The 555 timer is one of the most widely known and simple integrated circuits (IC) on the market. It can be used in many ways using different modes (monostable, astable, and bistable) with each mode used to produce a specific effect. For this project, we're going to focus on using the 555 timer in astable mode for pulse-width modulation to produce a fading LED effect. The 555 timer's astable mode outputs an oscillating pulse signal that switches between on and off states at a frequency and wavelength dependent on the circuit's resistors and capacitors. The Highs and Lows of the pulse signal will create the fade in and fade out effects of the LED.

Step 1: Components

Here's what we need to get started:

-555 timer

-20k ohm resistor

-2K ohm resistor (Depending on your LED and how bright you want it, you might need a lower value.)

-220µF capacitor

-NPN transistor (I used a 2N2222)


-9V battery

-jumper wires and breadboard

Step 2: 555 Timer

The 555 timer has 8 pins, each having a specific function. The pins are oriented according to the indicator dot on the chip. In the image, the dot is located on the bottom left corner of the chip, representing the location of Pin 1. The rest of the pins follow in order from left to right on the bottom, and right to left on the top with Pin 8 being directly above Pin 1.

Step 3: Wiring

Follow the circuit diagram making sure that the 555 timer is positioned correctly and all polarized components are oriented in the right position. Pin 1 is connected to ground(-). Pin 2 is bridged with Pin 6 and connected to the + end of the 220 µF capacitor. Pin 3 is connected to the 20K Ω resistor and linked between the NPN transistor's Base and the capacitor. Pin 4 is bridged with Pin 8 and connected to positive(+). The NPN transistor's Collector is connected to positive(+), while the Emitter is connected to the 2K Ω resistor. The LED is connected to the other end of the 2K Ω resistor and to ground(-). Pins 5 and 7 are not used. Check your circuit for any errors and connect the 9V battery. The LED should begin to fade in and fade out slowly.

Step 4: Changing the Circuit

The rate of the LED fading in and out can easily be modified by playing around with different resistor or capacitor values. You can even add a linear potentiometer or photo resistor in place of the 20K Ω resistor and see how it affects the LED. Removing the transistor will produce a blinking LED affect instead of the fading affect. You can also connect the circuit to an oscilloscope and visually see the pulse signal being produced by the 555 timer. Tinker around and have fun with your new pulsing LED!

<p>I loved that project! Just exchanged the R1 (20kohm) and R2 (2kohm) with a 10kohm and 5kohm potentiometers and put an ON/OFF switch. Also put an interchangeable LED input, so I can test the LEDs for in the future.<br>Great little project Atkun :)</p>
<p>Good day. The components for this project are for single LED only. I would like to ask if uses LED strip, what components to be replaced/substituted, even the supply voltage to be elevated to 12 volts. Thank you very much.</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>There is a very useful chip called a Decade counter 4017B. this fader could be paired up with one of these so that it is directed to the next LED with every 'count'.</p>
<p>Hi!<br>Is there any way to mix the mono and bistable mode? I mean <br>pressing 1 button to turn it on the led, and keep it on untill press the <br> other button (or the same button, this is not a critical issue) then <br>after a time, the led goes off?</p>
<p>Hoping you're still around to answer questions. I've built out the circuit with a few modifications:</p><p>I'm using a 5050 LED strip of three RGB LEDs. Normally a full strip requires 12v but 9 volts powers smaller lengths directly just fine.</p><p>In order to compensate for the higher power LEDs, I'm using a much lower rated capacitor at 4.7&micro;F. Additionally, I don't need the resistor to the LEDs themselves (built into the strips).</p><p>The LEDs fade out great, but never fade back in. Does that sound indicative of a bad component or did I just mess up my connections somewhere?</p>
<p>Addendum: I've switched out the capacitor with a 100&micro;F cap rated at 10v (I'm running 9v into it). After rebuilding according to the sheet, the LEDs just stay on. They appear to fade in very quickly once I apply power but then remain on. I tried to make it less complicated by using just one simple LED, properly resistored but the same thing occurs, it just fades up and stays bright.</p><p>The capacitor seems to be doing its job because after disconnecting the battery, I can see there is still light in the LED as it discharges. Do I have a bad IC? Or the transistor? I've tested all the capacitors I've used, as well as the two ICs I have on hand and nothing seems to be wrong, but I'm very new to all this, so it's quite possible I've missed something.</p>
I didn't have the right resistors or capacitor. but all went well.
<p>Thank you for this- I have LEDs and some 555s here and wasn't quite sure how to integrate the 555s into the project i've been working on; thank you! I'll post an 'i made it' soon. :)</p>
<p>I hope it works out! Just remember, if the LED isn't lighting up or it's too dim to see, try a lower value for the 2K ohm resistor (550-1.5K ohms).</p>
<p>If you would hook up the emitter of the transistor to the base of a transistor or the gate of a MOSFET capable of handling higher amps, could you use this to fade high power LEDs? Just an idea coming to mind after reading your instructable... </p>
<p>Yes, what you are talking about is a basic current amplifier circuit using two transistors. You can use another NPN transistor or a MOSFET like you said, but remember to make sure you use an N-channel FET transistor. Here's a link to help you out, and thanks for the input!</p><p><a href="http://www.circuitstoday.com/current-amplifier-and-buffers" rel="nofollow">http://www.circuitstoday.com/current-amplifier-and...</a></p>
Simple, but straight to the point. I look forward to incorporating this into one of my future projects. Great 'ible.
<p>Thanks! This circuit was made to be easy enough for beginners, and simple enough to incorporate into any project.</p>
Thanks Arteen this was really cool. -Tatiana
No problem Tatiana, I'm glad you liked the project!

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