EEVblog: The 555 Timer is 55 years old [video] | Hacker News Reader

EEVblog: The 555 Timer is 55 years old [video]

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333 pointsbrudgers95 comments

A couple of years ago I used a 555 in an attempt to fix a problem I had with my Xiegu G90 ham radio. When sending CW (morse code), the radio would sometimes not see a "dit" (the short tone in morse code). I could reproduce it by tapping the paddle too quickly. My theory is that the G90 doesn't use interrupts to detect paddle presses, but rather polls those lines, and sometimes misses when a pulse happens completely in between polls. I made a little circuit using a 555, where the dit side triggers the 555 and closes the dit line just long enough to always be picked up by the G90, but short enough to never cause two dits (at least not at the speed I was going at). I didn't bother doing the same for the dah side, because apparently my index finger is slower than my thumb and the problem never came up there. It worked flawlessly, but only when not transmitting. As soon as RF got involved, it behaved weirdly. I tried adding ferrite beads, but it didn't solve it. In the end I never used it, and just learned to not slap the dits so fast, but it was a fun experience and see the 555 work.

More details: https://www.reddit.com/r/amateurradio/comments/1eo9ki7/xiegy...

That's pretty clever. I've never used the G90, but apparently newer firmware improves the CW performance. The CW mode seems like almost an afterthought with that company.

It's too bad. It's a good mode for low power.

5:55 video released on May 5th, as per description :)

For something feeling like a fairly specific IC, I remember seeing many projects that use it throughout the years in wacky ways - and seeing it makes me happy to know that the sentiment for this little piece is shared.

The trick is that it's sold as a timer but it's really a kit of parts from which you happen to be able to build a timer.

There's a lesson in there somewhere.

Can even build a computer out of them

https://hackaday.com/2011/08/05/building-a-computer-out-of-5...

When I was designing hardware we used the 555 almost exclusively to build one-shots.

I learned (long ago) it’s trivial to fool my satellite receiver’s modem’s dial tone verification for remote pay per view ordering (it doesn’t phone home right away but gets angry if it’s not connected to a phone line).

Turns one a single frequency that’s remotely close to one of the two tones of a dial tone will convince it. Wasn’t sine wave either but not a problem! 555 powered by a 9V battery.

I remember reading somewhere that it's the highest-selling IC of all time, which is a little surprising! I'd have guessed the winner would be an op-amp of some kind.

555s are such delightful little guys. I used a pair of them, plus an ebay telephone line driver, to make an old telephone ring: https://hardfault.life/p/telco-2

One timer runs at the ~20Hz ring frequency, and the other runs at ~0.2Hz on a 20% duty cycle. The slow one's output feeds the enable line of the fast one, so you get 1-second burts of ringing, then a few seconds of silence, then ringing... just like a normal phone.

I moved about 5 months ago and haven't had time to get back to this project. The goal is to build a little phone company in a box, so I can have all my old PCs talk to each other with their modems.

Just a guess:

building an amplifier from transistors is sometimes simpler/cheaper than using an op amp. And some designs don’t need the benefit of op amps.

On the other hand, building a timing circuit from discrete components is less obvious. And the 555 does so much of what often needs doing.

Also, the design was not patented so they were commodity chips right away.

Two videos tomorrow at 5:56!

That's fine, but you know you have to concatenate them and sell them as one unit, right?

my favorite use of a 555 is in a solar charge controller. It is a voltage controlled switch!

i have the page archived, but it's called A New Solar _ Wind Charge Controller Based on the 555 Chip (2_7_2026 12

I can upload the webrip if anyone wants it

otoh i.m surprised the accelerometer was already available since 1927. since microcontrollers only the hardcore eecs kids build pid controllers from opamps for fun (only do hn on phone hard to link to that maker article of a fully analog segway where the writer missed the "analog" part and was like WOW a self balancing 2 wheeler by a grad student and not another baby's first Arduino bday kit

Big Clive is currently livestreaming to celebrate the 555's birthday: https://www.youtube.com/watch?v=jzNjFJdaw_I

I still have the Forrest Mims III Radio Shack "555 Engineer's Mini-Notebook" somewhere in my basement. And rumor has it that Sammy Hagar can't drive 555 because his car just isn't fast enough!

