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.

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.


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.

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.
<p>I needed a circuit to test etching with and this worked great!</p>
<p>I came along and made a PCB file for this design. I think I got it right.<br>https://www.dropbox.com/s/q5bkb4ay3jqmvet/Fader2.pcb?dl=0</p>
<p>Awesome! Glad you made it work. Nice etching too? What etching method did you use?</p>
<p>Use the photoetch method. It's the easiest and neatest way to put the resist on the copper board. just buy the positive acting presensitized PCB board. Here's a &quot;how to&quot; video. It's a piece o' cake :)</p><p>https://www.youtube.com/watch?v=tWnfnt2rNO0</p>
Used a proto-board instead of etching a PCB, but works just as fine. Thanks for the instructions!
<p>Glad it worked for you. Thanks for the comment!</p>
I've been wondering about two things:<br>-Is there a formula to compute the frequency of the throbbing based on the resistor and capacitor?<br><br>-If I connect the LED without a resistor (the 470 ohm resistor in your plans), then it'd light up, and just stay lit, without the throbbing. Could you explain why is this happening?
Short answer, yes, there is a formula but I cannot recall it exactly. If you look at astable 555 circuits, you can find the theory. Simplest way to change the frequency is to swap out the 33k resistor for a potentiometer and dial in your desired frequency.<br><br>As for the missing resistor problem, I can only guess that with that gone the capacitor is not getting dumped fast enough before it's recharged. Either that or it might be seeing the led as a dead short. Does the 555 get warm if you try to run it without the resistor?
<p>No, the 555 stays at room temperature, as far as I can tell by touch.</p>
<p>Thanks for the instructable, I made this last night, works as specified! :)</p><p><iframe allowfullscreen="" frameborder="0" height="281" src="//www.youtube.com/embed/OcQY17YL32k" width="500"></iframe></p>
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.<br /> <br /> The plus signs (+) are there to help with the polarity. They do not mean that you connect the positive voltage there.<br /> <br /> The main problems I had when prototyping this project were the following.<br /> <br /> Capacitor polarity<br /> LED polarity<br /> Proper/improper orientation of the NPN transistor.<br /> <br /> 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.<br />
*ETA*<br /> The orientation of the resistors usually does not matter though the capacitor, the led, the transistor, and the timer MUST be positioned correctly.<br />
Doing a project which includes 50 LEDs 10 of which are always on and have a momentary spdt button which activates the pulse circuit as long as the button is being held. Had these PCBs printed. Thanks for helping me with this!
<p>for those of you who need a schematic <a href="http://imgur.com/a/uNDe2" rel="nofollow">http://imgur.com/a/uNDe2</a></p><p>Thank you for the great instructable!!</p>
<p>For those of you who are looking for the schematic: </p>
Thanks for inspiration. I have used CMOS 555 and tried to make it work on 3V CR1225(I wanted it to only slightly glow once every while), however the voltage drop on NPN was too big. Works fine with 3.7 V lipo though ;-)
<p>Hi, do you have a layout or schematic for this 3V 3.7 option? I am interested in making a few of these. Looks like you used two leds? I want to use one. I could use 3 Cr1225 I suppose. Hope to hear your reply. Thanks in advance.</p>
<p>Can I swap the transistor out for a TIP120 to get more current to use long LED strip?</p>
<p>did u ever do this?</p>
How would i wire this up to a totlt switch and make it shut itself off after 10 seconds?
<p>What size capacitor is that? I'm using a 16v 100uf and the led just stays constant.</p>
<p>Great tutorial! How would I go about making a few LEDs pulse in sequential order? For example, LED #1 slowly lights up to full brightness, then decreases in brightness at the same rate LED #2 increases to full brightness, etc...</p><p>Can this be done without programming an attiny chip?</p><p>Thanks!</p>
<p>If I wanted to have a series of LEDs would I need to change any of the components?</p>
Assuming the voltage source is enough to drive the series of leds, the only thing you have to worry about is that the transistor will handle the current required by the strip. <br>For example, we want to drive 10 normal leds at a full brightness of 20mA each, your transistor would need to be able to handle 20mA* 10 led= 200ma. If you're using a 2n2222 transistor, you should be fine.<br><br>Let me know how many and what kind of leds you're using and I'll try to be more specific.<br><br>Good luck!<br><br>CB
<p><a href="https://www.facebook.com/MoistyQT/videos/1079885985356179/?l=2167306100864453543" rel="nofollow">https://www.facebook.com/MoistyQT/videos/107988598...</a></p><p>working led strip</p>
