Doin' It with a 555: One Chip to Rule Them All
(aashvik.com)138 points by MonkeyClub 5 days ago
138 points by MonkeyClub 5 days ago
I built one from discrete transistors in a lab class in college, on a breadboard. Fun times debugging and getting it to work. Then I flashed an led with it right next to another led flashed from a 555 chip. With the same discrete timer caps, the flashing frequencies were different due to the extra parasitics in the breadboard discrete 555 version. So had to compensate the caps to make the flashes match each other's frequency.
That's a great exercise. The hard part is always that in chips you can pull stuff that is rather tricky discretely, for instance, a multi-emitter transistor. So you can't always do a 1:1 conversion but for a 555 it is still doable.
I saw this a while ago:
https://www.instructables.com/Designing-a-555-Timer-on-Discr...
Only because odd components aren't marketable. There used to be 4-terminal MOSFETs, they weren't sold after ICs became normal. Never heard of a multi emitter transistor being sold discretely but it's possible.
Dual gate mosfets were a godsend when building RF/IF mixers or preamps. Luckily I have a small stash as they're almost unobtanium and costly these days, but for most uses such as mixers and preamps they can be swapped with a pair or normal jfets in a cascode configuration like this one: https://i.stack.imgur.com/6Nyhg.gif
Real men use Unijunction Transistors like the 2N2646.
One of the books I first tried to learn from was _Miniature Projects for Electronic Hobbyists_ by one Ken W. Sessions. It was really a unijunction transistor project book. You know how some people will say you'll learn maybe not the best mental models for electronics from Forrest Mims' books? (I don't get it, they seem OK to me) Well, Forrest has nothing on Ken W. Sessions. The circuits worked, though.
The ‘birthplace’ of the 555 is in downtown Sunnyvale - an easy trip if you’re in the Valley*. It’s in an alley between Murphy Ave. and the parking lot off S. Frances. There’s a realtor’s office opposite the side entrance to Fashion Wok. That’s the place.
It was invented by Hans Camenzind**, who was doing contract work for Signetics in an office he rented there. What a great location for your office, even back then!
There really should be a plaque or something.
* Go there then have dinner at Dishdash, across the street.
** RIP - he died in 2012, but his web site is still up: http://www.designinganalogchips.com/
Interesting links on Hans
https://web.archive.org/web/20260125061851/http://www.design...
https://en.wikipedia.org/wiki/Hans_Camenzind
( Please note , I posted the archive.org link to the Hans Camenzind site, because when I tried to access the site URl , my BitDefender virus thing popped up a warning about a certificate problem. I Have NO idea if this is a real problem (Im clueless) or not but just to be careful I use the archive.org link )
Hans wrote a text book, "Designing Analog Chips" which is available for free.
http://www.designinganalogchips.com/_count/designinganalogch...
Cool. I lived on E Evelyn for a few years in the 00's and dined many a night at Gumba's. And Hobee's and Denny's of course. I miss the days of raiding Radio Shack in the nearby mall perennially under construction for piles of :CueCats.
Another eatery of Valley folklore is Buck's of Woodside. Neat place on its own.
Gumbas is still there! Hobee’s near 101 too. Still my favorite diner.
The mall (and ‘downtown’ Denny’s) has finally, after literal decades of construction driven by multiple bankruptcies of the firms doing it, been replaced by walkable mixed use stores, apartments, and a cinema.
When I was in college I was not in an engineering program but I was self-learning electronics. I was trying to learn to use a 555 timer to do something and couldn't get it to work.
So I went to the office hours of a random EE professor thinking they would help me out. Instead I got scolded about how 555 timers are not real engineering and that I shouldn't waste his time.
I never used a 555 timer ever since.
I always get reminded of this when I see all the weird praise the 555 gets: https://www.electronicdesign.com/technologies/analog/article...
It's one of those poor/early designs like the 741 opamp that has since been superseded by much better chip designs but is thoroughly ingrained in hobbyist and EE101 classes to the point where people think it must be a good design because it's so venerated. It's meme driven really.
However, for educational and hobby use, eh whatever. If I was a professor and the curriculum called for 555 or 741 use I would thoroughly state to the students that A. these devices are historic and good teaching tools, however, in the real world their performance has been surpassed and you would use new designs. Maybe even present a few alternatives like the TL081 and what Pease mentioned for timing.
The TL081 family of op amps is definitely in the "old parts you should (sometimes) use" category (for price/performance) but there have been much better op amps for not much more money for a long time now. Both the now-ancient 2nd edition and the aging 3rd edition of Horowitz and Hill recommend the LF411 for a JFET-input general purpose jellybean, for example.
For learning you some analog, I would recommend the LM358 op amp and the LM393 comparator and all the old National material on them. The LM358 has its quirks so you won't think op amps are ideal but you still see them in a ton of stuff, because they're dirt cheap and adequate for a lot of things, and the LM393 comparator is still so good you really should know why you're choosing anything else - micropower or exotically high speeds or whatever.
