Delokaver,T1 is a triac.* When T1 is active it essentially shorts across one of the pots next to the 555 and has the effect of increasing the frequency of the pulse train coming out of the 555.* That is how you get the ... --- ... pattern that you are looking for.* For the ... part the triac is active and allows current to pass.* For the --- part the triac is not active, current has to pass through the extra pot, and the frequency of the pulse train being output by the 555 decreases.Boncuk, what do you think about this circuit?