automatic cycle lighting

1 2 0 DI R1 10 automatic cycle lighting Re1 R2 7 IC1 R4 5V 5_100mA La1 (:)6V 555 Cal Lag 3W 3W 6 6V Cl 4 x 1,2 V 450 mAh 4 x 1,2 V 450 mAh This simple circuit (figure 1) ensures a great improvement in road safety for nocturnal cyclists. The light remains on when the cyclist stops at traffic lights — a battery supplies the current. During the trip with lights switched on (supplied by the bicycle dynamo) the battery, a parallel connection of four nicads, is charged across D1 and R1 and the relay is operated. When the bicycle stops, the relay drops out and it now connects the bulb to the battery. The one thing to remember of course, is to switch off the lights at the end of the ride, but even this can be elec- tronicised. Figure 2 gives a suitably extended version of the circuit. Forgetting the lights need now no longer be a problem with this luxury version, which switches the lights off automatically after about 3 minutes. The circuit is of course a little more elaborate than the ...