LED Quilt Circuits

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Let's light up our quilt squares using the included LEDs (which stands for "Light-Emitting Diode") by making an electrical circuit with them.  Here are some things to note about electrical circuits and LEDs:

  • For this project, you can imagine that a circuit looks a bit like a "ladder", or a "web" of electronic parts.  Using the ladder analogy: the ladder "sides" are made out of one thread each.  The thread on either side will connect along each LED, which you can think of as a "rung" on the ladder.  The way we will be setting up our circuit is to start one side of the ladder on one side — or "pole" — of a power supply (a AA battery, for example, is a type of power supply), then connecting that ladder side across each of the same pole of all the LEDs.  To complete the circuit, we must do the same with a second "side" connecting to the opposite pole of the power supply, and linking across all the opposite poles of all the LEDs.  Another parallel configuration would be to connect each individual LED directly back to the battery, using two strings per LED, but this would likely use up a lot of your string!
  • A circuit set up in this "ladder-like" or "web-like" way, with two (or more) paths traveling from the opposing poles of the battery and across each LED — is called a "parallel" circuit!  Electricity can follow more than one path in this configuration.
  • You might wonder, "isn't there a way to have only one path for electricity to follow in a circuit?".  Yes! That is called a "series" circuit, where the positive pole of the first LED connects to the positive pole of the power supply, and the negative pole of that LED connects to the positive pole of the next LED (and so on, until you connect the negative pole of the last LED in the chain back to the negative pole of the power supply.)  However, you will find that combining the LEDs in series may result only up to two LEDs lighting up (and quite dimly, at that!).  At five volts (which is the output voltage of our power supply), there is just not enough voltage to light any more than two, and the string will essentially stop lighting if you were to add more LEDs.  So in short, you will have the most luck lighting all LEDs by hooking them up in parallel.  The order and actual position of the colors is all up to you, though!
  • LEDs are picky about the way they are wired up: they have a "positive/plus" pole (also called the "anode") and "negative" pole (or the "cathode").  It can be said that LEDs have a particular "polarity".  The reason is because LEDs *only* allow current to flow (and so will only light up) if the positive side of the LED is connected toward the positive side of the power supply, and the negative side of the LED toward the negative side of the power supply.  If your LED is not lighting up, it might be wired in backward! Try connecting it the other way around to see if that fixes it.
  • Extending the idea above: for LEDs wired in parallel, if any one LED in the circuit is wired in backward, it will not light — but all the rest should still glow (assuming there are no other connection problems).  This should make it very easy to spot which LED in the group might not be facing the right direction.
  • Be creative in terms of the layout of your quilt section; but one rule to follow is to have the positive "tail" (that is, where the power supply would connect) of your circuit placed at the the top edge of your quilt piece, and the negative tail placed at the bottom edge.  This will make running power to each piece easy when they are all combined into the final quilt.

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