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Build Your Own 30V LED Bike Light Circuit
Description
During my cycling adventures, I frequently encountered issues with those commonplace flashing LED lights available at local retailers. These lights often presented problems, including depleted batteries and loose attachments. As an aspiring electronics student, I recognized the potential for improvement. Initially, I acquired another front wheel featuring a built-in dynamo, generating a stable 30 Vpp sine wave when unburdened. Leveraging this knowledge, I engineered a straightforward power supply utilizing BD911 transistors. These transistors, while perhaps slightly excessive, were readily accessible within my educational institution, leading to their implementation. A smaller alternative would also prove effective. The power supply is connected to an astable multivibrator, which alternately powers the front and rear lights. The frequency is determined by the RC time constant of components R3 and C3, and R2 and C4. This duration can be calculated using the formula: t = R3×C3 = 20×103×10×10-6 = 0.2 s. A value of 22k (a standard selection) can be used for R2 and R3, without substantially impacting the outcome. Six LEDs, each paired with a voltage-dropping resistor, are mounted on a prototyping board.
The PCB design serves a dual purpose, accommodating both the front and rear illumination systems. White LEDs are employed for the front, while red LEDs illuminate the rear. This PCB with the core circuitry is strategically positioned beneath the seat, offering protection and demonstrating reliable performance over more than a year. Modifications are planned for the subsequent iteration. The inclusion of an on/off switch would enhance functionality, and utilizing Surface Mount Device (SMD) components would allow for mounting near the front light, simplifying wiring. The cable originating from the dynamo extends directly to the seat and subsequently to the front and rear lights.
Circuit diagram:
Such a PCB is used for both the front and the rear of the bike. Of course, you use white LEDs for the front and red ones for the rear. The PCB with the main circuit is mounted under the seat, where it is safe and has been working for more than a year now. There are a few things I would change for the next revision. An on/off switch would be nice. And if the whole circuit was built with SMD parts it could be mounted near the front light. This would also be more convenient when routing the wiring. Now the cable from the dynamo goes all the way to the seat and from there to the front and rear lights.