I have a paper copy of "IC 555 projects" kicking around on my bookshelf still!

PDF version here https://worldradiohistory.com/UK/Bernards-And-Babani/Babani/...

The Mims books are fantastic. As a kid I collected every mini notebook and the green Radio Shack "Getting Started in Electronics." They were my intro to electronics along with the Radio Shack kits.

Also consider the IC Timer Cookbook by Walter G. Jung.

You can learn about the origin of the 555 timer from its creator in his free book here: http://www.designinganalogchips.com/

Fun fact: his original concept needed 9 pins and therefore was going be forced to have a 14 pin package. A late epiphany got it down to the 8 pin version we know today.

The 555 timer is still the most popular chip that hobbyists add to their parts inventory (see rankings at https://partsbox.com/ecdb.html). I find this both interesting and curious — I'd say it has mostly nostalgic value at this point. Almost every practical problem today is better solved by something else. And yet it persists, I guess mostly because of beginner tutorials and first LED blinky circuits.

One nice thing about the 555 is that at least it aged well and still is very usable in those beginner tutorials. Unlike for example the uA741 which no one should use.

> Almost every practical problem today is better solved by something else.

I'm curious about this claim. It's certainly easier to just wire up a modern microcontroller, but is there a better option that involves no software and is likely to still work the same today as it did 50 years ago?

I find it much easier to write a ten line program for an 8 pin CH32V003 (or ATTiny85 in past times) to do exactly the timing or SDC comparisons I want than to figure out the circuit and component values for a 555 or op-amp.

For that matter, a 16 pin CH32V003 can emulate a vast array of 7400 series devices as long as you don't need ns timing — no problem for µs. It's also cheaper.

Using a cpu running software to emulate a handful of gates is just the furthest thing from interesting. It's the inverse of elegant.

Until you go to lay out your circuit board. There's a reason microcontrollers are used for tasks like debouncing switches.

I said uninteresting and inelegant. No one disputes that brute force is functional.

"There's a reason microcontrollers are used for tasks like debouncing switches."

Because people are too cheap (or fail that hard at basic analog electronic control) to get a proper single-pole single-throw switch with a pair of MOSFETs in a monostable mode, or use an S-R flip-flop latch to debounce, or even a very simple R-C filter circuit.

"Throw a microcontroller on it and call it a day" is the surest sign of someone not properly educated in electronic engineering.

I think it's like living under a waterfall.

If you live under a waterfall you'll use 1000 gallons of fresh water pumped at blasting high speed to wash a cup.

We live under a waterfall of cpus and gates in general, and organisms don't care if their environment is perverse. A thoughtless organism will happily consume 1000 units of a free resource just to get 1 unit of some other non-free resource.

And a lot of humans are the worst. Thinking beings who elect not to care about anything like that. Like spammers that operate simply because sending email is free for the sender. They get almost nothing from it, and it costs everyone else a lot, but it costs them even less than the tiny bit they gain, and the external costs don't matter to them the tiniest bit.

But the environment is perverse, created by economies of scale and Asian slave labor and the push for advancement for it's own sake which makes existing useful things artificially low value by being "obsolete".

A software version of that might be making apps with Electron. It doesn't matter how much cpu and ram and disk and general mass of tech stack it takes to make some trivial app. The developers precious time outweighs all other considerations. If they can make the app in a few minutes with no effort instead of a few hours, it doesn't matter how much of everyone else's resources they consume since their time is valuable and 1M other people's cpus are free.

All of that stuff is more expensive and uses more board space.

Which is why my bluetooth keyboard/mouse controller pad has that (specifically resistor/cap circuit under each key) riiiiiiiiiiiiiiight?

While it incurs a programming issue, the microcontroller will generally be more stable, less temperature sensitive, and consume less power.

For other posters saying 'just wire up a microcontroller': please self-reflect on your disregard for the concepts of simplicity & elegance. Never mind robustness, or educational aspects.

'Grab laptop, fire up IDE & plug in programmer cable' vs. 'configure the circuit using a soldering iron'. Both have their place.

Why is no software so important? If you design your board well enough, you can route the programming ports somewhere you can program it in-situ, possible with other components that also need programming.

