This is a simple little circuit that provides lighting for my Firefly Graphic that I had made for the plane.  I wanted a similar effect that copied what a real firefly flash in Nature would be. After looking at some videos, I determined that a soft on, soft off was needed as well as a duration that was similar as well. Here again the trusty 555 timer was used to provide the on/off function. The oscillator is very slow running and some pulse width adjust was necessary. I used some software called 555 timer pro to help model the circuit. I would suggest downloading it and playing with it as a lot of my circuits use them. The output pulse is applied to the base of the transistor switch through an RC circuit that takes a little time to charge and discharge. The result is that the saturation base current needed to turn the transistor fully on and off varies and the collector current varies as well. The result is a soft on/soft off effect with the varying collector current. You can play with the values of R and C to suit your needs. The Lm317 is being used as a current regulator so that I wouldn't overdrive my LED. The 317 regulator is optional if you are careful with the selection of the transistor emitter resistor to keep your max current within spec of your LED. The 317 resistor and transistor emitter are high wattage ceramic resistors. The currents here are determined by the "on" time of your circuit and can go over an amp.  I use a yellowish high power led in my install. I cut a hole in my fabric on the plane just smaller than the size of the tail on my graphic and mounted the led to the concave side of an inspection plate as a reflector. The grahic was then placed carefully so that the tail and hole lined up correctly.  Its a one shot deal so I had to be very careful here. Anyway, the result was good. I've had a lot of favorable comments. Home Page