In https://harp-tech.org/tutorials/hobgoblin-acquisition.html#exercise-5-controlling-digital-output Insert a [KeyDown](https://bonsai-rx.org/docs/api/Bonsai.Windows.Input.KeyDown.html) operator and set its Key property to change to Insert a [KeyDown](https://bonsai-rx.org/docs/api/Bonsai.Windows.Input.KeyDown.html) operator and set its Filter property to