Luxeon LED Strobe
One of the most popular scale accessories for model airplane is strobe light. It is very efficient device used by full scale airplanes helping pilots to "see and avoid" the other traffic. Strobe lights can be seen tens of miles away especially at night but also at full sun daylight the airplane with flashing strobes can be easy distinguished from the background. All airplanes certified in USA after March 1 1996 must have installed an approved aviation red or aviation white anticollision light system.
There are two most common types of anticollision lights: red beacon light and white strobe light. Quite often airplanes have both and sometimes combination of red-white lights. Older planes are equipped with incandescent red beacon. Newer airplane use LED based beacons. The most common white strobe contains xenon tube like in a flash in popular camera. Here are examples of full scale small planes anticollision lights (red beacon on the top of fin, xenon strobe on the wingtip in Cessna 172 and combination lamp on PZL-130 Orlik).
Xenon tube based flash has one bad flaw, that makes it difficult to use in radio controlled model airplanes: it creates RF noise. That RF noise can interfere with airplane receiver obstructing the signal from pilot's transmitter. Older PCM systems and new 2.5GHz digital systems are able to "mask" that interference because the RF noise is emitted by strobe only during the flash - a split of second every one or two seconds. However flying RC model airplane with traditional PPM systems is next to impossible as all servos would be jumping randomly during each flash.
On the other hand using incandescent bulbs or standard LEDs is not practical as they are not as bright as xenon tubes. We are flying RC model planes during the day, so dim lights are not really visible and the scale impression is lost. For RC model airplanes I needed something as bright as xenon tube flash but safe from RF noise as incandescent bulb and energy efficient as LED.
In march 2006 I found high power LED available for reasonable price. I bought 3 Lumiled's Luxeon V LED's Cool White color. Each LED can take up to 5W converting it into bright light. Actually at that time these LEDs were used as a flash in cell phone cameras. Thy were as bright as xenon tube - perfect for my need. Single LED need to be powered by 7V with regulated current not exceeding 700mA. Because I was going to use them in work cycle 1/10 or less, the heat dissipating was not an issue. I came out with very simple circuit with minimum count of common available electronic components. For flash generator I used popular flashing LED which is driving the high power Luxeon LED via MOSFET. IC current regular is limiting the current to 700mA. All components fit in small single layer PC board.
Here is the list of materials:
- One surface mounted voltage regulator LM317
- One surface mounted N-channel MOSFET NDT451N
- One 5V red blinking LED
- One Lumiled's Luxeon V LED's Cool White
- One SMC resistor 1.8ohm
- Two SMC resistors 470ohm
In 2009, Lumileds announced that the Luxeon V are unavailable for new designs, and will be replaced by the Rebel series. Luxeon Rebel LEDs are more efficient that old Luxeon V and can be powered by lower voltage (3.2V at 700mA). The price is better too. If you want to use Luxeon Rebel, because of lower voltage needed for that LED the values of resistors R2 and R3 will need to change and the whole circuit could be powered from 2s LiPo battery (7-8V).
After the original circuit has been tested I made three strobe lights that were used in Giant scale Wilga 35/80 (100 inch wingspan).
The lights are so bright that are clearly visible even in sunny day, what you can see on the video. The test of the strobe light working is shown on the video below.
Click on the black box below to play the video.