Instructables

Throbbing/Fading/Flashing LED with 555 Timer

Picture of Throbbing/Fading/Flashing LED with 555 Timer
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This tiny circuit is a simple way to make a fading led without having to program chips or writing code. Just a few simple components and you're ready to fade all day.
The end result is a constant fade up and fade down just like a Mac on standby.
Try it! See how small you can build it.
If you like it rate my Instructable. If you don't, rate my Instructable.
 
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Step 1: Gather Tool and Components

For this project you will need:

Electrical Components

470 ohm resistor (or a resistor to drop the current for your desired led from around 8 volts.)
33k resistor ( or a 100k potentiometer for adjustable fade times)
LED ( I used Blue)
100uf Capacitor
555 Timer
Generic NPN Transistor
Copper clad board. breadboard, or project board.

Tools

Dremel or other rotary tool for drilling
1/32" drill bit for wires
Cutting wheel or tin snips if necessary to trim board down
Soldering iron
Scotchbrite pad or fine sandpaper. ( I used sandpaper because it happened to be there)
Muriatic Acid (concrete cleaner or pool chemical) Home Depot and other hardware stores have it.
Hydrogen Peroxide (standard wound cleaner) Found in drugstores, grocery stores, you probably have some at home.


Misc
Latex or Nitrile Gloves
Acetone to clean ink off of board after etch.
Outdoors area to etch in
Plastic or glass container to put etchants in.
Helping Hands clamp with magnifying glass (nice to have a third hand)
I've included the files for Express PCB software. Free download.

Step 2: Breadboard it

Picture of Breadboard it
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Break out the breadboard and proto it up.

555 Timer
Pin 1- To Ground
Pin 2- Jumper to Pin 6, Jumper to Base of NPN
Pin 3- 33k resistor to base of NPN
Pin 4- Jumper to Pin 8
Pin 5- NC
Pin 6-Jumper to Pin 2
Pin 7-NC
Pin 8-Jumper to Pin 4, Connected to Positive voltage

Emitter of NPN to 470ohm resistor to LED
Base of NPN to + side of cap, then ground - side
Collector of NPN to + voltage
bobbotron made it!1 month ago

Thanks for the instructable, I made this last night, works as specified! :)

LED.jpg
MrBeta (author) 4 years ago
Here's the detailed schematic I printed to etch and drill my PCBs. Keep in mind that this image was flipped to hopefully reduce confusion. You're looking at the top of the board.

The plus signs (+) are there to help with the polarity. They do not mean that you connect the positive voltage there.

The main problems I had when prototyping this project were the following.

Capacitor polarity
LED polarity
Proper/improper orientation of the NPN transistor.

Hopefully this clears things up a bit. Post a comment if you have any further questions or if you get it to work. And don't forget to rate my instructable.
Schematic.jpg
MrBeta (author)  MrBeta4 years ago
*ETA*
The orientation of the resistors usually does not matter though the capacitor, the led, the transistor, and the timer MUST be positioned correctly.

This is a great project for a newbe like me. I finished it on strip board today and I am now reconstructing the circuit and expanding it to fire a 4017 decade counter where I can light as many as 10 LEDs, one after the other.

afultz119 days ago
Hello! I'm SUPER new to electronics so please forgive me. I checked and double checked the circuit step by step and I still can't figure out why my led doesn't fade in and out. I would really appreciate a little guidance. Here's a couple pics of the breadboard. Maybe one of you can spot a mistake I missed.
14, 2:13 PM.jpg14, 2:13 PM.jpg
gameshark8882 months ago
(removed by author or community request)
MrBeta (author)  gameshark8882 months ago

Well if you're connecting it to a led strip, you'll want to make sure that you're getting enough voltage out to the led strip and you'll also want to make sure that whatever transistor you use will handle the current required for the led strip. What are the specs on the strip you want to use?

hi again! I tried to connect your design to a 12vdc 2meters led strip.
(input voltage to the circuit was 12vdc by the way)
then I replaced the 33k resistor with a 100k pot. I get the fade in and fade out effect from the led strip, but my problem is the led strip is not bright enough.

