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PCB Fabrication
1 August 2011
Author: Giorgos Lazaridis
A 555 Breathing (Pulsing) LED


The control panel of my PC desk. I have not finish it yet.
January 2, 2012 Update: I uploaded another circuit with the same functionality but operates at 12V and can control any LED (or LED strip) from 12 volts and bellow.
Link: Flexible 555 LED Pulsing (Breathing) Circuit


During this very long period that my PC went bad, i had the time to do many thing like finishing the PC case mod that i began like two years ago... So i connected the power button, the reset button and the audio controls. The rotary encoder will be used for my next project that will be a gigantic scriptable 8-channel PC fan controller.

Now, regarding the power button, it has a blue LED that light when the HDDs are operating (write or read process). The effect is very cool, but i want to make it cooler. I want the LED to blink when the HDDs are used, and when no Read/Write operation occurs i want the LED to breath. A breathing LED is the effect that the LED turns on and off by fading in and fading out, which gives the feeling of "breathing"...







The Circuit

I do like microcontrollers, but i prefer analog electronics whenever possible. I quickly searched around the internet to get ideas of analog breathing LED circuits, but i did not found something that i liked. So i designed my own pulsing LED circuit with a 555 timer:






The circuit on a breadboard for test

Generally, when we talk about ramps and delays in analog electronics, we talk about the charging and discharging time of a capacitor. So, i began designing the circuit around a big capacitor. The 555 chip is connected as an astable multivibrator. If you put the oscilloscope probe across the capacitor, this is what you will get (click to enlarge):











For me, this is a very cool breathing ramp! So i get this ramp through a decoupling diode and a big resistor to the first transistor current amplifier, to amplify to a usable level without disturbing the charging/discharging process of the 555 chip. Then i further amplify the current with a second transistor amplifier, which finally drives the LED. So simple! Now look the voltage across the capacitor (yellow channel) in comparison to the voltage across the LED (blue channel):





Breath in... Breath out... But how fast? To get the most out of this circuit, i added the D1 diode. This diode allows the 555 timer to achieve duty cycles less than 50% (which normally doesn't). Moreover, i added 2 different potentiometers. The R2 potentiometer adjusts the fade-in time, and the R3 potentiometer the fade-out time. So, you may adjust the circuit to act as a breathing LED, or as a flash-in fade-out LED, or as a fade-in flash-out LED.

Finally, something about the LED voltage and current. Different LEDs require different forward voltages and draws different current. You may need to change the value of R5 to change the voltage across the LED and R6 to change the current.




Bill Of Materials
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 100 KOhm 1/4 Watt 5% Carbon Film 
R5Resistor 4.7 KOhm 1/4 Watt 5% Carbon Film 
R6Resistor 47 Ohm 1/4 Watt 5% Carbon Film 
Capacitors
C1Electrolytic Capacitor 470 uF 16 Volts
Diodes
D1-21N4148 Switching Diode 
Transistors
T1BC337 NPN Silicon AF Transistors 
T22N2222 Switching NPN Transistor 
Integrated Circuits
IC1555 Timer 




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Comments

  • At 6 May 2012, 16:28:16 user Giorgos Lazaridis wrote:   [reply @ Giorgos Lazaridis]
      • @Nuin You may need to change R4 and R5

  • At 5 May 2012, 14:26:27 user Nuin wrote:   [reply @ Nuin]
      • Can I use a 2N4401 in place of the BC337 NPN transistor? Thanks.

  • At 2 May 2012, 12:41:08 user Giorgos Lazaridis wrote:   [reply @ Giorgos Lazaridis]
      • @Rasmus the one on the video is 0805 smd blue

  • At 2 May 2012, 12:34:38 user Rasmus wrote:   [reply @ Rasmus]
      • what LED does you use?

