PAGE 138 OF 150 · PROJECTS
Build a Bicycle Safety Light
A flashing LED improves visibility at night.
LED SYMBOLTriangle points from anode to cathode; the arrows show light leaving the part.
The idea
A bicycle light should be bright and flashing so others notice it. A 555 timer makes the flash, and a transistor switches the LEDs.
Design
- Three AAA cells for 4.5 V.
- Three red LEDs in parallel, each with a 180 ohm resistor, giving about 14 mA each.
- 555 astable at 2 to 3 flashes per second driving a transistor.
Practical points
Use bright, narrow-beam LEDs and a weatherproof case. Check local rules, since some places require a steady lamp in addition to a flasher. A reflector is a useful backup.
REMEMBER
Test visibility at night before you rely on it.Try it yourself
Sketch the circuit on paper first, calculate the values, then build it on a solderless breadboard using a low-voltage supply. Measure with a multimeter before you make anything permanent.
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