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  • EEVblog #555 – 555 Timer Kit

    Posted on December 11th, 2013 EEVblog 25 comments


    Dave celebrates the classic 555 timer IC by building the Evil Mad Scientist “three fives” discrete timer kit.
    Some scope measurements and an explanation of the internal 555 timer circuitry follow.
    Video Highlights:
    Construction
    Testing
    Circuit Description
    Waveforms
    Classic old Signetics 555 timer datasheet
    The kit
    Han’s Book on Analog chip design
    Forum HERE

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    • Johm

      Very instructive! Even when you’re ranting while soldering, it’s nice to learn some tips and tricks.

      I’d liked more explanation regarding transistor arrangements and how do they actually work.

      Nice one, Dave.

    • http://telecnatron.com/ Steves

      Thanks Dave, am now waiting for the 741st episode.

    • Andy

      My favourite timer is the elusive MIL spec SE666T timer in a metal can to cope with the heat. It’s a beast!

    • Aaron

      Love it! It’s more exciting to watch you solder than you think! Of course you’ve got the right audience for it. Now, watching someone knit a 555 timer would be excruciating! More soldering please!

    • tchicago

      Great video! However, for me, as well as probably the rest of EE folks from former Soviet Union, this was not the first chip you’d usually get familiar with. The very first was the 7400 (known there as K155LA3, AKA 1LB553) It was very abundant, and it had a lot of amateur applications. There was even a radio receiver build purely on one 7400, where this poor guy was driven into a linear region, exposing a pretty high gain spreading into the RF :)

      The 555 replica became available a lot later, around the late 80′s. It was called K1006VI1 – no way to guess that this is actually the 555 :)

    • N2IXK

      Very good video!

      Another “classic” hobbyist chip that would be cool to do a video on would be the LM3909 LED flasher, which is sadly no longer in production.

    • PK

      Well done on the explanation of the 555 schematic!
      Just an idea, it may be nice to revisit the vintage LM3909 led flasher if you have any in your junk box. I remember building them up and running the flasher for years on alkaline batteries.
      Hmmm, starting to feel my age :-/

      • http://www.eevblog.com EEVblog

        Thanks. I think it’s probably the only explanation of the internal operation out there? I’ve had a look and can’t find any others.

    • PR

      This was great video Dave. For young players, like kids in school or f.e. my young dother are this “kit-building” videos very important. Don’t worry, you are doing a value job with producing videos like this.

    • robert

      if some of the transistors are effectivly diodes, why dosn’t it use diodes?

      • iliketux

        I think the purpose of the kit is to look like the internals of a real 555. And as far as I know the diodes in ICs are mostly built up using these transistor configurations instead of real diodes.

      • http://www.eevblog.com EEVblog

        Because inside the actual 555 (and other chips) a transistor is used in order to get better matching. A regular diode based based current source isn’t nearly as well matched.

        • Bob Weiss

          On the Signetics datasheet, those diode-connected transistors are drawn in an unusual way, with the base lead coming from the same side of the symbol as the other 2. And there is another transistor (Q19) with a second collector lead. Are these actually normal bipolar transistors, or something more exotic?

          • Wim Libaers

            Chip makers can make custom layouts on their semiconductor masks, they’re not limited to standard transistors only. So, yes, they can add multiple collectors or emitters if that simplifies things for them. It’s common, for example take a look at http://en.wikipedia.org/wiki/NAND_gate (there’s a TTL NAND schematic with dual emitter transistor).

    • http://Branchpoint.net Jeff Benshetler

      Dave,
      Watching you do the “triple nickel” kit, I picked up numerous useful pointers.
      First, to solder up a through hole board by component height.
      Second, to avoid gumming the leads/holes with adhesive residue.
      Third, watching your soldering technique.

      I’m well academically educated in EE but that very education has kept me insulated from hands-on aspects. I love watching your blog and picking things up.

      Thank you for taking the time to share what you know so well.

      • http://www.eevblog.com EEVblog

        I’m glad you pick up useful stuff, that always makes me happy :-D

    • http://www.nursebob.org Bob Dunlop

      Very enjoyable, despite your reservations. I did have to chuckle when you started placing the transistors backwards. Thanks for being just as human as the rest of us. :)

      Also, as a rank amatuer hobbyist, your insight about the connecting the collector and base to the same input yeilding the equivalent of a diode, had me down in the garage experimenting. Thanks for sharing your knowledge.

    • jimmc

      Great video, I love the look of that kit.
      My only complaint about the kit is that the circuit diagram has lost the clarity of the original in the datasheet. (Especially around the RS Latch and output stage.)

      Minor point about the video, the R-S latch is formed by Q16/17, (Q16 collector direct to Q17 base, Q17 collector via R11 to Q16 base).
      Q15 is the ‘set’ switch in your diagram.
      It’s so much clearer in the original Signetics datasheet

    • Agent24

      I don’t find these videos boring, I find them interesting, especially the insights scattered through the commentary.

      I already figured out the concept of populating the board from smallest to tallest a while back myself, but your point about black soldermask is not something I had thought of. And I liked your advice about the board house markings.

      And watching someone build something is always nice to see, I don’t know why, it just is.

    • http://www.pauljones.id.au Paul Jones

      I can see you’re in your element here Dave! :) Love the enthusiasm, great explanation. I never did really understand all those analogy things like current mirrors.

    • Robert123897158

      I did not think it was boring at all, I found it informative.

      I’d love to have that kit just sitting on my desk, looks sweet. :)

    • bob theunissen

      Hi Dave,

      lovely thought 555 on episode 555….

      cool thanks good show…

      Bob

    • Worf

      Perhaps the biggest complaint is the tardiness of this video because well, it’s a bit late to either ask for this as a gift, or to get it to give as a gift…

      It is one of the few perfect gifts for an up-and-coming EE.

    • HERB

      Thanks Dave!!

      I ordered a triple nickle kit after watching this video.

      A chip that I have used for years in ham radio receivers is the NE602A. It would be cool if there was a kit that EXACTLY modeled this chip with discrete components, board, etc.

      FYI. The NE602A might only be available in the smt version. We are worried as most homebrewers still like through-the-hole components.

      HERB/WR9H

    • Andrew

      very informative video love your presentation methods.

      Sometimes it feels like electronics are cloaked in jargon just to keep the numbers down as is the maths although I understand the need for it.

      Thanks for lifting the veil Dave well done.

      Best Wishes from the Uk.