Back To Basics With A 555 Deep Dive

Many of us could sit down at the bench and whip up a 555 circuit from memory. It’s really not that hard, which is a bit strange considering how flexible the ubiquitous chip is, and how many ways it can be wired up. But when was the last time you sat down and really thought about what goes on inside that little fleck of silicon?

If it’s been a while, then [DiodeGoneWild]’s back-to-basics exploration of the 555 is worth a look. At first glance, this is just a quick blinkenlights build, which is completely the point of the exercise. By focusing on the simplest 555 circuits, [Diode] can show just what each pin on the chip does, using an outsized schematic that reflects exactly what’s going on with the breadboarded circuit. Most of the demos use the timer chip in free-running mode, but circuits using bistable and monostable modes sneak in at the end too.

Yes, this is basic stuff, but there’s a lot of value in looking at things like this with a fresh set of eyes. We’re impressed by [DiodeGoneWild]’s presentation; while most 555 tutorials focus on component selection and which pins to connect to what, this one takes the time to tell you why each component makes sense, and how the values affect the final result.

Curious about how the 555 came about? We’ve got the inside scoop on that.

27 thoughts on “Back To Basics With A 555 Deep Dive

  1. 555 pins are labelled wrong – RESET, TRIG, DISCHARGE are active low, need a bar or dot on the pin. I guess it was not the usual in 1972-era schematics.
    Once I did that on my sch symbol, the IC is much easier to understand. Fight the Power! Label the pins better lol.

  2. From the T.I. datasheet: “The LM555 is a highly stable device for generating accurate time delays or oscillation.” That’s a laugh. Most of the specifications are typical only, few guaranteed minimums or maximums.

    The CMOS version (TLC555) is a little better, but it has pathetic drive capability.

    A thoughtful redesign for a drop-in replacement could be so much better.

    1. I’ve never been i in love with the 555; it just never seems to be the”best” way to solve any particular problem, though admittedly it is extremely versatile. But it always seems that theres some sort of deal breaker; power consumption, lack of r2r, or somethong else. Sort of a jack of all trades, but master of none. And with new mcus coming out for pennies… it’s rare that I reach for the 555

      1. “I’ve never been i in love with the 555; it just never seems to be the”best” way to solve any particular problem, though admittedly it is extremely versatile.”


        “But it always seems that theres some sort of deal breaker; power consumption, lack of r2r, or somethong else. Sort of a jack of all trades, but master of none.”

        ” And with new mcus coming out for pennies… it’s rare that I reach for the 555″

        Hm, I don’t know. It’s not just about functionality, but ethics.

        I couldn’t sleep very well if my “solution” to a simple would be an overkill.

        Like, for example, using an 10 GHz hexa core PC running Windows 10 and an application written in Visual Studio 2024 just to blink an LED.

        Instead of just using an traditional blinken light with a bi metal.
        Or an electro mechanical blinker relay.

        Or a blink LED. Or an ordinary LED with an transistor, a cap and some resistors.

        Maybe it’s also a generation thing, not sure.
        I can only say that for me, money and cost cutting isn’t everything.

        I don’t burn books or trow them away.
        Because these things have a meaning to me. It’s about respect, even if it’s an inanimate object.

        Likewise, I hate to throw away food.
        I feelaa bit guilty to throw an unfinished meal away.

        Again, it’s not about money. It just doesn’t feel right.

        Likewise, I value a PIC or Atmel chip.
        I see an highly sophisticated mechanism that’s at work.

        It’s way too precious to be misused.
        Because if I do, so I do degrade human ingenuity.

        Or to you Americans reading this, it’s like wiping your backside with pages of a math book. 😂
        And no, it doesn’t matter if that book had a discount. It’s about the principle. Money isn’t everything.

        1. what i like about mcus is that i can do more things with it. if i replace a 555 pwm dimmer circuit with an mcu, for example, i can implement additional features for free like gamma correction, battery management, custom dimming curves, shutdown timers, etc. all with a smaller BOM, to boot.

  3. Thank you! Beautiful and for me informative. I’ve known these things exist since the 70s(?) but never turned a page to learn about them. Now I will.

    (Is Python the 555 of the present day?)

  4. I’m so tired of the 555. The damn chip has been written about enough already. There’s no reason to use it today: it’s not accurate, it’s not low-power, it’s not small, it’s not cheap, and it’s not simple.

    More importantly, there’s no reason to study it academically, since it’s not particularly fundamental to other modern circuits, like digital logic or op-amps are.

    Instead, it’s a very particular application-specific circuit that was made at a time when nothing better was available. It’s just like the XR2206, or NJM2611 or LM13700 or a host of other curious oddities from a different era. All of these chips deserve a footnote or two in the history books, plus maybe a blog post or so, but little more.

      1. I disagree with Jay Carlson. The NE555 might not be a perfect IC compared to modern stuff, but it is still useful, doesn’t need any firmware (as opposed to microcontrollers, important for repair!), is cheap and just works. Currently in my home they are 3 NE555 regularly used for PWM for lighting applications.

        For your question, it all depends what you want to do. For me the NE555 as i said is still relevant, as it contains several important “pieces”: Voltage divider, comparators, an RS-flipflop, … And it’s simple and very well documented.

        For other IC like the LM358 there is little point studying the detailled internals, EXCEPT if you want to do analog electronics and have enough knowledge to understand the internal schematic of this beast. It is probably better to study a block diagram with stuff like differential input amplifier, output stage, … The 741 is another classic OPA but this one is really old and no longer useful (imho), except for studying OPA limitations.

        Then if you want to go digital the 74HC-series is what you (probably) should look at, like the ‘595 e.g. for adding more outputs to an Arduino or similar.

    1. From a educational point of view, well illustrated in the OPs video, the 555 for me when I was a kid was a great example of a simple to understand Integrated Circuit and also how passive components influence it’s operation.

      Again for me at the time this felt like learning BASIC.

    2. Actually there is one reason to use it today, it is generic and available. In an era where government over-reactions to all manner of semi-crises cause disproportionate disruption to supply chains, supply chains which are already far too vulnerable to disruption by using just-in-time logistics… there are times when a common chip from multiple manufacturers, a chip which will never go “out of fashion”, a chip for which equivalents with the same functionality and pin layout exist, can make sense.

  5. I found the 555 useful at times. With a couple of voltage dividers I made a low voltage disconnect. I needed a 7805 to stabilize the reference voltage, 10 turn pot in the voltage divider to bring the disconnect voltage down the 1/3 the 5 volts reference. Another voltage divider to adjust the reconnect voltage to 2/3 the 5 volt reference. Of course relays for the load. A second circuit was used for the charging.
    All because I could not find a comparator, replaced that with a Arduino Nano and a I2C voltage reader with built in reference, still needed the voltage divider.

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