Introduction: Test Tools: a Fairly Simple 555 Tester. Corrected and Updated.

Picture of Test Tools: a Fairly Simple 555 Tester.  Corrected and Updated.

Here I will give a small circuit that will test whether the 555 timer you just tried in another circuit (and it either heated up or didn't work at all) works or not.

Have you ever wondered if it was your circuit, or whether might have fried your 555? Well here is a way to test the little chip quickly and easily.

Step 1: Gathering the Parts

Picture of Gathering the Parts

Parts and cautions.

Depending on your hearing or what you find best as far as the sound produced by the output, you will need to figure out what resistors and capacitor you wish to use for the timer section of the circuit.

This is an Astable multivibrator circuit. When the switch is closed, the output is a square wave at the frequency determined by C1, R1 and R2.

The needed calculations to find the values are as follows:

f = 1.44 / (R1 + 2R2) X C1

The period (time - t) of the circuit is found with: t = 1/f = 0.69(R1 +2R2) X C1

The high and low times of each pulse can be calculated also with:

High time = 0.69(R1 + R2) X C1
Low time = 0.69(R2 X C1)

Take note that it is practical to keep the values of R2 between 1K and 1M. To keep the duty cycle around 50%, use R1 = 1K.

So, once you have the frequency you wish to generate, and have figured out what R2 and C1 are to be, and you have gather those parts the only things you need yet are

One PC board
One 8 pin IC socket
One 555 timer
One 47uF capacitor (C1)
One 10 nF ceramic capacitor
One 10k to 100k Potentiometer
some wire
a soldering iron (or prototype board)
and your goggles.

Step 2: Putting It All Together

Picture of Putting It All Together

As I said, it is pretty straight forward. If you get one of the PC boards made to put the socket in the center column of the board, and has traces that go from the initial solder point outwards and fan out a bit for easier soldering.

Solder in the parts and wires to connect the various parts as shown in the schematic.

Remember to solder pin 2 to pin 6. Solder the decoupling capacitor, C3 (not shown) between Power in and ground if you are not using a battery. If you wish to use the optional frequency adjustment, add it in series with R1. Power goes to pin 4 (5-15 v DC). R2 is the connection from pin 6 to pin 7. Since we are not going to use pin 5, the control voltage, we should decouple it to ground with a 10 nF capactor (C2 :-) .

Overview of the 555. Pin 1= ground
Pin 2=trigger
Pin 3=output
Pin 4=reset
Pin 5=control voltage
Pin 6=threshold
Pin 7=discharge
Pin 8=3-15 vdc

Step 3: Solder It, Then Box It

Picture of Solder It, Then Box It

Once you have all the parts soldered in, and have tested the circuit. You can add the Pot. inline ie in series with, R1 or R2 (I used R1 so I could adjust the duty cycle as I wished).

Find a decent box to put it in and remember to allow for a place to get to the socket so you can use this as a tester.

The entry point for the timer was altered and made so much more neater. I used an old gold colored aluminum card blank and cut the hole after measuring it for locationi.



xmitman (author)2013-03-16

I'm looking to purchase issues of Electronics Handbook magazine where this circuit came from. Does anyone have some to sell or scanned copies? email me:
info at chipencoders dot com

Goodhart (author)xmitman2013-03-18

Do you mean like one of these?

xmitman (author)Goodhart2013-03-21

yes, just like that. as many issues as I can get. do you know of any sources?

Goodhart (author)xmitman2013-03-21

Well, the one in the link above is one source....eBay may be anoter, and Amazon may have some for sale by some of the sellers there.

xmitman (author)Goodhart2013-03-30

Which Volume number of Electronics Handbook did this come from? how much do you want for it? Email me at

Goodhart (author)xmitman2013-04-01

I borrowed the picture from on line since I haven't much practice in using schematic rendering software. It was the same configuration as I would have used (and have used in the past). It isn't a "hard and fast" design however. ANY configuration of the 555 that will produce a decent sound can be used.

