Introduction: 41 LED Flasher Circuit Using 555 IC

Picture of 41 LED Flasher Circuit Using 555 IC

I made this as a quick project I made to use a lot of the LEDs I recently got. It basically connects via a 555 8 pin IC and allows for adjusting the time between the flashings by changing the resistor or capacitor values. It provides for a cool looking effect in a dark room. Use your favorite color LEDs and enjoy!

Step 1: Gather the Parts

Picture of Gather the Parts

Okay, so let's beign.
Here is what you will need:

1 - Timer 555 8 pin IC
1 - 2N3905 PNP general switching transistor
1 - 2N3053 NPN general purpose amplifier (I dont know if this is a switching or amplifer but I used MPSA2222A instead and it worked fine, I also tried 2N3904 and it worked, but a littler worse than the one I used)

20 - red LEDs (although you can use any color choice you want)
20 - blue LEDs (although you can use any color choice you want)
1 - LED (this is used to verify if your circuit works, can be any color)

1 - 1uF Electrolytic capacitor
1 - .1uF disc capacitor

1 - 150k resistor
1 - 4.7k resistor
1 - 160 ohm resistor
1 - 220 ohm resistor (although I used a 160 ohm)
20 - 100 ohm resistors (I didnt have 20 so I used 10 of 100 ohm and 10 of 120 ohm)

1 - 6V source

Step 2: Build the Circuit

Picture of Build the Circuit

So here is the layout of the circuit. It is pretty basic. Here are some notes so you can better understand what is going on.

The notes were taken from the page mentioned later.
"Two sets of 20 LEDs will alternately flash at approximately 4.7 cycles per second using RC values shown (4.7K for R1, 150K for R2 and a 1uF capacitor). Time intervals for the two lamps are about 107 milliseconds (T1, upper LEDs) and 104 milliseconds (T2 lower LEDs). Two transistors are used to provide additional current beyond the 200 mA limit of the 555 timer. A single LED is placed in series with the base of the PNP transistor so that the lower 20 LEDs turn off when the 555 output goes high during the T1 time interval. The high output level of the 555 timer is 1.7 volts less than the supply voltage. Adding the LED increases the forward voltage required for the PNP transistor to about 2.7 volts so that the 1.7 volt difference from supply to the output is insufficient to turn on the transistor. Each LED is supplied with about 20 mA of current for a total of 220 mA. The circuit should work with additional LEDs up to about 40 for each group, or 81 total. The circuit will also work with fewer LEDs so it could be assembled and tested with just 5 LEDs (two groups of two plus one) before adding the others."

Step 3: Modify the Final Project

Picture of Modify the Final Project

Here is the final product of mine. I have added a switch but that is not mandatory.

Okay, now editing the flashing rate is easy. You only need to change 1 or more of the 3 values of R1, R2, and C.

Use these equations to do so.

Positive Time Interval (T1) = 0.693 * (R1+R2) * C (time first set is flashing)
Negative Time Interval (T2) = 0.693 * R2 * C (time other set is flashing)
Frequency = 1.44 / ( (R1+R2+R2) * C) (flashes per second)

Step 4: View the Final Product

Here is a video of my final result. The colors I chose made it look like a police light. I should have thought this through and not have chosen those colors together :)

This project was found at in a beginners 555 timer circuit page.

I bought the LEDs from


MOOMANS (author)2016-08-30

can you put any ammount of voltage or current through this circuit.

TattooedJudge (author)2016-04-17

please tell me you do a step by step guide as this is exactly what i'm after for a cosplay build

ongerimirumbi (author)2016-03-14


HannahT16 (author)2016-02-08

what is the purpose of the 100 ohm resistor in the circuit?

Afrah96 (author)2015-09-30

the link is not work ,

I want to see the result ???

PremkumarJ (author)2015-08-26

i used a metal transistor for this circuit.but it not works

saiketd (author)2015-01-03

Dear Sir please tell me the circuit diagram for making string light of 20 led light with blinking

Iroh37 (author)2014-12-17

If I'm trying to get LEDs to flash at different rates, will I need several different timers or is there a timer that offers several rates for flashing?

