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Comment by foxglacier | Hacker News Reader

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.

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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.

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