difference value of mbed analog read and keil adc

RE: difference value of mbed analog read and keil adc

Anders Strand — Thu, 17 Dec 2015 11:48:53 GMT

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RE: difference value of mbed analog read and keil adc

FormerMember — Thu, 17 Dec 2015 02:07:45 GMT

Thank you :) I have a question, I am using servo motor with BLE. So I set data written interrupt from smart phone, and trying control servo in interrupt callback. The problem is servo didn't work.. Is this problem matched with what you tell me?

Therefore I put the flag in written callback, control servo motor in while() in main(), and it works.

RE: difference value of mbed analog read and keil adc

Anders Strand — Wed, 16 Dec 2015 09:47:40 GMT

Be careful when executing code withing an interrupt with priority NRF_APP_PRIORITY_HIGH. Long operations like printf should be avoided as it can impact BLE performance. This will not solve your problem, but is just a general tip :)

RE: difference value of mbed analog read and keil adc

FormerMember — Wed, 16 Dec 2015 04:53:00 GMT

Thank you, It works!

RE: difference value of mbed analog read and keil adc

monpetit — Wed, 16 Dec 2015 02:56:43 GMT

Because of the difference of the ADC reference. The mbed ADC API uses NRF_ADC_CONFIG_REF_SUPPLY_ONE_THIRD(1/3 of power supply) as a reference, and your adc_config() uses the default configuration of nRF5x SDK(1.2 V reference). Check the values of NRF_ADC_CONFIG_DEFAULT and void analogin_init(analogin_t *obj, PinName pin) of the mbed ADC API.

nrf_adc.h (nRF5x SDK):

/** Default ADC configuration. */
#define NRF_ADC_CONFIG_DEFAULT { NRF_ADC_CONFIG_RES_10BIT, \
				 NRF_ADC_CONFIG_SCALING_INPUT_ONE_THIRD,   \
				 NRF_ADC_CONFIG_REF_VBG }

analogin_api.c (mbed):

void analogin_init(analogin_t *obj, PinName pin)
{
    ...
    NRF_ADC->CONFIG = (ADC_CONFIG_RES_10bit << ADC_CONFIG_RES_Pos) |
                      (ADC_CONFIG_INPSEL_AnalogInputOneThirdPrescaling << ADC_CONFIG_INPSEL_Pos) |
                      (ADC_CONFIG_REFSEL_SupplyOneThirdPrescaling << ADC_CONFIG_REFSEL_Pos) |
                      (analogInputPin << ADC_CONFIG_PSEL_Pos) |
                      (ADC_CONFIG_EXTREFSEL_None << ADC_CONFIG_EXTREFSEL_Pos);
}