Using knewter/erlang-serial

iex.exs

iex(1)> {:ok, pid} = Ser.start("/dev/ttyAMA0", 115_200)
{:ok, #PID<0.97.0>}
iex(2)> send(pid, {:send, "ohai"})
Received serial data: ohai
{:send, "ohai"}
iex(3)> send(pid, {:send, "ohai"})
{:send, "ohai"}
Received serial data: ohai
iex(4)> send(pid, {:send, "ohai u GUYZ!"})
{:send, "ohai u GUYZ!"}
Received serial data: ohai u G
Received serial data: UYZ!
iex(5)> send(pid, {:send, "ohai u GUYZ! WAT IN THE WORLD"})
{:send, "ohai u GUYZ! WAT IN THE WORLD"}
Received serial data: ohai u G
Received serial data: UYZ! WAT
Received serial data:  IN THE
Received serial data: WORLD
iex(6)> send(pid, {:send, "Jurassic World is going to be ASUM SOS"})
{:send, "Jurassic World is going to be ASUM SOS"}
Received serial data: Jurassic
Received serial data:  World i
Received serial data: s going
Received serial data: to be AS
Received serial data: UM SOS

ser.ex

defmodule Ser do
  def start(device_string, baud_rate) do
    pid = spawn(Ser, :init, [self(), device_string, baud_rate])
    {:ok, pid}
  end

  def init(initiator, device_string, baud_rate) do
    device = :serial.start([speed: baud_rate, open: :erlang.bitstring_to_list(device_string)])
    loop(device)
  end

  defp loop(device) do
    receive do
      {:data, data} ->
        IO.puts "Received serial data: #{data}"
        loop(device)
      {:send, data} ->
        send(device, {:send, data})
        loop(device)
    end
  end
end