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Flexible 555 LED Pulsing (Breathing) CircuitAuthor
Giorgos Lazaridis
December 28, 2011


The circuit on breadboard for prototyping
Some time ago i uploaded a breathing LED circuit with the 555 timer chip. It became very popular and i received many comments and emails with people that made this circuit and worked fine, as well as comments with people that had troubles converting it to operate at 12 volts supply. It was designed to operate with 5 volts, because i plan to use it for a future PC mod. Since the PC power supply has 5 volts output, and since the LEDs that i plan to use require 3.8 volts to operate, choosing 5 volts for supply was the best choice to minimize power dissipation on the transistor.

Converting the original circuit to operate at 12 volts is not a big deal, but it requires some transistor knowledge. The only parts that should be changed were the biasing resistors R4 and R5. But i decided to take it one step further. I decided to make a more flexible breathing circuit. The new version as 2 more functions: It has an adjustable voltage oscillation amplitude, and an adjustable output DC offset. What this means is that it can be easily adjusted to operate with different LEDs. If for example the load is a 12V LED strip with operating voltage range 8 to 12 volts, the circuit can be adjusted to provide exactly this: 8 to 12 volts output. Similarly, it can be adjusted to operate with a high brightness LED that has voltage range from 2.4 to 3.8 volts.








The Circuit
Here is the schematic circuit for the new version:



 
The circuit (click to enlarge)		 





You can set the fade-in and fade-out durations with these potentiometers

You can set the output voltage amplitude and the output DC offset with these potentiometers.

You may need to add a heatsink to the power transistor.
As you may notice, the left portion of the circuit, the 555 astable multivariate - has not been changed. The functionality is exactly the same as described in the previous article. The two variable resistors R2 and R3 are used to set the fade-in and fade out time.

From the same position (across C1) i get the capacitor's voltage. This is the waveform that we will work with. I like the charging characteristic of the capacitor because it provides a more "natural" breathing effect. Instead, you may wanna use a triangular waveform as an input, but I've test it already and rejected it immediately.


Instead of using a diode to couple the 2 circuit parts, i use a large electrolytic capacitor. That is because i want to have a pure AC waveform to feed the first transistor amplifier. So, C2 is a coupling capacitor which cuts-off all DC currents form the 555 timer. A large resistor (R4) is used to minimize the effect of the transistor amplifier to the 555 operation.

The potentiometer R7 is the first new feature added to the circuit. This is the amplitude control potentiometer. This potentiometer changes the voltage amplitude that will be fed into the base of the transistor amplifier, and thus it controls the output signal amplitude. It works exactly as the volume control on an audio amplifier: the bigger the input signal, the bigger the output signal.

The first amplifier (T1) is a common emitter with fixed bias. R8 is the base resistor which sets the operation point, and R5 is the collector resistor which sets the amplification gain. The output of the amplifier is again coupled though a large electrolytic capacitor (C3). At the output of this coupling capacitor we have an AC signal oscillating around gnd, with the final amplitude that will be fed into the base of the second amplifier. Since the LEDs operate with voltages above 0V, we need to shift this oscillation to the proper position.

Suppose for example that we want to power an LED that operates from 2.4 to 3.8 volts. This means that the output oscillation amplitude should be 1.4 volts (3.3-2.4). At the output of C3 we will have an oscillation from -0.7 to +0.7 volts. So we need to shift this oscillation 3.1 volts. This is achieved by adding a DC offset. The potentiometer R6 does exactly this. It is connected as a voltage divider, and provides a DC voltage from 0 to 12 volts. This voltage is then injected at the AC voltage. The result is the required oscillation.

Finally, the signal is fed into an emitter follower amplifier (T2) to increase the current. I chose a power darlington pair transistor for this stage, so that it can provide sufficient current for the LEDs, and also to be able to dissipate enough power.

There is something that you should notice here: An emitter follower amplifier can provide maximum current, but the maximum voltage will be about 0.7 volts less than the supply voltage. What this means is that, if you plan to control a 12V LED strip (this is what most people told me that want to use), you will need at least 12.7 volts as supply to have full brightness.

