The Problem with SAADC Using RTC

[Jack Alex]

Hi, everyone,

I am pretty new to nRF52 development. Right now, I have an issue with the SAADC trigger by RTC, which I follow this example. The issue that I have right now is that it only works when I use the programmer to power it, which is a DAP Link programmer. If I power it with CR2032, it draws 5 mA and not advertise itself. It only draws 0.5 mA if I do not initialize the SAADC. It is still not working even I plug it back to the programmer to power it. I have to uncomment the lfclk_config() and rtc_config. Also, in the example, it calls saadc_init() in the main function. In my case, it doesn't work if I do that.

  

// My main function
    bool erase_bonds;

    // Initialize.
    saadc_init();
    log_init();
    timers_init();
    gpio_config();
    //lfclk_config();                                  //Configure low frequency 32kHz clock
    //rtc_config();                                    //Configure RTC. The RTC will generate periodic interrupts. Requires 32kHz clock to operate.

    power_management_init();
    ble_stack_init();
    gap_params_init();
    gatt_init();
    services_init();
    advertising_init();

    //saadc_init();





//    #ifdef UART_PRINTING_ENABLED
//    uint32_t err_code = NRF_LOG_INIT(NULL);
//    APP_ERROR_CHECK(err_code);                       //Configure Logging. LOGGING is used to show the SAADC sampled result. Default is UART, but RTT can be configured in sdk_config.h
//    NRF_LOG_DEFAULT_BACKENDS_INIT();
//    NRF_LOG_INFO("\n\rSAADC Low Power Example.\r\n");	
//#endif //UART_PRINTING_ENABLED	
//    
//#ifdef UART_PRINTING_ENABLED
//                                       //Configure UART. UART is used to show the SAADC sampled result.
//    NRF_LOG_INFO("\n\rSAADC HAL simple example.\r\n");	
//#endif //UART_PRINTING_ENABLED	

    // Start execution.
    NRF_LOG_INFO("started.");
    application_timers_start();
    advertising_start(erase_bonds);

    // Enter main loop.
    for (;;)
    {
        idle_state_handle();
    }

Thank you in advance

Jack

[Jared]

Hi,

Are you using a custom board?

Does it work if you replace the coin battery with a bench-top supply?

regards

Jared 

[Jack Alex]

Thank you for the reply, Jared!

I am using red bear nano v2, and the DAP Link is from Particle. Yes, I did replace the battery, but it still draws 5mA and not advertise, which is abnormal. I guess it might work with a lab bench supply because it works if it is powered by the programmer, but I need to use the coin cell battery as the power source for my project.

[Jared]

Hi,

The Low power example that you're referring to has been tested on the Development kit. The red bear nano v2 is an external board and my guess is that the issue is tied to that specific board. What do you measure on VDD when you supply it from the coin cell battery? Could you provide a schematic of the board?

[Jack Alex]

Hi,

The VDD is 3.25V, and this is the product info for the RedBear Nano V2.

[Jack Alex]

Thank you again Jared!

I finally get the code to work, It seems like I need to call nrf_drv_rtc_enable(&rtc) in the rtc_config() in the main function before advertising_start() function.