Measuring Vbat (2xAAA cell) with nRF52

RE: Measuring Vbat (2xAAA cell) with nRF52

yulya — Sun, 04 Jun 2017 06:46:04 GMT

thank you for the code info, i'll pass it to our firmware guy. My question initially was regarding hardware points. thank you for help. By the way i read the chapter on SAADC in spec before i published my question. thanks anyway. BR, Yulya

RE: Measuring Vbat (2xAAA cell) with nRF52

AmbystomaLabs — Thu, 01 Jun 2017 23:13:01 GMT

Sorry that the pagination is a little weird. Sometimes the code formats oddly on this website.

RE: Measuring Vbat (2xAAA cell) with nRF52

AmbystomaLabs — Thu, 01 Jun 2017 17:17:24 GMT

Finally this is the handler that you will trigger on an app timer to get the battery level. The callback handler is the bit above here:

static void bat_timer_handler(void * p_context)

{ UNUSED_PARAMETER(p_context); saadc_init(); nrf_drv_saadc_sample(); }

RE: Measuring Vbat (2xAAA cell) with nRF52

AmbystomaLabs — Thu, 01 Jun 2017 17:12:03 GMT

This is the handler:

volatile uint8_t state = 1;

static nrf_saadc_value_t m_buffer_pool[2][SAMPLES_IN_BUFFER];

void saadc_callback(nrf_drv_saadc_evt_t const * p_event) { uint32_t bat_level;

if (p_event->type == NRF_DRV_SAADC_EVT_DONE)
{
    ret_code_t err_code;
    err_code = nrf_drv_saadc_buffer_convert(p_event->data.done.p_buffer, SAMPLES_IN_BUFFER);
    APP_ERROR_CHECK(err_code);

    for (int i = 0; i < SAMPLES_IN_BUFFER; i++)
    {
				bat_level = p_event->data.done.p_buffer[i]>>2;
    }

//At this point your battery level is captured in bat_level. You can do whatever you want with it now

nrf_drv_saadc_uninit(); //Turns off SAADC
    NRF_SAADC->INTENCLR = (SAADC_INTENCLR_END_Clear << SAADC_INTENCLR_END_Pos);
    NVIC_ClearPendingIRQ(SAADC_IRQn);

}

RE: Measuring Vbat (2xAAA cell) with nRF52

AmbystomaLabs — Thu, 01 Jun 2017 17:10:44 GMT

Here is all the code you need to measure Vdd. It is up to you how you want to configure the app timer.

#include "nrf_drv_saadc.h"
void saadc_init(void)

{ ret_code_t err_code; nrf_saadc_channel_config_t channel_config = NRF_DRV_SAADC_DEFAULT_CHANNEL_CONFIG_SE(NRF_SAADC_INPUT_VDD); 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);

}

RE: Measuring Vbat (2xAAA cell) with nRF52

AmbystomaLabs — Thu, 01 Jun 2017 16:49:20 GMT

Here is the section of the product spec discussing the SAADC: infocenter.nordicsemi.com/index.jsp

RE: Measuring Vbat (2xAAA cell) with nRF52

yulya — Thu, 01 Jun 2017 16:49:16 GMT

HI, I didn't intend to use nFR with 1.6v operating voltage. I know the limitations. As i said we will stop system operation at 2v (there are other components that limits the operation). and i read the section about SAADC in spec.

RE: Measuring Vbat (2xAAA cell) with nRF52

AmbystomaLabs — Thu, 01 Jun 2017 16:38:23 GMT

Well, not really sure where you are looking and not finding the info.
This search alone brought up 226 answered questions on measuring battery voltage. devzone.nordicsemi.com/.../

But to answer it again, no you do not need additional hardware to measure Vdd. The SAADC can be configured through its registers to measure Vdd internally. See the nRF product spec in the SAADC section on how to configure this. The SAADC uses system voltage 1.3V as Vref. It has an internal prescaler to put voltages above Vref within its fullscale range.

With regard to operating at 1.6V, this is prohibited by the nRF. Vdd below 1.7V triggers a brownout reset. Refer to the power supply section of the nRF product spec for info on brownout behavior.

RE: Measuring Vbat (2xAAA cell) with nRF52

yulya — Thu, 01 Jun 2017 16:04:56 GMT

I did this before i published my questions! if i would find the right answer, i wouldn't ask my question. there are no dozens of answers - there are around 3 by the way.

I hope someone here can help with specific answer. thank you yulya

RE: Measuring Vbat (2xAAA cell) with nRF52

AmbystomaLabs — Thu, 01 Jun 2017 15:00:30 GMT

Just search in this blog for measuring battery voltage with saadc. There are literally dozens of answers and examples.