A little bit (scolding a beginner in this way is never acceptable), but I do feel like the 555 is really overrepresented in electronics learning materials. It's a quirky little chip, so learning about it doesn't really teach you much (most of the time it's just 'hook it up like so and it does this!', not 'here's how comparators and oscillators actually work'), and it's also now almost never the best or even a good solution for any of the problems it solves.
That's true but because it is a quirky useful little chip it is for many people their first exposure to integrated circuits that are a bit more 'analog' than gates and micro controllers. Opamps are the other gateway drug I guess.
It's excellent teaching material for that reason alone, you do learn about it if you try to understand what makes it tick (there are plenty of articles about it, including blown up versions). I agree it is not the best solution for most applications but I'm happy to admit that I've actually used it in production designs (more than once, actually) where it made good sense to have a component that didn't have to be programmed. If you have a soft component on a board and a spare io line then you are usually better off doing it in some different way.
I've seen some interesting applications of 555s that would have taken a lot more hardware otherwise, one of which was an oven controller with used a thermistor to directly affect the PWM output of a 555.
It's true. They're not useful for anything not hooked up to mains.
I was meaning to add footstep-activated lights to my stairs using vibration sensors and 555 timers, but then I learned that if I tried to operate them from a battery, the 555 would drain it in hours, while a much more sophisticated ESP32-c3, would last a month in sleep mode on two coin batteries or one li-ion in the same form factor all while being part of a development board that greatly increases idle current.
I never went back to that engineering department.
I ended up befriending a former Northrop RF Engineer and a (sadly) homeless genius who was involved in early silicon valley. Those two guys were incredibly impactful on me and got me all the way up to building RF equipment.
Very neat. I'm in the midst of some interesting hacking and I really regret giving away a lot of my workshop tools in the mid 90's when it all went to software. I still have a lot of hooks in electronics and such but I just couldn't justify lugging around a couple of cubic meters of parts stock & gear. But right now I'm seriously wondering whether that was a wise decision, on the other hand that world has definitely not stood still, and the prices have come down considerably. But I'd love to have my old frequency counter and pulse generator back :)
I'm really happy that you found an alternate path because such a put-down is terrible and should have never happened in any mature education institution.
Yes, but a successful way to prevent people from going to office hours. People generally don't become professors because they care about teaching, and universities don't reward professors for teaching.
> People generally don't become professors because they care about teaching
That's only true in the very twisted environment that is the modern research university. But universities do still exist which are focused on teaching students as the primary goal, and the faculty there love teaching.
I used to salvage components from electronic stuff and was always looking out for 555s but never found any, in a whole range of vintages from 1970's to 2000's. I ended up with the same conclusion - it seemed to be a hobbyist's chip that real consumer products didn't use and felt amateurish for some reason I didn't understand.
The big problem I ran into playing around with 555s was that capacitors are very rarely the capacitance they claim. Unless you're speccing an expensive capacitor, you'll find your time constant varies quite a bit across devices and temperature. That's fine for some use cases, but completely a deal breaker for others.
Yeah, in the typical value ranges (nanofarads) of a 555-timer-class analog design, you'll need film caps. Ceramic C0Gs are too small and class 2 dielectrics are dismal for anything but bypass. They don't just have temperature coefficients, they have voltage coefficients and are wildly nonlinear. And electrolytics are almost as dreadful as batteries. Worse in some ways. It's a tough bridge for beginners to cross - once you figure out capacitors are not all equivalent you have to do a deep dive on dielectrics and it's a bit of a chicken-and-egg problem - you don't know what you're doing so you don't when you'll need what.
That's funny because I have two objects on my desk for which I know that they use 555s. One is a no-name joystick with "autofire" function from the late 1980's. The other is a mass produced motor controller from the 2000's where the 555 generates the PWM signal for a FET.
Sure, it's kind of cringe. I've shipped stuff with 555 timers in it. I'm not proud, but I'm not telling what either.
You can do almost all of the 555 tricks with comparators and then some, and you'll learn more doing them. Check out the old National Semiconductor application notes for the LM393. You're more likely to see comparators used for little bits of analog/analogish-digital glue in professional designs.
555 timers were everywhere back in the day. It was one of the most mass produced chips at the time with over 1 billion made per year.
That is a terrible learning environment. Our profs always leave a box outside the laboratory with free expired textbooks, partial part lots, and damaged/old test equipment.
Some people get into Science, Software, and Electronics for the wrong reasons.. And end up miserable teaching after failing in the private sector.
A few 555 can teach people a lot, and burning out parts is part of the learning process. Most fold the DIP legs under like a "dead bug", as that is the tradition to prevent its accidental re-use.
In terms of component cost, ATTINY or PIC10 mcu have internal RC oscillators with configurable PWM pin hardware. Thus a single component is usually better than the accumulated precision error in discreet parts around a 555.
