LED flicker circuit?

[BellaCroix]

Hello all, been a while since I've been around but starting a new build and needed help trying to figure out how to do something and this was the first place I thought to come look for help.

I need to find a way to make 3 LEDs flicker like a candle flame. I thought about trying to gut a couple of those jack-o-lantern LED safety candles but they all run on 3 volt watch batteries and I'd rather hardwire them to the 5v rail (also I'd rather not have to use 3 seperate boards in the small space I have to work with).

I've searched on-line trying to find a schematic to do this but am coming up short.

So my questions:

1) Since I'm using 3 LEDs would it be okay to just use the guts from one LED candle?
2) If I'm stuck using three seperate boards from those candles what kind of resistor would I need to use to keep from blowing something up? I gutted one to see what was in there and how it worked and it already had a 47 ohm resistor inside it.
3) Anyone have a schematic to build my own instead of gutting one (or three) of these things?

Thanks for your help!

 

[theshadow27]

Unfortunately all (modern, < 100v) flicker circuits use a pseudo random algorithm on a microcontroler to simulate flickering. This includes the store bought candles, look for a blob of black stuff on the PCB, there's a chip under it. If there is no chip - just a resistor- it's integrated into the LED die. Unless you want to get a PICAXE or Basic Stamp the best way is by hacking what's there.

One option is to get four of the 3 volt units, and wire them in series to 12 volts; they'd get 3 volts each. All four 'candles' will flicker independently, which may or may not be the effect you want.

A second, and perhaps more involved, option is to find/buy/harvest a optocoupler(AKA optoisolator) which is basically an LED and a photo transistor in one package. Your LEDs would hook to the phototransistor side and the LED side will replace the LED on the board. All LEDs hooked to the optocoupler will flicker in unison.

Pardon the ASCII art:

 Candle PCB 
  -|         |+
   |---|<|---|                   (250 ohm)  for 20mA
       __
GND --/  \-----|<|----|<|----|<|----/\/\/\---- +12

   optocoupler

vdrop  .7      2.1    2.1    2.1       5

** voltage drop of 2.1v @ 20 ma is typical of yellow LEDs**
Red, orange  = ~1.6-1.9
White = ~ 3.4-3.6

V=I*R

Although this is over two months late, I hope it helps someone somewhere. JSD