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Comment by solomonb | Hacker News Reader

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.

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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It's one of those poor/early designs like the 741 opamp that has since been superseded by much better chip designs but is thoroughly ingrained in hobbyist and EE101 classes to the point where people think it must be a good design because it's so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.

Indeed, my professor mentioned that we used 741's so we would learn all of its deviations from the idealized op amp model. Plus, we had a huge pile of them.

What a spectacular failure of education.

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.

> 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

My whole workbench is mid to late 90s HP equipment I've picked up very cheap at swap meets. I love this older stuff but it is really crazy what you can buy out of China now. The Rigol Oscilloscopes and Spectrum Analyzers are crazy. They can actually replace a lot of other test equipment and do some pretty complex analysis.

> 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.

I actually had a near identical experience at a different university when seeking advice about how to read Hegel. I think this is a common issue with our academic system.

I've found that SDRs can function very nicely as impromptu spectrum analyzers.

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.

I saw 555 being used to implement the "Turbo" buttons in these old 8-bit pads for NES clones and similar. Also, I think that the mythic Gravis game pad uses a 555 to implement the same function when it is in two button mode.

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's really too bad. 555 timers are a lot of fun.

When the student is ready, the teacher will appear. What a wonderful fellow. Have you gone back and thanked him?

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.

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