Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Flickering (candle) LED to trigger 555

ThomsCircuit

Active Member
Im wanting to add additional random flickering and fading LEDS together to improve the flickering effect. im going to ultimately put this into a "once" solar powered fence post light.
I will be using red, orange, yellow and white LEDS to produce the desired effect.
Two will flicker
One will fade on and off
One will be constant on
What I have done so far is read about how the LED flicker circuit works. From what i understand it is a noise generator. Some are random while others are merely a short song (happy birthday) played gifing the illusion of a random effect. Regardless of how the random is generated I have no luck making a generator with what I have on hand. I do however have these old tea lights. I tested a few and 6 volts is the max voltage for these. They do illuminate up to 9v but they go steady after a while at that voltage so my circuit will run on 5 volts DC

Of course I need a starting point so this schematic is it. (originally a fake Geiger counter) I bread boarded this and of course both leds light but LED2 (regular LED) is not flickering. Ive noted some voltages so you could help me get the right resistor/cap combination to hopefully make both LEDS flicker. The desired effect is while the flickering LED1 pulses it triggers the mono 555 at pin2 and this makes LED2 flicker but slightly out of sink from LED1 giving the illusion of a candle.

I would then like to design another circuit (using the same flickering LED) to fade an LED on and off.

This image shows the sound generator (removed from tea light) bottom right.
It has 4 pins. outside pins are power. Inside pins are the led. Ive modified the schematic to show the connection.
20220627_142321.jpg


This is the schematic. It was suggested to place a .01 cap across R3. I dont know what that means so i put it where i thought is should be.
The current state of this circuit is the LED2 is lit but it does not flicker. I need assistance making it flicker.
mono flicker.png
 

ChrisP58

Well-Known Member
Most Helpful Member
I think you first need to define what you mean by flicker.

I would say it is a light that is mostly on, but blinks off with quasi random duration and period. It may also have random brightness levels.
 

ChrisP58

Well-Known Member
Most Helpful Member
And your assessment would be spot on.
For that, I would use a microcontroller.

Otherwise you can use a oscillator and counter/decoder like a CD4017 with different resistors/diodes/opens on it's outputs to create that kind of an effect. But it will be a fairly short, repetitive sequence.
 

ThomsCircuit

Active Member
For that, I would use a microcontroller.

Otherwise you can use a oscillator and counter/decoder like a CD4017 with different resistors/diodes/opens on it's outputs to create that kind of an effect. But it will be a fairly short, repetitive sequence.
I understand that. As Ive explained in post one that I have the quasi random already worked out. I'd like to work with the schematic that I have posted. "To use the 555 to respond to the output"
Let's start with this. Can the 555 respond to the output from the "flicker"?
 

ChrisP58

Well-Known Member
Most Helpful Member
I understand that. As Ive explained in post one that I have the quasi random already worked out. I'd like to work with the schematic that I have posted. "To use the 555 to respond to the output"
Let's start with this. Can the 555 respond to the output from the "flicker"?
Sorry, I guess I was confused by the last line of your original post.
" The current state of this circuit is the LED2 is lit but it does not flicker. I need assistance making it flicker."

But yes, the 555 can be triggered by capacitively coupling a low going edge to the trigger pin, which will cause the output of the 555 to go high. You can configure the 555 as a one-shot, in which the output will go low again after a delay, but I don't think that will conform to our definition of a flicker.
 

ThomsCircuit

Active Member
but I don't think that will conform to our definition of a flicker.
i only have a multi meter. I have not hooked this generator up to a speaker but im almost certain its flicker effect is based on a song passage. I can see through my DMM the voltage go from 2.6 to 2.7 almost in a pattern. I would say that the slight variation is not enough to register with the 555. What say you?
 

ChrisP58

Well-Known Member
Most Helpful Member
i only have a multi meter. I have not hooked this generator up to a speaker but im almost certain its flicker effect is based on a song passage. I can see through my DMM the voltage go from 2.6 to 2.7 almost in a pattern. I would say that the slight variation is not enough to register with the 555. What say you?
The the internal flip-flop of the 555 is set (output goes high) when the trigger pin goes below 1/3rd of its Vcc voltage. It stays set until the threshold pin goes above 2/3 of Vcc.

You can use a resistor divider to set the trigger DC level just above 1/3 Vcc, then capacitively couple your source to the trigger pin. But what do you want to happen then?
 

ThomsCircuit

Active Member
The original author had a speaker connected to pin 3. each time pin2 was triggered a tick sound would play. sounded like a Geiger counter. The additional led at pin3 also "flickered".
I understand that the right combination of resistors are necessary for the 555 to be able to respond correctly. I just do not know how to figure out what they would be. The original design was powered by 9 volts. Mine is connected to 5 volts.
The way it is configured now the 555 does respond to the led on pin2 as the led at pin3 does illuminate, It just does not blink as the original authors did. If i remove the connection at pin 2 the voltage goes high (5v) and the led at pin3 does out. when i connect it back the voltage drops to 2.6 (low) and the led at pin3 illuminates. the issue is that the led at pin3 remains on (solid) no blinking or flickering.
 

New Articles From Microcontroller Tips

Top