MrBeta (author)  gameshark8881 month ago
If the power source is 12 volts, the led strip is only getting around 10 volts because of the 555 timer voltage drop. You'll have to bump up the voltage to around 13 or 14 volts to get a full power to the LEDs.
MrBeta (author) 4 months ago
@gree7r
I'm not sure if I understand what you're asking. The 33k resistor controls the pulse time so that can be adjusted to flash/throb faster or slower. If you want it to fade out/decay slower than the fade in, you might have to play with the capacitor values. Please not I'm not an electrical engineer so you'll have to play around with it.
Be sure to post the results!
gree7r MrBeta4 months ago
@MrBeta
Here's a quick video I shot of mine so you can see. http://www.youtube.com/watch?v=CsX8QpLvq38

If you compare it to the video of yours running than you can see that when yours is on, the led is illuminated (whether fully or partially during the fade) most of the time with it only being fully off for a split second.
For some reason mine is doing the opposite, it's fully off for a longer duration with the led only being illuminated for a very quick duration.
Do you see what I mean, by comparing the video of mine to the one of yours?
When I try and change the resistor that controls the fade time, it only speeds up or slows down the fade of when the led is actually on but there is still a much longer period of time with the led fully off than in your video.
Does that make sense? Any idea what could be causing this?
MrBeta (author)  gree7r4 months ago
That's interesting. It seems like the capacitor is drained very quickly. Is that a large led? If so, have you tried swapping the led for a smaller one? You may be able to replace the capacitor with a larger capacity cap and see if that prolongs the fade. Keep me posted. I'd be curious what the solution turns out to be.
gree7r MrBeta4 months ago
Well this is embarrassing, it turns out it was just the battery. After replacing the 9v battery with a brand new one it now seems to be working properly.

Here's another question you might be able to answer though. Would it be possible to/what would be the best way to add 1 (or 4) additional LEDs to this circuit that would stay solid on? So that would make it so it has the 1 flashing LED and 1 (or 4) solid LED(s). If it's possible, where in the circuit should they go?
Thank you.
MrBeta (author)  gree7r4 months ago
Glad it works! It's always the simple things we least expect.
As far as the other LEDs, you can just wire them directly to the battery with the appropriate resistors. If you're adding 4 LEDs, you can wire two sets of two in series with a 150 ohm resistor on each set (assuming 3.2v @ 20mA). You can find an online led array calculator that will figure out the best way to wire it and give you the proper resistor values.
gree7r4 months ago
Hi, I'm trying to make this on a breadboard. I followed the instructions exactly and after watching the video of it I believe I have it set up correctly. When I connect the power it does turn on and start flashing/fading however it does it in a way where when the LED fades on its only on for a short time and then when it fades off it stays off for a longer time before it fades back on again. In the video (and others similar videos I've seen) the LED seems to fade on long and fade off short. Mine seems to be doing the opposite. It is off much longer than it is on where as yours is on much longer than it is off. Does that make sense? For my purposes I want it to work the way yours works but I'm not sure what's making it do this. Do you have any idea? I may not have explained this clearly/correctly so if you need me to explain further/better just let me know. Any help would be greatly appreciated. Thank you.

