ADC Conversion using 4096Hz for nRF52832 Chip?

[vishal]

Hello Sir,

We are using nRF52832 chip and Softdevice is S132. Is it possible to sample an analog signal using internal ADC conversion using 4096Hz?. Its look like it does at 3900Hz.

Thanks in Advance..

[Jørgen Holmefjord]

Hi,

If you trigger sampling through PPI on an RTC event, it should be possible to achieve 4096 Hz. The RTC runs at 32.768 kHz, and a CC value of 8 should give you your desired frequency. If you are triggering sampling from interrupt event, the softdevice might delay sampling if higher priority events occurs, giving you a lower sample rate than expected.

Note this issue if you are triggering sampling through PPI, and have multiple SAADC channels enabled.

[EDIT]: Added main.c file that implements sampling triggered by RTC over PPI in ble_app_uart__saadc_timer_driven__scan_mode example: main.c

Best regards,

Jørgen

[vishal]

Hi sir, I trigger sample through PPI on an RTC, but it achieved 3900Hz. The following have my program function in saadc sampling event init:

nrf_drv_timer_config_t timer_config = NRF_DRV_TIMER_DEFAULT_CONFIG;
timer_config.frequency = NRF_TIMER_FREQ_31250Hz;
err_code = nrf_drv_timer_init(&m_timer, &timer_config, timer_handler);
APP_ERROR_CHECK(err_code);
/* setup m_timer for compare event */
uint32_t ticks = nrf_drv_timer_us_to_ticks(&m_timer,SAADC_SAMPLE_RATE);
nrf_drv_timer_extended_compare(&m_timer, NRF_TIMER_CC_CHANNEL0, ticks, NRF_TIMER_SHORT_COMPARE0_CLEAR_MASK, false);
nrf_drv_timer_enable(&m_timer);

uint32_t timer_compare_event_addr = nrf_drv_timer_compare_event_address_get(&m_timer, NRF_TIMER_CC_CHANNEL0);

and in this function CC value is as per the following: Sampling Rate = 256us

m_timer = NRF_DRV_TIMER_INSTANCE(3);

[vishal]

Please sir tell me what should i do for achieving 4096Hz sampling frequency. you told me set CC value is 8, but my cc value is microsecond you said me this value is millisecond or other.

Thanks for your suggestion.

[Jørgen Holmefjord]

You are not using RTC in that code, you are using TIMER peripheral. Please have a look at this example on how to use RTC and PPI for triggering SAADC sampling. If you set the symbol RTC_FREQUENCY in main.c to 32768, the example should sample at 4096 Hz. Note that you should increase the calibration interval, or disable calibration for such a high sample rate.

[vishal]

Thanks sir for you valuable suggestion.. I changes in my program as per the given in above example using RTC. but now problem coming is when i upload this new program my board is not advertising. So i am unable to connect. I am using ble_app_uart__saadc_timer_driven__scan_mode this example. Can you tell me where exactly i need to change for RTC. Thanks....