  • At 23 April 2012, 1:33:25 user Giorgos Lazaridis wrote:   [reply @ Giorgos Lazaridis]
      • @Mike Thorpe I'm not quite sure if a PNP transistor would work for you but there is a good chance to try it

  • At 22 April 2012, 17:38:45 user Mike Thorpe wrote:   [reply @ Mike Thorpe]
      • Thank you. Have been looking for a 5v circuit to do just that. Is there a way to modify this circuit to run two LED's opposite each other. ex. have a blue LED breathing in as a red LED exhales

  • At 9 April 2012, 6:55:51 user nassershah wrote:   [reply @ nassershah]
      • Thank you sir.., for the above schematic.

  • At 8 April 2012, 7:58:35 user Giorgos Lazaridis wrote:   [reply @ Giorgos Lazaridis]
      • @nassershah I'm sorry mate, i do not do circuits on request

  • At 8 April 2012, 7:43:59 user nassershah wrote:   [reply @ nassershah]
      • Dear Sir,
      How can I make a fake alarm 1 LED with adjustable flash rate using potentiometers so that it doesn't flash fast and look so fake. I would really appreciate if you could help me with a simple circuit to diy.
      Thank you.

  • At 1 April 2012, 1:52:49 user Tomas wrote:   [reply @ Tomas]
      • I'm a prop maker in Los Angeles. I have no circuitry experience & a short time frame.

      Would someone be willing to make a few of these adjustable pulsing circuits for me, at a reasonable cost? I need one right away for a light box sign with LED's. And I would want a few more down the road for both low voltage LED's & 110v.

      CHEERS!

  • At 13 March 2012, 2:26:53 user Giorgos Lazaridis wrote:   [reply @ Giorgos Lazaridis]
      • @Otobeagod whatever. the circuit only needs a charging/discharging capacitor.

  • At 12 March 2012, 22:01:29 user Otobeagod wrote:   [reply @ Otobeagod]
      • Kammenos,

      Thank you. One last question. What about using a cmos 7555 instead of the 555?

      Till morrow,
      Joey

  • At 2 March 2012, 13:05:41 user Giorgos Lazaridis wrote:   [reply @ Giorgos Lazaridis]
      • @Otobeagod no, not possible. too low.

  • At 1 March 2012, 23:33:26 user Otobeagod wrote:   [reply @ Otobeagod]
      • Kammenos,

      What about operating at 3v?

  • At 2 January 2012, 12:29:18 user Kammenos wrote:   [reply @ Kammenos]
      • Ok, i've just made a new LED breathing circuit with variable output. It operates at 12 volts and can control any LED that operates from 12V and bellow (tested also with 21W 12V incandescence lamp and worked).

      Link: http://www.pcbheaven.com/userpages/Flexible_555_LED_Pulsing_Circuit/

  • At 20 December 2011, 1:35:31 user Kammenos wrote:   [reply @ Kammenos]
      • @vimal R6 has only to do with your LEDs, so you need to change R6 only if you change LEDs. As for the transistor, since it is am emitter follower, a darlington will work better than a simple transistor.

  • At 19 December 2011, 12:52:43 user vimal wrote:   [reply @ vimal]
      • when changing the npn transistor T2 to a higher one,should i change the resistor r6?

      will this darlington pairs work?

      tip142

  • At 14 December 2011, 21:42:45 user CN. wrote:   [reply @ CN.]
      • good idea for x-mas light.. thank you :)

  • At 8 December 2011, 4:08:07 user binoy wrote:   [reply @ binoy]
      • sir. what all changes i have to make in this circuit for using a 9v supply instead 5v ?

  • At 7 December 2011, 16:14:07 user Kammenos wrote:   [reply @ Kammenos]
      • @vimal not yet, no 12v mod. For more current use a bigger resistor for T2. Maybe a power darlington pair resistor.

  • At 6 December 2011, 14:05:28 user vimal wrote:   [reply @ vimal]
      • hello,nice work,

      is there any modification for 12v input?

      what are the things to change if i need 2amps output for led strips?

      thanks

  • At 10 November 2011, 12:07:14 user Sam Fischer wrote:   [reply @ Sam Fischer]
      • As an add-on to my last post, I forgot to thank the author Kammenos. This schematic helped me figure out what to put where. Initially it did not work, but I was also using different transistors so I did not expect it to work on the first try.

