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.
FarmerPotato•May 5, 2026
Two videos tomorrow at 5:56!
zephen•May 5, 2026
That's fine, but you know you have to concatenate them and sell them as one unit, right?
regularfry•May 5, 2026
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.
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.
genewitch•May 6, 2026
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
mrsvanwinkle•May 6, 2026
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
nom•May 5, 2026
also today's date is 5.5. and the video is 5m55s
davidwritesbugs•May 5, 2026
Oh god I feel old. I remember being an excited schoolboy thinking how magic this was when it debuted.
davidwritesbugs•May 5, 2026
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.
nickcw•May 5, 2026
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.
Brian_K_White•May 5, 2026
For me that is blue leds.
davidwritesbugs•May 5, 2026
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."
mhh__•May 5, 2026
"rareleds" on Instagram is fantastic. Vintage LEDs set to apex twin and so on
tuvix•May 5, 2026
Built an atari punk console using these with my late father. Still have it hanging on my wall in a shadow box.
swed420•May 5, 2026
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.
robofanatic•May 5, 2026
and this is the fifth comment
ilvez•May 5, 2026
killer oneshot, laughed hard..
kazinator•May 5, 2026
Time to slow it down to lower frequencies and give it more frequent checkups.
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!
stevekemp•May 5, 2026
I have a paper copy of "IC 555 projects" kicking around on my bookshelf still!
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.
jshprentz•May 6, 2026
Also consider the IC Timer Cookbook by Walter G. Jung.
encom•May 5, 2026
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.
MostlyFragile•May 6, 2026
Love the dude. Met him in line of a Chris Hadfield/smarterEveryDay talk. Absolutely fan-boyed haha. Super nice in person too
amelius•May 5, 2026
What component values do you need to time exactly 55 years?
Maybe it could work if you used 5 timers?
megous•May 5, 2026
I don't think you could do it. Not with the original BJT variant anyway. :)
floxy•May 5, 2026
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 ;-)
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
ua709•May 5, 2026
How exactly is exactly? Can I make it measure 1 hour with an allowed tolerance of 55 years, plus or minus. :)
aj7•May 5, 2026
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.
pryelluw•May 5, 2026
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.
raverbashing•May 5, 2026
Makes me wonder if we could have a 555 circuit with a trigger time of 55 yrs
mnw21cam•May 5, 2026
How many capacitors do you have that can hold their charge for 55 years?
chromacity•May 5, 2026
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?
PunchyHamster•May 6, 2026
You don't check the eeprom value by flowing current thru the cell as you do with cap
brucehoult•May 6, 2026
Trivial with a 10c microcontroller ...
postalrat•May 6, 2026
Easier with a calendar reminder
raverbashing•May 6, 2026
"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
mishellaneous•May 6, 2026
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
darrinm•May 5, 2026
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 :(
fortran77•May 5, 2026
There was a 556 on the Apple ][ disk controller (a dual 555).
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.
aidenn0•May 5, 2026
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.
PunchyHamster•May 6, 2026
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
tmoertel•May 6, 2026
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:
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!
OldSchool•May 5, 2026
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
mnw21cam•May 5, 2026
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.
jacquesm•May 5, 2026
That says a lot more about them than it did about you.
jwr•May 5, 2026
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.
ocdtrekkie•May 6, 2026
> 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?
brucehoult•May 6, 2026
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.
Brian_K_White•May 6, 2026
Using a cpu running software to emulate a handful of gates is just the furthest thing from interesting. It's the inverse of elegant.
pjc50•May 6, 2026
While it incurs a programming issue, the microcontroller will generally be more stable, less temperature sensitive, and consume less power.
RetroTechie•May 6, 2026
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.
nqzero•May 5, 2026
!remindme 500 years
JKCalhoun•May 5, 2026
Evil Mad Scientist makes a giant, discrete version as a soldering kit:
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.
FpUser•May 6, 2026
And the topic had 55 comments when I first looked at it
jve•May 6, 2026
5 hours have passed since you ruined the comment count.
rezaprima•May 6, 2026
I got lucky I saw and screenshot when this had 222 points with 55 comments.
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.
deepspace•May 6, 2026
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.
(I just made half y'all crash out with old internet nostalgia. The rest of you are like "huh?")
wkjagt•May 6, 2026
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.
31 Comments
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.
There's a lesson in there somewhere.
https://hackaday.com/2011/08/05/building-a-computer-out-of-5...
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 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
Though surprising the family at dinner with a small explosion was a much more innocent purpose.
PDF version here https://worldradiohistory.com/UK/Bernards-And-Babani/Babani/...
Maybe it could work if you used 5 timers?
https://www.digikey.com/en/products/detail/tecate-group/PBLH...
though i take you were thinking about counting clock cycles or something in which case surely your register would overflow
See: https://mirrors.apple2.org.za/Apple%20II%20Documentation%20P...
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.
https://www.applefritter.com/appleii-box/APPLE2/NibbelingAtT...
https://displate.com/displate/2002057
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.
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?
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.
'Grab laptop, fire up IDE & plug in programmer cable' vs. 'configure the circuit using a soldering iron'. Both have their place.
https://shop.evilmadscientist.com/productsmenu/tinykitlist/6...
Very cool. (Looks like it uses 26 transistors. I assume the die is similar.)
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.
<http://ibb.co.com/1Y7QFB8N>
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.
(I just made half y'all crash out with old internet nostalgia. The rest of you are like "huh?")
More details: https://www.reddit.com/r/amateurradio/comments/1eo9ki7/xiegy...