But in terms of cost, a simple microcontroller is usually cheaper than a 555 nowadays, often doesn't require external components, and so even if all you wanted was a single function like an edge-triggered pulse, or generate a single frequency, it probably still makes sense to use a microcontroller from a board design perspective. As soon as you want anything slightly more complicated, odds are you can replace a ton of other circuitry on the board with that single chip and a small program.

"Why is no software so important?"

Because nothing is faster and more responsive than direct hardware logic.

"a simple microcontroller is usually cheaper than a 555 nowadays, often doesn't require external components,"

Often? Every UC I've ever used has required a whole slew of caps and resistors just to get the thing to take in operative firmware through a programming port. Even the simple light flashers for vehicles that I've made using a UC and accelerometer need at least two caps and two resistors to make a proper circuit that allows for flashing info to the controller.

"so even if all you wanted was a single function like an edge-triggered pulse, or generate a single frequency, it probably still makes sense to use a microcontroller from a board design perspective."

Frequency generation? Inductor, capacitor, input voltage. Zero UC required and guaranteed to be cheaper.

"As soon as you want anything slightly more complicated, odds are you can replace a ton of other circuitry on the board with that single chip and a small program."

And accomplish things at a glacial speed that a basic hardware-only solution would've solved. As an example - BOSS pedals have basically zero latency because it is all analog. All these newer Line 6 and POD and other digital FX pedal makers have horrible latency, some I've measured past 50ms (almost as bad as trying to live-monitor a Windows Audio device.) It has been this way for the over 30 years I've been playing guitar.

Most times, raw hardware with zero software is THE way to go. Anything else is just a performance loss.

> "a simple microcontroller is usually cheaper than a 555 nowadays, often doesn't require external components,"

> Often? Every UC I've ever used has required a whole slew of caps and resistors just to get the thing to take in operative firmware through a programming port.

ATtiny for example. Many others only requiring an external capacitor, and complaining about a decoupling cap on a chip replacing a 555 that also needs an RC network to function seems rather petty.

> And accomplish things at a glacial speed that a basic hardware-only solution would've solved.

Most of these uCs operate at least 1 MHz or higher. The ATtiny85 can run at 8MHz from the internal oscillator and has an interrupt latency of 4-6 cycles. To achieve anything that's replacing something you'd do with a 555, you'd have to try incredibly hard to get latency as bad as you're describing. Perhaps they're actually doing something significantly more complicated than just replacing a 555?

Yes. Look at the old national app notes for the lm339 family of comparators.

When I was a camp counselor in my 20s I designed a one-octave "piano" out of one of these, a battery, paperclips for keys, and a shitload of resistors. We had the kids build them on proto board. They sounded harsh but you could play Mary Had a Little Lamb on them!

As a kid I didn’t understand what the 555 timer chip on the Apple II disk controller was doing but I learned the hard way that when you misalign the pins on the drive connector cable and the 555 chip releases its blue smoke you can’t use the drive anymore :(

There was a 556 on the Apple ][ disk controller (a dual 555).

See: https://mirrors.apple2.org.za/Apple%20II%20Documentation%20P...

I have read as well that the 555 was used in the game paddles for the Apple II. 555 + potentiometer (the part you turned) varied the length (duty cycle?) of a square wave which the Apple II used to determine the paddle position.

The Apple II family did indeed use 555 timers, in either 558 or 556 chips, to drive the timing circuit used to read paddle and joystick positions. The following article explains both the circuit and the reading code:

https://www.applefritter.com/appleii-box/APPLE2/NibbelingAtT...

The port that was standardized on for PC joysticks was the dumbest possible one:

The joystick itself just had 1 potentiometer per axis, wired directly to the port. The port had no A/D, no timer, and no interrupt. Instead there was a GPIO and a capacitor. You discharged the capacitor with a GPIO write, and then polled the GPIO to measure when the capacitor was charged again. The number of iterations through your polling loop would be proportional to the position of the axis.

This is a pain to emulate if you aren't doing cycle-accurate emulation. IIRC Dosbox has a bunch of kludges and still doesn't get the joystick right for every game.