IF I recall correctly, I got it from this site or something ver much like it.

Phil B (author)2008-10-14

Back a few years when you could still buy magazines featuring electronic circuits, I found a schematic for a capacitor tester based on a 555 timer. It worked very well for capacitors 1 microfarad and larger. I did a quick search and found a capacitor tester using a 555 timer and another IC at: It runs off of a computer's serial port rather than a 9 volt battery, and its range goes much lower than the tester I built. I found it very helpful to be able to test a capacitor and know if it is good.

Goodhart (author)Phil B2008-10-14

Thanks, yes I have always wanted that function on my Multimeter, but that makes them quite pricey :-) BTW: Do you know if the magazine you referred to was either Electronics Now, Popular Electronics, or Nuts 'n' Volts? I remember getting those and could kick myself for letting them get hauled away in the trash I will look into your link then, thanks again.

Phil B (author)Goodhart2008-10-14

I still have the magazine. Its name is Electronics Handbook. I cannot find a month and year, but it was on the newsstands about 1989 or so. It does say it is volume VI. It was published by C & E Hobby Handbooks of North Branch, NJ. Notes I made indicate I built the project in December 1989. I think the magazine came out every couple of months. I got Popular Electronics for a couple of years and still have all of my copies. I did some work to index the projects and circuits, but have seldom looked up anything. It is too easy to search the Internet for a particular circuit. An exception was when I looked for information on battery powered electronic fly swatters and found none. I had to figure it out myself. Then I published an Instructable on it. You may have seen it. Search under Phil B if you have not.

xmitman (author)Phil B2013-03-30

Hi Phil,

I’m a longtime electronics hobbyist. I’m looking to purchase all original issues of Electronics Handbook magazine. Are you willing to part with yours or do you know anyone that would be willing to sell them to me?

Phil B (author)xmitman2013-03-30

We have moved to another state since I posted and I gave away my electronics magazines to a Habitat for Humanity Restore as a donation.

xmitman (author)Phil B2013-03-31

Thanks anyway.

Goodhart (author)Phil B2008-10-14

Oh ok, thanks. I never came across that one. The other three I was subscribed to until Electronics Now and the sister mag. Pop. Electronics, merged. Nuts n Volts started getting TOO much into micro controllers and such and away from a lot of the practical stuff the DIY people were more into (like me :-) I had some trouble finding many of the schematics that were a part of the "early" issues of Nuts n Volts on line. So I have kind of missed not having the monster sized mag around.

geeklord (author)2008-12-23

okay tryin to learn how to use 555 timers here, so correct me, PLEASE!

pin one-ground from power source

pin two- trigger,ahhhh put a current through it and it starts the sucker???

pin 3-output, too the LED/Speaker/Nuclear Detonator

pin 4- reset, kinda like the trigger connect it to the power source with a switch?

pin 5-offset, no idea

pin 6&7-discharge and threshold, connect the capacitor/resistor combo to these pins(positive of electrolytic caps going to which one?)

pin 8- 3-18v from power supply

If you could explain the ones that I got wrong and had questions on great, if you can teach me more great, if you can direct me to a super good guide somewhere (once again) GREAT.
I feel so long winded....:D

Goodhart (author)geeklord2008-12-23

pin two- trigger,ahhhh put a current through it and it starts the sucker???

Kind of, the trigger need only be a pulse.

pin 5-offset, no idea

Also labeled control voltage or Bypass.

6 is "threshold" and 7 is discharge

Now, a little bit about the chip: 555s are configured as a multivibrator by adding a few components to the pins. This is a circuit that oscillates from one state to another over time, in this case, creating a square wave. There are two basic forms of timers, both being multivibrators: monostable and astable.

The monostable is also called a one-shot. A single trigger creates a change in the output (either bringing it down to zero or turning it on). The astable swings back and forth, from one state to the other and back again.

