This Instructable is to bridge the gap between circuit theory you would find in your books and the application to a real working circuit. This circuit uses some of the most basic and common components. Everything used in this project can be purchased at a local Radioshack or electronic parts store. 


The final outcome of this project is to build a circuit which results with an LED that blinks on and off. This project is centered around the 555 timer chip, a short description of how the 555 timer chip works will be helpful. 

The 555 Timer

The 555 timer is an integrated circuit (a circuit built on a piece of semi conductor material that performs a defined function) which can be used in many applications which require oscillator, pulse generation, or timer controlled devices. The 555 timer has 3 operating modes; monostable, astable, and bistable. This utilizes the 555 in astable mode, thus we will focus on the basics of astable operation. 

Astable operation - in astable mode, the 555 outputs a constant stream of rectangular pulses. The rectangular pulses will be outputted at a specific frequency that is defined by the components that are placed in between the pins of the 555 timer. Lets start by looking at the Pin connections and functions of the 555 IC.


     Pin 1 (GROUND) -  The ground (or common) pin is the most-negative supply potential of the device, which is normally connected to circuit common when operated from positive supply voltages.

     Pin 2 (Trigger) - This pin is the input which causes the output to go high and begin the timing cycle. Triggering occurs when the trigger input moves from a voltage above 2/3 of the supply voltage to a voltage below 1/3 of the supply. For example using a 12 volt supply, the trigger input voltage must start from above 8 volts and move down to a voltage below 4 volts to begin the timing cycle. The action is level sensitive and the trigger voltage may move very slowly. To avoid retriggering, the trigger voltage must return to a voltage above 1/3 of the supply before the end of the timing cycle in the monostable mode. Trigger input current is about 0.5 microamps.

     Pin 3 (Output) - The output pin of the 555 moves to a high level of 1.7 volts less than the supply voltage when the timing cycle begins. The output returns to a low level near 0 at the end of the cycle. Maximum current from the output at either low or high levels is approximately 200 mA.

     Pin 4 (Reset) - A low logic level on this pin resets the timer and returns the ouput to a low state. It is normally connected to the + supply line if not used.

     Pin 5 (Control) - This pin allows changing the triggering and threshold voltages by applying an external voltage. When the timer is operating in the astable or oscillating mode, this input could be used to alter or frequency modulate the output. If not in use, it is recommended installing a small capacitor from pin 5 to ground to avoid possible false or erratic triggering from noise effects.

     Pin 6 (Threshold) - Pin 6 is used to reset the latch and cause the output to go low. Reset occurs when the voltage on this pin moves from a voltage  below 1/3 of the supply to a voltage above 2/3 of the supply. The action is level sensitive and can move slowly similar to the trigger voltage.

     Pin 7 (Discharge) - This pin is an open collector output which is in phase with the main output on pin 3 and has similar current sinking capability.

     Pin 8 (V +) - This is the positive supply voltage terminal of the 555 timer IC. Supply-voltage operating range  is +4.5 volts (minimum) to +16 volts (maximum).

Step 1: Gather Materials

First you are going to want to gather all the materials necessary to build this circuit. If this is the first or one of the first circuit you will be building, it may be a good idea to purchase either a kit or some starter packs that include an assortment of parts. FutureLEC provides very reasonably priced packs of different components. Everything used in this Instructable is available in one of the value packs from FutureLEC. Any local Radioshack should carry everything required in this Instructable as well.

FUTURLEC Value packs

Parts Required

4.7k Ohm Resistor
100k Trim Potentiometer
330 Ohm Resistor
10 Microfarad Electrolytic Capacitor
.1 Microfarad Ceramic Capacitor
9V Battery
Battery Clip
Jumper Wires
Bread Board

Reading Resistor Values
Many times, you will receive resistors in a large pack that contains resistors of varying level of resistance. Resistor values are written on the resistor by means of color bands. Being able to read the values from these color bands is essential for any circuit. The color band code works as follows.

1st Band
The first band represents the first digit in the value of the resistor (e.g. If the first band color is orange, the first figure is a 3).

2nd Band
The second band represents the second digit in the value of the resistor (e.g. If the second band color is orange, the second figure is a 3)

3rd Band
The third band represents the multiplier for the value of the resistor (e.g. If the third band color is red, then the multiplier is 100.

4th Band
The fourth band represents the tolerance (how close the actual resistance of the resistor is to the claimed resistance given by the color bands) of the resistor (e.g. if the 4th band is silver, then the tolerance is + or - 10%)

Resistor with the following color bands:

1st Band -  Orange
2nd Band - Orange
3rd Band -  Red
4th Band -  Silver

=33 * (100) = 3300 ohms + or - 10% (Actual value could be anywhere from 3000 to 3660 ohms).
<p>I believe I have set this up but it isnt blinking. should it be wired differently for a NE555P I have vs the NE555N shown here? </p><p>the photo attached shows pin 1 going to the ground. but it works with or without that ground wire. the LED lights up but doesnt blink. changing the setting on the potentiometer only changes how slowly the LED fades out when cutting the power</p>
<p>One of the best Instructables I have seen. Very well written and excellent pictures and documentation! </p>
blinking time!
I made is and it is working well in flashing one LED,though I used 1microfarad capacitor instead of 0,1 microfarad. So, what must I do if I wanna use that circuit to flash more than 200 LEDs? Pls,help!
<p>Use a transistor; hook up the output (pin 3 from the 555) to a resistor and then to the base of the transistor; wire up the LEDs to the collector, and the emitter to ground.</p>
<p>somebody please help me ..its urgent..coz in my circuit my led id only glowing..its not blinking..what should i do??</p>
<p>Can you plz explain how exactly circuit works?</p>
<p>can I use 10k potentiometer instead of 100 k??</p><p>i dont have enough material to make this circuit so I wanna buy some things..</p><p>if I buy this product (http://www.ebay.in/itm/Bread-Board-kit-with-Resist...</p><p>will i have enough material to make this circuit?</p><p>is there any difference between capacitor (not electrolytic, just capacitor) and ceramic capacitor??</p><p>can i use less resistance resistor instead of 4.7k ohm??</p><p>thanx a lot..</p>
<p>Yes you can use a 10K potentiometer and yes you can use a lower resistor than 4.7K. The only thing this will affect is the flashing rate and the time that the led will be ON or OFF (duty cycle).</p><p>The positive output is high for T(h) seconds based on this formula:<br> Time High (secs) = 0.693 * (R1 + R2) * C<br> </p><p>The negative output is low for T(l) seconds based on this formula:<br> Time Low (secs) = 0.693 * R2 * C<br> </p><p>The frequency is derived by the formula:<br> Frequency = 1.44 / ((R1 + R2 + R2) * C)<br> </p><p>The duty cycle percentage is the relationship of the high time to the overall cycle time and is derived by the formula:<br> DCP = (T(h) / (T(h) + T(l))) * 100<br> </p><p>Where resistance is in ohms and capacitance is in farads.</p>
<p>http://www.ebay.in/itm/Bread-Board-kit-with-Resisters-capacitors-Diodes-LEDs-Transistors-Batteries-etc-/131280939078?_trksid=p2054897.l4275 </p>
My led is not glowing..... cn someone help... asap plz
<p>You followed this schematic, right ?</p><p><img alt="Circuit as initially proposes" src="https://cdn.instructables.com/FQB/IYN8/H8TTO2KJ/FQBIYN8H8TTO2KJ.LARGE.jpg" style="width: 460.0px;"></p><p>Perhaps your LED isn't connected properly, double check the polarity. The &quot;notch&quot; goes to the negative side of the battery, which is also pin 1 of the 555 IC. Also, if you used different values for the potentiometer or capacitor, the delay might longer, leading you to believe it doesn't work but in fact you simply didn't allow enough time for the cycle to complete.</p><p>Finally, the way the schematic indicate the potentiometer connections is rather confusing. The wiper, pin 2 of the pot, should connected to pin 6 of the IC. The schematic indicates that pin 3 of the pot is connected to pin 6 of the IC, which would lead to a situation where regardless of the wiper's position, the flashing rate would remain the same.</p><p>Hoping this will help.</p>
<p>This is the schematic that I use for fading LEDs using the 555 timer. Changing the values of the capacitors will alter the delay time etc.</p>
<p>Hi,</p><p>I realized that I goofed when I did the copy/paste of the GND.</p><p>Here's the schematic as it should be.</p><p>Note : I have to admit that I'm still concerned about the current peak that will go through the LED at power up. If we look at the LED1 for instance, one end is connected to V+ and the other is connected at the R3-C3 junction. When powering up, a current effectively higher than 20-30 milliamps will flow through the LED1 in order to charge C3.</p><p>Anyhow, the circuit is giving an idea of what can be done. With some tuning, things will be just fine.</p>
<p>I attempted to simulate the circuit with LTSpice IV and Multisim, although without any success.</p><p>After looking more closely to the schematic, the problem was because the pin 5 was connected to V+, which shouldn't have.</p><p>I joined my updated version, which works as expected, therefore whoever is interested in a working version will have one.</p><p>I'm a bit surprised that you had that many views for your project and nobody reported the error. Oh well.</p><p>Have a nice day.</p>
<p>cheers - works a treat.</p><p>I didn't have a 330 ohm resistor and my LED is 2v. So I used 4 100 ohm resistors and it still worked. </p>
<p>If I am using 12V LED instead of 3V, should there be any change in the circuits. Do I need to change the values of any resistors? I am to use 12V power source also.</p>
<p>Hello, I am new to electronics and I am trying this circuit out. I had to use a different type of potentiometer (100k ohm Cermet Square 22-Turn Preset Potentiometer). The circuit did not work. I am also using a breadboard without the positive and negative horizontal pin spaces and so I had to improvise the wiring of the board. Could you tell me whether the circuit has gone wrong because I have used the wrong potentiometer or could it be the breadboard or both. I know this maybe a silly question! Cheers</p>
<p>Make sure that when you are wiring anything that goes to the 9V source or ground, that you run a jumper out to a location on the breadboard that is not on the same vertical column as the 555 IC or any other component. I am sure the potentiometer is fine, just double check you indeed have it wire correctly. I would bet your issue is with the wiring of the power pins so look there first.</p>
<p>Thank you! Managed to get it working :)</p>
<p>Nice n' easy to follow! Thanks BR.</p><p>where could one throw a couple of capacitors into this circuit for FADING on n' off? yeah there is a couple of 'ibles on this but, they focus more on making the pcb from scratch and very little on the actual circuit. Whaddaya think?</p>
where to putt photo diode for trigering the sistem?
I don't use a photo diode in this particular tutorial. <br>Maybe you could place one in series with the positive or negative lead of the battery.
thanks for providing total tutorial... <br>be nice
thank you very much. A well explained tutorial step by step. Important for someone starting out like me. <br>Added to Favorites. <br> thanksssss!
Nicely done. Great ible! Thanks for posting. <br> <br>AptPupil
Good explanations! Just a small caution tip: leave the power supply for the very end. This will avoid shorting the battery while you build the circuit. When you are done, observe the final design and maybe measure here and there and just then plug the battery.
The old blinking LED......never gets old, does it??

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