Chapter 2. API Reference
Application Extensions
For a full example see esp-idf: peripherals/adc/single_read
Characterizing an ADC at a particular attenuation:
#include "driver/adc.h"
#include "esp_adc_cal.h"
...
//Characterize ADC at particular atten
esp_adc_cal_characteristics_t *adc_chars = calloc(1, sizeof(esp_adc_cal_
,→characteristics_t));
esp_adc_cal_value_t val_type = esp_adc_cal_characterize(unit, atten, ADC_WIDTH_
,→BIT_12, DEFAULT_VREF, adc_chars);
//Check type of calibration value used to characterize ADC
if (val_type == ESP_ADC_CAL_VAL_EFUSE_VREF) {
printf("eFuse Vref");
} else if (val_type == ESP_ADC_CAL_VAL_EFUSE_TP) {
printf("Two Point");
} else {
printf("Default");
}
Reading an ADC then converting the reading to a voltage:
#include "driver/adc.h"
#include "esp_adc_cal.h"
...
uint32_t reading = adc1_get_raw(ADC1_CHANNEL_5);
uint32_t voltage = esp_adc_cal_raw_to_voltage(reading, adc_chars);
Routing ADC reference voltage to GPIO, so it can be manually measured (for Default Vref):
#include "driver/adc.h"
...
esp_err_t status = adc_vref_to_gpio(ADC_UNIT_1, GPIO_NUM_25);
if (status == ESP_OK) {
printf("v_ref routed to GPIO\n");
} else {
printf("failed to route v_ref\n");
}
GPIO Lookup Macros
There are macros available to specify the GPIO number of a ADC channel, or vice versa. e.g.
1. ADC1_CHANNEL_0_GPIO_NUM is the GPIO number of ADC1 channel 0.
2. ADC1_GPIOn_CHANNEL is the ADC1 channel number of GPIO n.
API Reference
This reference covers three components:
• ADC driver
• ADC Calibration
• GPIO Lookup Macros
Espressif Systems 217
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