Instead of going into long explanations, maybe this will be of some is a site that has a bunch of schematics and explanations on it, AND has a calculator to boot :-)

I am willing to help in any way you might need, but a few simple reads should get you up to speed.

There is a nice tutorial at this link here that should answer any questions you have for now. If not, myself or someone else here can help .

PS: if you wish to use an even LOWER powered chip that is otherwise the same as the 555, you can get the CMOS version, namely the 7555 as it is capable to operate from 2.7v to 18v. At 5v, the 7555 will consume about 900 microwatts, making it ideally suitable for battery operated circuits. The internal schematic of the 7555 is similar to the standard 555 but with current-spiking filtering, lower output drive capability, higher nodal impedances, and better noise reduction system. The pinout is the same.

gmjhowe (author)2008-10-14

wow! i made one of these in school a while back. (talking 5 years here)

Goodhart (author)gmjhowe2008-10-14

Yeah, last time (before the current one) I made one was around 1988 or so.

gmjhowe (author)Goodhart2008-10-14

Contructive comment, the whole thing would be alot nicer in a neater case, one where you havnt clawed holes in it :P

Goodhart (author)gmjhowe2008-10-14

Yeah, I was trying to figure a way to make the holes look nicer.....I am not as good at "pretty" as I should be :-)

gmjhowe (author)Goodhart2008-10-14

well, the words, drill, file, and knife, come to mind!

Goodhart (author)gmjhowe2008-10-14

File.....soft plastic, knife....yeah, I will try not cut my finger off, drill....that is how I got the hole started....and I thought my nippers would make clean cuts....I will work on that and update the pictures....when I am home and have a little time ;-)

gmjhowe (author)Goodhart2008-10-14

I think your best bet would be to melt a hole. Heat up a metal rod using a gas job or a blow torch, then slowly push it through!

Goodhart (author)gmjhowe2008-10-17

I have updated the piece and added the picture. Is this any better ? (Last step)

gmjhowe (author)Goodhart2008-10-17

good job! see, doesn't that look alot nicer now?

Goodhart (author)gmjhowe2008-10-17

My Title is sometimes Capt'n RushThroughItToGetItDone LOL

gmjhowe (author)Goodhart2008-10-17

haha! i used to be exactly the same, wanting to get the final thing done and in my hands, but as you probs know, the longer you take, the more professional the final piece! I wouldnt have half my featured ibles i had rushed them all.

Goodhart (author)gmjhowe2008-10-17

It's just that my time is so short as it is many times *sigh*

gmjhowe (author)Goodhart2008-10-17

haha, i know that feeling. i only have a short amount of spare time, probably about 20 hours a week to work on projects

Goodhart (author)gmjhowe2008-11-24

My biggest problem is that I get a bunch of time, but it is only in 5 - 10 minute spurts :-)

Goodhart (author)gmjhowe2008-10-14

My soldering iron made those after I drilled a small hole and failed to be able to use my nippers (luckily I don't have any smoke alarms inside the computer room at home LOL).

Goodhart (author)gmjhowe2008-10-21

If I can figure out how to cut a clean square hole in a piece of aluminum, that is about 1/8 thick, I have an even better "upgrade" to the appearance....

gmjhowe (author)Goodhart2008-10-21

well, you can drill aluminium, so, draw your square, drill around the outside. Then pop it out, and file the edges.

Goodhart (author)gmjhowe2008-10-21

:-) Now, if I can get TO my drill and vise, I will be in business ;-)

Gjdj3 (author)2008-10-20

I like it! I use a lot of 555 timers so I think this would definitely be a good thing to make. Nice job!

Goodhart (author)Gjdj32008-10-20

Thank you. My next project (which I was starting to work on before this one) will also involve a 555 timer. I want to make MY version of the MAKE mag. annoying whining thing. :-) (when I made it the first time, I thought I had fried the 555, so I had to make a tester to check it.....then I discovered I didn't HAVE a 555 in the socket, but rather a 741 opamp *sigh* no wonder it was getting hot LOL

Gjdj3 (author)Goodhart2008-10-20

Haha, well I'm looking forward to your new project. I never saw the original annoying whining thing though. I think I should probably look it up.

