Initial MQTT binary sensor page

source/_components/binary_sensor.mqtt.markdown

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+---
+layout: component
+title: "MQTT binary sensor"
+description: "Instructions how to integrate MQTT binary sensors within Home Assistant."
+date: 2015-05-30 23:21
+sidebar: true
+comments: false
+sharing: true
+footer: true
+logo: mqtt.png
+ha_category: Binary Sensor
+---
+
+
+This MQTT binary sensor implementation uses the MQTT message payload as the sensor value. If messages in this state_topic are published with *RETAIN* flag, the sensor will receive an instant update with the last known value. Otherwise, the initial state will be off.
+
+To use your MQTT binary sensor in your installation, add the following to your `configuration.yaml` file:
+
+```yaml
+# Example configuration.yml entry
+binary_sensor:
+  platform: mqtt
+  state_topic: "home-assistant/window/contact"
+  name: "MQTT Sensor"
+  qos: 0
+  payload_on: "ON"
+  payload_of: "OFF"
+```
+
+Configuration variables:
+
+- **state_topic** (*Required*): The MQTT topic subscribed to receive sensor values.
+- **name** (*Optional*): The name of the sensor. Default is 'MQTT Sensor'. 
+- **qos** (*Optional*): The maximum QoS level of the state topic. Default is 0.
+- **payload_on** (*Optional*): The payload that represents on state. Default is "ON".
+- **payload_off** (*Optional*): The payload that represents  state. Default is "OFF".
+
+
+For a quick check you can use the commandline tools shipped with `mosquitto` to send MQTT messages. Set the state of your sensor manually:
+
+```bash
+$  mosquitto_pub -h 127.0.0.1 -t home-assistant/window/contact -m "OFF"
+```
+