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ADC

Remover o jumper no pino 34 (ADC1_CH6) ao gravar

Funcionality

  • ADC1 (8 channels, attached to GPIOs 32 - 39)
  • ADC2 used within wi-fi module

unit work modes

  • ADC-RTC
  • ADC-DMA mode

ADC-RTC

configured before reading

  • adc1_config_width() precision

    max resolution 12bits)

  • adc1_config_channel_atten() attenuation

    attenuation: This is a voltage scaling factor. By default, the allowable input range is 0-1V but with different attenuations we can scale the input voltage into this range. The available scales beyond the 0-1V include 0-1.34V, 0-2V and 0-3.6V.

    (tipo avr/arduino)

  • adc1_get_raw() conversion result

  • adc_vref_to_gpio() used to route internal reference voltage to a GPIO pin

    calibrate ADC reading

Minimizing Noise

Higher precision approach.

connect a 0.1uF capacitor to the ADC input pad in use

Calibration

The esp_adc_cal/include/esp_adc_cal.h API provides functions to correct for differences in measured voltages caused by variation of ADC reference voltages (Vref) between chips

characterizing one of the ADCs at a given attenuation to obtain a characteristics curve (ADC-Voltage curve) that takes into account the difference in ADC reference voltage. The characteristics curve is in the form of y = coeff_a * x + coeff_b and is used to convert ADC readings to voltages in mV

calibrations values stored in eFuse or provided by the user

Three sources of calibration values

  • Two Point values represent each of the ADCs’ readings at 150 mV and 850 mV. To obtain more accurate calibration results these values should be measured by user and burned into eFuse BLOCK3.

  • eFuse Vref represents the true ADC reference voltage. This value is measured and burned into eFuse BLOCK0 during factory calibration.

  • Default Vref is an estimate of the ADC reference voltage provided by the user as a parameter during characterization. If Two Point or eFuse Vref values are unavailable, Default Vref will be used.