50 lines
1.2 KiB
Markdown
50 lines
1.2 KiB
Markdown
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# ADC Module
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The ADC module provides access to the in-built ADC.
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On the ESP8266 there is only a single-channel, which is multiplexed with the
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battery voltage. Depending on the setting in the "esp init data" (byte 107)
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one can either use the ADC to read an external voltage, or to read the
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system voltage, but not both.
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The default setting in the NodeMCU firmware can be controlled via user_config.h at compile time, by defining one of ESP_INIT_DATA_ENABLE_READVDD33, ESP_INIT_DATA_ENABLE_READADC or ESP_INIT_DATA_FIXED_VDD33_VALUE. To change the setting
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at a later date, use Espressif's flash download tool to create a new init data block.
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## adc.read()
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Samples the ADC.
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####Syntax
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`adc.read(channel)`
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####Parameters
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- `channel`: Always zero on the ESP8266
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####Returns
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number:the sampled value
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####Example
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```lua
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val = adc.read(0)
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```
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___
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## adc.readvdd33()
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Reads the system voltage.
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####Syntax
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`adc.readvdd33()`
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####Parameters
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`nil`
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####Returns
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The system voltage, in millivolts.
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If the ESP8266 has been configured to use the ADC for sampling the external pin, this function will always return 65535. This is a hardware and/or SDK limitation.
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####Example
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```lua
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mv = adc.readvdd33()
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```
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___
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