ADC Conversion Value - CC2530

I am trying to measure some off-chip voltage. I have already done the test you suggested. I used two different devices and a power supply. For the same voltage they gave me different values. For example: for 0.9V one gave me 2570 and the other gave me 2717 14-bits resolution). I think there's a sort of reference voltage that i don't know how to correct it. I think ADC is using the Vdd voltage as reference, but the Vdd can change for one device to another and so the value of Adc. What do you think I should do?

Hi Victor,

do you solve the problem of precision with a stable Vref?

I'm doing some test with CC2530 and the internal 12-bit ADC but the results are very poor..

I use a very high precision Vref of 2500mV in P0_7 and I do a 12bit conversion as in the hal_adc.c file, but the result are very different from the multimeter measure.

I set the input voltage from 0 to 2500mV and I read the ADC value, but the ADC have a drift from -10mV to 10,15mV after 1995mV from the real value!!

What do you think I should do?

thank you

Emanuele

Hello,

I am using CC2530 with CCdebugger and cc22531 usb dongle and IAR 8051 as IDE.

Based on the code in sensors demo I am trying to use the adc to read the voltage

My question is how to check the read value of the adc, how can I see if I got a plausible value or not.

Hi Filippo,

You can use a power supply to give a fix voltage, for examples 2.4V and measure it from ADC input. Convert and see if result is correct .

Many thanks.

I was wondering if there is a way to visualize that data directly on the PC.

Hi Filippo,

If you connect the coordinator to PC by UART, you can sent ADC reading to coordinator and coordinator send it to PC by UART . then, you can show it on OC.

Hello,

I'm testing the ADC, using HAL ADC api, with an external thermistor.

I connected the output of the voltage divider (thermistor and resistor) as input of the P0.5 and code as follow:

ADCIF = 0;

ADCCON3 = (HAL_ADC_REF_125V | HAL_ADC_DEC_128 | HAL_ADC_CHN_AIN5);
while ( !ADCIF );

/* Get the result */
value = ADCL;
value |= ((uint16) ADCH) << 8;
value;

when I watch the "value" in debugging session I got the same value every time (ADCL=252), no matter what appen to the thermistor.

 what's wrong?

Regards,

Filippo

Hi Filippo,

Why don't you use HalAdcSetReference and HalAdcRead APIs in hal_adc.c ?

I extracted that code from the simple app in Zstack and working based on that.

I supposed that work as well.

Could I ask you if you have some sample for that?

Thanks for your help, anyway.

Hi filippo,

If I remember correctly, your code should be revised as the followings:

ADCCON3 = (HAL_ADC_REF_125V | HAL_ADC_DEC_128 | HAL_ADC_CHN_AIN5);

 while (!(ADCCON1 & HAL_ADC_EOC));

reading = (int16) (ADCL);

reading |= (int16) (ADCH << 8);  

Hi,

in the HAL_ADC I took form Zstack (for cc2530) there is not decleration of HAL_ADC_EOC

In the HAL_adc.c file, I add as follow:

#define HAL_ADC_EOC         0x80    /* End of Conversion bit */

I tried that code, but still I got the same data.

I check with the multimeter the voltage at P0.5 pin, and it follows the thermistor.

You mention a resistor divider before going into the ADC.  Can you tell us the impedance of the divider?  It may be too high compared to the ADC impedance.  When the ADC is off it may be fine and that could explain why you see a correct voltage at P0.5 pin.

BK

it's a divider with a 16k and a thermistor of 10K

Ok that impedance sounds fine as the ADC impedance is ~174k. 

What voltage is the thermistor connected to and what voltage to you see at P05 around room temp?

BK

the voltage divider is connected at Vcc (about 3.2V) and the thermistor is connected to the out of the divider and the ground, having a voltage about 1.7V at room temperature, that is the same voltage as P0.5 input

Ok, I think that explains it.  The ADC input can not exceed the reference voltage to the ADC.  I believe you have selected the 1.25V reference voltage so you will have to configure the divider such that you do not exceed that.

For a quick sanity check that this is the issue, can you try switching the reference to be AVDD5?

BK

Thanks.

I connected P0.7 to VDD and code as follow:

ADCIF = 0;
ADCCON3 = (HAL_ADC_REF_AIN7 | HAL_ADC_DEC_128 | HAL_ADC_CHN_AIN5);

/* Wait for the conversion to finish */
while (!(ADCCON1 & HAL_ADC_EOC));

/* Get the result */
value = ADCL;
value |= ((uint16) ADCH) << 8;

It seems to have different data from time to time. I will check if the value I got it is the right one.