ONE LAST THING!!! BE CAREFUL! As you see, i have no limiting resistor for the LEDs. You need to add a limiting resistor if required, otherwise bot the LEDs and the transistor may be damaged. I chose not to add a resistor, since the circuit can provide exactly the voltage required for the LEDs. If you set the circuit correctly, then you do not need to add any resistor. This is one good advantaged if you plan to use high power LEDs, since a high power LED would require a high wattage resistor. But make sure that you have set the circuit properly before connecting your expensive LED!



Adjusting the circuit
It is very important to correctly adjust the circuit before you connect the LED. The adjustment has to do with the output voltage amplitude and DC offset. The maximum voltage of the oscillation must NOT exceed the maximum forward voltage (Vf) of the LED. As for the minimum oscillation voltage, this can be adjusted to any value.

If the LED forward voltage is the same as the circuit's supply then you can adjust the circuit more freely. But if the supply is much higher than the LED's voltage, you must follow these steps. First, you need to have a volt meter. It will be easier if the voltmeter has analog display.

Step 1:

Connect the voltmeter at the output of the circuit (pads LED+ and LED-).

Step 2:

Adjust the 555 to maximum fade-in and fade out duration, by turning the potentiometers R2 and R3 to maximum resistance

Step 3:

Turn the potentiometers R6 and R7 to the middle. The volt meter must now show readings. Notice that the readings are not stable, the voltage must increase and decrease slowly.

Step 4:

Now you need to decide what will be the voltage oscillation. You may wanna start with a typical 2 volts oscillation for a simple 3.2 or 3.8 Volts LED, or 4 volts oscillation for a 12 Volts LED strip. Turn the potentiometer R7 to adjust this oscillation. The maximum voltage shown on your volt-meter minus the minimum voltage is the oscillation amplitude. So, if for example you want to have 4 volts oscillation and the minimum voltage shown on the voltmeter is 4 volts, then turn the R7 slowly until the maximum voltage becomes 8 volts (8-4=4).

Step 5:

Now you need to adjust the DC offset. Slowly turn the potentiometer R6 until the maximum voltage of the oscillation becomes equal to the forward voltage of the LED. Do not rush finishing this step. Watch the multimeter for one minute or so and make sure that the voltage does NOT exceed the forward voltage of the LED.

If you finish all the previous steps successfully, you can connect the LED. Since the transistor has an internal collector resistance, you may wanna repeat step 5. That is because if the LED draws too much current, there will be a high voltage drop across VCE.

Good Luck.


This is the output when the circuit operates as a flasher The fade-in is faster than the fade out The fade in is much slower than the fade out.



No DC offset added - The oscillation is around the zero line. Added 4 volts DC offset - The oscillation is from 2 to 6 Volts The amplitude is decreased. It is less than 2 volts The amplitude is increased. It is about 11 volts





Bill Of Materials [BOM]

Resistors
R1Resistor 100 Ohm 1/4 Watt 5% Carbon Film 
R2Potentiometer 10 KOhm Linear Rotary 1/2W
R3Potentiometer 10 KOhm Linear Rotary 1/2W
R4Resistor 82 KOhm 1/4 Watt 5% Carbon Film
R5Resistor 1 KOhm 1/4 Watt 5% Carbon Film 
R6Potentiometer 100 KOhm Linear Rotary 1/2W
R7Potentiometer 470 KOhm Linear Rotary 1/2W
R8Resistor 470 KOhm 1/4 Watt 5% Carbon Film
R9Resistor 1 KOhm 1/4 Watt 5% Carbon Film 
R10Resistor 100 KOhm 1/4 Watt 5% Carbon Film 
Capacitors
C1Electrolytic Capacitor 470 uF 16 Volts
C2Electrolytic Capacitor 470 uF 16 Volts
C3Electrolytic Capacitor 470 uF 16 Volts
Diodes
D11N4148 Switching Diode 
Transistors
T1BC338 NPN Silicon AF Transistors 
T2TIP142 Complementary Silicon Power Darlington Transistor 
Integrated Circuits
IC1555 Timer 















Comments

  • At 16 May 2013, 16:46:31 user Sparky3489 wrote:   [reply @ Sparky3489]
      • @Giorgos Lazaridis

      @Jani this circuit will not sync with another.

