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* Update resistance.rst Spent many hours to figure it out why my NTC reading are incorrect. Found out that ADC readings must be multiplied by 3.3 because built-in voltage divider on ADC pin on some boards. * Update resistance.rst
82 lines
2.6 KiB
ReStructuredText
82 lines
2.6 KiB
ReStructuredText
Resistance Sensor
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=================
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.. seo::
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:description: Instructions for setting up resistance sensors in ESPHome
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:image: omega.svg
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The ``resistance`` platform is a helper sensor that allows you to convert readings
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from a voltage sensor (such as the :doc:`ADC Sensor <adc>`) into resistance readings
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in Ω (ohm).
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In order to calculate the resistance, the circuit needs to be set up in a
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`voltage divider circuit <https://learn.sparkfun.com/tutorials/voltage-dividers/all>`__.
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This consists of three parts:
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- A voltage reference, usually this is connected to 3.3V (VCC). For example in the image
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below it is 5V (though on ESPs you should not use that voltage)
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- A reference resistor with constant resistance. For example below it is R₁ with a value
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of 5.6kOhm.
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- The variable resistor we wish the read the resistance of. Here R₂.
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There are two kinds of configurations for this circuit: Either the variable resistor
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is close to GND (DOWNSTREAM) or it is closer to VCC (UPSTREAM).
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.. figure:: images/resistance-downstream.png
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:align: center
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:width: 25.0%
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Example voltage divider configuration of type "DOWNSTREAM" and a voltage
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reference of 5V.
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.. code-block:: yaml
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# Example configuration entry
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sensor:
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- platform: resistance
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sensor: source_sensor
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configuration: DOWNSTREAM
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resistor: 5.6kOhm
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name: Resistance Sensor
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# Example source sensor:
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- platform: adc
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id: source_sensor
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pin: A0
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Note:
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------------------------
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Some boards like NodeMCUv2 needs to multiply ADC reading by 3.3 to provide accurate result because they have built-in voltage divider on ADC pin (https://arduino.stackexchange.com/a/71952)
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.. code-block:: yaml
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# Example source sensor:
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- platform: adc
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id: source_sensor
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pin: A0
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filters:
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- multiply: 3.3
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Configuration variables:
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------------------------
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- **name** (**Required**, string): The name for the sensor.
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- **sensor** (**Required**, :ref:`config-id`): The sensor to read the voltage values from
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to convert to resistance readings.
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- **configuration** (**Required**, string): The type of circuit, one of ``DOWNSTREAM`` or
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``UPSTREAM``.
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- **resistor** (**Required**, float): The value of the resistor with a constant value.
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- **reference_voltage** (*Optional*, float): The reference voltage. Defaults to ``3.3V``.
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- **id** (*Optional*, :ref:`config-id`): Set the ID of this sensor for use in lambdas.
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- All other options from :ref:`Sensor <config-sensor>`.
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See Also
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--------
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- :doc:`adc`
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- :doc:`ntc`
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- :ref:`sensor-filters`
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- :apiref:`resistance/resistance_sensor.h`
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- :ghedit:`Edit`
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