154 lines
6.2 KiB
C
154 lines
6.2 KiB
C
// Copyright 2015-2016 Espressif Systems (Shanghai) PTE LTD
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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#ifndef __ESP_ADC_CAL_H__
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#define __ESP_ADC_CAL_H__
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#ifdef __cplusplus
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extern "C" {
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#endif
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#include <stdint.h>
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#include "driver/adc.h"
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/** @cond */
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#define ADC_CAL_GAIN_SCALE 16
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#define ADC_CAL_OFFSET_SCALE 10
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#define ADC_CAL_IDEAL_V_REF 1100 //In mV
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#define ADC_CAL_LOW_V_REF 1000
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#define ADC_CAL_HIGH_V_REF 1200
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#define ADC_CAL_MIN 0
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#define ADC_CAL_MAX 4095
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/** @endcond */
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/**
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* @brief Structure storing Lookup Table
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*
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* The Lookup Tables (LUT) of a given attenuation contains 33 equally spaced
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* points. The Gain and Offset curves are used to find the appopriate gain and
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* offset factor given a reference voltage v_ref.
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*
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* @note A seperate LUT is provided for each attenuation and are defined in
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* esp_adc_cal_lookup_tables.c
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*/
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typedef struct {
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uint32_t gain_m; /**<Gradient of Gain Curve */
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uint32_t gain_c; /**<Offset of Gain Curve */
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uint32_t offset_m; /**<Gradient of Offset Curve */
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uint32_t offset_c; /**<Offset of Offset Curve */
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uint32_t bit_shift; /**<Bit shift used find corresponding LUT points
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given an ADC reading*/
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uint32_t voltage[]; /**<Array of voltages in mV representing the
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ADC-Voltage curve */
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} esp_adc_cal_lookup_table_t;
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/**
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* @brief Structure storing ADC characteristics of given v_ref
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*
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* The ADC Characteristics structure stores the gain and offset factors of an
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* ESP32 module's ADC. These factors are calculated using the reference voltage,
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* and the Gain and Offset curves provided in the lookup tables.
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*
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* @note Call esp_adc_cal_get_characteristics() to initialize the structure
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*
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*/
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typedef struct {
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uint32_t v_ref; /**<Reference Voltage of current ESP32 Module in mV*/
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uint32_t gain; /**<Scaling factor used to correct LUT voltages to
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current v_ref. Bit shifted by << ADC_CAL_GAIN_SCALE
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for uint32 arithmetic */
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uint32_t offset; /**<Offset in mV used to correct LUT Voltages to current v_ref */
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uint32_t ideal_offset; /**<Offset in mV at the ideal reference voltage */
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adc_bits_width_t bit_width; /**<Bit width of ADC e.g. ADC_WIDTH_12Bit */
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const esp_adc_cal_lookup_table_t *table; /**<Pointer to LUT */
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} esp_adc_cal_characteristics_t;
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extern const esp_adc_cal_lookup_table_t esp_adc_cal_table_atten_0; /**<LUT for atten0 */
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extern const esp_adc_cal_lookup_table_t esp_adc_cal_table_atten_1; /**<LUT for atten1 */
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extern const esp_adc_cal_lookup_table_t esp_adc_cal_table_atten_2; /**<LUT for atten2 */
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extern const esp_adc_cal_lookup_table_t esp_adc_cal_table_atten_3; /**<LUT for atten3 */
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/**
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* @brief Calculate characteristics of ADC
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*
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* This function will calculate the gain and offset factors based on the
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* reference voltage parameter and the Gain and Offset curve provided in the LUT.
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*
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* @note reference voltage of the ADCs can be routed to GPIO using
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* adc2_vref_to_gpio() from the ADC driver
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*
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* @note The LUT members have been bit shifted by ADC_CAL_GAIN_SCALE or
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* ADC_CAL_OFFSET_SCALE to make them uint32_t compatible. This bit shifting will
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* accounted for in this function
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*
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* @param[in] v_ref true reference voltage of the ADC in mV (1000 to 1200mV). Nominal
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* value for reference voltage is 1100mV.
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* @param[in] atten attenuation setting used to select the corresponding lookup table
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* @param[in] bit_width bit width of ADC
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* @param[out] chars pointer to structure used to store ADC characteristics of module
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*/
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void esp_adc_cal_get_characteristics(uint32_t v_ref,
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adc_atten_t atten,
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adc_bits_width_t bit_width,
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esp_adc_cal_characteristics_t *chars);
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/**
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* @brief Convert raw ADC reading to voltage in mV
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*
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* This function converts a raw ADC reading to a voltage in mV. This conversion
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* is based on the ADC's characteristics. The raw ADC reading is referenced
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* against the LUT (pointed to inside characteristics struct) to obtain a voltage.
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* Gain and offset factors are then applied to the voltage in order to obtain
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* the final result.
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*
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* @param[in] adc ADC reading (different bit widths will be handled)
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* @param[in] chars pointer to structure containing ADC characteristics of
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* the module. Structure also contains pointer to the
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* corresponding LUT
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*
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* @return Calculated voltage in mV
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*
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* @note characteristics structure must be initialized using
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* esp_adc_cal_get_characteristics() before this function is used
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*/
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uint32_t esp_adc_cal_raw_to_voltage(uint32_t adc,
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const esp_adc_cal_characteristics_t *chars);
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/**
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* @brief Reads ADC1 and returns voltage in mV
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*
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* This function reads the ADC1 using adc1_get_raw() to obtain a raw ADC
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* reading. The reading is then converted into a voltage value using
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* esp_adc_cal_raw_to_voltage().
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*
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* @param[in] channel Channel of ADC1 to measure
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* @param[in] chars Pointer to ADC characteristics struct
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*
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* @return voltage Calculated voltage in mV
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*
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* @note ADC must be initialized using adc1_config_width() and
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* adc1_config_channel_atten() before this function is used
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*
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* @note characteristics structure must be initialized using
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* esp_adc_cal_get_characteristics() before this function is used
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*/
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uint32_t adc1_to_voltage(adc1_channel_t channel, const esp_adc_cal_characteristics_t *chars);
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#ifdef __cplusplus
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}
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#endif
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#endif /* __ESP_ADC_CAL_H__ */
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