Quite awhile back I was looking for a way to make LEDs flicker without having to use an Arduino or program a chip. I am not good with circuit design outside "calculate the resistor needed to make an LED work". Using a flicker LED in series might work if I was using 12v, but won't work well with 3v and 4.5v battery combinations, I came across this thread with (what looked like) a simple circuit showing how to use a 2N2222 transistor and an LED taken out of a tea light / candle to drive a 1W star.

http://brassgoggles.co.uk/forum/index.php/topic,36566.0.html

I wanted to make a basic green 5mm LED flicker, not a star. I bought the transistors and LEDs, thinking I could figure out how to modify it, but the rest of the project I was working on wasn't repairable and I never built the circuit. I'm trying to fix some old Halloween lighting now, and I wanted to do the same thing, except make 3mm warm white LEDs flicker instead of green. Unfortunately when I pulled up the bookmark I had saved, the photobucket with the circuit design had been deleted!

I found a second tutorial here, but I do not know the reason for the resistor values chosen. They don't match what 3 red LEDs in series would need whether they were 5mm or 1W stars. I don't understand how the transistor changes the calculation for the resistors needed or how to modify it for other types of LEDs, or understand the reasoning for having the 45 ohm resistor in front of the transistor circuit with a 10 ohm on the collector.

http://spookyblue.com/spookyblog/build-a-flickering-led-candle-amplifier

I found a third tutorial here that uses a PNP transistor instead of an NPN, again with no understanding of how the resistor values were chosen. I can see using a higher resistor than needed for the flicker LED since you only want it to drive the signal and not necessarily shine at full brightness (since it won't be used anyway). But I don't understand the resistor choice to light up the white LED.

https://www.evilmadscientist.com/2011/does-this-led-sound-funny-to-you/

I have 200 2N2222 transistors and I would really like to try to make this work with what I have, but I understand if it's just not going to work.

Basically: Use a 2N2222 transistor and a flicker LED taken out of a tealight to make one 3mm warm white LED (~3.2v/30mA) flicker, using a 3xAAA 4.5v battery pack. I just wish the circuit diagram on the first forum was still active. I tried making the circuit via the /text/ description in that link, with the 56 ohm resistor on the flicker LED and a 39 ohm resistor on the warm white LED, but the warm white is on steady and the flicker LED doesn't light at all. I also tested it with 120 ohm, 240 ohm, and 1k ohm resistors on the flicker diode.

 

This circuit should work but if you want to use a '2222 then just reverse the battery and the two LEDs.

 

This circuit should work but if you want to use a '2222 then just reverse the battery and the two LEDs.

THANK you. I swear I tried this by swapping the power on the breadboard and nothing lit up but I must have had the circuit built wrong. I never would have tried it again. I knew there had to be a simple solution I wasn't seeing. (I'm still curious as to what the diagram on the original website looked like!)

 

I swear I tried this by swapping the power on the breadboard and nothing lit up

You have to reverse the LEDs as well.

 

I like to think I remembered to do that but I probably didn't.

My final attempt I used all new components since one of the legs broke off the flicker LED and the transistor was pretty bent up because I was trying this with alligator clips until I was able to dig up the breadboard. Could be I shorted something out on an earlier attempt, though the LEDs were still lighting up on their own.

I really do need to learn more than very rudimentary basics about circuits but for now I just needed to fix this. Thanks!

 

The circuit above will not work for a couple of reasons.
The current through the flickering LED does not change very much, even through the LED is flickering as the current is divided between the LED and the microcontroller.
I don't know what the 620R is doing as the flickering LED has its own internal resistor.
By the time you add the 620R and 0.8v drop across the emitter-base of the transistor you will be lucky to get 1mA base current.
But this current will vary very little and the 1 watt LED will just sit there "sheepishly."

 

I don't see a microcontroller in the circuit. I also don't see a "flickering LED (which) has its own internal resistor."

 

I do.

 

Have you considered using LED's that flicker by themselves and need no additional circuitry?

https://lighthouseleds.com/led-component-lighting/animated-leds-flashing-blinking.html

 

Here's the micro:

 

From a post " Cob Led Candle Light ", a plot of LED current shows 10.6 mA to 1.5 mA with a 7.5 V supply. Driven LED is 1W yellow, driver 2N2222.

 

The reverse of the posted circuit does work, at least with 3mm warm white LEDs and not a 1W star LED.

The flicker circuit/microcontroller is inside the orange/amber LED taken out of an LED tea light. I do not know if there is also a resistor as part of it. Tea lights use 3v but also rely on the standard CR2032 battery to provide its own internal resistance - it's basically not capable of blowing out the LED. This becomes more of an issue when hooked up to AA batteries or a 4.5v AC adapter.

I made one circuit with the suggested 620ohm resistor and distributed it over 6 warm white LEDs (over 3 candles) in parallel (calculated 8.2ohms, only had a 10 ohm resistor so I used that) and let it run all night. If I was to do it again, I would use a separate circuit for each candle since it looks silly for them to all flicker in sync.

Currently attempting to integrate a circuit board out of an LED Christmas candle with an 8-hour timer inside it into this as well.