modules/pins/analog: add adc for the esp32#37
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fivdi wants to merge 504 commits intoModdable-OpenSource:publicfrom
fivdi:esp32-adc
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modules/pins/analog: add adc for the esp32#37fivdi wants to merge 504 commits intoModdable-OpenSource:publicfrom fivdi:esp32-adc
fivdi wants to merge 504 commits intoModdable-OpenSource:publicfrom
fivdi:esp32-adc
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This PR adds ADC for the ESP32. The ESP32 has two ADC peripherals, ADC1 and ADC2. This PR only adds support for ADC on ADC1 but all eight channels are supported. Support for ADC2 was not added as ADC2 can only be used when Wi-Fi is not used. For additional info see http://esp-idf.readthedocs.io/en/latest/api-reference/peripherals/adc.html#overview.
Note that there are still a number of issues with ADC on the ESP32.
ADC is non-linear and V-REF varies from chip to chip. See espressif/esp-idf#164 and in particular espressif/esp-idf#164 (comment) for more information.
ADC noise and cross coupling. See espressif/esp-idf#1517 for more information.
This PR calls
adc1_to_voltagewhich uses look up tables to avoid the non-linear issue. The millivolt value returned byadc1_to_voltageis then converted to a value between 0 and 1023 which should be linear.