Odd led question I hope

[PixelsnPrint]

Ok I know there are all sorts of posts about blinky and flashing circuits on this and other forums using Lm3909 and 555 chips. But what I'm looking for is a way to mimic an actual perceived strobe effect.. that being an led starts in the off state there is a sudden on state then a fall off state to full off again does that seem possible. What I'm trying to mimic here is the after glow one would perceive from a strobe, I'm working on some large scale miniature work and I am trying to have some differences between some of the flashes that are required.

Tia

Richard

 

[audioguru]

I am guessing that when you say "fall off" and "afterglow" then you mean for the brightness to fade slowly after each bright pulse?

 

[PixelsnPrint]

yes I was trying to come up with a way to properly describe it, guess you could use the terms of attack and decay so the voltage graph would look like a right angle triangle. Is that clear as mud now?

 

[audioguru]

A transistor can quickly charge a capacitor then the capacitor is slowly discharged by a resistor. The voltage across the resistor will rise quickly then fall slowly. An emitter-follower transistor can "follow" the capacitor's voltage and dim an LED in series with a current-limiting resistor.
The LED might dim a little then suddenly turn off because the voltage ramp should be a current ramp which takes a 3rd transistor.

 

[PixelsnPrint]

That seems to make some sense, but as to designing it. Ya this is the place where I hit you up for additional help don't ya know

 

[audioguru]

What is the voltage and current ratings of the LED?
What battery voltage?