diff --git a/firmware/mix.lock b/firmware/mix.lock
index 0c17b4b..6e5fd46 100644
--- a/firmware/mix.lock
+++ b/firmware/mix.lock
@@ -1,4 +1,5 @@
 %{
+  "circuits_gpio": {:hex, :circuits_gpio, "0.4.1", "344dd34f2517687fd28723e5552571babff5469db05b697181cab860fe7eff23", [:make, :mix], [{:elixir_make, "~> 0.5", [hex: :elixir_make, repo: "hexpm", optional: false]}], "hexpm"},
   "connection": {:hex, :connection, "1.0.4", "a1cae72211f0eef17705aaededacac3eb30e6625b04a6117c1b2db6ace7d5976", [:mix], [], "hexpm"},
   "cowboy": {:hex, :cowboy, "2.6.3", "99aa50e94e685557cad82e704457336a453d4abcb77839ad22dbe71f311fcc06", [:rebar3], [{:cowlib, "~> 2.7.3", [hex: :cowlib, repo: "hexpm", optional: false]}, {:ranch, "~> 1.7.1", [hex: :ranch, repo: "hexpm", optional: false]}], "hexpm"},
   "cowlib": {:hex, :cowlib, "2.7.3", "a7ffcd0917e6d50b4d5fb28e9e2085a0ceb3c97dea310505f7460ff5ed764ce9", [:rebar3], [], "hexpm"},
diff --git a/morse/lib/morse.ex b/morse/lib/morse.ex
index 402a6c7..e921788 100644
--- a/morse/lib/morse.ex
+++ b/morse/lib/morse.ex
@@ -1,13 +1,67 @@
 defmodule Morse do
+  alias Circuits.GPIO
+
   @moduledoc """
   Functions to control the signal lamp connected with GPIO.
   """
 
+  @relay_pin 17
+  @sleep_short 200
+  @sleep_delay 400
+  @sleep_long 700
+  @sleep_pause 1000
+  @sleep_start 3000
+
+  @on 0
+  @off 1
+
   @doc """
-  Takes a string composed of dots and dashes, and signals them with the
-  signal lamp.
+  Signal the provided symbols using GPIO.
+  Also setup the GPIO.
   """
-  def signal(msg) do
-    IO.puts(msg)
+
+  def signal do
+    case System.get_env("MORSE_MESSAGE") do
+      nil ->
+        # Signal for SOS if the env variable wasn't found :)
+        signal("...---...")
+      message -> signal(message)
+    end
+  end
+
+  def signal(symbols) do
+    {:ok, gpio} = GPIO.open(@relay_pin, :output)
+    GPIO.write(gpio, @off)
+    Process.sleep(@sleep_start)
+    signal_sentence(gpio, String.graphemes(symbols))
+  end
+
+  # Signal a whole sentence of symbols with GPIO.
+  defp signal_sentence(gpio, []) do
+    GPIO.write(gpio, @off)
+    GPIO.close(gpio)
+    :ok
+  end
+
+  defp signal_sentence(gpio, [symbol | rest]) when symbol in [".", "-"] do
+    GPIO.write(gpio, @on)
+    case symbol do
+      "." -> Process.sleep(@sleep_short)
+      "-" -> Process.sleep(@sleep_long)
+    end
+    GPIO.write(gpio, @off)
+
+    Process.sleep(@sleep_delay)
+    signal_sentence(gpio, rest)
+  end
+
+  defp signal_sentence(gpio, [" " | rest]) do
+    Process.sleep(@sleep_pause)
+
+    signal_sentence(gpio, rest)
