cc2538 ADC output interpretation

Vasanth,

how do you read the ADC result?

Hi Dennis Thanks for the reply. I am using contiki's built in function to read the ADC output; Which is as follows:

int temperature = temperature_sensor.value(0);



/*---------------------------------------------------------------------------*/
void
adc_init(void)
{
/* Start conversions only manually */
REG(SOC_ADC_ADCCON1) |= SOC_ADC_ADCCON1_STSEL;
}
/*---------------------------------------------------------------------------*/
int16_t
adc_get(uint8_t channel, uint8_t ref, uint8_t div)
{
uint32_t cctest_tr0, rfcore_xreg_atest;
int16_t res;

/* On-chip temperature sensor */
if(channel == SOC_ADC_ADCCON_CH_TEMP) {
/* Connect the temperature sensor to the ADC */
cctest_tr0 = REG(CCTEST_TR0);
REG(CCTEST_TR0) = cctest_tr0 | CCTEST_TR0_ADCTM;

/* Enable the temperature sensor */
rfcore_xreg_atest = REG(RFCORE_XREG_ATEST);
REG(RFCORE_XREG_ATEST) = (rfcore_xreg_atest & ~RFCORE_XREG_ATEST_ATEST_CTRL) |
RFCORE_XREG_ATEST_ATEST_CTRL_TEMP;
}

/* Start a single extra conversion with the given parameters */
REG(SOC_ADC_ADCCON3) = (REG(SOC_ADC_ADCCON3) &
~(SOC_ADC_ADCCON3_EREF | SOC_ADC_ADCCON3_EDIV | SOC_ADC_ADCCON3_ECH)) |
ref | div | channel;

/* Poll until end of conversion */
while(!(REG(SOC_ADC_ADCCON1) & SOC_ADC_ADCCON1_EOC));

/* Read conversion result, reading SOC_ADC_ADCH last to clear
* SOC_ADC_ADCCON1.EOC */
res = REG(SOC_ADC_ADCL) & 0xfc;
res |= REG(SOC_ADC_ADCH) << 8;

/* On-chip temperature sensor */
if(channel == SOC_ADC_ADCCON_CH_TEMP) {
/* Restore the initial temperature sensor state and connection (better for
* power consumption) */
REG(RFCORE_XREG_ATEST) = rfcore_xreg_atest;
REG(CCTEST_TR0) = cctest_tr0;
}

/* Return conversion result */
return res;
}

Hi,

Your post has been moved to the ZigBee®, 6LoWPAN & 802.15.4 MAC Forum as I believe they should be able to provide you with the information that you need.

Thanks,

David

Battery voltage monitor can be implemented by using internal A/D. Please refer to section 15.2.1of CC2538 UG (SWRU319C)

Hi YK Chen,
Thanks for your reply. I will try out the example and share the out come.

You are welcome.

Hi YiKai,

The examples are very helpful and  It had the formula to calculate the temperature.  However the sensor reading is much higher than my room temperature.

My room temperature is :  76F  24.44C

The sensor reads:   88.76F  31.534C

The sensor temperature goes down if I take it near to a AC vent. However there is a discrepancy. Does it need any offsetting?

Thanks,
Vasanth

Yes, it needs to do calibration.

hi Vasanth,
how to convert the adc value to voltage ?
now i call adc_get(0x07,0<<6 , 3<<4) function read the adc value is 32764

hi vasanth,
i call the function:adc_get(0x7,0<<6,3<<4) the adc value is 32764 , how to convert it to voltage value?