This circuit was found in General Electric documentation from 1968. The circuit uses triac from the time as well as transistors that can be replaced by modern equivalents.
This timer for short intervals was found in a documentation from 1966. The transistor is made of...
The frequency of each note depends on R2, which must be replaced by a keyboard. The circuit is...
In fact, this 1986 documentation circuit consists of a set of rhythmic LEDs that blink to the...