ADC Sampling with Softdevice

RE: ADC Sampling with Softdevice

Jørgen Holmefjord — Wed, 26 Apr 2017 07:45:20 GMT

@xonano, you can take a look at the proximity example in SDK 13. This example use the SAADC to measure the battery voltage. You should be able to extend it to more channels and higher sample rate. I will also be porting the examples on GitHub to SDK 13 as soon as I got time.

RE: ADC Sampling with Softdevice

XOnano Smartfoam — Wed, 26 Apr 2017 05:07:27 GMT

@Jorgen, is there any example code that could be used with the nRF52840 with softdevice 140? I am interested in testing the sampling rate on up to 8 ADC channels on the development kit. Any help would be much appreciated!

RE: ADC Sampling with Softdevice

Jørgen Holmefjord — Fri, 21 Apr 2017 13:07:55 GMT

There is no way to calculate this exact for your application, as it will depend on many factors. You should get at least 2 kHz with one channel. If using PPI and a timer to trigger the ADC sampling, you should be able to get beyond your requirements. There are some examples available in this GitHub repo. You will have to try it out to see what the maximum sampling rate for your application is.

RE: ADC Sampling with Softdevice

dev_000 — Thu, 20 Apr 2017 14:29:41 GMT

Thanks for that file. I am using S110 V8.

RE: ADC Sampling with Softdevice

Jørgen Holmefjord — Thu, 20 Apr 2017 13:05:42 GMT

Are you using S110 or S130 softdevice, and which version are you using?

The sampling should not be limited on the nRF52840, but you will have to handle the samples in some way when your buffers are filled.
I think you are looking for the nRF51 series Reference manual.

RE: ADC Sampling with Softdevice

dev_000 — Wed, 19 Apr 2017 17:41:11 GMT

@Jorgen Thanks. I haven't tested it out yet. Still in design phase. Hence wanted to know which platform to use before jumping in.

Can I know how 2-8KHz is calculated? I saw this link and Pg 41 of S110 SD Specification V2.0 but I still unclear how those actual numbers came about.
I am assuming the above sampling limitation wont there for nRF52480 because of Easy DMA transfer?
Is there a better product datasheet for nRF51822 than this? I am not seeing enough details on it as compared to lets say, objective product specification sheet v0.5 of nRF52480, which explains the subystems in great detail. Am I looking at the wrong files of NRF51822?

RE: ADC Sampling with Softdevice

Jørgen Holmefjord — Wed, 19 Apr 2017 12:18:59 GMT

Hi,

Have you tested this with your own application? As Stefan mentioned in the 3rd post you linked:

If you use softdevice and have 3rd revision nRF51, you can obtain sampling frequency approximately 2-8 kHz, depending on how much data you send over the air.

Your data requirements does not look that high, that you should not be able to maintain the sample rate you desire. Here is an example that you can try if you want a ready-made example.

The nRF52840 PDK (or nRF52 DK) would be a better choice, as it has a faster SAADC peripheral and support for EasyDMA, allowing you to continue sampling directly to RAM, while BLE activity is going on.

Best regards,

Jørgen