      I used 2x 3904 NPN transistors (instead of a bc337 & 2n2222)
      'C1' I used 2 470 uF caps in parallel
      'R5' I used a 420 ohm resistor
      'R6' I used a 100 ohm resistor (but this will change depending on the current requirements of the LED and the Vsat of the transistor)

      With this I get a nice smooth fade around 3 seconds off to off (longer with higher 'C1' value) and a quick blink if I adjust the 10k pots the other way.

  • At 10 November 2011, 10:12:03 user Sam Fischer wrote:   [reply @ Sam Fischer]
      • FOR EVERYONE WITH QUICK ON/OFF OR CONSTANT-ON LED...

      If constant on....increase R5 (POTs are good for testing)

      If quick on then off forever....decrease R5

      For longer fades and more control with the 10K POTs....increase C1

      ABOVE ALL triple check wiring...I have yet to wire a circuit with more than few parts correctly the first time.

  • At 25 October 2011, 19:49:37 user toby wrote:   [reply @ toby]
      • I am trying to make a similar circuit but I cannot get it to work. the led just stays on and does not fade on and off. The only thing I can think of is I am using 1/8 watt resistors and not 1/4 watt. Here is the link to what I want to build http://www.instructables.com/id/ThrobbingFading-LED-with-555-Timer/ . Also does the voltage of the capacitor matter? Thank you.

  • At 9 October 2011, 16:54:21 user Roger wrote:   [reply @ Roger]
      • YUP that Yenka simulation software is amazing as usual! I built the original circuit with these modifications and it works perfectly!! R2= 100k , R3= 100K, C1= 100uf, R4=110K, R5=3K. The only reason I changed the pots was because I didnt have spare 10K pots so the original 10k values with the 470uf cap should work the same. Its resistor R4 & R5 that made the difference for me.

  • At 9 October 2011, 16:19:23 user Roger wrote:   [reply @ Roger]
      • I was having problems with this circuit so I decided to draw it out in the Yenka simulation software. Same issues until I starting varying the resistor values R4 & R5. Right now I have R4=120K & R5= 3K its working great now! Seems to be finiky matches these values to your LED then once this is working using the pots to vary the dimming seem to work as seen in the video, at least through the software. I'll try it on the breadboard soon.

  • At 4 October 2011, 9:49:30 user Kammenos wrote:   [reply @ Kammenos]
      • @RCC bc337 has much larger hfe than 2n2222, and 2n2222 has metal package which can take heat sink and manage almost double power dissipation than bc337

  • At 4 October 2011, 9:35:54 user RCC wrote:   [reply @ RCC]
      • Why are T1 and T2 different? The specs between BC337 and 2N2222 are more similar than they are different and these 2 often can be interchanged.

  • At 3 October 2011, 16:26:45 user Jayson wrote:   [reply @ Jayson]
      • Kammenos:

      I appreciate your efforts. I will patiently standby and await your masterpiece. :-)

      Thanks
      Jayson

  • At 3 October 2011, 14:07:23 user Kammenos wrote:   [reply @ Kammenos]
      • @Jayson i'm working hard and intensive to get it right and get it fast. I do not want to be "yet another transistor theory". I get knowledge from 3 different books and i have email conversation with a transistor manufacturer to make something nice. It will take me some more time, because this weekend i could not work, and this week may be hard as well.

  • At 3 October 2011, 9:52:15 user Jayson wrote:   [reply @ Jayson]
      • Kammenos:

      Have you finished re-writing your transistor theory? Before I continue my attempt to have this circuit work for 12VDC I would like to read your additional theory information.
      Thanks again.
      Jayson

  • At 28 September 2011, 10:52:23 user Kammenos wrote:   [reply @ Kammenos]
      • @Jayson something like that, but not exactly. The second transistor will not work exactly as an amplifier. The output of T1 may be around 5 and 9 volts (these values are not be real, just an example). The intermediate transistor has to change these numbers to the min and max voltage that your LEDs need to operate (for min and max brightness). That could be 5 to 12 volts or something different. An oscilloscope would be a great help for you at that point.