MROHM (author)2011-07-20

Hi! Just a Suggestion Here,,,,I built this little baby and noticed one thing,,after leaving this circuit on i noticed the transistors were getting warm especially the 2N3053 (Max Ic of 600 M.A.) To Alleviate the Problem I subbed 2N3053 for Tip31(Power transistor,,,Ic of 3 amps) and 2N2905 for TIP41 (Power Transistor Ic of 3 amps) 2 advantages here,,,,, 1) Transistors will remain cooler here. 2) you will be able to add a pile of extra Led's to this circuit and the Tip's should be able to Handle the extra loads.. This is still a really Good Instructable,, but If we can improve the circuit why Not??!!?? We might be able to double or even triple the Led output and the TIP's should be able to take it!!! Supes this is a SUPER INSTRUCTABLE!!!

luis.arturo.35 (author)MROHM2014-12-02

If I use the TIP31 and TIP41, can I use 100mA LED per stripe? and if so, how many?
I would like to use this project to be seen day, like the LED traffic lights.

MROHM (author)luis.arturo.352014-12-03

@luis..Hi!!,,,,, I checked the Data Sheet for the Tip41 and if properly Heat Sinked for DC,,Ic= 6A and Pulsed Ic=10A If you used Ic=6A the max stripes @100ma would be 6 / .1 =60 but I would use only 30 so I would provide the Transistor with proper headroom as to not push the Tip 41/42 into DESTRUCTIVE MODE!!! Remember The 555 Timer can source or sink 200ma so that is where the Tip 41/42 come into play..I hope This helps you!!!! If you don't use a Transistor with proper power ratings you will cook this 555 into the danger zone!!!

luis.arturo.35 (author)MROHM2014-12-04

Thanks for respond.
I put the TIP31 and TIP41 with 160 ohm resistor in each transistor base. I use two 100mA LEDs per stripe with 15 ohm resistor, for 5 stripes in parallel . My power supply are two 3.7v ultra fire batteries to get 7.4v. I don't know if the base resistor in the transistors are correct. I'm getting 6.7v to 36.5mA in the 555 output, I suppose its correct to the 200mA limit. Should I use heatsink for transistors?
PD. I don't know to much about electronics.

MROHM (author)luis.arturo.352014-12-06

Please use a Heat Sink!!! I purchased Mine On E/Bay..Good Luck With Your Project!!!!

SHAHROZALI (author)2013-01-05

Hello sir i m very interested in learning electronics works so please tell me about my questions my second question is how can check a 555 I.C With multi Meter???

I dont know if you would be able to read the pulses of a 555 ic using a multimeter. But if you have acess to an oscilloscope you more than likely would be able to see the pulses on it. I have never done such a thing, but Im sure its likely.

MROHM (author)out-of-the-box2014-12-03

I used a Logic Probe connected to pin 3 of the 555 timer to "see" the Pulses..Just a Suggestion!!!

chirag1996 (author)2014-06-17

i dont want switching between red and blue i want combine flickering of 41 leds what can i do

plz.. tell

chirag1996 (author)2014-06-17

can i use 6v dc output transformer

Nikhil Kedia (author)2014-05-20

J-Five (author)2013-05-24

That's a lot of LED's!!!
A video would be nice.

isholamoses (author)2013-01-17

I want help on this, i have a project to build for 200 flashing LEDs and i need help on circuit diagram and the type of parts needed. please my email is any help will be greatly appreciated

SHAHROZALI (author)2013-01-06

HELLO i shall wait your questions and i want to make to flasher circuit with 555 I.C

SHAHROZALI (author)2013-01-04


vince26 (author)2012-12-05

if i wanted 5 set of leds to flash simotaniously instead of 2 what all would need done?

Bulantuy (author)2012-10-29


mrmerino (author)Bulantuy2012-10-30

Yes, they are the same thing.

scottinnh (author)2010-12-20


Could this be modified to not do flashing at all, or to flash at such a quick rate that it is not visible flicker? (I'm assuming that removing the flash altogether would be hard on the batteries, if they even can supply enough current.)

