How do you do a double tap?

[dpyy]

I tried with the following pattern but nothing simulates a double tap, how do I do that?

addButton(pattern: "O")
addButton(pattern: "o")
addButton(pattern: ".")
addButton(pattern: ".-.")
addButton(pattern: "o-o")
addButton(pattern: "O-O")
addButton(pattern: "..oO-Oo..")
addButton(pattern: "O--O")
addButton(pattern: "o--o")
addButton(pattern: "o---o")
addButton(pattern: "O---O")
addButton(pattern: "o--O--O--o")
addButton(pattern: "o--O---O--o")
addButton(pattern: "O--O---O--O")
addButton(pattern: "OOO------------------------OOO")