      I have just began (today) re-writing the transistor theory that i already have in my site. The new theory will have more than 4 pages and it will explain in details how you can calculate and design the most commonly used transistor amplifiers. One of the chapters is the type of amplifier that you need here. Maybe this will help.

  • At 28 September 2011, 10:35:29 user Jayson wrote:   [reply @ Jayson]
      • Kammenos:
      Are you suggesting to build a Darlington pair with T1 C to T3 B, T3 E to T2 B and T3 C + R to Source? If so I will try tonight. Obviously this problem would be easier to handle with a PIC but what fun would that be :-).

      Thanks
      Jayson

  • At 28 September 2011, 7:46:32 user Kammenos wrote:   [reply @ Kammenos]
      • @Jayson the easiest solution is to add a 3rd transistor between t1 and t2. T2 works as a voltage follower, which means that it will output the same voltage as it receives at its base, it cannot scale the voltage. T1 operates as an amplifier, the output voltage depends on the current of the base and R5. You could add some potentiometers to try and scale the t1 output, but it is kinda difficult. I suggest you add a transistor in between to scale the voltages. I cannot suggest you which resistors to use because you have to find yourself.

  • At 27 September 2011, 23:21:40 user Jayson wrote:   [reply @ Jayson]
      • Kammenos:

      I'm unfamiliar with transistor polarization. If you have a extra moment would you explain it?

      I had no luck with add a resistor/pot(100k) to the right side of R4. In fact when connected to base of T1 it disabled the Leds.
      The voltage divider did work to help bring up the brightness a bit but did nothing for the min light level.

      I experimented more with changing the values of R1, R4 and R6 with no luck. Would I have better luck using a power transistor, a 3rd transistor or possibly a op-amp?

      Again thanks for your time and help with this. I hope to have this working in the near future.

      Jayson

  • At 27 September 2011, 13:28:53 user Kammenos wrote:   [reply @ Kammenos]
      • @Jayson the whole problem is at the polarization of the first transistor. It is calculated for 5V. The 555 has nothing to do wit the LEDs, and nothing can change on the 555 side to work better. If the MAX brightness is ok but the MIN is not, then you have to pull the base of the transistor to positive a little bit.
      So, next step is to add a resistor from the right side of R4 to +12V. The resistor must be very large, larger than 47K. To save time, i recommend you use a potentiometer with a resistor. The pot is 100K and the resistor 33K (together make 133K). Connect the left pin of the potentiometer to the 12V. then connect one side of the resistor to the mid connector of the pot, and the other side goes to the right side of R4 (at the base of T1). Rotate the potentiometer to both sides and tell me what happens.
      If this does not work, then you have to polarize the transistor with a voltage divider, like Fabio did (previous comments) and worked.

  • At 27 September 2011, 11:48:53 user Fabio wrote:   [reply @ Fabio]
      • i've resolved! since it is a problem with T1 polarization i've made a really simple voltage divider adding a 33k resistor from T1 base to ground. now it work pretty well. I hope it will be usefull for other people! enjoy this circuit!

      Fabio

  • At 27 September 2011, 11:23:43 user Jayson wrote:   [reply @ Jayson]
      • @Kammenos

      Thanks for the quick response. To clarify my technical issue at 12VDC the led's are bright. At 12VDC the problem is the Led's do not fade to off or nearly off. They simply dim and then fade to bright. I suppose my voltage is not getting low enough to turn them off. To be honest I’m a little stuck on what to do next. Is it possible the duty cycle of IC 555 is too fast for 12VDC?

      Thanks again.
      Jayson

  • At 27 September 2011, 11:18:28 user Fabio wrote:   [reply @ Fabio]
      • 3mm blue led i think is 1.5v 20ma but not sure of this. can be the 100k's resistor that doesn't let flow the least amount of current?

  • At 27 September 2011, 11:11:07 user Kammenos wrote:   [reply @ Kammenos]
      • @Fabio then i suppose that t1 is the problem. what led you use?

