Can't get a ADC result that makes sense

[Nikolaj]

Hi,

I'm working on a simple ADC application where I sample using analog channel 1 and then read the value through the debugger. However my results are nonsense. I have connected a potmeter with VDD on the right pin, ground on the left and the analog input as the center pin. No matter which analog pin I connect the center potmeter pin to, i get a value around 0x50. I feel I have forgotten to set-up the analog input pin. It's like there's missing a connection between the input-pin and the ADC.

\#include <stdbool.h> 
\#include "nrf.h" 
\#include "nrf_delay.h" 
\#include "nrf_gpio.h" 


uint32_t result = 0;

/** Configures port 1 as output */
static void gpio_config(void)
{
  nrf_gpio_range_cfg_output(8, 15);
  nrf_gpio_port_write(NRF_GPIO_PORT_SELECT_PORT1, 0);

    nrf_gpio_cfg_input(20, NRF_GPIO_PIN_PULLUP);		//BUTTON 4
    nrf_gpio_cfg_output(23);						//LED 3
    nrf_gpio_cfg_output(24);						//LED 4

    //Interupt on button 4
    NVIC_EnableIRQ(GPIOTE_IRQn);
        NRF_GPIOTE->CONFIG[0] = (GPIOTE_CONFIG_POLARITY_HiToLo << GPIOTE_CONFIG_POLARITY_Pos)
                        | (20 << GPIOTE_CONFIG_PSEL_Pos)				//BUTTON 4
                        | (GPIOTE_CONFIG_MODE_Event << GPIOTE_CONFIG_MODE_Pos);
NRF_GPIOTE->INTENSET = GPIOTE_INTENSET_IN0_Set << GPIOTE_INTENSET_IN0_Pos;

}

void GPIOTE_IRQHandler(void)
{
    // Event causing the interrupt must be cleared.
    if ((NRF_GPIOTE->EVENTS_IN[0] == 1) &&
        (NRF_GPIOTE->INTENSET & GPIOTE_INTENSET_IN0_Msk))
    {
        NRF_GPIOTE->EVENTS_IN[0] = 0;
				nrf_gpio_pin_toggle(23);
				NRF_ADC->TASKS_START = 1;
    }
}

/** Configures and enables the ADC */
void ADC_init(void)
{	
/* Enable interrupt on ADC sample ready event*/		
    NRF_ADC->INTENSET = ADC_INTENSET_END_Msk;
    NVIC_EnableIRQ(ADC_IRQn);	


NRF_ADC->CONFIG	= (ADC_CONFIG_EXTREFSEL_None << ADC_CONFIG_EXTREFSEL_Pos) 										/* Bits 17..16 : No external reference. */
									| (ADC_CONFIG_PSEL_AnalogInput1 << ADC_CONFIG_PSEL_Pos)											/*!< Use analog input 1 as analog input. */
									| (ADC_CONFIG_REFSEL_SupplyOneThirdPrescaling << ADC_CONFIG_REFSEL_Pos)			/*!< Use VDD/3 */
									| (ADC_CONFIG_INPSEL_AnalogInputOneThirdPrescaling << ADC_CONFIG_INPSEL_Pos) 			/*!< Analog input specified by PSEL with 1/3 prescaling used as input for the conversion. */
									| (ADC_CONFIG_RES_8bit << ADC_CONFIG_RES_Pos);															/*!< 8 bit */

/* Enable ADC*/
NRF_ADC->ENABLE = ADC_ENABLE_ENABLE_Enabled;	
}

/* Interrupt handler for ADC data ready event */
void ADC_IRQHandler(void)
{
/* Clear dataready event */
  NRF_ADC->EVENTS_END = 0;	

  /* Write ADC result to port 1 */
 	//nrf_gpio_port_write(NRF_GPIO_PORT_SELECT_PORT1, NRF_ADC->RESULT); 
    nrf_gpio_pin_toggle(24);

    //Use the STOP task to save current. Workaround for PAN_028 rev1.2 anomaly 1.
  NRF_ADC->TASKS_STOP = 1;

    //Write result
    result = NRF_ADC->RESULT;  
}