This type of blinker is primarily used in model vehicles, where it can be used to achieve a realistic imitation of the dual flasher bar on an ambulance or fire engine. The LEDs, which are connected to the two open collectors, blink twice on the right and then twice on the left. The visual effect is simply fantastic. The electronics consists of a simple 555-based clock generator and a 4017 decimal counter. The 555 is wired as a free-running oscillator.