I'd like to just run this many batteries off AAs without requiring a million resistors, or losing 1/3 the energy as dissipation through the resistors.

dragon7689 (author)scottinnh2011-08-21

If your flash rate is too fast they will come on but be very dim. You can make this work very easily without flashing involved. For a beginner i would suggest finding a different diagram to follow rather than trying to figure out what components to remove. (IC, Caps, extra resistors, even possibly the transistors (depending on Ea - Applied Voltage).

miguelvelarde10 (author)2011-08-04

where is the negative side of the battery??? i cant see it

The negative side of the battery is everywhere you see the
- ofcourse there are three little lines but everyone of those should be connected to ground or in this case the negative (-) side of battery

MROHM (author)2011-07-20

Excellent Instructable!!!!!!!!! 41 LED Flasher is Awesome,,,,,,Yee-Ha!!

hummvee3 (author)2010-04-14

I bought everything needed to build this but i have a problem understanding how to read a schematic and the photo does not show where all wires go. if any one has built this please email me some photos to it would be much appriciated. i would really like to make this and this is my fisrt time making a circuit of any type and i like the idea. please help with photos that shows where to place wires on the bread board. thanks again

rcisneros (author)hummvee32010-10-17

I know what you mean. A lot of diagrams are made for people who already know electronics.

The simpler ones show (+) & (-) wires so us novices can follow them. This diagram has many different ground symbols when I believe it's where the (-) lead goes.

MROHM (author)rcisneros2011-07-20

You are right on this one my Friend!!! My only advice to you is to build or breadboard Simpler Circuits and once you feel comfortable you can move on to more complex ones. I have been in electronics a long long time and enjoy simple circuits over complex circuits,,,,because;;; 1) They work~~~~100% of the time and 2) they are easier and faster to construct, 3) you can build your knowledge faster so you can tackle the tougher circuits at a later date!!! Good Luck and Happy Building!!! I must go now,,,, I smell my Weller!!!!

benny_resendez (author)hummvee32011-04-19

did anyone ever send you anything to help on your problem? If so can you send it to me I am trying this for a project and just cant seem to figure it out..

72bobbert (author)hummvee32011-01-14

the ground is negative. the leade on the transistor that has the arrow is the emitter, the center one is the base, and the other one is the collector. all l.e.d.'s are polarized. if you look at the two leads one will be longer than the other. the shortest lead is negative. thats basically all what a novice wouldnt know. go to to see my modified schematic for 12-14 volts.

miiwii3 (author)hummvee32010-06-22

it does show where all wires go you just need to use jumper wires to connect things. the schematic does not show wher wires go but what they connect to just draw it out trust me i built this and like from 6 to 2 just use a jumper wire either over the ic or around it. it is easier if you use a breadboard for this.

umair naqash (author)2011-05-04


mased007 (author)2011-03-22

So cheap LEDs. I live in Slovakia and I bought 1LED=0,50€

kctess5 (author)2011-03-08

if you don't have a pnp transistor you can always just add more leds on the same circuit with the npn transistor with some minor changes

scottinnh (author)2010-12-20

The project inspiration URL is now (not

I'd actually never seen that site before, so I got 2x value from reading this instructable. Thanks!

barbaros4ever (author)2010-11-18


markee2 (author)2010-11-10

i have a   

similar flasher circuit but the rate of flashes is variable 

the difference is it has a potentiometer taken from

bfaridnia (author)2010-11-04

Got it to work but now I notice the stand that is connected to2n3053 is way dimmer than the other stand. I played with the resistor between the transistor and the 3 pinout but nothing worked. Can someone explain this to me? I think it had to do with forward voltage at the high output being less that at the low. But not sure how to correct. Thanks

bfaridnia (author)bfaridnia2010-11-04


Complex12 (author)2010-10-18

Hey, your supplies list a 2N3905, but the picture of the schematic you have uploaded shows a 2N2905 in use.

Please clarify.


bfaridnia (author)2010-10-14

Connected everything and the led lights but doesn't flickr. I replaced the 150k r with a 1 meg pot and still nothing. There is a noticeable haze of a flickr. Not sure what's going wrong. Could I try a 10mfd capacitor instead of the.1? Any one else have same problem.

bfaridnia (author)2010-10-14

Connected everything and the led lights but doesn't flickr. I replaced the 150k r with a 1 meg pot and still nothing. There is a noticeable haze of a flickr. Not sure what's going wrong. Could I try a 10mfd capacitor instead of the.1? Any one else have same problem.

geeklord (author)2008-12-30

so do PNP's stop conducting when there is a current at the base?

miiwii3 (author)geeklord2010-06-22

positve negative postive negative is the base and since the timer output is + - + - it turns on and off with the positve and negative votage. its like you quickly switch the red a black wire on the battery it would go + then when u switch it becomes - make sense? basically the 555 switches th polarity for you at a specific rate.

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