Thanks & Regards

Jaydip

RE: How can we find accurate voltage in ADC channel in nRF9160?

Sigurd — Mon, 14 Oct 2019 07:54:44 GMT

Have you verified that the output from the power-supply is accurate? E.g. with a external multimeter?

I’m seeing ~30 mV accuracy on a v0.8.5 nRF91-DK with 1.8V input signal.

RE: How can we find accurate voltage in ADC channel in nRF9160?

jaydip kavaiya — Thu, 10 Oct 2019 06:34:26 GMT

Hi Sigurd

Thank for your Valuable reply

We are testing ADC value on Link monitor like this.

We are giving voltage to nRF9160 DK via This type of Power supply in Pin no. P0.13.

and the voltage range is like

supply voltage (mV) Showing in Link monitor (mV) Difference(mV)

1503 1393 to 1412 95-110

1202 1097 to 1105 90-105

We are using This Example with No changes

How can I get the exact value?

Thanks in Advance

Jaydip

RE: How can we find accurate voltage in ADC channel in nRF9160?

Sigurd — Tue, 01 Oct 2019 13:45:51 GMT

Hi,

The absolute maximum voltage you can supply to a GPIO pin is VDD_GPIO (+ 0.3). VDD_GPIO is on the DK the same as VDD_IO. See the Absolute maximum ratings chapter in the PS. Outside this value you will not get valid results, and you risk damaging the chip.

[quote userid="81359" url="~/f/nordic-q-a/52633/how-can-we-find-accurate-voltage-in-adc-channel-in-nrf9160"]we want to find voltage given by power supply to nRF9160[/quote]

Instead of using SAADC for this, you should instead use the AT command %XVBAT. See this link

Using the %XVBAT command, measuring battery voltage up to 5.5V is supported.

RE: How can we find accurate voltage in ADC channel in nRF9160?

jaydip kavaiya — Tue, 01 Oct 2019 10:38:38 GMT

Hi Sigurd

It is v0.8.5.

and VDD_IO is set to 1V8.

Thanks In Advance

RE: How can we find accurate voltage in ADC channel in nRF9160?

Sigurd — Tue, 01 Oct 2019 09:09:04 GMT

Hi jaydip,

What version of the DK do you have(should be printed on white sticker) ? is it v0.8.5?

What is the position of the VDD_IO? Is it set to 1V8 or 3V ?

RE: How can we find accurate voltage in ADC channel in nRF9160?

jaydip kavaiya — Mon, 30 Sep 2019 05:53:37 GMT

Thanks for the reply

I do not want to switch my kit to 3V GPIO. I read this link like if VDD_GPIO higher than 2.1 V. Not able to read out correct value from SAADC output. But my only question is

I provide supply voltage to nRF9160 DK is below then 2.1V but still, I am not getting correct value is there any suggestion for me

I used the ADC example with no Changes.

RE: How can we find accurate voltage in ADC channel in nRF9160?

jbrzozoski — Thu, 26 Sep 2019 13:34:55 GMT

Did you happen to switch your dev kit up to 3V GPIO? There was an errata with the older demo silicon on a lot of the dev kits:

infocenter.nordicsemi.com/.../anomaly_160_16.html