Goodhart (author)Gjdj32008-10-20

yeah, annoying whining or beeping or something.....thing :-) They didn't have a schematic out for it at first, and then when I complained they put one out without any values to the parts....grrrrr....but it is out there now with the values they used.....I have a trick up my sleeve to make it even more annoying though :-)

Shadowmang (author)2008-10-13

Very nice :] as I am a newbie in electronics I have 2 questions. OK lol, what is a potentiometer? and I'm guessing it makes a sound to verify whether it is fried or not, but how do you interpret the sound

Goodhart (author)Shadowmang2008-10-14

First, thank you. :-)

And Alex is correct about the Potentiometer.

Alex is also correct concerning the interpretation. In the case of my crude tester, it only verifies that does function and not so much whether it is functioning perfectly.

With or without the potentiometer, there will be a sound / i.e. a kind of whine that comes from the speaker if the 555 can oscillate. A fried one (damaged by being overheated in the soldering process or a shorted joint or whatever may occur) will not oscillate....and no sound will come from the speaker.

Goodhart (author)Goodhart2008-10-17

In short, a potentiometer is a rheostat. :-)

digital0129 (author)Shadowmang2008-10-14

A potentiometer is a device that allows you to manipulate the resistance by turning a dial. By changing the resistance in this circuit, you can change the speed of the beeps produced by the speaker.

Sandisk1duo (author)Shadowmang2008-10-13

Potentiometer; pot for short is a variable resistor You can interpret the sound as how fast the 555 is oscillating, low tones for slow oscillation, high tones for faster oscillation

Plasmana (author)2008-10-14

Hmm, I could really use this as my 555 timer chips often get exposed to high voltage spikes...

Plasmana (author)Plasmana2008-10-14

Oh, and 5 stars!

Goodhart (author)Plasmana2008-10-14

Well thank you :-) My original circuit whined pretty loudly, but when I asked my wife if she could hear it, she said no. So I had to slow the frequency down a bit, so people over 40 could hear it (I have an odd sense of hearing, and hear more if the upper ranges then many others my age). I am glad you can use this. I have been building simple testers like this for quite a few years now....I guess I should get some of them out and reverse engineer them (since I have long since lost schematics and such :-)

inventorjack (author)2008-10-14

I like this Instructable a lot! This is the sort of thing we need more of. Practical, fun projects. Not sure if this helps or hinders, but I rendered your schematic in Eagle. The chip layout was somewhat different than in your drawing. I'm still new at Eagle, so perhaps there's a way to rearrange the pins, but I haven't found it yet. Anyway, thanks for posting your project.

Goodhart (author)inventorjack2008-10-14

Thank you very much. The pin labeling is the same however (I just compared them ;-) so whichever is most clear to a person, I would say go with it. I have to fiddle more with the little program I have for this kind of thing....Paint is just SOOOO crude when trying to make a decent looking schematic. Bur there is a little learning curve, and I normally have so little time. Thanks again.

amk503 (author)2008-10-13

This is the kind of thing I love seeing on instructables! I built a similar device as an extension of the typical 555 hello world blinking LED thing. Nice post Goodhart. Good on the details. As a side note, I've seen weird 555 pin specifications in the EAGLE library that don't match what you've posted, a data entry error perhaps, as the 555s I've used personally do match your data.

Goodhart (author)amk5032008-10-14

Thank you for your kind words...I was kind of afraid to post this since I have had the feeling that, if it doesn't make loud noises, have bright flashing lights, turn water into fuel, or blow something up, it might be boring.

Sandisk1duo (author)2008-10-13

Make a port for capacitors, so that you can get an even wider range of frequencies

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Bio: I am, most definitely older than 00010101 and to put it simply, still curious about nearly everything :-) I then tend to read and/or experiment ... More »
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