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Elixir "poncho" project with Nerves firmware and Phoenix LiveView UI

Masatoshi Nishiguchi
Updated on ・3 min read

Today I learned how to make a poncho project with the Nerves firmware and Phoenix LiveView UI and how it generally works.

My dev environment

MacOS BigSur 11.4
MacBook Pro (13-inch, 2018, Four Thunderbolt 3 Ports)

erlang 23.3.1
elixir 1.12.0-otp-23
node 12.13.0

export MIX_TARGET=rpi0
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How-to (A)

The easiest way to do it is just clone the Nerves Project's official example hello_phoenix. The Nerves core team and the community keep the example up-to-date. It should just work.

Clone the example project

cd some/location
git clone
cd nerves_examples/hello_phoenix
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then follow the instructions in the README.

How-to (B)

I was curious how I could create something similar from scratch so I did. Here is my secret recipe I ended up with.

Create a base project

cd some/location

# Decide on the project name

# Create the project directory and move into it

# Create
echo "Copied from\n\n$(curl -L" >

# Initialize Git
git init && git add . && git commit -m "Initial commit"

# Create Nerves firmware subproject
mix archive.install hex nerves_bootstrap
mix "$MY_PROJECT_NAME"_firmware
git add . && git commit -m "Create Nerves firmware subproject"

# Create Phoenix LiveView UI subproject
mix archive.install hex phx_new
mix "$MY_PROJECT_NAME"_ui --no-ecto --live
git add . && git commit -m "Create Phoenix LiveView UI subproject"
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Add to the Firmware subproject the UI subproject as a dependency

# hello_poncho_firmware/mix.exs

{:hello_poncho_ui, path: "../hello_poncho_ui", targets: @all_targets, env: Mix.env()},
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Set up WiFi in the Firmware subproject

# hello_poncho_firmware/config/target.exs

    type: VintageNetWiFi,
    vintage_net_wifi: %{
      networks: [
          key_mgmt: :wpa_psk,
          ssid: System.get_env("WIFI_SSID"),
          psk: System.get_env("WIFI_PSK")
    ipv4: %{method: :dhcp}
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Configure web server in the Firmware subproject

According to the Nerves official User Interfaces documentation:

If we're using a poncho project structure, we'll need to keep in mind that
the my_app_ui configuration won't be applied automatically, so we should
either import it from there or duplicate the required configuration.

# hello_poncho_firmware/config/target.exs

# Import default UI config based on MIX_ENV
import_config "../../hello_poncho_ui/config/config.exs"

# Override some UI config for firmware
config :hello_poncho_ui, HelloPonchoUiWeb.Endpoint,
  # Nerves root filesystem is read-only, so disable the code reloader
  code_reloader: false,
  # Use compile-time Mix config instead of runtime environment variables
  load_from_system_env: false,
  # Start the server since we're running in a release instead of through `mix`
  server: true,
  # "<firmware's hostname>.local"
  url: [host: "nerves.local"],
  http: [port: 80],
  check_origin: false,
  root: Path.dirname(__DIR__)
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Build the firmware and burn (or upload) it

Follow the instructions in Nerves official Hello Phoenix example.

Specify MIX_ENV=prod so that we can build the production UI.

MIX_ENV=prod mix firmware
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Verify the UI config is loaded correctly

Application.get_env :hello_poncho_ui, HelloPonchoUiWeb.Endpoint
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Visit http://nerves.local or your specified host or IP.

Folder names

The folder names can be verbose if a project name is prepended. I once considered to shorten them somehow, but I decided not to because it is nice to be obvious about what exactly they are.

├── hello_poncho_firmware
└── hello_poncho_ui
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Final Thoughts

At first, the poncho project looked scary to me, but it is actually pretty simple concept. The Nerves firmware combined with the Phoenix LiveView seems so powerful that I may consider using this pattern for my other Nerves projects. Now that I know how to make a poncho project, it is time to make some UI for my devices.

That's it! Here are some resources I read and found helpful.



  • Sometimes I have an issue resolving dependencies for some reason, then I run mix deps.clean --all.

Discussion (0)