I usually recommend an RC car/truck build, https://eater.net/6502 , and or an LDOmotors Voron kit. Getting your Ham Radio technician license will also introduce you to an intuitive understanding of EE component model limits.
This covers a lot about discreet analog circuits, and I recommend trying to figure out how every circuit works on your own:
https://archive.org/details/encyclopediaofelectroniccircuits...
Simulators are not perfect, but they are a lot cheaper when starting out. =3
Tutorials:
https://www.youtube.com/@FesZElectronics/videos
Tools:
https://www.analog.com/en/resources/design-tools-and-calcula...
https://web.archive.org/web/20200218212700/http://spectrum-s...
This requires a GPU on Windows, but is a more advanced newer Spice simulator:
https://www.qorvo.com/design-hub/design-tools/interactive/qs...
How hilariously transparent that he didn’t know how to use a 555 and didn’t want to admit it.
That’s why the Beach Boys made a song about the 409, the predecessor chip.
I designed the electronics for a heavy-duty industrial 3D printer and used a 555 in the failsafe circuit (alongside the manual e-stop). If it didn't get reset by a heartbeat from the embedded computer/software, it would unpower the heaters and actuators.
That's the only use for one that isn't (always) a design smell - it makes a really nice missing pulse detector, better than you can easily do with comparators. But if you have the budget, a purpose-made watchdog chip or a tiny microcontroller really can make a better watchdog.
In the same voice as saying that some language is Turing complete, we can now say that an electronic component is 555 complete.
Depends what you want to achieve; from fundamental educational point of view it is not a good device, too high level; most of the stuff you can build with 555 you can do with standard BJTs, and you'd be able in fact in understand how it works. To me, 555 is good only for dumbed down entertaintment, not true learning.
Obviously TFA is satire/tongue in cheek and while you can do all sorts of awesome stuff with a 555 you can't patch those implementations without physically rewiring them which in many cases means throwing out the board and fabbing a new one, whereas a microcontroller-based board can often be fixed with a simple jtag debugger.
So, yeah, 555 timers are cool and doing things with analog ICs is groovy but there's a reason everyone just stuffs a small microcontroller in places where we used to just stuff a 555, and it's maintainability.
Two thoughts on situations where the 555 may be preferable, if anyone has experience how these compare :
1. Low-noise applications. I’d naively expect the 555 to be less noisy than a clocked digital microcontroller, though it’s been awhile since I’ve worked in this space.
2. Low power applications. How does latent power draw compare between a 555 and a typical low power microcontroller?
> Low power applications. How does latent power draw compare between a 555 and a typical low power microcontroller?
The 555 is very power hungry compared to a typical cheap low-power microcontroller. IIRC there are lower power variants but the 555 still fundamentally does timing by draining current through a resistor, which is going to result in losses.
> I’d naively expect the 555 to be less noisy than a clocked digital microcontroller
TTL ones were exceptionally noisy because the output transistors "shot through" - both output transistors would conduct for a moment shorting the supply rail to ground and crowbarring ridiculous interference onto other parts of the circuit.
and it comes with new set of problems: Now you need a FW guys to write and maintain software for it, then your hardware team may need to wait that FW guy to release software to test, or the FW guy need to wait hardware to test his software, etc.
Then in production, you need another stage to flash the FW, which add time and complexity.
Then security, cheap MCU usually has bad software protection, that means your software can be read out easily, not a big deal since the FW replacing the 555 would be dead simple anyway, but try to explain it to a non-technical CEO when he read about it on his morning's newspaper.
Puya? First time I hear of these things .. (having used ESP32, RPI Pico, Nordic and STM). Googling led me to OpenPuya https://py32.org/en/
Do it. Build a couple, then build a simple opamp mixer (it's a single opamp and a handful of resistors, and a couple of capacitors across the power supply), and then - get adventurous - a PT2399 delay kit.
Then take a look on https://yusynth.net at some of the VCF designs, and build one of them.
You won't have a synthesizer, you'll have some crazy homebrew drone machine that you can make scary movie sountracks with.
Definitely do it.
Obligatory link to Forest Mims' book: https://archive.org/details/555-designs
I'm really looking forward to the LLM results of all these posts.
> Doin’ It With A 555: One Chip to Rule Them All
> We also know that microcontrollers implement logic gates – AND, OR, NOT, NAND, etc. But you don’t have to deal with those complicated logic functions, or worse, the software that runs on those microcontrollers. Get down to brass tacks and use hardware (555 ICs and 555 timer ICs, to name a few the only important ones) that just works!
Come on, you haven't even described how to implement combinational logic using 555 timer chips. Just show us how to build NAND, please.
I won 2011's "555 Timer Contest" artistic category. As a bonus I got a phone call from Hans Camenzind, who offered to design a custom chip (for free) to perform the same function.
LeDominoux vid: https://youtu.be/PQOjkuJtBfM?si=pS9Qloekm7JJKCoE
555 contest archive: http://web.archive.org/web/20120121212136/http://www.555cont...