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  • EEVblog #443 – Mailbag

    Posted on March 25th, 2013 EEVblog 10 comments


    Dave opens his mailbag.

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    • Patrick

      In german the word rectifier translates to “Gleichrichter”.
      Since those selenium rectifiers emit smelly toxic fumes when they fail,
      many service technicians call them “gleich riecht er” which translates to “He’s gonna smell.”

    • elgonzo

      Guys, please, pretty please…, stop propagating this awful myth of QWERTY was being invented to slow typing down.

      The opposite is true and really not that hard to understand. QWERTY was invented to allow fast typing without the types becoming jammed in mechanical typewriters — so, in fact, QWERTY was invented to SPEED UP typing (in English language).

      And since it prevailed over other competing layouts which were being invented in the same time period, one can surly argue that QWERTY did its job reasonably well…

      • elgonzo

        Dave, your Mailbags and other videos are are just great. I just wanted to make clear, that despite my nitpicking above, i really appreciate and love what you do and how you do it. Thanks!

    • maestr0

      Dave, those press-fit pins in TRW module are called “Compliant pins” and yes, they are verry reliabe. Actually are more reliable than soldered ones in over life worst case conditions.

      I could tell more about this module but I won’t – sory classified data ;)

    • chartle

      Funny story I just remembered when I heard the whole Australia not Austria thing.

      In grade school in the early 70’s they put up a world map and you were supposed to put a string pointing to where your family came from. I asked my mom since her parents came over on the boat and were still alive and I heard Australia.

      So I put my string all the way over to to that big island in the Pacific. It was all by itself. Now my teacher was like really? Since almost everyone else’s was in Europe, mostly Germany and Italy.

      Well yes I was wrong and had to move it to that country under Germany where all the other pins where.

      I now understand that my Grandpap’s and Grandma’s accent was NOT Australian but hey this was before Crocodile Dundee and all that “Shrimp on the barbie” stuff. :-)

    • Worf

      Republic of China (ROC) == Taiwan
      People’s Republic of China == China

      @elgonzo: You’re absolutely right. The reason isn’t that typewriters were slow (they were purely mechanical so they moved as fast as your fingers), but that when two letters are beside each other on the type bar (that semicircular ring of type that flies up and hits the paper), if you press both keys, they lifted up and got “stuck” midway through since only one type was supposed to be there. If you space them out on the keyboard, the region where the type will hit is a lot less so the timing has to be a lot tighter in order for it to jam, allowing for faster typing because the user wasn’t clearing the jams as often.

      Additionally, one of the problems with Dvorak is that back in the days, there was a huge lack of objective information – turned out Dvorak was the one running the tests that showed his keyboard layout was superior and faster. Superior it may be, but apparently faster it wasn’t (he conducted the tests for the Navy, so…).

      @maestr0: Yes, those pins are more reliable. The thing is – solder joints crack under vibration, which can lift the pads from the PCB because a solder joint has less mechanical “give” than a press-fit one. So the joint can break or it can be the PCB that gives instead. This is especially important for stuff like connectors which require a lot more mechanical freedom due to thermal expansion, contraction, and different movement from the rest of the unit.

      Selenium rectifier question – do you have to replace a selenium rectifier with another one of the type? Couldn’t you replace it with a more modern silicon diode (or since you need the voltage drop – several in series)?

    • chartle

      @elgonzo

      One side note I had heard that the keys on a touch tone phone were inverted to slow you down.

      They were afraid accountants would hit the numbers too fast and confuse the system.

      • Worf

        False.

        At the time the touch-tone system was invented, people didn’t use calculators, but adding machines. If you look at the adding machine, the keys are arranged as a row of 0s, followed by a row of 1s, 2s, … all the way to the bottom as a row of 9s. (Cash registers were arranged in a similar fashion).

        The phone system of the day (pulse dialing) had the numbers arranged as 1, 2, 3, … 8, 9, 0 around the rotary dial. (Phone phreaks – remember how ‘0’ produces 10 pulses?)

        When they were deploying the touch-tone keypads, they were evaluating how people dialed and found that dialing numbers, people expected the 0 to be near the 9, because it always has been. So the 0 came to be put near the 9 no matter the layout (the common 3×4, or less ocmmon 5×2 or 2×5).

        When calculators were created, they faced a similar issue – and found accountants expected 0 to be near 1 because their old adding machines and cash registers had it laid out that way.

        Typewriters had it going “both ways” depending on the layout (prior to QWERTY). The layout of them tended to favor the phone system as phones became more established and more people used them.

        And look at your PC keyboard. It goes both ways as well! The 0 is next to the 9 on the regular keyboard, while the 0 is next to the 1 on the numeric keypad.

      • elgonzo

        Yupp, Worf pretty much explained it all with the phone number pad.

        Also, think about how much an inverted num pad would you really slow down. Aside from the possibility that in the beginning you might dial the wrong number with normal typing speed, you will probably adapt very fast to the layout and any intended slow-down effect would just not pay off…

    • http://www.geppettoelectronics.com/ Nick

      Wells-Gardner takes me back.

      They made vector CRT monitors for Atari video games back in the late 70s and early 80s. I used to own a Tempest game, and was FOR-EVER replacing the 6 chassis mounted TO-3 transistors in the damn thing.