I see no reason that would be a problem. If you do switch it out, please add a video or a picture and let us all know how it goes.
<p>My first ever instructable project and first ever electronic attempt and it works! Thank you!</p>
<p>hi,</p><p>how do I download the PCB file to make the board? the link saves as a .tmp</p>
<p>Any help would be great, I made this, and after swapping a few components, it works ok. I swapped the Cap for a larger value to slow the pulses, and used a 100k pot as instructed. the 100k had a very limited 'sweep' where only 10% of the pot had useable light so i swapped and changed. i found, the lower the value, the more useable it was so i went with a 1k. at the low end it's fine, and pulses nicely, but the top end strobes out about 75% and the light stays on constantly. Any ideas how to sort the top end out? Input would be great! :) Thanks guys!</p>
<p>It sounds like you're using a logarithmic potentiometer (audio pot). You need to find a linear taper pot to be able to utilize the full range of the pot. Hope that helps!</p>
<p>can I use the same circuit and components with just 5V from the usb port ?</p>
I'm not sure if the circuit would still function at 5V. Due to the voltage drop of the 555, the LED might not fully light.<br>I'd suggest getting it to work with a 9V battery and then plug in your working circuit to 5V to see if it still runs. It will probably not function but removing the resistor for the LED and lowering the resistor value for the 33k resistor might help.
<p>Hey i can't download the pcb layout. ओिूाी ्दैलतदो्गलु गू रहेू ेोबे गलनोतग् गसोुा.....</p>
<p>but i like &quot;programming chips and writing code&quot;</p>
<p>can I use a 1k pot in place of the 33k? and if I can, how could I hook it up? it has 3 prongs so I get lost on how to apply it</p>
I don't think that a 1k would work since 1k will be the max value. You can certainly try it and see what it does. Connect the outer legs to either side of where the resistor would be and ignore the middle pin for this application. If you don't get the desired results, swap out the 1k for a larger pot and try again.
<p>This took me a couple of tries to get right, but I finally got it by switching out the 33k resistor with a 100k potentiometer that I had laying around. I'm also using an 1800 microfarad cap instead of the 100. Works well! I'll probably switch out the pot for something smaller and then turn it into my first pcb. Thanks for the 'ible! </p>
<p>Awesome! I'm glad you were able to get it working. The 100k pot is great for adjusting the pulsing to your preference before soldering the corresponding resistor in place.</p>
<p>Hi! This is very neat! I'd like to ask you one thing: if I'd like the LED to not fade out completely but to periodically dim, what would be the best way to go about that?</p><p>Thanks!</p>
<p>Could your circuit replace the switch in the second circuit on http://www.pcbheaven.com/circuitpages/LED_Fade_In_Fade_Out_Dimmer/ ?</p>
<p>hello and thank you for this guide. i managed to breadboad this and swap the 33k res for a 50k pot. the pot lets me control the pulsing speed great. now im stumped at how i would swap out the pot and attach this to say an anolog pc fan controller. the fan controller should function as a pot? but it would also be a 12v power source. any help would be magnificent.</p>
<p>hello the fan controller is a NZXT Sentry 3 its touch screen. </p>
It's difficult to say without looking at your fan controller. Most fan controllers use a similar circuit to this one as a PWM circuit. You could gut the fan controller and use your own pot or just tap into the existing pot. No telling what the specs of the fan controller pot are. With more details and pics, I might be able to assist further.
Hi I need help with this can't get it to fade <br>Thanks <br>
<p>Thanks so much for this circuit. I made 6 of these for some halloween decorations. Dolls with red glowing eyes are creepy as hell. </p><p>I had to make a few changes. At first this just stayed on. I'm in New Zealand so maybe our parts differ a little. First was 2 leds in series after the 470 ohm resistor. I didn't have time to etch boards so I made them on some predrilled boards, messy but they do the job. </p><p>I wanted a very slow fade in and out so I swapped out the 33k resistor for a 100K pot, I should have used a 50K pot as the range of where this works from so slow it's stopped to strobing is about 5 degrees. </p><p>I also had to increase the capacitor to get a reasonable fade. I ended up using 570uf, try stacking a few in parallel to work out what works for you &ndash; you can add the value of capacitors in parallel to get the total.</p>
<p>Thanks OP, can I ask what part do I change If Im going to use a 12v supply with several super bright green LEDs?</p>
<p>For 12v, you'll want to change the resistor for the LEDs. In my case the 470ohm resistor (blue).. You'll also want to make sure that all of your components will handle 12v.</p><p>Good luck!</p>
<p>Any ideas why the light is so dim when I made this??</p>

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