  • At 27 September 2011, 11:01:28 user Fabio wrote:   [reply @ Fabio]
      • although voltages on capacitor is ok, on the base of T1 (bc337) i found 0.7 voltage stable, isn't it wrong?

  • At 27 September 2011, 10:55:12 user Fabio wrote:   [reply @ Fabio]
      • i've checked but diode is right. on capacitor i have voltages from 1.7 to 3.4 volt which is right i think, but led remains dark. can be a problem with T1? i have tried bc547

  • At 27 September 2011, 10:28:51 user Kammenos wrote:   [reply @ Kammenos]
      • @Jayson To tell you the truth, this is not going to be very easy. I have not test the circuit with 12 volts, but i know that you will need to add an additional transistor between T1 and T2 to scale the voltage to the desired level. This circuit works fine for 5V because there is no much scaling to do for an LED, as the voltage across the capacitor is pulsing between 2 and 3.5 volts, perfect for the LED.

  • At 27 September 2011, 10:11:09 user Kammenos wrote:   [reply @ Kammenos]
      • After the complaints regarding this circuit, i remade it following the posted schematic. At first, the same error happened to me! So, i watched the video to find a close shot of the circuit. it is here:
      http://www.youtube.com/watch?v=f5BSn9xLXhk&feature=player_detailpage#t=14s

      So, i made the changes according to what i see from the video and worked. Then, i redraw the schematic and guess what! It was exactly the same as the one i have already post! Most probably i made the same mistake that most do: Put the diode D1 wrong! Make sure that the strip of the diode (cathode) is facing pin #6 of the 555. If the strip faces pin#7 then he LED will flash instantly on and then fade out.

      Please check your connections. If necessary use the forum to post images (close and clear) from your breadboards to see. If there is indeed a mistake in the schematic, please let me know to fix it.

  • At 27 September 2011, 9:49:11 user Fabio wrote:   [reply @ Fabio]
      • i've completely reassembled the entire circuit but problem still remain. i think there is a mistake in schematic, if anyone can fix it please advice we others.

  • At 27 September 2011, 9:26:23 user Ron T wrote:   [reply @ Ron T]
      • Hi all,
      I just tried to register on to the forum so I can post some pictures I took of my setup on this project but I did not get my acctivation email,tried resending a couple of times to no avail.My email adress is current and working fine.Any thoughts on how to fix this?
      Thanks,
      Ron T.

  • At 27 September 2011, 8:43:20 user Jayson wrote:   [reply @ Jayson]
      • First I would like to thank you for sharing your knowledge with the rest of us. Like the others I have built the circuit and are experiencing some technical difficulties with the LED of choice. I am using two segments of a strip led. They are 12 VDC, 300mA and have their own resistor per 3 led light segments.
      The problem that I face is that I can get the breathing to work at 9VDC but I had to change C1 to 100uF, Both POT are 100K , R5 2.2K, T1 is MPS2222A and the IC is NE555P. With these values and at 9VDC it doesn’t dim completely and doesn’t get bright enough. When another 3 VDC is added to the circuit the breathing effect is barely noticeable. I have tried different combinations of resistors and capacitors and have no luck.
      I realize that my pots could be to large but it should only effect the fading times and not the brightness. Correct?
      Any ideas on what I should do to have the circuit work as yours but only at 12VDC?

      Thanks again
      Jayson

  • At 27 September 2011, 4:43:40 user Fabio wrote:   [reply @ Fabio]
      • hi guys! i've just realized this circuit but have a small problem like others, my led suddenly get on and slowly dimmer off but for only one time? can be a mistake with the schematic posted? all my components are new and i've realized it on pcb.

      Fabio from Italy

  • At 26 September 2011, 20:02:34 user Ron T wrote:   [reply @ Ron T]
      • I've tried 3 different leds as follows,
      1.85 V @ 20 mA

      4.0 V @ 20 mA

      2.1 V @ 20 mA

      Pictures of my setup will follow.Thanks,
      Ron.

  • At 26 September 2011, 12:56:57 user Kammenos wrote:   [reply @ Kammenos]
      • @Ron T what LEDs have you used? What is the forward voltage and current? Are they high brightness or simple LEDs? Post some detailed images of the breadboard in the forum for more.

