Simple analog read on nrf52

[Remo]

Hello. How i can do a simple read an 0 -> 3 Volt (vdd) signal on Analog 0 P0.03? I try it with saadc without sucess

            int result = 0;
		
			NRF_SAADC->CH[0].CONFIG = (
						SAADC_CH_PSELN_PSELN_AnalogInput0 << SAADC_CH_CONFIG_BURST_Pos |
						SAADC_CH_CONFIG_BURST_Enabled << SAADC_CH_CONFIG_BURST_Pos |
						SAADC_CH_CONFIG_MODE_SE << SAADC_CH_CONFIG_MODE_Pos |
						SAADC_CH_CONFIG_TACQ_10us << SAADC_CH_CONFIG_TACQ_Pos |
						SAADC_CH_CONFIG_REFSEL_Internal << SAADC_CH_CONFIG_TACQ_Pos |
						SAADC_CH_CONFIG_GAIN_Gain1_5 << SAADC_CH_CONFIG_GAIN_Pos |
						SAADC_CH_CONFIG_RESN_Bypass << SAADC_CH_CONFIG_RESN_Pos |
						SAADC_CH_CONFIG_RESP_Bypass << SAADC_CH_CONFIG_RESP_Pos );

			NRF_SAADC->CH[0].PSELP = SAADC_CH_PSELP_PSELP_VDD;
			NRF_SAADC->CH[0].PSELN = SAADC_CH_PSELN_PSELN_NC;
		
			// Configure the SAADC resolution.
			NRF_SAADC->RESOLUTION = SAADC_RESOLUTION_VAL_14bit << SAADC_RESOLUTION_VAL_Pos;
			NRF_SAADC->OVERSAMPLE = SAADC_OVERSAMPLE_OVERSAMPLE_Over256x << SAADC_OVERSAMPLE_OVERSAMPLE_Pos;

			//Setup memory location
			NRF_SAADC->RESULT.PTR = (uint32_t)&result;

			// No automatic sampling, will trigger with TASKS_SAMPLE.
			NRF_SAADC->SAMPLERATE = SAADC_SAMPLERATE_MODE_Task << SAADC_SAMPLERATE_MODE_Pos;

			// Enable SAADC (would capture analog pins if they were used in CH[0].PSELP)
			NRF_SAADC->ENABLE = SAADC_ENABLE_ENABLE_Enabled << SAADC_ENABLE_ENABLE_Pos;

[Jørgen Holmefjord]

Hi,

You can find an example of a simple read using the SAADC on the NordicSnippets GitHub page.

If you want to use the SAADC driver, included in the SDK, you can find a simple example in this thead.

Best regards,

Jørgen

[Jørgen Holmefjord]

You are correct. The example is set to a resolution of 14 bits, and measures the VDD voltage of the board. You can change which pin is measured on line 22. The SAADC result is converted to voltage and stored in the variable precise_result.

[Rabe]

Excuse me Jorgen, I used that simple code from NordicSnippets GitHub page with saadc project as background to compile and when I start the program with Segger I always get 0 as result. Any idea? Would I have to change something from sdk_config.h? I would like to read the battery level of my DK PCA10040. Thanks

[Jørgen Holmefjord]

Hard to know what you have done without seeing your code. Please post a new question where you described your steps and post the code/project. That way we can help you debug the issue.

[Rabe]

It's already fixed. Thanks

[BelvitaSoft]

Hi guys, I have the same problem - I got zero when I try to print the variable precise_result. I measure a pin 3 (A0) with voltage divider that output voltage is equal to 2.7 V. It is also confused for me that it is printed only twice, although it is in while loop.

Any advice about solving this problem? Rabe Jørgen @restoftheworld

Best regards :) 

[BelvitaSoft]

Ok, I also solved the problem. Pin Analog A0 is defined as P02 on the development kit, although on the bottom of the board is written that pin P3 in A0. I changed the connection and it works.