Configure sampling rate for nrf5340 SAADC

[jala]

I'm working on the nrf5340 with a modified sample found here (main.c of the base sample here) and nrf connect sdk 1.7.1

I see that adc_sequence_options .interval_us can set the time between samples in microseconds, so I tried to use that to set my sampling rate like so:

const struct adc_sequence_options sequence_opts = {
	.interval_us = 17, // 17 us between 1000 samples
	.callback = NULL,
	.user_data = NULL,
	.extra_samplings = BUFFER_SIZE - 1,
};

, but the board prints Error in adc sampling: -16.

Is there a way to either resolve my interval_us bug or another way to configure the sampling rate?

Thanks

[ChrtistophAT]

Hi Edvin,

didnt know about the small amount of reference voltages you can choose, I believe I one time saw some mor like real VDD and simple Gain 1. Anyway saw now the 

https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/nrfx/drivers/saadc/hal.html?highlight=nrf_saadc_reference#c.nrf_saadc_reference_t

right way how to do 

and now everything is fine -> 512 when 2.5V applied by 10bit resolution.

-22 failer code when wrong ADC_REF was selected. Sorry for writing in this -6 ticket.

Edvin said:

What are you trying to implement?

I have some dry muscel signal sensor, which is amplifying and filtering the signal with reference to 2.5V (VCC/2) from the PCB. For purpose of powerline noise 50Hz, I would like to ADC the amplified signal from the sensor and transfer through bluetooth package.

Questions:

adc mode single or differential to 2.5V reference?

do I have to use ADC/driver lib for this fast sampling (15-20us)?

exists some better example like the one I am struggling around?

ChrtistophAT said:

github.com/.../quote]

Unfortunately ther is no example/peripheral/ saadc in the sdk connect 1.9.1

Thank you for your advice in advance,

Christoph

[Edvin]

ChrtistophAT said:

Unfortunately ther is no example/peripheral/ saadc in the sdk connect 1.9.1

Not that I am aware of. 

I suggest that you take a quick peek at the nRF5 SDK\examples\peripheral\saadc, to familiarize yourself with how the ADC works, and then you can use the nrfx driver ADC instead of the zephyr implementation. This way you should be able to get a higher sample rate.

But again, for further questions, please open a new ticket. 

BR,

Edvin

[ChrtistophAT]

Thank you very much Edvin!