Flashing Rear Light

by J Donhauser This rear light for bicycles is fed from a battery charged with current from the dynamo, and starts to flash when the cyclist halts. To preserve battery power, the unit automatically switches off 4 minutes after halting. The circuit is essentially com- posed of a battery charger and a logic switching section. The NiCd battery is charged from a voltage doubler C1-C2-Di-D2-C3 to ensure a charge current of about 20 mA when riding at a reasonable speed. This makes it possible for a charge of 3 mAh to be available after a 10 minute ride, i.e., enough for the light to flash for about 4 minutes after the bicycle is halted. A relay is used to switch between operation while riding and while standing still. When the bicycle is in motion, the voltage from the dynamo, G, ensures that N4 is enabled, so that T1 actuates Re, and the small 6 V bulb is illuminated. Since C3 is only slowly discharged via N4 remains enabled for about 4 minutes after halting. Push- button Si enables im...