Innovative Aspects of this Circuit
This circuit showcases innovation in more than one aspect, earning its place in Elektor’s Small Circuits Collection. Firstly, it introduces a creative application of combining a blue and a white LED to simulate a camera flashlight realistically. Secondly, it utilizes the venerable 555 IC in a novel configuration that may be unfamiliar to many — alternating between monostable and astable modes — with minimal external components. Initially, C3 is uncharged, pulling output pin 3 to +12 V, and illuminating the blue LED, D1, through R3. Subsequently, C3 begins to charge via R2, concurrently, C1 accumulates charge through R1 and D3.
Dynamic Voltage Control for LED Operation
When the voltage on C3 reaches approximately 8 V (two-thirds of 12 V), pin 3 of the 555 IC switches low, as does pin 7, illuminating the white LED. The energy for the white LED is drawn from C1, causing its energy to deplete rapidly. Consequently, D2 dims in an exponentially decaying manner, resembling the fading effect of a camera flashlight. As the 555’s output goes low, the voltage on C3 decreases. Once it drops to 4 V (one-third of 12 V), the cycle restarts. R4 acts as a current limiter, ensuring safe levels of current through the 555 IC.
Enhanced LED Experimentation and Potential Applications
For experimentation, high-intensity white LEDs like SDK’s AlInGaP LEDs, which claim to be three times brighter than regular white LEDs, can be used. Multiple blue LEDs can be connected in series, although this option is not feasible for white LEDs. For optimal visual impact, the white and blue LEDs should be mounted closely together. When positioned near the extra brake light in a vehicle, the bluish-white flash can deter tailgaters effectively. It’s essential to note that the legality of this application may vary in different countries.