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This tutorial provides sample circuits to set up a 555 timer in monostable, astable, and bistable modes as well as an in depth discussion of how the 555 timer works and how to choose components to use with it.  The 555 timer is a chip that can be used to create pulses of various durations, to output a continuous pulse waveform of adjustable pulse width and frequency, and to toggle between high and low states in response to inputs.  By wiring the 555 timer with resistors and capacitors in various ways, you can get it to operate in three different modes:

Monostable Mode is great for creating time delays.  In this mode an external trigger causes the 555 timer to output a pulse of an adjustable duration.  Jump straight to an example circuit for monostable mode here.

Astable Mode outputs an oscillating pulse signal/waveform.  In this mode the output of the 555 timer is switching between high and low states at a tunable frequency and pulse width.  Jump straight to an example circuit for astable mode here.

Bistable Mode causes the 555 timer to toggle its output between high and low states depending on the state of two inputs.  Jump straight to an example circuit for bistable mode here.

Some applications that come to mind include:

- a steady clock/trigger to keep time in a circuit (astable mode)
- the core oscillator of an analog synthesizer, with the addition of some op amps and other components this pulse wave can be shaped into a triangle, saw, and even sine shapes
- a very basic chiptune style noise maker (see atari punk console)
- time delay for an incoming signal (monostable mode)
- very basic storage of input data/management of two button control system (bistable mode)

The 555 timer is flexible, cheap, and easy to find (you can even pick them up at Radioshack).  It's also a great starting point for audio projects because its output can be wired directly to a speaker.  Feel free to use any of the info or example circuits I've provided in this tutorial as a starting point for an entry in the DIY Audio Contest! We're giving away an HDTV, DSLR cameras and tons of other great stuff!  (ends November 26)
 
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I'm planning on creating an astable multivibrator with as close to 50% duty cycle as possible. Thank you for the equations!

brent7890 made it!3 months ago

I followed your Astable guide to make a 200 Hz tone using Ra=2700, Rb=2200, and C=1uF. Was going crazy at first because I had two broken 555 chips in a row and didn't know. I wanted to say that this instructable is such good documentation to have, it is both thorough and informative -- thank you!

IMG_0945.JPG

thanks for the post... the bistable circuit was exactly what i needed to toggle 2 hall effect sensors (A3144E) when all i had laying around were some 555 chips.

andrew.l.arth3 months ago

Im working on a model train layout, what i want is for a kid to press a button the train goes for 2 min then stops. the child does this 4 more times. after the train stops for the 5th time it activates a cool down clock for 10 min. it would have to work with electricity from an out lit. Any ideas?

Martinv14 months ago

I want this circuit, but I have 741 opamps in stead of the momentary switches. Can I connect the 741 output to the bottom of the pull-up resistors to set or reset the 555? or is some sort of buffering or isolation necessary between the 741 and the 555?

pTEARgriffin4 months ago
question looking a building a 555 monostable mode can I use a switch that when trigger high, it will delay off after x seconds and stay off without the trigger input going back to low?
savdd7 months ago

does anyone know how to configure the 555 timer as a monostable multivibrator with a delay of about 100-500ms?? thx

achand87 months ago

Nice! Well written.

seanohbe8 months ago

Hey everyone, I need to run a motor for a 3 second pulse, but only once, not a continuous on-off situation. and i need it to run in both directions. Is it possible to use this circuit for that or will i need something else?

amandaghassaei (author)  seanohbe7 months ago

sounds like you will need a microcontroller

saheli19 months ago

Hi.. I have tried to make the monostable mode of 555 timer exactly as it is shown here for 5.17s pulse width. But i m not getting the output.The pulse becomes high when the push button is on but it comes to low only when the push button is switched off. I have checked the circuit connections numerous times but there is no error. Can you please tell me what might be the problem?

rmikel saheli19 months ago

i had the same problem on my first trial,try changing your breadboard,and see it is works. :)

dshin310 months ago

Thank you :)

jomolu11 months ago
hi,pls am new in d electronic world but understand the basis.how can i increase or amplifer dc 2v to 12v dc to charge 12v battery.pls state all d component require and the diagram to build dis circult,and i want the 12v dc to constant.
thanks
hwahwa671 year ago
For astable mode,when I added a load to output, the frequency increase. But it seems like the frequency is independent of load. Anyway to overcome it?
amandaghassaei (author)  hwahwa671 year ago
I'm not sure why that's happening, try putting a buffer between the load and the 555, use an op amp or transistor wired up like this:
http://en.wikipedia.org/wiki/Buffer_amplifier
Thanks a million :)
rclark1 year ago
Is there a way to adjust the low pulse so it's not 0?
amandaghassaei (author)  rclark1 year ago
nope sorry, these are digital circuits so 0 and 5V is all you can get. Do you have something specific in mind that you'd like to do?
I was looking for a way to make a pulse feature for my TIG welder. It's an inexpensive one and does not have a feature that helps control the amount of heat input to a weld. For my welder, it takes an input between 0 and 10v and, based on your amp settings, applies a percentage of the current to the weld. I'm looking for a way to take the voltage input and pulse it with the ability to adjust frequency, duty cycle and background (what % of the max voltage the low should be). I thought I might be able to use an op amp on the output of an arduino, but I am not well versed in electronic circuitry.
amandaghassaei (author)  rclark1 year ago
you can do this, but you will need to learn about biasing (also called dc offset) and amplification
plz, if i want to find the water level by using 2 plates capacitor, then i will connect the output of the timer to a f/v converter and display the voltage
which capacitor i should change with the 2 plates??
do you have any idea how to install into a XBOX360 Controller? can it be a two or three wire hookup?
no idea, can you give me any more info? what are you trying to do?
trying to hook it up so i have a rapid fire controller using a momentary on button, but no idea where to wire in the 555 timer at :/ since my controller doesn't have a crystal oscillator.
I've never tried modding a controller like that, but I know it's possible, do you have a schematic?
no lol i don't, that sure would be helpful though.
"In the equation above, when RA is much larger than RB (you can ignore the RB terms) you end up with a duty cycle ~= 1 and when RB is much larger than RA (you can ignore the RA terms) you get a duty cycle =~ 1/2. So the limits of the duty cycle with the circuit shown in fig 2 are 50% to 100"

Note that this is not true.

