Beginner Concepts: Analog Circuits

We look at a lot of projects that have microcontrollers in them. That’s because microcontrollers do cool stuff, but there are still plenty of tricks you can pull off with analog circuits. [Osgeld’s] latest project explores this realm, controlling the discharge of capacitors through an LED. His setup uses just nine components and, if you’ve been collecting broken electronics from your friends and neighbors like a good hacker, you can scavenge all of these parts. Try it, you’ll like it!

38 thoughts on “Beginner Concepts: Analog Circuits

  1. Unless you want to learn particle physics you have to learn electrical engineering by abstract functions.

    You don’t need to though unless you want to do computer engineering or something. You can make FPGAs and SBCs just knowing characteristics of passive components. You can get brain fry off particle physics.

  2. @xorpunk

    You are every thing that is wrong with the community .

    Thanks for posting this H.A.D. We need more analog circuit explanation here, and if any of you out there think this can/should be done with a mC, you are missing the point. Designing an elegant solution using cheap components is the essence of Electrical Engineering. This are concepts every hobbyist should be reading up on.

  3. I’m everything that is wrong with this community. I’m an analog computer and POV circuit away from greatness xD

    oh wait I forgot I was doing that stuff in grade school 20 years ago and winning grants..

    lecture someone who wasn’t here before nerd was cool..

  4. That’s the real reason I got interested in electronics, to learn how things work at the lowest level available while still being able to play with at home. I agree this is the real electronics, I started three months ago with microcontrollers and haven’t seen many things I didn’t hear of before at my CS studies, so I jumped right into uC programming with ease, but I have problems understanding anything more complicated than 555-based negative voltage generator.

    MOAR articles like this!

  5. “oh wait I forgot I was doing that stuff in grade school 20 years ago and winning grants..”

    good for you we are all really happy for you, since your so awesome

    I would like to add another 2 cents, this “project” is a result of me walking in the door, noticing that there was a LED contest on instructables, pounding 7 beers and then spending 20 minuets on the bench at like 9pm (and most of that was cleaning off the breadboard)

    so please dont think that this is the greatest achievement of my life, I only posted it cause its dead easy, and can be made by anyone with some junk laying around (which is a good thing for an instructables contest)and it seems to be a semi common question

    If it inspires someone to sit down and fiddle fart at the electronics bench, great! that was the point, at least someone will learn something about some basic electronics, and hopefully will have fun doing so

  6. I really love analog electronics. I actually get kinda annoyed whenever someone uses a microcontroller for something extremely simple that could be done with a few minor analog components. I strongly believe everyone should learn analog before using digital electronics.

  7. “oh wait I forgot I was doing that stuff in grade school 20 years ago and winning grants..”

    Whoopee doo for you; I built my first radio about 30 years ago and I’m still in my mid 30s, I didn’t even use a soldering iron, the kid’s book that had the plans in showed you how to do it by screwing the components onto a piece of softwood with brass screws and caps.

    Not quite valves, but better than a total black box which is all non-discrete circuits ever are. I know which way I’d rather learn and it isn’t by simply taking abstract concepts for granted.

  8. Im trying to get my head around analogue and digital circuits from non microcontroler components so Im glad to see something like this on Hackaday.

    How often have you spent loads of mc resources trying to do something that could be done by a few discrete components.
    When you could have used the mc cycles on the job in hand and had a simple secondary circuit attached to the mc to, for example flash an led or produce a warning sound.

    Sounds like the circuit wasnt perfect but it gets people playing and finding out how it works or how it should work :)


  9. I graduated in Computer engineering but analog circuitry was one thing I never got really taught. The professor that taught Electronics 1 screwed us all over by ONLY showing the theory and none of the practicality of the elements. Could Hack-A-Day do an analog tutorial series over at Answers.H-A-D with a large number of links to projects doing small parts?

    Oh and @osgeld, this wasnt just a link in a roundup because it is really informative to how things can get done without needing many complex pieces.

