nRF52840 DK lpcomp reads 0 (zero) no matter what voltage is applied to the input

[Stefan_B]

I want to use a comparator without interrupt.

The measurement is not time critical.

Therefore, I chose the LPCOMP.

For initialization I use the following code:

static void lpcomp_init(uint8_t ref)
{
    nrf_lpcomp_config_t config;
    config.reference = (nrf_lpcomp_ref_t)ref;
    config.detection = NRF_LPCOMP_DETECT_CROSS;
    config.hyst      = LPCOMP_HYST_HYST_Hyst50mV;
    // config LPCOMP, from this point LPCOMP will be active
    nrf_lpcomp_configure(&config);
    nrf_lpcomp_input_select(PIN_REGENSENSOR);

    nrf_lpcomp_enable();
}

For reading the value I use the following code:

  uint8_t  lpcomp_result;

  nrf_lpcomp_task_trigger(NRF_LPCOMP_TASK_SAMPLE); 
  lpcomp_result = (uint8_t)nrf_lpcomp_result_get();

Although the input is approximately VDD I get the value 0 back.

How can I use the LPCOMP (or COMP) without interrupts?

[ketiljo]

The LPCOMP have two inputs, VI+ and VI- where VIN. VI+ is the external input and the VI- is the reference. The comparator will give you the value 1 only if VI+ is higher than VI-. What have you configured VI- to be connected to?

https://infocenter.nordicsemi.com/topic/ps_nrf52840/lpcomp.html

[Stefan_B]

I've tried different internal values. Currently I have uint32_t ref = NRF_LPCOMP_REF_SUPPLY_1_8;

[Stefan_B]

    uint32_t ref = NRF_LPCOMP_REF_SUPPLY_1_8;
    nrf_lpcomp_config_t config;
    config.reference = (nrf_lpcomp_ref_t)ref;
    config.detection = NRF_LPCOMP_DETECT_CROSS;
    config.hyst      = LPCOMP_HYST_HYST_Hyst50mV;
    nrf_lpcomp_configure(&config);
    nrf_lpcomp_input_select(NRF_LPCOMP_INPUT_7);

    nrf_lpcomp_enable();

    while (true)
    {
      nrf_lpcomp_task_trigger(NRF_LPCOMP_TASK_SAMPLE); 
      lpcomp_result = (uint8_t)nrf_lpcomp_result_get();
      nrf_gpio_pin_write(BSP_BOARD_LED_1, lpcomp_result);
      NRF_LOG_INFO("LPcomp: %d", (int)lpcomp_result);

      NRF_LOG_FLUSH();
      nrf_delay_ms(500);
    }

[Einar Thorsrud]

Hi,

The problem here is that the LPCOMP has not been started before you try to sample. You need to call the following line once when enabling the LPCOMP:

nrf_lpcomp_task_trigger(NRF_LPCOMP_TASK_START);