      Actually it will for brief periods at a time.

  • At 16 May 2013, 6:27:36 user Giorgos Lazaridis wrote:   [reply @ Giorgos Lazaridis]
      • @Jani this circuit will not sync with another.

  • At 15 May 2013, 10:41:47 user Jani wrote:   [reply @ Jani]
      • Hi,
      I like Your design and want to know some more.
      Does it work if I make five of them and connect them in paraller in 12VDC?

      I tried different design and found out that they went in sync after a couple of flashes. So how would Your design work in paraller?

  • At 26 April 2013, 9:36:25 user Sparky3489 wrote:   [reply @ Sparky3489]
      • @Amit kishor shama

      It works. Recheck your work.

  • At 26 April 2013, 6:56:33 user Amit kishor shama wrote:   [reply @ Amit kishor shama]
      • sir ,
      its not working . please upload video in which you make it

  • At 13 April 2013, 2:43:07 user Giorgos Lazaridis wrote:   [reply @ Giorgos Lazaridis]
      • @Roger You can use a 500K which is more common

  • At 12 April 2013, 17:34:37 user Roger wrote:   [reply @ Roger]
      • @Giorgos Lazaridis

      Where do I find the 470K Ohm potentiometers same to what you some in your video?

  • At 23 March 2013, 15:01:09 user Giorgos Lazaridis wrote:   [reply @ Giorgos Lazaridis]
      • @Giorgos Pan sure ;)

  • At 20 March 2013, 6:53:21 user Giorgos Pan wrote:   [reply @ Giorgos Pan]
      • I didn't manage to find a 555 but a ka556, i've been told it's like 2 555s / Do you believe it's going to work?

      Thank you and congratulations for your work!!

  • At 5 March 2013, 12:06:44 user Giorgos Lazaridis wrote:   [reply @ Giorgos Lazaridis]
      • @bruno Try this one:
      http://www.pcbheaven.com/circuitpages/Ambient_light_Level_Equalizer
      It is easier to reverse its operation

  • At 1 March 2013, 4:26:13 user bruno wrote:   [reply @ bruno]
      • Thanks for your circuits , I'm looking for it for my home external IP cam.
      Just one thing : I would like the led brightness is automaticaly adjusted according to the ambiant light : very bright if sunny, medium if cloudy, low (but not 0) during nighttime. I think about add a lightCellResistor near R7, but since I didn't play with electronics since 25 years, could you help me please, before I build the circuit.
      Thank you very much.

  • At 27 February 2013, 6:44:38 user ilauzirika wrote:   [reply @ ilauzirika]
      • I know I know, that is why I am trying different stuff right now :)! and PICs are also our friends!

      thank you for all your help, Never give up there is always some way to do it!

  • At 26 February 2013, 15:33:37 user Sparky3489 wrote:   [reply @ Sparky3489]
      • @ilauzirika

      ANYTHING is possible in electronics.

  • At 26 February 2013, 13:10:37 user Giorgos Lazaridis wrote:   [reply @ Giorgos Lazaridis]
      • @ilauzirika No. This is not possible with this circuit.

  • At 23 February 2013, 18:59:11 user ilauzirika wrote:   [reply @ ilauzirika]
      • Thank you for all the wonderful circuits you have shared!

      I just have a question. Could this circuit be adapted to drive an octocoupler which then would drive a triac and finally get the breathing effect in a bigger 220v lamp?

      I love this pulsing effect and would love to be able to use it in a bigger project.

      thank you for your help!

  • At 4 February 2013, 10:28:56 user kyle wrote:   [reply @ kyle]
      • I'm having trouble obtaining voltage swings above 1 volt. Any ideas what could be wrong?@Giorgos Lazaridis @Giorgos Lazaridis

  • At 25 January 2013, 12:12:55 user Giorgos Lazaridis wrote:   [reply @ Giorgos Lazaridis]
      • @Moein normally you shouldn't have any problem.

