AIN0 not measuring on pca10028

[gaminn]

Hello, measuring ADC signal on P0.26/AIN0/XL2 and P0.27/AIN1/XL1 doesn't work (I get constant value from the ADC not reflecting actual voltage on the pin). AIN2 - AIN7 seem to work.

I hope 32khz xtal (it occupies these two pins) is disabled by calling SOFTDEVICE_HANDLER_INIT(NRF_CLOCK_LFCLKSRC_RC_250_PPM_4000MS_CALIBRATION, NULL);

What else can it be?

[xtting]

I believe you should attach all of your config code.

[RK]

Just because the nrf51 isn't using the crystal itself doesn't mean it disappears from the universe, or from the circuit. So unless you've physically removed it from the board you are shorting your AIN0/AIN1 voltage across a crystal, which depending on frequency of your input is acting anything from a small resistance to a large one. So it's probably not going to work.

[gaminn]

Please correct me, but in school, they told us, that for DC crystal acts as infinite resistance, so it won't influence slowly changing ADC signal. Also my multimeter shows me correct voltage on AIN0 and AIN1. But ADC won't measure it.

[gaminn]

I init my ADC for 10 bit, 1/3 divider and VDD/2 reference.

[Stefan Birnir Sverrisson]

Hi gaminn

To disconnect the crystal and enable the pins as GPIO/AIN pin you need to perform the steps described in the nRF51 DK User guide, section 5.6