555 timer teardown: inside the world's most popular IC | Hacker News Reader

555 timer teardown: inside the world's most popular IC

righto.com

318 pointsdezgeg59 comments

Probably a coincidence, but 0x555 == 0b010101010101. Just like the flip flop output signal.

Cool!

I was curious and looked this up on Wikipedia [0]:

> It has been hypothesized that the 555 got its name from the three 5 kΩ resistors used within, but Hans Camenzind has stated that the number was arbitrary. [1]

[0] https://en.wikipedia.org/wiki/555_timer_IC#Design [1] http://www.semiconductormuseum.com/Transistors/LectureHall/C...

Maybe was the most popular chip for a while until the 90s, but these days they are not in very many things that sell in high quantities unless it is like a really cheap toy or something.. smartphones for example don't have 555 timers in them. Battery charger IC's probably are the biggest total seller.. but many companies sell similar types under different names, so not sure if you could call them all "one chip" like you can call the 555 timer and all of its clones..

Probably not in smartphones, but I remember seeing a 555 in a recent (i.e. few years old) laptop before, where it was being used for power sequencing.

The functionality on the 555 can be replaced by any basic microcontroller hence only the cheapest products have a 555 timer.

The cheapest ones at Digikey are going for 10 cents (compared to 35 cents for the cheapest small microcontrollers [PSOC or a 10F200]).

So I guess they still have some use.

Probably sell mostly to hobbyists, universities and old designs though.

The microcontroller doesn't need the external resistors and capacitor. If the 555 circuit needs a big capacitor then the microcontroller circuit could be cheaper.

The microcontroller does, however, need a decoupling capacitor and the inclusion of a program in manufacturing. It may also be pickier about power supplies.

True, but ideally the 555 should have a decoupling capacitor too, and the decoupling capacitor is very small and cheap.

Hobbyists hardly use these things anymore, because they require all that external stuff -- resistors, capacitors -- before you get what you want out of them. They're not self-contained.

These days you can just program a PIC or something, drop it on your broadboard, and you get whatever signal you want out of them with software, without any components besides the chip itself, and maybe a quartz crystal if you want better accuracy (although I really wish they'd package a crystal inside the DIP as well to make it even more self-contained).

The DS3231 RTC clock chip indeed has an accurate crystal oscilator inside the package, so, yeah, put em in an AVR why not!

The biggest seller might actually be one particular lithium battery protection chip, because it seems to show up all over the place with less variation than the actual charging chips.

The DW01? It's certainly one of the high-volume chips, but consider that there are also quite a lot of products that don't use lithium batteries.

Yea so true.. that chip is very popular in many lipo packs.. It would be interesting to see how many gazillions of those that are sold..

Chris Gammell (of Contextual Electronics) and Jeri Ellsworth (of Technical Illusions) held a really neat 555 timer contest a few years ago. You can see some of the results here:

http://makezine.com/2011/04/21/555-contest-winners-announced...

http://makezine.com/2012/08/22/555-timer-contest-highlights/

I started writing a sort of tutorial for the NE 555. Most documents give you just the formula to have the values (multiply the value by Ln2 and stuff), not how we got there.

It's not finished yet, but here are the first few pages:

http://j.mp/ne555calc

It will also deal with duty cycle and things like that.

Here's the French version (old lab report when I was in college):

http://j.mp/ne555fr

This one of the reasons I hang on to old databooks and app note books. The National Semiconductor, Motorola and Signetics appnote collections in particular are very good for delving into the theory of how the devices work.

I may never need them again for real work, but are they ever fun to read!

Right on! Well since you seem to like that, I've shared a link once here on HN but it went unnoticed. It's about Analog Design and it has a ton of information. Don't get lost:

http://www.wisewarthog.com/

It give recommendations depending on what you want to do, discusses books and application notes, gives links to treasures, advice, pointers, and insights.

You might know the site; otherwise, I hope you'll enjoy it.

Thanks! Bookmarked.

If you want to play with a simulated 555 - and are willing run an old java applet - my favorite (educational) circuit simulator includes several 555 circuits (and an implementation of the 555's internals).

http://www.falstad.com/circuit/e-555pulsemod.html

Paul Falstad's Java applets were my biggest regret about deciding to uninstall it.

Wow, I didn't know them before. Cool stuff!!

PS. I entered with my android mobile and to my surprise it works... Another thing I was not aware is that I have Java applets on by default...

Android doesn't support Java applets. The site uses JS.

Somebody ported the circuit simulator to JavaScript: http://lushprojects.com/circuitjs/

It's been rewritten in JavaScript so you don't need Java at all.

There was a project in Elektor a few years ago to program some cheap 8-bit microcontroller to emulate a 555. https://www.elektormagazine.com/magazine/elektor-201511/2819...

They also did a kit to build your own 555 from discrete transistors. https://www.elektor.com/the-three-fives-555-discrete-timer-k...

I have that kit! It was great fun to build it, make some simple circuits, and trace the voltages through the "chip". The kit is really nice quality and thoughtfully designed.

This kit is actually from Evil Mad Scientist [1], the same people who make the EggBot and other nifty stuff. Their own site has a lot more information about it, and they sell it cheaper than Elektor. [2] They also have a similar μA741 op-amp kit. [3]

Back in the '70s I used to make blue boxes [4] with a bunch of 555s in them. This was probably not the best way to design a DTMF box - I remember I had a heck of a time keeping the frequencies stable. Woz's blue boxes probably worked a lot better!

