use saadc AIN2 on the custom board, read value is differ from nrf52 dk.

RE: use saadc AIN2 on the custom board, read value is differ from nrf52 dk.

nrfcho — Wed, 22 Jul 2020 07:35:58 GMT

I have exactly same problem with TTN.

So did you solve this problem with shorting other ain pins to be ground?

RE: use saadc AIN2 on the custom board, read value is differ from nrf52 dk.

theslawek — Sat, 08 Sep 2018 05:37:38 GMT

Did you find a solution? When I short AIN0 and AIN1 to Vss (GND) I see similar values like your screenshot (36-39) AIN2-4 seem to act normally.

RE: use saadc AIN2 on the custom board, read value is differ from nrf52 dk.

TTN — Fri, 01 Jun 2018 07:31:23 GMT

I expect the value that i got from saadc's change trend looks normal, can be changed when i change the potentiometer, not always the values in the picture.

EX:

input saadc value

1v 1024

2V 2048

3V 3072

RE: use saadc AIN2 on the custom board, read value is differ from nrf52 dk.

MartinBL — Fri, 01 Jun 2018 07:03:32 GMT

Are these still not the values you expect? If so, what values do you expect?

RE: use saadc AIN2 on the custom board, read value is differ from nrf52 dk.

TTN — Fri, 01 Jun 2018 01:27:34 GMT

Thanks for reply, will review the data sheet again,maybe try another fet, which i want to close the fet when i not measure the potentiometer voltage, trying to save battery consume.

for now i can control the fet open when set P0.25 high and close when clear.

I have tried measure voltage without the MOSFET and connect VDD and GND to the potentiometer.

ADC input Range 0~1.6(with fet)
0~VDD(without fet)

I always gets values like below pitcure.

RE: use saadc AIN2 on the custom board, read value is differ from nrf52 dk.

hmolesworth — Thu, 31 May 2018 17:10:04 GMT

Incorrect use of the 2N7002; have a close look at the data sheet and then try a different type of FET as the 2N7002 will not do what you expect in this configuration. I would also consider not using a FET if the nRF52 uses VDD for a supply; instead remove the FET and connect P0.25 to the top of R6 which is what Martin is suggesting

RE: use saadc AIN2 on the custom board, read value is differ from nrf52 dk.

MartinBL — Thu, 31 May 2018 12:25:13 GMT

Hi,

Have you tried without the MOSFET just to rule out any errors on that end?

Is the error always exactly the same or does it vary between 4 and 5x?

What values do you get when you set the potentiometer to minimum and maximum?