  • At 25 January 2013, 5:31:42 user Moein wrote:   [reply @ Moein]
      • Hi Giorgos,

      The Pots you have listed are 0.5watt, I've ordered 0.15watt miniatures, can you tell if these are suitable to use? Or do I need to get 0.5watt units?

      Thanks for sharing and thanks for your response in advance!

  • At 16 January 2013, 3:31:19 user Emthelimey wrote:   [reply @ Emthelimey]
      • This might be just what I need! Recon it'll work with a 12v EL panel?

  • At 6 November 2012, 3:57:10 user Giorgos Lazaridis wrote:   [reply @ Giorgos Lazaridis]
      • @tvc Well, i think that yes, you can do it... You can try it! Then post the results back to us...

  • At 5 November 2012, 3:10:57 user tvc wrote:   [reply @ tvc]
      • Hi, thank you for your great designs!
      This really helps me out.

      I have a small question: can i replace the leds with a 12vDC fan?
      So that the fan is fading in and fading out.
      I guess it's the same? I only need a diode to prevent the flyback voltage.


      Thank you in advance!

  • At 22 October 2012, 3:20:07 user Giorgos Lazaridis wrote:   [reply @ Giorgos Lazaridis]
      • @Andrew most often problem is that the diodes are not properly connected

  • At 21 October 2012, 9:12:06 user Andrew wrote:   [reply @ Andrew]
      • First, thanks for sharing your circuit designs, these make for some cool projects. I'm having trouble with both of your breathing LED circuits. I believe I've followed your specs exactly, but both oscillators decay quickly (within ~1.5 cycles) to a steady voltage. So typically the voltage will increase over the course of 3-4sec, then decrease slowly for ~2min and stabilize. Adjusting any of the pots perturbs the voltage, but then it settles back to a steady value following the same pattern. The only pot that seems to do anything else is R6, which also adjusts the resting voltage as stated.

      Any idea what might cause that?

  • At 3 September 2012, 20:11:56 user Raman wrote:   [reply @ Raman]
      • @Giorgos Lazaridis
      Oh i got it...very thanks to you Giorgos...

  • At 2 September 2012, 21:33:37 user Giorgos Lazaridis wrote:   [reply @ Giorgos Lazaridis]
      • @Raman 2 is the middle one. 1 and 3 are the sides. does not really matter how you connect 1 and 3. if the circuit works the wrong way (e turning CW the potentiometer goes slower) then change 1 with 3 and it will reverse operation (turning CW it will go faster).

  • At 2 September 2012, 13:19:55 user Raman wrote:   [reply @ Raman]
      • @Giorgos Lazaridis
      @Giorgos Lazaridis
      Thanks Giorgos for reply..
      wana ask one more question,
      in schematic u show the potentiometer pins as 1 2 3 so how to determine that which pin is 1 and which pin is 2 and which is 3...i am very new in circuits and components so please help me...


      Thanks

  • At 29 August 2012, 1:01:56 user Giorgos Lazaridis wrote:   [reply @ Giorgos Lazaridis]
      • @Raman it works at 9v

  • At 28 August 2012, 11:58:46 user Raman wrote:   [reply @ Raman]
      • hi friend, please help me,

      will this circuit work on 9 volt DC? if not then what changes i have to made to do this possible....

      Thanks..am waiting ur answer, please mail me too if u can..:)...

  • At 10 August 2012, 1:07:09 user Giorgos Lazaridis wrote:   [reply @ Giorgos Lazaridis]
      • @Carl LaMonte sorry Carl, i just missed to approve your message and did not answer. For different breathing rates you will need different circuits.

  • At 8 August 2012, 15:35:13 user Giorgos Lazaridis wrote:   [reply @ Giorgos Lazaridis]
      • @Squigly You can use bigger R1, bigger potentiometers (R2/R3) and bigger capacitor C1. Whatever you like.

