Nerves Remote LED

This is an example demonstrating how to connect Nerves embedded devices to a Phoenix server and control the device remotely using websockets.

Using websockets allows controlling devices over a firewalled network since it can open a bi-directional TCP connection to the server over port 80, and outgoing connections to port 80 are generally allowed on most home/corporate routers/firewalls.

TOC

• Hardware Requirements for Running the Demo
• Running Locally
• Deploying Server

Hardware Requirements for Running the Demo

This example was constructed using a Raspberry PI Zero WH (the wireless version with headers pre-soldered).

For easy setup you can use a solderless breadboard to connect the LED to the different wires.

You will also need an LED, (and maybe a resistor that came with your LED if you are concerned about frying out your LED, I didn't use one).

Finally some jumper wires, female to male if you have the Zero WH.

Oh and an SD card to burn your firmware to.

Here are a few pictures of my setup:

For the GPIO, I chose GPIO 21, however if you want to change that you can do so by changing the @pin constant in the firmware's LedWorker module.

Running Locally

Note: This guide assumes you have both the Nerves and Phoenix archive installed on your machine. If you do not, please consult their respective documentation. Also I recommend installing Elixir and Erlang via the excellent asdf version manager - be sure to read the asdf-elixir plugin repo's instructions for compiling Elixir with an up to date erlang version.

First clone the repository to your machine:

git clone https://github.com/dkarter/remote_led.git && cd remote_led

To connect it to your local network you will need to add your network's SSID and password to your environment variables like so:

export NERVES_NETWORK_SSID="mynetwork"
export NERVES_NETWORK_PSK="mypassword"

If you are running the device against a locally hosted server on your host machine, you will need to change the websocket url in the firmware (client/config/config.exs) to the IP of your host machine.

config :remote_led, RemoteLed.LedSocket,
  url: "ws://YOUR_IP:4000/socket/websocket",
  serializer: Jason

Also make sure to export your MIX_TARGET. For this example we will be using RPi Zero:

export MIX_TARGET=rpi0

Place the Micro SD card in a card reader connected to your computer and run the following:

cd client
mix do deps.get, firmware, firmware.burn

At the end of this script you will be asked to type your sudo password so that you can burn the SD card. When the burning is done the SD card will be ejected. At that point you can remove the card from the card reader and place it in the Raspberry Pi.

Start the Phoenix server by navigating to the server dir and running mix phx.server:

cd ../server
mix do deps.get, phx.server

Once the server is running, plug in the power cord to your nerves device.

After a few seconds you should be able to connect to the device via ssh:

ssh remote_led.local

Hopefully at this step you are able to connect successfully and are seeing the iex repl. I suggest tailing the logs and then attaching to receive future log messages:

iex> RingLogger.tail
iex> RingLogger.attach

To test you wired the LED correctly you can try to run:

iex> RemoteLed.LedWorker.on

and

iex> RemoteLed.LedWorker.off

To connect the channel manually type:

iex> RemoteLed.Client.connect

If everything worked correctly you should be able to see that a new client has connected to the Phoenix server by checking the logs on the server.

Now the final and most exciting step, turning the LED on and off from the server. Open up http://localhost:4000 on your host machine and click the On and Off buttons. Follow the code in server/priv/static/js/app.js to figure out how this is done and open an issue if you have any questions.

Deploying Server

• TODO: add instructions for deploying to heroku / digitalocean and pointing your device there