Added examples for uart text sensor (#468)

* Added examples for uart text sensor

components/text_sensor/uart.rst

@@ -0,0 +1,124 @@
+Custom UART Text Sensor
+=======================
+
+.. seo::
+    :description: Instructions for setting up a custom uart text sensor.
+    :image: language-cpp.png
+
+Lots of devices communicate using the UART protocol. If you want to read 
+lines from uart to a Text Sensor you can do so using this code example.
+
+With this you can use automations or lambda to set switch or sensor states.
+
+.. code-block:: cpp
+
+    #include "esphome.h"
+
+    class UartReadLineSensor : public Component, public UARTDevice, public TextSensor {
+     public:
+      UartReadLineSensor(UARTComponent *parent) : UARTDevice(parent) {}    
+
+      void setup() override {
+        // nothing to do here
+      }    
+
+      int readline(int readch, char *buffer, int len)
+      {
+        static int pos = 0;
+        int rpos;
+      
+        if (readch > 0) {
+          switch (readch) {
+            case '\n': // Ignore new-lines
+              break;
+            case '\r': // Return on CR
+              rpos = pos;
+              pos = 0;  // Reset position index ready for next time
+              return rpos;
+            default:
+              if (pos < len-1) {
+                buffer[pos++] = readch;
+                buffer[pos] = 0;
+              }
+          }
+        }
+        // No end of line has been found, so return -1.
+        return -1;
+      }    
+
+      void loop() override {
+        const int max_line_length = 80;
+        static char buffer[max_line_length];
+        if (available() && readline(read(), buffer, max_line_length) > 0) {
+          publish_state(buffer);
+        }
+      }
+    };
+
+(Store this file in your configuration directory, for example ``uart_read_line_sensor.h``)
+    
+And in YAML:
+
+.. code-block:: yaml
+
+    # Example configuration entry
+    esphome:
+      includes:
+        - uart_read_line_sensor.h
+    
+    logger:
+      level: VERBOSE #makes uart stream available in esphome logstream
+      baud_rate: 0 #disable logging over uart
+
+    uart:
+      id: uart_bus
+      tx_pin: D0
+      rx_pin: D1
+      baud_rate: 9600
+
+    text_sensor:
+    - platform: custom
+      lambda: |-
+        auto my_custom_sensor = new UartReadLineSensor(id(uart_bus));
+        App.register_component(my_custom_sensor);
+        return {my_custom_sensor};
+      text_sensors:
+        id: "uart_readline"
+
+Example usage
+-------------
+
+Here is an example switch using the uart text sensor to set switch state.
+
+Here we use interval to request status from the device. The reponse will be stored in uart text sensor.
+Then the switch uses the text sensor state to set its own state.
+
+.. code-block:: yaml
+
+    switch:
+      - platform: template
+        name: "Switch"
+        lambda: |-
+          if (id(uart_readline).state == "*POW=ON#") {
+            return true;
+          } else if(id(uart_readline).state == "*POW=OFF#") {
+            return false;
+          } else {
+            return {};
+          }
+        turn_on_action:
+          - uart.write: "\r*pow=on#\r"
+        turn_off_action:
+          - uart.write: "\r*pow=off#\r"
+    
+    interval:
+      - interval: 10s
+        then:
+          - uart.write: "\r*pow=?#\r"
+
+See Also
+--------
+
+- :doc:`/components/uart`
+- :doc:`/custom/uart`
+- :ghedit:`Edit`

index.rst

@@ -288,6 +288,7 @@ Text Sensor Components
     WiFi Info, components/text_sensor/wifi_info, network-wifi.svg
     Template Text Sensor, components/text_sensor/template, description.svg
     Custom Text Sensor, components/text_sensor/custom, language-cpp.svg
+    Custom UART Text Sensor, components/text_sensor/uart, language-cpp.svg
 
 Climate Components
 ------------------