  • At 8 August 2012, 14:10:58 user Squigly wrote:   [reply @ Squigly]
      • Finally got down to building the circuit, again thank you for this! I have also built your previous fader but find this one seems to fade the led's in and out much faster, is there any way to slow the effect? R2 & 3 are already set to max.

  • At 7 August 2012, 22:54:44 user Carl LaMonte wrote:   [reply @ Carl LaMonte]
      • Is it possible to make this to control 4 different LED's with different breathing rates? Or do I just need to make 4 of these one for each led? I would like to control 4 different led's and have all four of them breath at different rates.

      Also if you made a board to make these and supply the parts you could probably make so good money off them:)



      Thanks, Carl

  • At 29 July 2012, 21:19:46 user Marco Hernandez wrote:   [reply @ Marco Hernandez]
      • Greetings,

      I a sculptor who would like to incorporate the breathing led effect in some sculptures. However, being I have very little experience with electronics and schematics readings, I was wondering if you could share step by step directions in assembling a unit that controls 3 or more led's.

      Thanks in advance for your reply.

  • At 26 July 2012, 10:56:14 user Giorgos Lazaridis wrote:   [reply @ Giorgos Lazaridis]
      • @Jeet Verma sure, depends on the supply and the power that the LEDs require

  • At 26 July 2012, 8:01:09 user Jeet Verma wrote:   [reply @ Jeet Verma]
      • dear sir can i use more led with this circuit..?

  • At 25 July 2012, 6:28:39 user evo wrote:   [reply @ evo]
      • i have done the circuit but it seem the light is dim and not fading

  • At 4 July 2012, 8:26:03 user Giorgos Lazaridis wrote:   [reply @ Giorgos Lazaridis]
      • @BARIS DOGAN you're right. so i uploaded fairchild datasheet. Thanks

  • At 4 July 2012, 5:30:45 user BARIS DOGAN wrote:   [reply @ BARIS DOGAN]
      • in Bill Of Materials section , the link to BC338 datasheet, open the SIEMENS datasheet. Package: TO-92

      http://www.futurlec.com/Transistors/BC338.shtml in this datasheet, C and E pins different. Be carefull when you connect it.

      My T1 was not work , i will try it again tonight. i hope it will work this time.

  • At 12 June 2012, 22:15:00 user Giorgos Lazaridis wrote:   [reply @ Giorgos Lazaridis]
      • @igor no not with circuit. this circuit fades in and out continuously.

  • At 12 June 2012, 15:10:50 user igor wrote:   [reply @ igor]
      • it's possible to stop de breathing effect be some sort of a switch? like fade in then stop full bright and then start to fade out to idle and stop again?

  • At 21 May 2012, 5:50:52 user Giorgos Lazaridis wrote:   [reply @ Giorgos Lazaridis]
      • @BARIS DOGAN This circuit is flexible so the output can vary by the potentiometer. You do not need to go strictly 82 Ohms, because you can simply supply less voltage to the LEDs. I would say 47 Ohms is pretty much fine, the reason for this resistor is for balancing, not really limiting.

  • At 21 May 2012, 5:08:29 user BARIS DOGAN wrote:   [reply @ BARIS DOGAN]
      • thanks for your reply. I can not see your answer, and not sure is posted or not, and posted again.

      i found a LED ARRAY WIZARD on a site , and its calculate 3 LEd 82 ohms ( with 3.5V and 20mA)

      its right or not =

  • At 21 May 2012, 4:24:49 user Giorgos Lazaridis wrote:   [reply @ Giorgos Lazaridis]
      • @BARIS DOGAN Hello! The best solution is to connect 3 LEDs in series and then connect 8 of these series in parallel. You need to use also a small limiting resistor in series to each 3-series LEDs (so you will need 8 resistors). These are balancing resistors in case that something goes wrong. Also, to connect LEDs in parallel you need to be sure that all LEDs are exactly the same, otherwise one or more branches will not work. There is a relative article for this:
      http://www.pcbheaven.com/wikipages/LEDs/

      This resistor can be for example 10 to 47 ohms.