[edit]

To clarify the game port used a 558 (quad stripped-down version of a 555) as a schmitt trigger, so it generated pulses of a width proportional to the potentiometer position. I looked up the Apple II interface and it looks very similar, but with the caveat that accelerated versions (e.g. the IIgs) would always clock to 1MHz when reading the joystick port, compared to the PC that could run at a huge range of clocks (and CPI) over the lifetime of the port.

I remember using similar trick to use LEDs to sense light. Basically, charge the (reverse biased) LED capacitance, then measure how long it takes to discharge. The lil circuit I had was LED bar, so I used it to sense finger position using that (other leds providing light, LED doing the sensing judging that light and comparing to rest

Yea, definitely don’t let out the magic smoke. That stops all the fun right away.

Oh god I feel old. I remember being an excited schoolboy thinking how magic this was when it debuted.

I also remember being amazed, and did a forehead slap, when an old army bomb disposal man explained how, what I thought was an innocent device, was used by the IRA in bombs.

Ha. When I was a teenager I used to build 555s into timers for the same purpose using a no PCB rats nest construction.

Though surprising the family at dinner with a small explosion was a much more innocent purpose.

For me that is blue leds.

Yes! I remember thinking "damn you band gap physics, if we only had blue leds we could do colour displays with LEDs, but that can never happen."

"rareleds" on Instagram is fantastic. Vintage LEDs set to apex twin and so on

Haha, for me it was "LEDs".

Up until I was about 10 or 12 we only needed to dial 4 digits.

Evil Mad Scientist makes a giant, discrete version as a soldering kit:

https://shop.evilmadscientist.com/productsmenu/tinykitlist/6...

Very cool. (Looks like it uses 26 transistors. I assume the die is similar.)

I believe they based the design off of the reference schematic from a datasheet of one of the popular 555 timers, but I don't remember which one.

it's based off the original Signetics design :)

Built an atari punk console using these with my late father. Still have it hanging on my wall in a shadow box.

I recently dug one out to use as a hardware shutdown timer to power off an rpi's PSU once it has presumably halted without having to resort to a dedicated MCU for the task.

My favorite 555 use was as a one-shot to power off a NIC after using its wake-on-LAN signal to reset a hung motherboard:

https://www.i3detroit.org/reset-on-lan-an-ethernet-aware-rem...

Can't watch it right now, but upvoted for Dave Jones. He's taught me so much. Absolute treasure, and the host of one of the last great active forums. Thank you for not blackholing all that info on the disaster that is Discord, like so many other communities.

Love the dude. Met him in line of a Chris Hadfield/smarterEveryDay talk. Absolutely fan-boyed haha. Super nice in person too

I used one of these to win an inter-school science competition when I was ~13. It was a minute timer. The competition board doubted I had built it all myself, so they plonked it down in front of me and demanded I draw the circuit diagram in front of them.

That says a lot more about them than it did about you.

I was on my college fencing team. One summer, I had an internship at HP and they paired me with a grizzled old hardware designer, Fred, as a mentor to build a summer project. Fred had a lab bench with drawers overflowing with old resistors, caps, ICs, and even some tubes (“Fred, what the hell are you going to use those for?” “You never know. Tubes might come back!”). Fred had once accepted a promotion to be a manager and quickly renounced it because he hated it and just wanted to design hardware. I decided to build the electronic scoring system used in fencing matches. Our school had one professional system, but I figured I could replicate it for a lot less money. It was all based on a couple of 555s, some 74-series TTL counters, a few LEDs, buttons, and a speaker. Fred was the guy who showed me how a 555 worked. I built it, it worked, and the school used it for at least a year or two after I left. Happy memories. God bless Fred, wherever he is.

Another allrounder and close cousin in time and but with much more functionality is the 4046 CMOS Phase Locked Loop.

It can be configured as a versatile oscillator like the 555, but it can also implement an FM modulator / demodulator, a FSK modem, a tone discriminator, a clock multiplier, a phase detector, a voltage to frequency and frequency to voltage converter a speed control loop and much more.

Not bad for a $1 chip. My circuits professor always carried a bunch in his lab coat pocket and handed them out like candy almost everyone anyone needed a circuit to do something to do with oscillation.

