Is the 555 still a viable IC?

[schmitt trigger]

I originally posted this question on another EE forum, but I believe that the technical expertise and the geographic distribution of members is significantly different between the two, to warrant posting it again here.
DISCLAIMER: I am not building anything with a 555, this question is only sheer curiosity..... Having cleared that out of the way:

It can be safely said that the 555 is one of the most ubiquitous and influential ICs in history. I am also sure that most if not all of the old-time forum members have used it at least once.
But the IC is almost 52 years old, and although it has been updated to CMOS versions, its age and limitations show up.
The question would be: do you think that the 555 is still a viable IC in 2024?
Let me give my personal opinion; the problem with the 555 are the required external passive components. To obtain a modicum of stability and accuracy, the cost of those components may exceed the cost of the IC itself.

[tooki]

Define “viable”.

Because clearly it’s a viable product, in that the manufacturers can manufacture them at a cost low enough that customers are still buying them in volumes sufficient to keep production going, but with a sale price that makes it worthwhile. (The sales number always thrown around is “over 1 billion per year”.)

They ceased being sensible as accurate timers long ago. If they ever were to begin with. But clearly they’re being used for something.

[MarkS]

Depends on your use case. If you need accuracy, no. If close enough is good enough, yes. What you'll find is that 99% of the time, "close enough" is perfect.

[schmitt trigger]

You are correct, "viable" is a very elastic word. Its meaning can be stretched in a number of ways.

By viable, as a narrow definition, I was thinking whether it could still find a place on low to medium volume commercial products. Nowadays, in 2024.
High volume I believe is out of the question, whatever function the 555 can do, it could be integrated somewhere else.

Yet, they still sell..... Who would be the potential customers?

As previously mentioned, this is only curiosity.

[exe]

Ha-ha, did same research ago. There are plenty of threads like this on the Internet.

As of me, I used it to generate square pulses to drive a mosfet. It worked flawlessly, can't complain. I used CMOS-version of time because it's presumably less noisy. I decided not to go with MCU as I didn't want to mess up with firmware and programming.

The only thing I didn't really like is that, in order to get less than 50% duty cycle, I had to use some "wizardy" with a diode.

[ejeffrey]

If you just need a roghly accurate square or pulse generator, they are fine. I would use them for low to medium volume.  A tiny MCU is cheaper in volume but needs to be programmed, which adds steps to manufacturing.  In addition, I'm certain I will be able to buy 555s in 10 or 20 years, so for low volume products with long life I would really consider a 555 over an MCU.

There are 555 variants at a wider range of operating voltages without a level translator.  That could be a slight bonus for the 555.

For low volume you might even choose to use a simple discrete solution like a 555 even over integrating into an MCU that's already part of the design just because it keeps the development simpler.  In many projects, the software development is the overwhelming driver of development costs.  If dropping an extra chip on the PCB can reduce software development complexity then it's often worth it.  Of course for high volume products, manufacturing costs outweigh development and it you want to minimize the BOM cost.

[coppice]

There are lots of variants of the 555, like the various CMOS versions. Between them they still sell by the billion. I wonder how close any of the currently available ones are to the original die developed at Signetics?

[selcuk]

Most of the digital circuits include a MCU nowadays since you can fit them to any budget. Then you set timers and PWM outputs of the MCU to do the job of 555 in a versatile way. It is not required as in the past anymore.

Nevertheless, I'm using it in my designs frequently (not the original one, but TLC555). If I use a watchdog chip and want to extend the output pulse, then I use it. Easy to find and cheap.

[jpanhalt]

Like a Schmitt inverter, they can be stabilized with a crystal for better timing (see attachment).

[Gyro]

Viewed as a pair of analogue comparators with bias network, an RS latch, and a couple of fairly beefy output stages, one P-P and the other O/C, with a wide supply voltage range and all in a single 8 pin package, it can still be a handy IC. It's not just a timer, and you can't directly match it with a micro (within its niche).

[SiliconWizard]

Yeah, not sure what "viable" means here. But I've used the TLC556 (dual) just a couple years ago for a simple application that would otherwise have required either more discrete ICs, or a MCU with firmware.
Sometimes simplicity just wins.

[Psi]

Yeah, It's useful, but not all that common for a production design any more due to cheaper and more flexible options, like a cheap mcu, but any MCU option requires coding and flashing so has it's own disadvantages even if it is more flexible

There's plenty of situations where you might want a 555 for a quick and dirty solution to a problem.
You could throw together a test jig for something in under an hour if the accuracy isn't all that critical.

[xrunner]

Yet, they still sell..... Who would be the potential customers?

As previously mentioned, this is only curiosity.

My guess is learners and classes are buying many of them. One hobbyist after another, one learner after another, year after year. Each person learns using one or two, burns a few by mistake, and moves on. Look at all the tutorials for 555 timers that are out there.

I wonder what the quantity of new or good 555 timers are just sitting in parts drawers never to be used again. Nothing wrong with them. If we could only get these to new learners they'd never have to make any more ever again. 

[Psi]

There is also the LM555-MIL  for military stuff.
It's active apparently, but I've never seen it for sale at the usual places.

[EPAIII]

Consider, if you built a circuit with a 555 timer 50 years ago, which is still in use and the chip went bad, you could just get another 555 and drop it in and the circuit would still work today. About a one hour repair, including the time spent ordering the new 555.

