LYWSD02 docs (#292)

* Add xiaomi_lywsd02

* Fix, Title underline too short.

* Fix, img link

components/sensor/xiaomi_lywsd02.rst

@@ -0,0 +1,93 @@
+Xiaomi LYWSD02 BLE Sensor
+=========================
+
+.. seo::
+    :description: Instructions for setting up Xiaomi LYWSD02 bluetooth-based temperature and humidity sensors in ESPHome.
+    :image: xiaomi_lywsd02.jpg
+    :keywords: Xiaomi, LYWSD02, BLE, Bluetooth
+
+The ``xiaomi_lywsd02`` sensor platform lets you track the output of Xiaomi LYWSD02 Bluetooth Low Energy
+devices using the :doc:`/components/esp32_ble_tracker`. This component will track the
+temperature, humidity of the LYWSD02 device every time the sensor
+sends out a BLE broadcast. Note that contrary to other implementations, ESPHome can track as many
+LYWSD02 devices at once as you want.
+
+.. figure:: images/xiaomi_lywsd02-full.png
+    :align: center
+    :width: 60.0%
+
+    Xiaomi LYWSD02 Temperature and Humidity Sensor over BLE.
+
+.. figure:: images/xiaomi_lywsd02-ui.png
+    :align: center
+    :width: 80.0%
+
+.. code-block:: yaml
+
+    # Example configuration entry
+    esp32_ble_tracker:
+
+    sensor:
+      - platform: xiaomi_lywsd02
+        mac_address: 3F:5B:7D:82:58:4E
+        temperature:
+          name: "Xiaomi LYWSD02 Temperature"
+        humidity:
+          name: "Xiaomi LYWSD02 Humidity"
+
+Configuration variables:
+------------------------
+
+- **mac_address** (**Required**, MAC Address): The MAC address of the Xiaomi LYWSD02 device.
+- **temperature** (*Optional*): The information for the temperature sensor.
+
+  - **name** (**Required**, string): The name for the temperature sensor.
+  - **id** (*Optional*, :ref:`config-id`): Set the ID of this sensor for use in lambdas.
+  - All other options from :ref:`Sensor <config-sensor>`.
+
+- **humidity** (*Optional*): The information for the humidity sensor
+
+  - **name** (**Required**, string): The name for the humidity sensor.
+  - **id** (*Optional*, :ref:`config-id`): Set the ID of this sensor for use in lambdas.
+  - All other options from :ref:`Sensor <config-sensor>`.
+
+Setting Up Devices
+------------------
+
+To set up Xiaomi LYWSD02 devices you first need to find their MAC Address so that ESPHome can
+identify them. So first, create a simple configuration without any ``xiaomi_lywsd02`` entries like so:
+
+.. code-block:: yaml
+
+    esp32_ble_tracker:
+
+After uploading the ESP32 will immediately try to scan for BLE devices such as the Xiaomi LYWSD02. When
+it detects these sensors, it will automatically parse the BLE message print a message like this one:
+
+.. code::
+
+    Got Xiaomi LYWSD02 (3F:5B:7D:82:58:4E): Temperature: 26.9°C
+
+Note that it can sometimes take some time for the first BLE broadcast to be received. You can speed up
+the process by pressing the grey bluetooth button on the back of the device.
+
+Then just copy the address (``3F:5B:7D:82:58:4E``) into a new ``sensor.xiaomi_lywsd02`` platform entry like
+in the configuration example at the top.
+
+.. note::
+
+    The ESPHome Xiaomi integration listens passively to packets the xiaomi device sends by itself.
+    ESPHome therefore has no impact on the battery life of the device.
+
+See Also
+--------
+
+- :doc:`/components/esp32_ble_tracker`
+- :doc:`/components/sensor/xiaomi_mijia`
+- :doc:`/components/sensor/xiaomi_miflora`
+- :doc:`/components/sensor/index`
+- :apiref:`xiaomi_mijia/xiaomi_mijia.h`
+- `Xiaomi Mijia BLE protocol <https://github.com/mspider65/Xiaomi-Mijia-Bluetooth-Temperature-and-Humidity-Sensor>`__
+  by `@mspider65 <https://github.com/mspider65>`__
+- `OpenMQTTGateway <https://github.com/1technophile/OpenMQTTGateway>`__ by `@1technophile <https://github.com/1technophile>`__
+- :ghedit:`Edit`

index.rst

@@ -141,6 +141,7 @@ Sensor Components
     WiFi Signal Strength, components/sensor/wifi_signal, network-wifi.svg
     Xiaomi MiFlora, components/sensor/xiaomi_miflora, xiaomi_miflora.jpg
     Xiaomi MiJia, components/sensor/xiaomi_mijia, xiaomi_mijia.jpg
+    Xiaomi LYWSD02, components/sensor/xiaomi_lywsd02, xiaomi_lywsd02.jpg
     ZyAura, components/sensor/zyaura, zgm053.jpg
     Custom Sensor, components/sensor/custom, language-cpp.svg