convert ADC readings
Posted: Fri Nov 03, 2017 2:04 am
Hi,
I'm trying to measure input voltage by adc1 in range 0 - 3,3 V.
This is how I expected to convert raw values to voltage:
adc_input_voltage = (Vref * adc_RAW ) / 4096
and here is part code & settings:
My conversion is not correct. I studied https://github.com/espressif/esp-idf/bl ... iver/adc.h and was confused with ADC_ATTEN_DB_11 options:
1.
1) does this value will be reduced by 1/3,6 as noted in first note? So, actual input voltage would be decreased to 0,208 V to be able compare it with Vref (which is 1,0 ... 1,1 V)?
2) actual full scale would be 0 ... 3,3 V for ADC_ATTEN_11db option? Can I use formula that I mentioned at start and assume Vref = 3,3 ?
3) how can I calculate adc voltage without using adc1_to_voltage function?
I'm trying to measure input voltage by adc1 in range 0 - 3,3 V.
This is how I expected to convert raw values to voltage:
adc_input_voltage = (Vref * adc_RAW ) / 4096
and here is part code & settings:
Code: Select all
float convert_adc_to_voltage(uint32_t adc_val)
{
float adc_volt = (3.3 * adc_val) / 4096;
return adc_volt;
}
void adc_task(void *pvParameter)
{
// initialize ADC
adc1_config_width(ADC_WIDTH_12Bit);
adc1_config_channel_atten(ADC_CHANNEL,ADC_ATTEN_11db);
uint32_t adc_value;
float adc_voltage;
while(1)
{
adc_value = adc1_get_raw((ADC_CHANNEL));
adc_voltage = convert_adc_to_voltage(adc_value);
printf("ADC(GPIO34):%d(raw), %.3f (V)\n",adc_value, adc_voltage);
vTaskDelay(1000/portTICK_PERIOD_MS);
// output example (real input voltage is 0,75V):
// ADC(GPIO34):724(raw), 0.583 (V)
// ADC(GPIO34):726(raw), 0.585 (V)
}
}My conversion is not correct. I studied https://github.com/espressif/esp-idf/bl ... iver/adc.h and was confused with ADC_ATTEN_DB_11 options:
1.
2.input voltage of ADC will be reduced to about 1/3.6
3.(ADC_ATTEN_11db) gives full-scale voltage 3.9V
Let say, I set 0,75 V to adc pin as I tried before.11dB attenuation the maximum voltage is limited by VDD_A, not the full scale voltage
1) does this value will be reduced by 1/3,6 as noted in first note? So, actual input voltage would be decreased to 0,208 V to be able compare it with Vref (which is 1,0 ... 1,1 V)?
2) actual full scale would be 0 ... 3,3 V for ADC_ATTEN_11db option? Can I use formula that I mentioned at start and assume Vref = 3,3 ?
3) how can I calculate adc voltage without using adc1_to_voltage function?