88b05f9391
Added component containg API that is able to correct raw ADC readings into a voltage in mV. Also provided a helper function that combines the process of getting the raw ADC1 reading then converting it to a voltage in mV. In doing so, the adc1_get_voltage() function of the ADC driver has been deprecated. Instead there is now adc1_get_raw to obtain the raw ADC1 reading, and adc1_to_voltage() that gets the raw reading and converts all in one function. Functions using the deprecated adc1_get_voltage() have also been updated to use adc1_get_raw(). Conversion is based on ADC characteristics. The characteristics are based on the ADC's v_ref, herefore the appropriate structure and functions have been provided to obtain the ADC characteristics. The existing ADC driver has also been modified by adding a function to route the internal ADC reference voltage to a GPIO allowing users to measure it manually. Relevant documentation has also been updated
102 lines
3.2 KiB
ReStructuredText
102 lines
3.2 KiB
ReStructuredText
Analog to Digital Converter
|
||
===========================
|
||
|
||
Overview
|
||
--------
|
||
|
||
ESP32 integrates two 12-bit SAR ("Successive Approximation Register") ADCs (Analog to Digital Converters) and supports measurements on 18 channels (analog enabled pins). Some of these pins can be used to build a programmable gain amplifier which is used for the measurement of small
|
||
analog signals.
|
||
|
||
The ADC driver API currently only supports ADC1 (9 channels, attached to GPIOs 32-39).
|
||
|
||
Taking an ADC reading involves configuring the ADC with the desired precision and attentuation settings, and then calling adc1_get_raw() to read the channel.
|
||
|
||
It is also possible to read the internal hall effect sensor via ADC1.
|
||
|
||
Application Example
|
||
-------------------
|
||
|
||
A full example using the ADC driver and the esp_adc_cal is available in esp-idf: :example:`peripherals/adc`
|
||
|
||
Reading voltage on ADC1 channel 0 (GPIO 36)::
|
||
|
||
#include <driver/adc.h>
|
||
|
||
...
|
||
|
||
adc1_config_width(ADC_WIDTH_12Bit);
|
||
adc1_config_channel_atten(ADC1_CHANNEL_0,ADC_ATTEN_0db);
|
||
int val = adc1_get_raw(ADC1_CHANNEL_0);
|
||
|
||
Reading the internal hall effect sensor::
|
||
|
||
#include <driver/adc.h>
|
||
|
||
...
|
||
|
||
adc1_config_width(ADC_WIDTH_12Bit);
|
||
int val = hall_sensor_read();
|
||
|
||
The value read in both these examples is 12 bits wide (range 0-4095).
|
||
|
||
API Reference
|
||
-------------
|
||
|
||
.. include:: /_build/inc/adc.inc
|
||
|
||
|
||
ADC Calibration
|
||
===============
|
||
|
||
Overview
|
||
--------
|
||
The esp_adc_cal API provides functions to correct for differences in measured voltages caused by non-ideal ADC reference voltages in ESP32s. The ideal ADC reference voltage is 1100mV however the reference voltage of different ESP32s can range from 1000mV to 1200mV.
|
||
|
||
Correcting the measured voltage using the esp_adc_cal API involves referencing a lookup table of voltages. The voltage obtained from the lookup table is the scaled and shifted by a gain and offset factor that is based on the ADC's reference voltage.
|
||
|
||
The reference voltage of the ADCs can be routed to certain GPIOs and measured manually using the ADC driver’s adc2_vref_to_gpio() function.
|
||
|
||
Application Example
|
||
-------------------
|
||
|
||
Reading the ADC and obtaining a result in mV::
|
||
|
||
#include <driver/adc.h>
|
||
#include <esp_adc_cal.h>
|
||
|
||
...
|
||
#define V_REF 1100 //ADC reference voltage
|
||
|
||
//Config ADC and characteristics
|
||
adc1_config_width(ADC_WIDTH_12Bit);
|
||
adc1_config_channel_atten(ADC1_CHANNEL_6, ADC_ATTEN_11db);
|
||
|
||
//Calculate ADC characteristics i.e. gain and offset factors
|
||
esp_adc_cal_characteristics_t characteristics;
|
||
esp_adc_cal_get_characteristics(V_REF, ADC_ATTEN_11db, ADC_WIDTH_12Bit, &characteristics);
|
||
|
||
//Read ADC and obtain result in mV
|
||
uint32_t voltage = adc1_to_voltage(ADC1_CHANNEL_6, &characteristics);
|
||
printf("%d mV\n",voltage);
|
||
|
||
|
||
Routing ADC reference voltage to GPIO::
|
||
|
||
#include <driver/adc.h>
|
||
#include <driver/gpio.h>
|
||
#include <esp_err.h>
|
||
|
||
...
|
||
|
||
esp_err_t status = adc2_vref_to_gpio(GPIO_NUM_25);
|
||
if (status == ESP_OK){
|
||
printf("v_ref routed to GPIO\n");
|
||
}else{
|
||
printf("failed to route v_ref\n");
|
||
}
|
||
|
||
|
||
API Reference
|
||
-------------
|
||
|
||
.. include:: /_build/inc/esp_adc_cal.inc |