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Flame imitating lighting ?

smokiedabong

Oct 3, 2009
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I'm looking to build a pulsating light that imitates a flame , something like the flameless candles but much more powerful .
At first I bought some flameless candles because I was thinking to hook the oscilator of the electric candle to a transistor and power a more powerful bulb . But to my surprise they have no oscillator inside , it's actually the LED that's pulsating . Is there a component that will variate current like that so it'll pulsate an ultrabright LED or a small bulb ? Or a simple circuit that will do that without using an Arduino ?
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Jan 21, 2010
25,510
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25,510
You may well be able to use the flickering LED.

The LED is actually not a simple LED (as you have no doubt realised). It is packaged with a small IC that makes it flicker. If it's like the flashing LEDs I've seen, it probably doesn't have a series current limiting resistor either, that function being carried out internally too.

A trick you could do with flashing LEDs was to place one or two normal LEDs in series with them and they would flash along with the flashing LED. This technique may also work with the flickering LED.

The first thing to try is placing another LED in series with a flickering LED, and using a slightly higher supply rail, see if they both flicker. If they do then you may well have a simple solution.

My suggestion would be to detect the changing current through the flickering LED and use it to control a higher powered LED.

This suggestion is really only worthwhile if you like the flickering of the LEDs you have, AND if another LED in series with them also flickers.

The other solution would be to use 2 oscillators with slightly different frequencies and mix their output. I'd suggest a triangular output and frequencies around 0.5 to 2 Hz.
 

smokiedabong

Oct 3, 2009
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I have built the following circuit . IC are the special flickering LEDs and the transistors are 2N2222A . The 8 LEDs are white with 3.5V voltage drop and 25 mA . All the LEDs light up at the same intensity and flikered nicely . The problem is when I tried to measure the amps to the LEDs the reading for three of them was 2mA and for the fourth was 55mA and after a minute or so the first burned out . I checked the circuit and there are no shorts , is there something wrong with this design ?

circuitcopy-1.jpg
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Jan 21, 2010
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Yup, there's something wrong.

remove the 3k3 resistors, and place a 10k resistor in series with each base.

One transistor was turning on at a slightly lower voltage .

Also select a resistor value that will limit the current to 25mA. I suggest that at least one of your 82R resistors is something other than 82 ohms -- could you have selected an 8.2 ohm resistor? Or is your 5V supply 9V?

82 ohms should limit the current to18mA -- less if you factor in the Vce(sat)
 

smokiedabong

Oct 3, 2009
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Oct 3, 2009
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Thanks for all your help

I made this changes to the circuit . The problem is when the switches A and B are open , the LEDs still have a dim light and after a while a group of 4 will get brighter and brighter . When I close the switches the LEDs will flicker for a 10-15 seconds and after that they will stay fully light . Do you think I need a drain resistor ?

PDF013.jpg
 
Last edited:

Resqueline

Jul 31, 2009
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Sounds fishy.. Maybe some transistor is bad or you have contaminants on the pcb conducting current. What kind of solder/ method do you use? May try to wash the pcb.
To find out what's going on you have to measure the voltage drops over each base resistor when it's "acting up", noting its polarity.
You could also just try to add two pull-down resistors (1k-10k), one to each base drive.
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Jan 21, 2010
25,510
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WHat Resqueline says, and also...

With those resistor values, you would be struggling to get more than about 20mA through the LEDs.

Check the resistance of them. Is it possible you have a mixture of 82, 820, and 8.2 ohm resistors?

If you can, wait until the LEDs are all ON (when they should be flickering) and disconnect the signal from the bases of the transistors, one at a time. Is one particular transistor causing the behaviour? Was it (probably not just by chance) one that was connected to a LED that "burned out"?
 
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