Although commonly referred to as a ‘timer IC’, the venerable NE555 and derivatives are in fact not timer ICs. This perhaps controversial statement is the open door that gets kicked in by [PKAE Electronics] over at YouTube, as he explains with excellent diagrams and simulations how exactly these ICs work, and what it takes to make it actually do timer things. For anyone who has ever used one of these chips there is probably nothing too mind-blowing, but it’s an infinitely better way to wrap your way around an NE555 and kin than a datasheet.
At its core, the 555 contains three 5 kOhm resistors as a voltage divider, which has been incorrectly postulated to be the source of the chip’s name. This voltage divider controls two comparators, which in turn control an SR flipflop. These comparators are used for the voltage trigger and threshold inputs, which in turn toggle the flipflop, respectively setting and resetting it. This by itself just means that the 555 can be used as a threshold detector, with settable control voltage. How a 555 becomes a timer is when the discharge, trigger and threshold pins are combined with external resistors and a capacitor, which creates a smooth square wave on the 555’s output pin.
There are many ways to make basic components into an oscillator of some type, but the 555 is a great choice when you want something more refined that doesn’t involve using an entire MCU. That said, there’s far more that the 555 can be used for, as [PKAE] alludes to, and we hope that he makes more excellent videos on these applications.
In 1997 I bought 555s and using my hands to hold the wires according to pinout to run the signal into my Sony boom box. I powered with a 9v, and cycled through available time modes with one pin.
The word “venerable” is very popular around here
Venerable is a perfectly cromulent word… 😅
Indeed. It has been used for a very long time.
“Why The 555 Is Not A Timer, But Can Be One”
The 555 IS a Timer! If a 555 “can be” a timer and is configured properly to be a timer, then the 555 is a timer. After all, the official Texas Instrument datasheet for the LM555 is titled: “Highly Stable 555 Timer”.[1] Sure the 555 can be configured to be many things, not just a timer. But the 555’s primary reason for existance is to be a timer.
* Reference:
1. LM555 Highly Stable 555 Timer
https://www.ti.com/product/LM555
And you can still buy the Texas Instruments 555 in a 0.3 Inch 8-Pin PDIP, In-Stock: 6,552, Qty.-1 $1.31 USD Each
https://www.digikey.com/en/products/detail/texas-instruments/LM555CN-NOPB/6575
I doubt this TI PDIP 555 is a Chinese copy.
The 555 is not a timer in the same way that an engine is not a car and a pendulum is not a clock. It needs other components to function as a timer so it is part of a timer but not a timer by itself.
The 555 is a timer in the same way that a car is still a car without the wheels or engine. It still needs the wheels and engine to function as a car. Those can even be changed to suit the needs of the user.
I’d say it more like: is a transmission a car without an engine. Neither a transmission nor engine make a car alone. I think the important thing is that a 555 is not a timer because it lacks the critical feature of measuring time. The time part comes from external RC circuitry. The 555 makes the time constant functionally useable. Together they make a timer(or maybe more precisely a clock)
I would argue that if you take the engine and wheels away you don’t really have a car anymore just most of one but that’s getting into philosophy.
There are ICs that are fully functional self contained timers and the 555 is not one of them and there is value in pointing that out.
> a pendulum is not a clock
Yes it is. It’s just not measuring a very long time period.
I saw someone using an inductor on a 555 to make a theremin :)
A youtube video “infinitely better” than a datasheet? No thanks, give me a datasheet.
Or a web page with words and diagrams.
But can it be done with an MCU?
The ATtiny85 is the same form factor and cost but much more versatile. :)
I see what you did there.
Everyone did.
Please stop wasting electrons using these chips! 10 mA quiescent compared to 30 nA for a TPL5110, (3.33 x 10^6 worse)
10 mA? How old is the chip you’ve been using? CMOS 555 variants have been around forever. TI’s LMC555 draws 180 microamps (typical) at 5V. The Analog Devices (nee Maxim) ICM7555 draws 30 microamps (typical) from 2 to 16.5 volts. Barring ultra-low current scenarios, there’s no need to stray from the comforting arms of a true 555.
What about impedance and eletrostatics?
Aren’t these extreme low-power types not rather fragile and high-impedance in comparison to a 555 from, say, the 1970s?
Dude, seriously? A humble LED can draw twice than (20 mA). That’s 0.02 A, almost nothing!
For comparison, an ordinary 6,3v incandescent lamp drew between 150 and 300 mA.
Still less than half an Ampére.
Every bicycle had two of them installed when I was young.
And our bikes didn’t have batteries, even! Just a dynamo.
Seriously, please consider getting some better power source if you can’t afford powering an original 555. 🙂
The venerable 3R12 battery has 4,5v and can be used to run TTL (5v) components.
It has roughly 3 to 5A capacity, depending on type (coal, alkaline, etc).
That’s 3000 to 5000 mA in nowadays terminology.
It can power an original 555 for hundreds of hours.
So you don’t have to worry about power loss.
https://en.wikipedia.org/w/index.php?title=Lantern_battery
I mention it, because the 4,5v battery used to be the tinkerer’s standard battery in Europe and Russia.
Before it had been replaced in this application in 21th century by the 9v battery so common in NA.
I think the classic 4,5v battery was much more versatile, though.
A pair of them could substitute a 9v battery and three of them could provide ca. 12v.
It also was very forgiving. An 4,5v battery rarely did catch fire or got hot.
Well power is power, why use more if you can do the same work using less?
what? why? this is news to me. the datasheet that is at hand says typical 10mA at 15V. that seems 10x too high??? wouldn’t it be 15V/15kOhm = 1mA for the voltage divider? the rest of it’s just a comparator and a flip flop. the flip flop draws 9mA just to maintain state?? now i feel like i need to test the ones sitting in my basement
ANYONE who doubts that this is a “timer IC” should reference the ORIGINAL National Semiconductor datasheet, that states “LM555 Timer IC”. I think that if the guys that created the part in the first place call it a timer IC then that’s what it is.
As for the ATtiny 85 comment, I’ll refer you to the late Bob Pease’s comment, that my favorite programming language is SOLDER. True statement.
>>> I’ll refer you to the late Bob Pease’s comment, that my favorite programming language is SOLDER.
That quote is from Steve Ciarcia. Pease probably wouldn’t have deigned to write code at all.
love the 555, been making fake car alarms (blinkey LEDs) with them for years. ;-)
Dumb question (maybe), but how do YOU pronounce “555”? I first used one in about 1972, and my friend and I called it a “five fifty-five”, so that’s what I’ve always called it since. This video says “five five five”, but I think I’ve heard “triple-five” as well.
Remarkably, you still know what it is, no matter what people say.
“That which we call a rose, by any other word would smell as sweet.”
One of the first uses I had for the 555 was as half bridge drivers for old high voltage stepper drives. Scavenged from very old disk drives. The 555 could easily drive the 160mA at 12V. Multiply that by 3, with some bobbins, and you have a cable driven electro magnet moving in 3D space. Add an 8086 XT, with a printer port and it’s playtime.
The half bridge output was often my most used feature of a 555.