  • At 21 May 2012, 2:04:41 user BARIS DOGAN wrote:   [reply @ BARIS DOGAN]
      • @Giorgos Lazaridis

      Hello , and thank you too much for this great job , this is what i need...

      i am new @circuits, just wonder and trying to be learn. I have a question , if you can answer, i will be happy.

      I am trying to build a nightlamb / shaded lamb , with this circuit. I will use 18 or 21 pieces 5mm diffused type LED.

      How can i do this, can i connect all of leds paralel ? or i have to connect3 Leds 1 ressistor serial , and then 6 or 7 group paralel ?

      if you (or anyone) can help me, i will be very happy. This is very simple question for you, but i am very new @electronics.

      thanks for all

  • At 29 March 2012, 19:40:24 user Scott wrote:   [reply @ Scott]
      • You do know you can put in component values in Eagle CAD, right?

      http://sparky3489.webs.com/pcinterfaceproject.htm

  • At 21 March 2012, 10:49:49 user werner wrote:   [reply @ werner]
      • @Giorgos Lazaridis
      means a battery of heatsinks for the transistor...;)
      at least the collector current is up to 10A...
      I'll try it...

  • At 21 March 2012, 10:30:33 user Giorgos Lazaridis wrote:   [reply @ Giorgos Lazaridis]
      • @werner 3w LED will have probably 1A of current (about) so the dissipation on the transistor will be huge. If this does not bother you, it will work.

  • At 21 March 2012, 5:14:08 user werner wrote:   [reply @ werner]
      • Hi Giorgos,

      really great job! I will try out and look if I manage to fade away (i.e. my LEDs...;)
      Do you think it's possible to trigger a normal 3W LED-bulb with the circuit (probably after changing the resistors in the bulb which are for 240V)?

  • At 3 February 2012, 23:52:00 user Giorgos Lazaridis wrote:   [reply @ Giorgos Lazaridis]
      • @Brian Yes sure, it will work

  • At 3 February 2012, 14:04:58 user Brian wrote:   [reply @ Brian]
      • Thanks for the response. Would a 500 Kohm pot work in lieu of the 470? I can't seem to locate a 470 anywhere!
      thank you!

  • At 3 February 2012, 12:37:54 user Giorgos Lazaridis wrote:   [reply @ Giorgos Lazaridis]
      • @Brian from local market, ebay, internet... different sources every time. i have a stock of parts now, and i do not really remember.

  • At 2 February 2012, 13:51:29 user Brian wrote:   [reply @ Brian]
      • Kammenos, Wonderful job! Can you tell us where you purchased the transistors and potentiometers? Thankyou for you insight!
      Brian

  • At 22 January 2012, 14:26:33 user Kammenos wrote:   [reply @ Kammenos]
      • @Usman better post photos in the forum. we cannot help you otherwise.

  • At 16 January 2012, 13:14:44 user Usman wrote:   [reply @ Usman]
      • I CAN INCREASE THE BRIGHTNESS OF THE LED BUT I CANNOT FADE IN AND FADE OUT WHAT WILL BE THE MISTAKE PLZ LET ME KNOW ASAP

  • At 15 January 2012, 0:01:08 user Kammenos wrote:   [reply @ Kammenos]
      • @Usman first, have you tried to control the LED brightness with R6? Also, what LED do you use (forward voltage) and what is your power supply voltage?

  • At 14 January 2012, 14:54:08 user Usman wrote:   [reply @ Usman]
      • You are genius sir but i am not need your help

      i had hired a guy to make this for me everything is ok but i can not make the led bright.The light is very dim on led what can be done to increase the light on it

  • At 10 January 2012, 10:14:23 user Kammenos wrote:   [reply @ Kammenos]
      • @Squigly yes indeed. one is decoupling capacitor for the supply, you may need to add one or you may not, depends on your power supply.

  • At 10 January 2012, 9:57:40 user Squigly wrote:   [reply @ Squigly]
      • Hi there

      Thanks for sharing this!! Just a question, in your video it seems you have 4 Capacitors, but in the BoM you have 3 (all identical)


     

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