what I'm using:
2n2222 npn transistor
100uf 16v capacitor
33k ohm resistor
led with 330 ohm resistor
9v battery
555 timer
MrBeta (author) 5 months ago
@9W2XO
What are you trying to do?
9W2XO5 months ago
this is a cool weekend project...
can anyone share the fading 12vdc LED circuit(when power off)
thank you
Marctttt9 months ago
Hi folks - I've built two of these using the schematic posted by Brit. Thank you!
Wonderful project. Both circuits work fine if I use an old 9V battery. However, if I use a new 9V battery, the LED turns on but does not fade off. It just stays on. Any ideas what could be going on?
dan108k9 months ago
Thanks for the instructable! Made it and it works perfectly! With this setup the LED fades from fully-off to fully-on repeatedly... Have you any idea what I would have to change if I wanted the LED to fade from half-on to fully-on repeatedly?
MrBeta (author)  dan108k9 months ago
Well I'm no electrical engineer so I'd have to play around with it but I'm thinking that if you replaced the 100uf capacitor with a larger one, it might lengthen the fade time allowing the next pulse to begin before the previous pulse ends. This is just a guess, though. Let me know how it works out!
dan108k MrBeta9 months ago
Thanks very much, I'll give it a go!
Platfus1 year ago
Hey man!
I'd like to ask. I have no clue, how to do it, in order to the LED will be ON only for about 2 sec. I'm planning to build a TARDIS. Timing can be seen here:
http://www.youtube.com/watch?v=r3Ng91qfNkE
Any idea how to makde the fade quicker/shorter? Because I am kind of noobie haha :)
MrBeta (author)  Platfus1 year ago
It's quite easy. The timing is controlled by the 33k resistor. The best way to dial the timing in is get a 100k potentiometer and install it in the place of the 33k resistor. Literally turn the pot until you get a timing to your liking, and then measure the resistance of the pot. You can then find a resistor with the same or similar value, or just leave the potentiometer connected.
Hope that clears it up. Please let me know if you have any further questions and don't forget to rate the 'ible!
Platfus MrBeta1 year ago
Thanks man! Very fast reply :) I will buy the parts I need and then will do so :)
Alex3371 year ago
When I have more than 2 LEDs with this array, they only fade up once and stay on. I'm using 6, and they're all wired in parallel. White. 25mA 3.3-3.6v When I used 100 ohm resistor at the LED it stays on, so i'm using 270 instead. They obviously don't get as bright as they could, but the main problem now is them not fading at all. Do you think I need to switch my 33k-ohm resistor out for something smaller now that there's more resistance in the total circuit?
MrBeta (author)  Alex3371 year ago
What kind of transistor are you using and what is it rated for? You might be overloading the transistor. Just a guess though.
Alex337 MrBeta1 year ago
So now a new problem. Running a total of 8 LEDs. I'm under the rating of the 555 and the transistor. Using an adjustable pot, I can get the LEDs to blink, but they won't fade anymore. It's either blinking like a strobe light or about 3 times a second. Do I need to adjust the size of the cap?
Alex337 MrBeta1 year ago
I am using a regular NPN 2n222 rated for 600ma. I figured it out though! This was my first attempt at something like this, so wiring diagrams are still a little confusing (which is ironic because I look at them when working on cars a lot). Anyway, I switched out the 33k resistor for a 100k pot, found where the LEDs started flashing (~7.3k), went to radioshack and bought a 10k pot, and stuck it in there. I have great control over the speed of the flash now. If I used a different sized cap, would that effect the dwell?
EET19821 year ago
Just thought i would let you know i made your LED fader without the homemade board. It was pretty cool. Thank you for the instructable. People underestimate the 555 :).
biteme5564 years ago
i have just made the fadeing light but i cant get it to fade when i put the battery wires in difrent places on the 555 timer and it will be bright in one spot and dimm in another but it doesent fade can you help me?
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brit biteme5564 years ago
Try it like this..
thismightwork.bmp
I'm trying to follow your schematic on perf-board but the only thing that happens when I apply power is that the 555 gets really effing hot. :( I've spent 2 days on a 30 minute project. lol I don't have a clue what I'm doing right or wrong. -.-
Check you have not bridged the tracks on your board with Solder. Also check you have the pin numbers correct. It may be you have done the Soldering upside down and not allowed for the Pins being mirrored.
Hmmm. I did have pin 2 bridged with pin 7 instead of 6 but when I fixed it I still got the same result. Maybe i fried the 555? Aside from a couple Velleman kits from Radio Shack I've never done any circuit building. Guess I'll buy a breadboard and try to get it working on there first. Thanks for the help.
If you cooked the 555 then it will more than likely need replacing. The Breadboard is a good idea. You did remember to Cut the tracks Under the 555 to prevent the Pins shorting?.
Let me know how you get on.Good Luck :-)
I finally got it with a new 555 and after watching a youtube video of someone who already had it set up. The breadboard confused me at first but I think I have the basic concept. Was using round pad perf board so no tracks to cut. Here's a short video of my project all finished and working. http://youtu.be/LvWgBM89QBs. Thanks for the help. :)
Good Job, well done!!
mischka brit2 years ago
Thanks for the schematic. It helped a lot building the circuit!
Ugifer brit2 years ago
Thanks for the schematic - very clear and useful.

And MrBeta - good project. Thanks.
I only succeed fading once.. after nothing happens..what would be wrong??

thanks !:)
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