You can set r1 to 0, and this gives you a %50 duty cycle. The only reason to have a resistor at R1 is to modify the duty cycle, and to keep a straight VCC from burning up the internal transistor at pin 7. This can be rectified by adding a resistor at GND. giving you a pure 50% duty cycle for the full range of r2.

Note that output is HIGH while charging through R1 + R2, and low while discharging through R2 only. IE the High duty time can never be smaller than the low duty time. limiting the duty cycle to greater than %50.
jojokeo2 years ago
Why doesn't the "print pdf" or save file to .pdf functions ever work for this site!???
scroll down on the page...were you signed in?
dstahl32 years ago
Thank you for this. This compliments the datasheet nicely...
Does step 6 have the wrong schematic? How you have it wired and how the schematic says to wire it, appear to be different. (I am still a complete noob when it comes to a lot of this, so I could be completely wrong)
Shouldn't the variable resistor be tied directly to to pin 6 without the 10k ohm resistor in series? And the 10k ohm resistor should be between pin 6 and pin 7. At least that is how fig 14 of the datasheet appears to wire it.
11-29-2012 11-32-19 AM.png
amandaghassaei (author)  dstahl32 years ago
great question, this schematic is for the 50% duty cycle oscillator, which is a type of astable mode. This circuit is great if you really need a square wave output (50% high, 50% low) as opposed to a pulse output, but one annoying thing about it is that the frequency is given by:

f = 1/(Ra+Rb)

so in order to change the frequency of the timer you have to increase both Ra and Rb, in the circuit I provided you increase Ra and/r decrease Rb and vice versa to change the frequency, which makes it easy to use a single potentiometer as both Ra and Rb so you can physically dial in your frequency by turning a knob. But if you want to learn more about the 555 timer I'd recommend trying this schematic out and seeing what happens when you start changing things!
Great 'ible, even if the part is older than the hills.

All these circuits can be easily simulated using the free (as in beer) LT Spice circuit simulator (get it here: http://www.linear.com/designtools/software/ ) . You'll find the NE555 chip in the "misc" catalog of components.

In recent years it has been possible to do most of the 555 's functions (plus many more) using low pin count (6-8 pins) uCs. It frequently takes fewer components and performance is less variable with temperature than a 555 circuit. Of course, uCs require a programmer of some sort, but once you have that you usually find all sorts of uses for uCs.

Dear sir,
In LT spice link u given it has many appli to download. in that which i need to download for this type simulation.(my id r.navaneethan1991@gmail.com)
Big Ditto re. LTspice!
Been using it for 10yrs now, awesome!
It does everything, free!
I highly recommend it.

Actually, a great way to wet yer feet in controllers is Arduino.
Ive been playing with the Uno and Rainbowduino for a year now, and
the development tool is Way easier than
the other mfrs tools.
I wont go back if i can help it.

Real coders scoff at it, but
its very easy to use.
That coming from a long time analog weenie.
I'm a PIC man.

I have limited experience with Arduino and it hasn't been very good. I am building a 3D printer that uses an Arduino ATMega2560 controller board. The firmware was developed by others, apparently on an outdated version of the Arduino IDE. The lastest Arduino IDE broke a lot of older Arduino stuff. I had to hunt down an old copy of the IDE, then I had to hunt down and fix an error because the mathematical function "round" was being defined in two places and the compiler didn't like it. All that screwing around was just so I could modify the source code for the printer firmware and upload it to the Arduino board. Documentation is practically nonexistent, so I had to wade through hundreds of posts on dozens of internet forums to find out what to do to solve the problem.

PICs are well documented, the IDE works, the programmers work. Assembly language is extremely efficient, though it can be tedious. C compilers are available if you don't like the work required to program in assembly.

I've seen too many Arduino projects where someone uses an Arduino to read a switch and turn on a light. Some people seem to use them as a matter of fashion rather than because their application actually requires some sort of intelligence. Meh!
Also, if you have an iPad, I highly recommend iCircuit. It has most basic passives and several popular and useful ICs, including the 555, and a scope to watch what's going on in your circuits. They make a Mac desktop version, as well.
pfred22 years ago
Guess what IC is supplying the step pulses in this circuit?

http://www.youtube.com/watch?v=GU2GaSMPxNI

I'll give you a hint, the number starts with a 5, ends with a 5, and has a 5 in the middle too. Over the years I've come up with a number of other clock generation circuits but none as easy to make, and control as the good old 555.
swander2 years ago
can anyone whip up a 5vdc fuel injector pulse generator for cycling/calibrating cleaner through said injectors? Ideally it would consist of 4-8 channels outputting 5vdc at about a 10ms pulse, frequency about 10 cycles per second? Im no where close to designing this but it would be cool to have to bench test your injectors, along with an old fuel rail, an EFI pump and 4-8 graduated cylinders.
OTC makes one. And its not that pricy.
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