nrf52840 saadc ladder 160k resistors

[Oleg]

hi Engineers! I am trying to use int. pullup of 160k but no effect. the voltage remains zero on pin.

config.resistor_p = NRF_SAADC_RESISTOR_PULLUP;

what problem?

thx.

[Jørn]

Hi, could you post your saadc init function? As well as your config initialization?

[Oleg]

Hi dear J0rn, if I use nrf_gpio_cfg_input(2, NRF_GPIO_PIN_PULLDOWN) (it is ADC0) it works, but 13K too much for me.

// CODE:

void saadc_init(void)
{
    ret_code_t err_code;

    // nrf_gpio_cfg_input(2, NRF_GPIO_PIN_PULLDOWN); // < IT WORKS (13K Resistor)

    nrf_saadc_channel_config_t channel_config =
        NRF_DRV_SAADC_DEFAULT_CHANNEL_CONFIG_SE(NRF_SAADC_INPUT_AIN0);

    channel_config.resistor_p 	= NRF_SAADC_RESISTOR_PULLUP; // < 160K NOT Connected !!!
    channel_config.pin_n 		= NRF_SAADC_INPUT_DISABLED;
    channel_config.reference 	= NRF_SAADC_REFERENCE_INTERNAL;//NRF_SAADC_REFERENCE_VDD4;

    err_code = nrf_drv_saadc_init(NULL, saadc_callback);
    APP_ERROR_CHECK(err_code);

    err_code = nrf_drv_saadc_channel_init(0, &channel_config);
    APP_ERROR_CHECK(err_code);

    err_code = nrf_drv_saadc_buffer_convert(m_buffer_pool[0], SAMPLES_IN_BUFFER);
    APP_ERROR_CHECK(err_code);

    err_code = nrf_drv_saadc_buffer_convert(m_buffer_pool[1], SAMPLES_IN_BUFFER);
    APP_ERROR_CHECK(err_code);
}

[Oleg]

added code

[Jørn]

Do you measure the voltage during sampling or when not sampling?

[Oleg]

just do read ADC value. with or without no difference.