Creating Eye-Catching LED Bike Lights with Recycled Components
To enhance the visibility of cyclists on the road, attention-grabbing pulsing LED lights were developed, providing an alternative for those without such lighting. The project’s focus was on utilizing cost-effective and recycled components. The primary expense, at £3.99 ($6.50), was the 24-LED work light featuring a magnet and a retractable hook. A DB3 diac, crucial for the circuit, was salvaged from an 18-watt Philips CFL. It’s essential to note that lower wattage CFLs like the 8 W and 11 W versions often lack the necessary DB3 diac.
Substituting Transistors and Addressing Sourcing Challenges
Originally, a 2SD1266 transistor was used in the prototype, later replaced by the more readily available BD433, a TO126 device that requires proper cooling. One potential sourcing challenge lies in the ferrite toroid core, with specific dimensions of 9.16 mm inner diameter, 17.76 mm outer diameter, and 6.63 mm thickness. These cores can be salvaged from old, discarded PC motherboards. Local computer shops often have dead motherboards available for salvage, making it possible to find the required components.
Designing a Straightforward Blocking Oscillator Circuit
Electrically, the circuit is intentionally kept as simple as possible, employing a basic blocking oscillator configuration. However, one notable downside is the need to wind 60 turns of very thin wire on a toroid. The wire used for winding was obtained from a 6-volt power adapter. To simplify the process, begin by winding the two 12-turn windings using 0.5 mm (AWG24) wire. Winding the 60-turn coil can be facilitated by initially winding half the turns in one direction and the other half in the opposite direction.
Using approximately one meter (a little over three feet) of thin wire (0.1 mm/AWG38), thread it through the toroid. Find the middle of the wire by holding both ends while allowing the core’s weight to locate the center. Starting from the midpoint, wind 30 turns (secure the loose end to an AA battery to prevent tangling). Once you complete the first 30 turns, release the other end and wind it through the toroid another 30 times to achieve a total of 60 turns.
Winding and Phasing the Collector and Base Windings
To ensure proper phasing for the collector and base windings, the easiest approach is to wind the initial 12 turns, then extend a loop and securely twist it back to the core. After this, proceed to wind the remaining 12 turns. Since the two windings are identical, the center tap serves as the +1.5 V power connection. Either end can be collector or base, allowing flexibility in phasing the secondary. You can adjust the flash rate by reversing the leads if the circuit flashes only a few times per minute. Additionally, turning the 470 Ω potentiometer will alter the flashing speed. The 180 Ω resistor is included to safeguard the transistor against excessive base current.
Converting Pulsed Voltage into LED Illumination
On the secondary side of the circuit, the pulses generated are rectified by a UF4007 diode to charge an electrolytic capacitor. When the voltage on the capacitor reaches around 32 V, the DB3 diac is triggered, releasing the charge into 24 LEDs connected in parallel. The DB3 diac provides pulses of 2 A, sufficient to flash the LEDs. The choice of a 47 µF electrolytic capacitor was determined empirically for optimal pulse brightness. Increasing this to 100 µF would intensify the flashes, although their duration would be shorter.
Expanding the Application for Dark Cycleways
While the pulsing light is highly noticeable to other road users on well-lit roads, it may not be as effective for enhancing visibility on unlit cycleways located away from main roads and streetlights. An effective solution would involve adding a second flash rate potentiometer and a changeover switch. The existing unit can be adjusted to flash at a rate close to the persistence of vision. A switch for transitioning to the maximum flash rate would facilitate navigation on dark cycleways in complete darkness.
Important Considerations for Road Use
It is essential to note that, in some countries, road legality and type approval regulations may apply to such lighting devices. Furthermore, the most rapid flash rate, while providing enhanced visibility, may be irritating or even confusing to drivers. Consequently, it should be used exclusively in unlit areas away from road traffic. It’s also worth mentioning that the highest flash rate places additional stress on the components, particularly the battery.