Ultrasonic sensor

ピンを開く

{:ok, trig} = Circuits.GPIO.open("GPIO23", :output)
{:ok, echo} = Circuits.GPIO.open("GPIO24", :input)

距離測定モジュール

defmodule UltrasonicSensor do
  def distance(trig, echo) do
    Circuits.GPIO.write(trig, 0)
    Process.sleep(1)

    # 1 msec の超音波を送信
    Circuits.GPIO.write(trig, 1)
    Process.sleep(1)
    Circuits.GPIO.write(trig, 0)

    # 最初は 0 の状態を確認
    time_1 = wait_for(echo, 0)

    # 1 になるまでの時間を取得
    time_2 = wait_for(echo, 1)

    during = Time.diff(time_2, time_1, :microsecond)

    # 空気中の音速を使って距離(cm)に変換
    during * 340 / 2 / 10000
  end

  defp wait_for(echo, value) do
    1..10000
    |> Enum.reduce_while(nil, fn _i, _acc ->
      if Circuits.GPIO.read(echo) == value do
        {:cont, Time.utc_now()}
      else
        {:halt, Time.utc_now()}
      end
    end)
  end
end

距離を一定時間連続計測

1..100
|> Enum.map(fn _ ->
  UltrasonicSensor.distance(trig, echo) |> IO.inspect()

  Process.sleep(100)
end)

距離のグラフ化

distance_plot =
  VegaLite.new(width: 700)
  |> VegaLite.mark(:line)
  |> VegaLite.encode_field(:x, "index", type: :quantitative)
  |> VegaLite.encode_field(:y, "distance", type: :quantitative)
  |> Kino.VegaLite.new()

Kino.VegaLite.clear(distance_plot)

1..300
|> Enum.map(fn index ->
  distance = UltrasonicSensor.distance(trig, echo)

  IO.inspect(distance)

  plot_data = %{
    index: index,
    distance: distance
  }

  Kino.VegaLite.push(distance_plot, plot_data)
  Process.sleep(100)
end)

ピンを閉じる

Circuits.GPIO.close(trig)
Circuits.GPIO.close(echo)