Two transistor are used in this configuration, They control two LEDs that blink alternately. Speed of the effect is given by C1 and C2. In the simulation we used 1 µF instead 4,7 µF to speed up the simulation. You can change the values to see how they affect the speed.
Simulation:
Obs.: we used transistors 2N222 instead the BC548.
To download the simulation files and Netlist - click here (msb0056.zip)