If you built a circuit with a micro processor 20 years ago and the chip went bad, that micro processor would probably not be currently available. You would probably need to build a completely new circuit with either an "improved" version of that processor or with a completely different one and then wonder where the original code was. Oh, that's right, your IS department replaced the desktop where the code resided 10 years ago and they don't keep back-ups for over 5 years. So you would wind up re-writing the code from scratch.

So in order to save a few pennies and use the latest and greatest technology, 20 years ago, you wind up spending several days building the new circuit and writing the code for it and testing, of course. Now, tell me which would have been a better choice.

[Psi]

Consider, if you built a circuit with a 555 timer 50 years ago, which is still in use and the chip went bad, you could just get another 555 and drop it in and the circuit would still work today. About a one hour repair, including the time spent ordering the new 555.

If you built a circuit with a micro processor 20 years ago and the chip went bad, that micro processor would probably not be currently available. You would probably need to build a completely new circuit with either an "improved" version of that processor or with a completely different one and then wonder where the original code was. Oh, that's right, your IS department replaced the desktop where the code resided 10 years ago and they don't keep back-ups for over 5 years. So you would wind up re-writing the code from scratch.

So in order to save a few pennies and use the latest and greatest technology, 20 years ago, you wind up spending several days building the new circuit and writing the code for it and testing, of course. Now, tell me which would have been a better choice.

Yep, speed of repair and maintenance is very important, especially with fixing production test jigs or any production line equipment where down-time is expensive.
Not having to worry about firmware is a big time saver. Not just because of the time required to code and flash it but having to test it and any regulatory or procedural hoops required to change it.
On the other hand having a MCU makes diagnostics easier as you can easily add hardware checks and warnings in code to quickly diagnose and find faults.
So it depends on the situation and is often a trade-off

[Smokey]

I've only done one design that used a 555.  I needed an adjustable frequency and duty square wave that would be user settable with pots to drive a pneumatic valve as an air burst thing for machining.  While it "worked" it's fiddly to adjust since the duty and frequency are not fully independent.  I should have just used a micro. 

[johnboxall]

They're easy, you can find success without much effort which is great for education.

[baldurn]

As a counter argument against the 555 I have observed that nobody here at the local makerspace would use the 555. The typical hobby person is doing Arduino or ESP32 for everything. People tend to solve everything with the one tool they know, so the 555 does often not even get considered. We do have some classes where we play with old chips, and where we might do something fun to learn the 555 - but the day after everyone are back with their ESP32 project.

Funny that you say software development is the reason to avoid a MCU and use 555. These days most people think the other way around. We go with a MCU even when a 555 would have done the job. It is easier to figure out a simple program than it is to do "real" EE with discrete components.

[SiliconWizard]

Funny that you say software development is the reason to avoid a MCU and use 555. These days most people think the other way around. We go with a MCU even when a 555 would have done the job. It is easier to figure out a simple program than it is to do "real" EE with discrete components.

Yes. That is, until people actually have to make stuff that is provably reliable - that's usually when they reconsider doing everything with software.
But for tinkering, it may look easier.

[JPortici]

Funny that you say software development is the reason to avoid a MCU and use 555. These days most people think the other way around. We go with a MCU even when a 555 would have done the job. It is easier to figure out a simple program than it is to do "real" EE with discrete components.

Yes. That is, until people actually have to make stuff that is provably reliable - that's usually when they reconsider doing everything with software.
But for tinkering, it may look easier.

You don't have to prove to a committe that your independent software timer that resets everything in case of a failure actually works as intended
and it's another independent MCU you don't have to program

[baldurn]

A new YouTube video about this exact topic: https://youtu.be/SgV6_Y_sg4k?si=hC28IX6KcHHjxwQU

He proposes using ATTiny 412 instead of 555.

[jpanhalt]

Way back in 1999, High Tech Chips produced several Microchip 12F PIC-based devices that were pre-programmed to do 555 type stuff -- of course, VCC and GND were reversed.  I thought, there's a gold shovel without a handle.  The name is still found by Google, but its not clear whether they still produce those items.  I have included 2 pdf's of their datasheets from that time.

Google link: http://www.hightechips.com/   Yes, it is spelled differently.

[Warhawk]

A new YouTube video about this exact topic: https://youtu.be/SgV6_Y_sg4k?si=hC28IX6KcHHjxwQU

He proposes using ATTiny 412 instead of 555.

Maybe for hobby but not for production. Go and find the second source for ATTiny. Or just pre-programming ICs for production is pain.
I know about automotive projects using 555. It is not stupid as long as it does the job.

[SeanB]

Yes as a relatively robust driver nothing to beat it, especially as you can get level shifting, from almost any voltage logic level above 3V, to 12v for almost free, just add in a single resistor or a zener diode, plus you get the ability to drive an indicator LED to show output low almost free as well, and it can also drive another load active low as well. 2 of them, and a single small signal transistor as inverter, and a few resistors, and you get a robust full bridge driver, and add in another small signal transistor and a pair of resistors and you also get the ability to turn the bridge off as well, using the reset inputs. Level shifting from logic to 15V included free as well, plus well defined switching thresholds for slow edges included as a bonus. Most of the non CMOS bipolar ones will do a half amp as well no problem, the CMOS at least 100mA which is a good drive for a lot of things. Just need a 1000uF 16V capacitor close by for power decoupling.