Steve Wald

Important changes to forums and questions

All forums and questions are now archived. To start a new conversation or read the latest updates go to forums.mbed.com.

6 years, 3 months ago.

How can I get the implementations of ADC_VREF and ADC_TEMP?

How can I get the implementations of ADC_VREF and ADC_TEMP imported into the nRF51 library? These defines were used in the answer posted by os.mbed.com/users/rajhanssingh/ for the stm32l152re in os.mbed.com/questions/75910/How-to-get-the-value-of-inbuilt-vref-int/

Error: Identifier "ADC_VREF" is undefined in "shields/main.cpp", Line: 29, Col: 19 Error: Identifier "ADC_TEMP" is undefined in "shields/main.cpp", Line: 30, Col: 19

Steve

2 Answers

Kenji Arai
6 years, 3 months ago.

Hi Steve,
we cannot read ADC_VREF value directly on nRF51822.
So the following program measures VDD then you can compensate Vref value if you want to do it.

Import programBLE_Temp_Vdd_via_UART

Send VDD voltage data and chip temperature data via BLE UART Service. You can see the data on iPhone nRF Toolbox UART application.

Last commit 09 Aug 2018 by Kenji Arai


Please see nRF51_Vdd.cpp line35 to line49.
Input voltage sets internal Vdd/3 (CPU power line voltage).
Reference voltage sets VBG/1 (internal reference voltage (Voltage Band Gap reference) = 1.2V +/-1.2%).
Get 10bit ADC result as value name "wrk".
Then VDD = (wrk/ 1024) * 1.2 * 3.0.
If your VDD measurement value (by DVM) and above VDD are different, you can compensate 1.2V(VBG).

Temperature measurement, you can use SoftDevice function.
Please see main.cpp line120,121.

Accepted Answer

Thanks Kenji! I am sure I would never have found the sd_temp_get() function without help... where does one find the Mbed functions and/or SoftDevices available for a system peripheral? I am only slowly getting any answers from the Mbed documentation, which seems like more of a reference guide for those who know already where everything is. I got lost in the SDK versions for the several nRF51 and nRF52 devices... how does one keep them sorted? Is there a forum discussion on the docs?

posted by Steve Wald 09 Aug 2018
Karen Yen
6 years, 3 months ago.

Hi Steve,

Are you asking about internal ADC inside the nRF51? If you look in the mbed-os libary, I believe most STM boards have ADC_VREF and ADC_TEMP as pin names to the internal ADCs. I don't believe the nRF51 has internal ADC channels therefore they produce an undefined error. Let us know if you have any more questions!

-Karen, team Mbed

If this solved your question, please make sure to click the "Thanks" link below!

I pretty much figured that there is no connection for these as inputs to the ADC after getting the errors and looking again at the part documentation, but had to try. I do have more questions about configuring the ADC. Thanks for the advice.

posted by Steve Wald 09 Aug 2018