Wednesday, January 13, 2010

Chapter 2 - Post Exercise 7 Contest Submissions Here


Please post your contest submissions as comments in this post, thanks.

And don't worry - there will be more contests... I've got a few more Maker's Notebooks from the MakerSHED folks to give away over time.


  1. The circuit is closed through the bottom "tongue" of the relay. It starts at +12VDC, goes up and hangs a right, hops under the LED lead, goes thru the relay, coming out the bottom lead.
    Then it goes thru that LED lead it ducked under before, hangs a right, and exits thru the 680 Ohm resistor, to the blue "negative" circle.

    (I'm kinda new at this too, so forgive my terminology ... but that maker notebook looks much better now that you've flipped thru it for us!)

  2. The drawing in figure 2-59 does a better job of showing the closed circuit, but you can see it fairly easily in the schematic, too. Ignore the button for a second and notice that the positive voltage also goes up to the middle contact of the relay. You can then see, even in the schematic, that the relay's default state connects the positive voltage to the bottom relay pin (bottom o the top three, I should say), which is in turn connected to one of the LEDs (the red one in your example). The other side of the LED is connected to the 680 ohm resistor that is connected to ground. Thus, a complete closed loop is created. I recommend tracing it with your finger to help see it.

  3. I'm tempted to post an animated GIF or something showing the flow. If I knew how to make an animated GIF, that is...

  4. I believe the reason this schematic is confusing (and many other schematics are) is because it is easy to forget the following bit of knowledge on page 52 of the book (1st edition): "... when you build a circuit, all the wires leading to grounds must actually be connected together, to the negative side of the voltage supply."

    I think what he's saying here is that even though the (+) and (-) signs are on opposite sides of a schematic and don't look connected.. in reality, they are the ends of a battery/power supply. This is where the closedness comes from.

    Furthmore.. the gray box of the push button has two states: open and closed.. When closed, it turns on the magnet inside the relay. When open, the magnet inside the relay is off (has no power to create the attraction necessary.. etc etc).

    1. My apologies, maybe I misunderstood your question. Current runs from the (+), to the relay (the triangle pointing upward in the gray box is actually touching that middle straight line that has a negative slope, even though it is not drawn touching). From there the current travels to the left LED, then to the resistor, then to the (-). If the button is pressed, then the relay's magnet is activated and that middle line in the relay will be pushed upward, touching the downward facing triangle and switching the current to the right LED.

      Thanks for making the blog and getting me interested in completing this book! It's a lot of fun coming on here and comparing notes.