When clearing out the basement a found an old chain of lights for christmas decoration. Many bulbs were burned out but a litte box at the end looked worth opening, as the lights could blink in different patterns. Inside the biox was an IC and four transistors for driving the lamps.
I plugged it in and measured the signals at the pins of the IC and discovered, that the chip was clocked by the mains frequency but needed no other signals except a button for switching the pattern.
I decided to replace the lamps by leds and place everything on a small circuitboard.
At every channel of the IC there are four blue leds. All sixteen leds are placed in a circle around the other parts.
The clock is generated by a good old NE555 timer.