Demo blog post (#3813)

* Add Demo blog post

* Update title

* Rename blog post

* Update link to image

* Let link point to the upcoming docs

* Some small spelling & grammar fixes

source/_posts/2017-10-28-demo.markdown

@@ -0,0 +1,106 @@
+---
+layout: post
+title: "Home Assistant Demo"
+description: "Showing a demo of Home Assistant to an audience."
+date: 2017-10-28 10:00:00 +0200
+date_formatted: "October 28, 2017"
+author: Fabian Affolter
+author_twitter: fabaff
+comments: true
+categories: How-To
+og_image: /images/blog/2017-10-interactive-demo/demo-random.png
+---
+
+If you are planning to host a Home Assistant meetup or doing a talk, then you probably want to show Home Assistant to an audience. You could use a Wireless router, bulbs, switches, and a single board computer to do a realistic demo. For a workshop, this is what I usually do because I think that working with physical hardware is more fun for the participants. The issue is that you need time to set up, power and space. For a talk or in a location, where you only have a beamer and a table or a lectern, the physical hardware approach is not very convenient.
+
+The simplest way to show Home Assistant to others is the online demo at [https://home-assistant.io/demo/](https://home-assistant.io/demo/)
+
+<p class='img'>
+  <img src='/images/blog/2017-10-interactive-demo/online-demo.png' />
+  Home Assistant's online demo
+</p>
+
+<!--more-->
+
+## {% linkable_title `--demo-mode` and Demo platform %}
+To be safe for your talk, you don't want to depend on an internet connection. The demo mode [`--demo-mode`](/docs/tools/hass/) allows you to run a demo locally including the latest features. Make sure that you have a backup of your configuration.
+
+```bash
+$ hass --demo-mode
+```
+
+If you already have a `configuration.yaml` file in place then you will get a combination of your setup with all available  [`demo`](/components/demo/) platforms. This can be overwhelming for the audience. The suggestion is that you tailor the demo to your needs by only showing a few selected platforms. For example:
+
+```yaml
+sensor:
+  - platform: demo
+binary_sensor:
+  - platform: demo
+switch:
+  - platform: demo
+```
+
+<p class='img'>
+  <img src='/images/blog/2017-10-interactive-demo/demo-platforms.png' />
+  Home Assistant's demo platforms
+</p>
+
+## {% linkable_title `random` platforms %}
+Till now the frontend is static. Nothing is changing over time. Starting with 0.57 we ship a [`random` binary sensor](https://github.com/home-assistant/home-assistant.github.io/blob/next/source/_components/binary_sensor.random.markdown) platform in addition to the already available [`random` sensor](/components/sensor.random/).
+
+By adding those platform to your `configuration.yaml` file, your demo will become more interactive.
+
+```yaml
+sensor:
+  - platform: demo
+    name: Temperature
+    unit_of_measurement: "°C"
+binary_sensor:
+  - platform: random
+    name: Front Door
+  - platform: random
+    name: Back Door
+    scan_interval: 5
+```
+
+<p class='img'>
+  <img src='/images/blog/2017-10-interactive-demo/demo-random.png' />
+  Demo with `random` platforms
+</p>
+
+The `random` and the `demo` platforms can, of course, be used together. With a little work and some of the [`template`](/components/#search/template) platforms or the [`input_*`](/components/#search/input) components it would even be possible to simulate a complete apartment or a house. For a hint check the sample below:
+
+{% raw %}
+```yaml
+input_boolean:
+  on_off:
+    name: On or off
+binary_sensor:
+  - platform: template
+    sensors:
+      on_tester:
+        value_template: "{{ states.input_boolean.on_off.state == 'on' }}"
+        friendly_name: 'Movement'
+        device_class: motion
+```
+{% endraw %}
+
+## {% linkable_title MQTT Discovery %}
+This is a section for advanced users as it will require to run a separate script. Instead of adding `demo` platforms to the configuration this setup make use of [MQTT discovery](/docs/mqtt/discovery/) and the [embedded MQTT broker](/docs/mqtt/broker/#embedded-broker). Simply add MQTT to your `configuration.yaml` file with `discovery:`
+
+```yaml
+mqtt:
+  discovery: true
+```
+
+Download the [sample script](https://github.com/home-assistant/home-assistant-dev-helper/blob/master/ha-mqtt-demo.py). It depends on [paho-mqtt](https://pypi.python.org/pypi/paho-mqtt). If you run the script inside your [Home Assistant's virtual environment](/docs/installation/virtualenv/) then you are good to go as the dependency should be present if you have used MQTT before. Otherwise, install it with `$ pip3 install paho-mqtt`. The same applies to the embedded broker.
+
+```bash
+(ha)[ha-demo]$ python3 ha-mqtt-demo.py
+Demo is running... -> CTRL + C to shutdown
+```
+
+It will create sensors, a light, and a switch and update the states as long the script is running. It possible to stop and restart script without losing the entities.
+
+Some users share their slides and other documents in [our assets repository](https://github.com/home-assistant/home-assistant-assets). Also, take a look at that repository if you need a logo for your slides.
+