how to resign pins in saadc example

[Cindy]

Hi 

I'm not familiar with C language, I tested the saadc example in SDK, it worked well in P0.02

But I dont see how they set CH[X].PSELP or CH[X].PSELN (V(p) and V(n)) in main.c

I dont know how to implement this code to work with other ADC pins.  

Please help me with it and correct me if I was wrong. 

I'm using nrf52 dk and segger embedded studio. 

Cindy

[ovrebekk]

Hi Cindy

These parameters can be found in the channel_config struct, which is used to initialize the ADC channel inside the saadc_init() function. 

By default this function will just use the default settings, defined by the NRFX_SAADC_DEFAULT_CHANNEL_CONFIG_SE(PIN_P) macro, but you can override the various parameters after initializing the struct if you like. 

As an example, to override the positive pin, you just run the following code: 

channel_config.pin_p = NRF_SAADC_INPUT_AIN1;

Then the full saadc_init() function would look like this:

Best regards
Torbjørn

[Cindy]

thanks, that's very helpful. but I assume the default negative pin is GND, but when I connect the GND to P0.02, it shows negative value, is that normal?

[ovrebekk]

Hi Cindy

Yes, this is quite normal. In single ended mode the full range of the ADC is actually -REF to REF, and if there is some offset error or noise you will occasionally see negative values when the input is 0V. 

Best regards
Torbjørn

[Cindy]

ovrebekk said:

Instead it should be enough to set up the TIMER, PPI and GPIOTE modules to toggle a pin when the timer overflows, and then you just change the compare value of the timer to change the frequency of the pin. 

I made an example showing how to do this a while back and I will see if I can find it, hopefully by tomorrow. 

Hi did you find the example?

Cindy

[ovrebekk]

Hi Cindy

Sorry for not getting back to you. 

I couldn't find the old example unfortunately, but it was quite simple and I should be able to create something similar shortly. I will get back to you by the end of the week with a similar example. 

Best regards
Torbjørn