  • At 26 September 2011, 5:58:22 user Ron T wrote:   [reply @ Ron T]
      • I built your circuit last night and can't get it to work.I have the same problem as Fung had just one flash.If I disconnect and connect the power multiple times in a row the led slowly gets dimmer and dimmer and then finnaly stops lighting even with the power still connected.All the components are new and I followed the circuit diagram and put the components on the breadboard as shown in the pictures.Any help you can give me would be great.
      Thankyou,
      Ron T.

  • At 22 September 2011, 4:30:24 user Laurentus wrote:   [reply @ Laurentus]
      • I would like to use that circuitry
      to achieve the pulsating effect for the
      back up beeper. Would keep ya posted . .

  • At 14 September 2011, 7:21:26 user Kammenos wrote:   [reply @ Kammenos]
      • @Frits Jan most probably this will not work for your led, because of the circuitry that your LED has.

  • At 12 September 2011, 10:46:14 user Frits Jan wrote:   [reply @ Frits Jan]
      • I want to use this for a 12V led lamp which is build to replace a 12V halogen lamp. The led is 12V and 1W.
      There is elektronics in the led which makes it run on normal 12V halogen transformer and also dimmable.
      How can I change this schematic to power this led bulb?
      Do I for example need to add a fet or something?
      I need all to work on 12V dc power.

      Thanks for your help.

      (I also need a small motion sensor (the one with a spring inside which act as a switch) to power this on and a timer to power it off after for example 1 minute without motion. Could I use the same 555 for this, with an separate C and R?)

  • At 11 September 2011, 10:49:03 user Kammenos wrote:   [reply @ Kammenos]
      • @sandaruwan i suppose so...

  • At 11 September 2011, 4:59:01 user sandaruwan wrote:   [reply @ sandaruwan]
      • can i use this circuit for my bick with 20 leds

  • At 24 August 2011, 15:43:23 user Stefan wrote:   [reply @ Stefan]
      • Where I can find the rotary encoder?I need one,but I can't find it.

  • At 24 August 2011, 13:17:02 user Kammenos wrote:   [reply @ Kammenos]
      • @marvi you have to change the resistors of the 2 transistors, but this is something that you must find yourself.

  • At 24 August 2011, 8:41:26 user marvi wrote:   [reply @ marvi]
      • i made the circuit, and works well, but i wont supply wiyh 12 volt, and it doesn.t work at all!

      whoth shoud i nodify

  • At 11 August 2011, 5:53:01 user Kammenos wrote:   [reply @ Kammenos]
      • @Fung make some good photos and upload them in the forum (http://pcbheaven.com/forum/) so that we can help you

  • At 9 August 2011, 0:25:13 user Fung wrote:   [reply @ Fung]
      • I tested this circuit on breadboard referring to the circuit diagram above, it is found that the LED has been flashed once and no breathing effect is observed, I have checked the routes are correct, where is the problem and why?

  • At 8 August 2011, 10:00:37 user Kammenos wrote:   [reply @ Kammenos]
      • @Fung when C1 decreases, then you must increase R1 R2 R3, but the effect will not be the same. You need to make several tests to achieve a nice breathing effect.
      There is no allowed range for C1. If you decrease the capacitor to 100uF for example, then you have a flashing rate x4 which is very fast. It all depends on what you ask for. You may then consider using 100K potentiometers or even 500K.

  • At 8 August 2011, 9:26:09 user Fung wrote:   [reply @ Fung]
      • What is the allowed range of the capacitance of C1?

      If small capacitance of C1 is used, what modifications should be taken on R1-3?

  • At 3 August 2011, 0:37:08 user Kammenos wrote:   [reply @ Kammenos]
      • @Fung yes the output is a typical square wave but i do not use it.

  • At 2 August 2011, 23:10:09 user Fung wrote:   [reply @ Fung]
      • What a good circuit, however I am going to know about the output of the timer because it is not used in this circuit. What is the expected output pattern at the output of the timer? Just the normal square waves?


     

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