Computing stuff tied to the physical world

Electric circuits

In Hardware on Dec 5, 2010 at 00:01



Here’s an example I found on the web:





Here’s part of the Infrared Plug, as a circuit diagram:

Screen Shot 2010 12 04 at 23.47.50















  1. Very informative, found these last couple of articles very usefull. The receiver bit on the above diagram, does it only consist of the 2 components i.e. C2 & the TSOP?

    • Yes. Well, C2 is a “decoupling cap” which affects all components (it filters out some noise on the power line). It’s normal to sprinkle a few 0.1µF caps in various places in a circuit to get a better (stable) power supply everywhere.

      The TSOP34838 does the reception and decoding all by itself. It detects an IR signal pulsing at 38 KHz and has all the amplification + filtering built-in. So the receiver side of this sort of IR communication is really extremely simple, in terms of connections and components.

  2. Your posts are always interesting, not boring. I read them each day, your way of describing things is easy to understand , you talk my language, keep up the good work.

  3. I find this ( really useful to get an idea about how circuit work.

  4. Very usefull !!! can you mention what is the difference between different transistors types ? i’ve never sorted this out

  5. Great with some technical background on the circuits. Being a electric engineer it’s nice to see these “simple” analogies you use, making it simple to understand even for the not-so-technical savvy people. Keep up the good work (As suggested by Mike above, a few good topisc for future posts could be to dive into some of the discrete components used in different JeeLab projects)


  6. Also quite a ‘magic’ component, the TSOP34838. I noticed on the IR plugs, when utilising only the receiver (TSOP) and with no infrared source pointing at it, you sometimes gets a brief drop in voltage, enought to set this !ir.digiRead2() function to true. I was wondering if there was a way to add to the circuit to prevent these false readings?

    The thing to note though, when there’s a constant 38khz signal pointing at the TSOP, its as stable as you can’t believe. Even with direct ambient light and distances over 5m.

    • a way to add to the circuit to prevent these false readings?

      I’d try to do this in software: ignore short glitches based on their duration.

      Note also that although the 38 KHz carrier is easily detected, you can’t be sure of where the signal comes from, as might be important in your case of using it for beam interruptions. Any remote will be picked up.

      One idea would be to “modulate” the 38 KHz beam, by pulsing it at 500 Hz, for example, i.e. 1 ms on, 1 ms off. Then the receiver can make better decisions based on whether it really is receiving this particular pulsating signal, and not something else or some glitch.

  7. Wow, thanks! I really didn’t expect these reactions.

    I picked up an understanding of most of this as a teenager, while tinkering with it all – first analog, then digital, then microcontroller-based. There are absolutely tons of marvelous and clever circuits out there, and nowadays all of it can probably be found online.

    I’ll see if I can fold in some more stories about this stuff, without completely turning it into an electronics-only weblog. Because, believe it or not, there are just as many neat tricks and inventions to discover on the software side, and on the mechanical side!

    Another big task ahead: start indexing these 650+ posts, preferably with a brief summary. Long overdue!

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