  10. I am very surprised Osgeld drew the second transistor incorrectly in his schematic. He is so critical of other HAD posts and yet he misses something incredibly simple like this in his own circuit… Maybe from now on he will be less critical of other peoples’ simple mistakes?

  11. in any case if you’re going to insult people at least know what you’re talking about..and don’t be bitter when you find out you’re in over your head ^_^

    I agree Art of Electronics is an awesome reference.

  12. hmmm… surely analog circuits is art for me. I’m still a little bit confused about T2, and well I kinda understand what Jen said. Yes, it could be used as a current source, but I can’t relate that explanation with the one on instructables.
    I just can’t understand how began to discharge C1 if is reverse-biased, maybe just through the reverse leaks?

    Well I’ll say it again, analog circuits is art XD, not that some uC’s projects aren’t art though. I loved the micro mini video player with 8bit avr uC, and even some of those art projects with arduinos.

  13. “This ‘project’ is a result of me walking in the door, noticing that there was a LED contest on instructables, pounding 7 beers and then spending 20 minuets on the bench at like 9pm (and most of that was cleaning off the breadboard).”

    Osgeld, you are my hero. Here, I thought getting drunk and working on electronics was socially unacceptable. You just made it sound cool.

    Thanks for the analog post.

  14. ok lots of catch up to play

    “all i can say is look at that thumbnail! he should stop biting his nails.”

    yes I bite my nails, a lot

    “Doesn’t it work as good without T2?”

    not really, the only path the cap has to discharge without T2 is through the led, which causes it to glow a very long time

    “I am very surprised Osgeld drew the second transistor incorrectly in his schematic.”

    its that way by design so thank you for that

    “T2 bother me as well… shouldn’t that be a PNP?”

    it could be but then I would have to use 2 different types, try it out let us know

    “maybe just through the reverse leaks?”

    we have a winner!

    “Thanks for the analog post.”

    your welcome

  15. The problem, Reizake, is that it’s not reverse-biased, it’s just upside-down. An NPN transistor is intrinsically a symmetric device, even if the doping is highly asymmetric. Putting the “collector” down makes it behave like the emitter, while the “emitter” behaves like the collector.

    There’s some problems with that, though. Due to the highly asymmetric doping, the hFE is going to be a lot smaller in reverse-active mode. For a 2222, it’ll be something like 300 in forward mode, and usually 3 or so in reverse-active. The other problem is that you have to hold the emitter reverse-biased to make this happen. This is fine with a 5V supply, but if you raise it above 7V or so, the transistor will enter EBJ breakdown – and unlike the CBJ, if you break down the EBJ, you start to damage the transistor, lowering its beta over time.

    T2 is held biased in the reverse-active mode by R3, either pulling from the rail when the switch is closed or from the capacitor through R1 when it is open. T2 will then pull reverse-beta times the current in its base from its emitter. If you flip T2 around, the beta becomes a lot higher, and it’ll pull too hard to allow C1 to charge at all.

  16. Thanks for that, I didn’t know that the reverse leaks are big enough to discharge that fast a capacitor. Then, I suppose you choose a transistor for that task because you can control whether helps to charge or discharge the C…

    Hmmm you really could have explained that in the instructables XD.

    Cool little thing btw.

  17. Wow Jen, that’s completely new for me! That’s something I didn’t learn in school for sure.
    Thanks a lot.

    It should be one “Why this works?” category in HaD XD. With those obscure and rarely taught electronics.

  18. This is a good primer project.

    I remember learning this stuff at about 8 years old from one of those 100-something-in-one electronic lab kits, and this is a great little excerpt from the past.

  19. Careful with selection of T2. Some transistors work like oscillators when collector and emitter are mixed up. In reverse active mode hfe is usually 10 to 12 times lower and Vcesat could be as low as 50mV.

    Happy hacking analog.

  20. For anyone who’s still in school and is interested in what Jen is talking about, take a class related to the principles of semiconductors, and how they work. It’s a difficult (but awesome) subject, with a good prof you will probably learn more useful information in that class than you will in almost any other class. I would also recommend taking a VLSI class if you have the chance!

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