[1] http://shop.evilmadscientist.com/

[2] http://shop.evilmadscientist.com/tinykitlist/652

[3] http://shop.evilmadscientist.com/tinykitlist/762

[4] https://en.wikipedia.org/wiki/Blue_box

Yep. Those links were nostalgia for me, 'cos I remember first using the 555 when I was a kid building projects from Elektor and ETI ...

The old elektor magazine was super good. Every issue had something on just about every level of competence in it. I learned so much from those. The most complex thing I built from them was the 2D graphics accelerator, hooked that up to the Beeb and wrote a fully functional vdu driver for it.

HN readers: what products do you know of that used the 555 IC?

I'm working of a catalog of popular consumer electronic devices that used this chip. Anything you know of that used this chip would be helpful.

Cool! Will it be something on the web?

Personal project to start. See if it turns into something more.

I'm imagining something like 'reverse-dns' for electronic chips.

That is, today if you take apart a consumer device, you can can see what chips are in them and get the datasheets pretty easily (a 'Whois' lookup) - but there isn't an equivalent for looking at a chip and seeing which products it was used in ('reverse lookup'). I've done this successfully with a few radio modules but I wanted to start with something more iconic like the 555.

My question is if there is a product that exists solely because of the 555 just as the Texas Instruments Speak & Spell existed solely because of the TMC0280.

It's actually incredibly rare in consumer products. Especially since an 8-bit micro controller can cost much much less in bulk today.

Edit: and 8-bit micros come much cheaper than Digikey when you buy consumer product volumes directly.

Do you know what it is was used for in non-consumer products?

It's in a number of ancient DC time-delay relays.

I design and manufacture an electronic cigarette device that uses a 555 to PWM a MOSFET for variable power output. Super simple and robust but will be switching to MCUs soon for more features.

BBC micro http://www.8bs.com/inbbc.htm

I've found this related IC to be useful in modern circuits: http://www.ti.com/lit/ds/symlink/tlc551.pdf

It's a low-power version of the 555. It runs down to 1.0V!

I've used it in inductor circuits to chop-boost small voltages.

Link to the original chip designer's free book:

http://www.designinganalogchips.com/

Thanks for this, I've got a few pages in and I really like his writing style.

I had no idea the 555 chip that we use today, is the same as it was in 1970. I would have (incorrectly) guessed that as time went on, that it would have undergone improvements/revisions as technology improved.

Just before the conclusion he addresses that; there was a revised/improved version in 1997 that was a commercial failure. Presumably due to the 555's ubiquity.

Well, there are lower power CMOS versions of the 555 available.

A 555 timer chip can deliver 200mA at the output, so it can drive small lamps and relays directly. The output load usually dwarfs the current used for timing. So, for most applications, a lower power version is pointless.

The CMOS version helps quite a bit when the 555 is configured for monostable or bistable mode.

I doubt that most applications of the 555 are driving relays and lamps, it probably is mainly used to generate timing signals. But that's besides the point, the low power versions can function with low voltages, allowing to power the chip with a single 1.5V battery, which would be impossible with the standard version, so it's far from pointless.

Any re-spin will cost money (and a lot of it). As technology improves, the old processes usually become cheaper too.

Analog chips can be real cash cows. Unlike digital microprocessors, a successful design can last for decades without any change in process node. You still get some really old process nodes being used on the analog side because they're still functional today.

Power applications in particular need larger transistors for sourcing and sinking large currents. Smaller process nodes don't help much for many of those applications.

I just about died when I saw "banana for scale" on the photo near the bottom.

I wonder if they make a giant expensive high voltage/amperage/speed EMP proof military space hardened version of the 555, for use in LED atomic bomb count-down clocks, etc.

Here's a cool DIY project: Make a drop-in replacement kit for the 555 integrated circuit with discrete transistors and resistors [1]

[1] http://spectrum.ieee.org/geek-life/hands-on/build-your-own-g...

Who actually makes the 555 these days? Or is everything old stock?

digikey hardly sells everything, but they do sell various 555 chips from 12 manufacturers, at least per the parametric search.

Its fun to look at the weird options available. A UFBGA-8 package is available... weird, never used one of those before. TI sells chips that go up to 3 MHz. TI will also sell bare dies if you have a wire bonder. Supply currents are available down to 30 uA.

Buying bare dies would be really convenient for my die photos / analysis, but unfortunately with the Digikey minimum quantities, I'd need to buy 25 @ $4 each which isn't worthwhile.

I have used a UFBGA. It was awful, taking three revisions of paste mask to get the thing soldered properly.

Maybe get some indication from Octopart[0], quick scan tells me that there are relevant prodcts by at least TI, Fairchild, STMicro, Intersil, Maxim, New Japan Radio, Diodes Inc., NXP have parts in stock. I'd be surprised if those are all just old stuff and not still being produced.

[0]: https://octopart.com/search?q=555&start=0&filter%5Bfields%5D...

this is a super cool write up of something plenty of us neglect. I wasn't expecting the excellent interactive explorer at the bottom! Click on the component diagram and see the component highlighted in the actual image!

For those interested in understanding the general operation, this type of circuit is called a relaxation oscillator.

feel so nostalgic reading this! I remember my first contact with the 555 was through the Chip-chap electronics kit when I was 10. good times making LED timers, metronome, etc.

cool to see the mix of images, schematics, interactive graphics

Reply on news.ycombinator.com