+  end
+
+  defp signal_sentence(_gpio, [symbol | _rest]) do
+    {:error, "Undefined symbol: " <> symbol}
   end
 end
diff --git a/morse/mix.exs b/morse/mix.exs
index 05d2095..9232c4c 100644
--- a/morse/mix.exs
+++ b/morse/mix.exs
@@ -21,8 +21,7 @@ defmodule Morse.MixProject do
   # Run "mix help deps" to learn about dependencies.
   defp deps do
     [
-      # {:dep_from_hexpm, "~> 0.3.0"},
-      # {:dep_from_git, git: "https://github.com/elixir-lang/my_dep.git", tag: "0.1.0"}
+      {:circuits_gpio, "~> 0.4.1"}
     ]
   end
 end
diff --git a/morse/mix.lock b/morse/mix.lock
new file mode 100644
index 0000000..9d12430
--- /dev/null
+++ b/morse/mix.lock
@@ -0,0 +1,4 @@
+%{
+  "circuits_gpio": {:hex, :circuits_gpio, "0.4.1", "344dd34f2517687fd28723e5552571babff5469db05b697181cab860fe7eff23", [:make, :mix], [{:elixir_make, "~> 0.5", [hex: :elixir_make, repo: "hexpm", optional: false]}], "hexpm"},
+  "elixir_make": {:hex, :elixir_make, "0.6.0", "38349f3e29aff4864352084fc736fa7fa0f2995a819a737554f7ebd28b85aaab", [:mix], [], "hexpm"},
+}
diff --git a/ui/lib/ui_web/controllers/page_controller.ex b/ui/lib/ui_web/controllers/page_controller.ex
index 1e56767..c7be9ba 100644
--- a/ui/lib/ui_web/controllers/page_controller.ex
+++ b/ui/lib/ui_web/controllers/page_controller.ex
@@ -22,7 +22,7 @@ defmodule UiWeb.PageController do
     case get_start_time() do
       start_time when start_time + 35 <= now ->
         System.put_env("MORSE_START_TIME", Integer.to_string(now))
-        Morse.signal("...---...")
+        Morse.signal()
         text(conn, "Done.")
       _ ->
         text(conn, "It is still in progress...")
diff --git a/ui/mix.lock b/ui/mix.lock
index 7244de7..6ff1088 100644
--- a/ui/mix.lock
+++ b/ui/mix.lock
@@ -1,6 +1,8 @@
 %{
+  "circuits_gpio": {:hex, :circuits_gpio, "0.4.1", "344dd34f2517687fd28723e5552571babff5469db05b697181cab860fe7eff23", [:make, :mix], [{:elixir_make, "~> 0.5", [hex: :elixir_make, repo: "hexpm", optional: false]}], "hexpm"},
   "cowboy": {:hex, :cowboy, "2.6.3", "99aa50e94e685557cad82e704457336a453d4abcb77839ad22dbe71f311fcc06", [:rebar3], [{:cowlib, "~> 2.7.3", [hex: :cowlib, repo: "hexpm", optional: false]}, {:ranch, "~> 1.7.1", [hex: :ranch, repo: "hexpm", optional: false]}], "hexpm"},
   "cowlib": {:hex, :cowlib, "2.7.3", "a7ffcd0917e6d50b4d5fb28e9e2085a0ceb3c97dea310505f7460ff5ed764ce9", [:rebar3], [], "hexpm"},
+  "elixir_make": {:hex, :elixir_make, "0.6.0", "38349f3e29aff4864352084fc736fa7fa0f2995a819a737554f7ebd28b85aaab", [:mix], [], "hexpm"},
   "file_system": {:hex, :file_system, "0.2.7", "e6f7f155970975789f26e77b8b8d8ab084c59844d8ecfaf58cbda31c494d14aa", [:mix], [], "hexpm"},
   "gettext": {:hex, :gettext, "0.17.0", "abe21542c831887a2b16f4c94556db9c421ab301aee417b7c4fbde7fbdbe01ec", [:mix], [], "hexpm"},
   "jason": {:hex, :jason, "1.1.2", "b03dedea67a99223a2eaf9f1264ce37154564de899fd3d8b9a21b1a6fd64afe7", [:mix], [{:decimal, "~> 1.0", [hex: :decimal, repo: "hexpm", optional: true]}], "hexpm"},