The late Harold DuBose use to use the 555 as a power inverter as it could sink 200ma at the laser companies he worked for. Convenient and cheap.

also today's date is 5.5. and the video is 5m55s

I have a Displate of a decapped 555 hanging near my EE workbench:

https://displate.com/displate/2002057

I got lucky I saw and screenshot when this had 222 points with 55 comments.

<http://ibb.co.com/1Y7QFB8N>

Back when radio shack still existed I would buy a 555 timer during every visit. I live collecting them and still have a bunch somewhere stored. I continue to do it with the 328p arduino boards as well whenever I visit my local microcenter.

As an electronics-enthusiast kid in the 70's, just before home computers showed up at all, I wished the 555 was for Time Travel

What component values do you need to time exactly 55 years?

Maybe it could work if you used 5 timers?

How exactly is exactly? Can I make it measure 1 hour with an allowed tolerance of 55 years, plus or minus. :)

I don't think you could do it. Not with the original BJT variant anyway. :)

Hmm, why not? For the astable configuration, you could use a 100F capacitor with R1 = 10 Meg and R2 = 7.5 Meg, for a 55 year period. Base current for the Threshold NPN will come from the Trigger PNP (and hopefully temperature drift matches OK). Other than maybe the 100F capacitor might have some variation in capacitance and leakage current over the course of 55 years ;-)

https://www.digikey.com/en/products/detail/tecate-group/PBLH...

Once you get above a couple meg, the oils on your fingers start affecting the resistance. Better hope no-one touches with your 55 year counter

at 1% initial precision of just eg. LM555 itself, you're looking at +-0.5 year just from the chip's contribution. If you ever find 100F 1% precision capacitor and 0% precision resistors, you may maybe hit +- 1 year if the other conditions are perfectly predictable, which they are not.

For your chosen capacitor, manufacturer doesn't even bother providing the tolerances. :) Good luck with that.

Time to slow it down to lower frequencies and give it more frequent checkups.

Makes me wonder if we could have a 555 circuit with a trigger time of 55 yrs

Trivial with a 10c microcontroller ...

"Trivial" But then you realize you forgot to account for a 32 bit counter wrapping up. Or potential failures in the power supply or other capacitors

That 10c microcontroller has 15 32 bit registers, allowing you to make up to a 480 bit counter. That ought to be enough until long after the heat death of the universe.

It also has 2k (16384 bits) of SRAM, allowing even larger counters.

It runs off 2.8V - 5.5V DC, so supplying power is pretty trivial. Doesn't need a crystal, though of course adding one will improve the timing accuracy.

somewhere else they were discussing how to use a 555 to time 55 years, and how for such a long period you'd need impractical resistance and capacitance values. easy workaround would be to set a more reasonable period, say, 1 sec, and use a counter to know when you hit 55 years. coincidentally, 55 years is 2 ** 30.7 seconds, so it'd just fit in a 32 bit register.

though i take you were thinking about counting clock cycles or something in which case surely your register would overflow

The size of a register is not the largest value you can conveniently count on a computer. You can use multiple registers.

Old computers often had a "carry flag" specifically to make this easier e.g.on Arm:

    add r0,r0,#1
    adc r1,r1,#0

But even on RISC-V, often criticised for not having a carry flag, it's not hard:

    addi  a0,a0,1
    sltiu t1,a0,1 # set to 1 if a0 wrapped back to 0
    add   a1,a1,t1

Easier with a calendar reminder

How many capacitors do you have that can hold their charge for 55 years?

Every EEPROM is basically that, and they're designed for data retention of around 100 years. I imagine it wouldn't be hard - embed two metal plates in glass?

You don't check the eeprom value by flowing current thru the cell as you do with cap

I used to get exited about this. Hahaha I think I miss those days.

And the topic had 55 comments when I first looked at it

5 hours have passed since you ruined the comment count.

!remindme 500 years

killer oneshot, laughed hard..

The schfive-five-five is schfifty-five! https://m.youtube.com/watch?v=-XccUMOQ978

(I just made half y'all crash out with old internet nostalgia. The rest of you are like "huh?")

Just another 500 years to go. I missed the beginning, probably will miss that last milestone as well.

and this is the fifth comment

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