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Help creating a series of 2 LEDs

  1. Oct 6, 2013 #1
    Hi, electrical engineering has always interested me and recently I have been trying to trying pick it up as a hobby by doing simple soldering exercises. While everything has gone smooth so far, I have hit a snag with the current little project I have been working on.

    So my goal is to light 2 LED lights (which I believe is 1.9-2V @20mA) using a battery pack that contains 4 AA batteries (should be 6V) and a 100 ohm resistor. The tricky part for me is that I want to be able to switch these lights on and off using one 5A 125VAC SPDT switch (toggle).

    I've tried many LED series calculators to try and find the right configuration and just when I thought I did something went wrong. What I had was, the 2 lights soldered together by wire in which one end had the positive leg and the other negative (is that always called ground?). The positive side continues to the resistor, and this is where I had to improvise. The toggle has 3 prongs, and I believe the two on the outside corresponds to the binary position of the toggle, so I connected the resistor to one of the ones on the outside. I then soldered he middle prong with the positive wire coming out of the battery pack with the 4 batteries. The prong furthest from the first that is connected to the resistor, received the negative wire coming from the battery pack as well as the negative end of the LEDs legs.

    When I flipped the switch the lights finally glowed with much trial and error, but I did not celebrate for long because after 10 seconds I saw the pack containing the batteries begin to smoke, so I cut the power. So that leads me here. I know exactly what it means when an LED glows brilliantly then suddenly fizzles out, however I did not foresee the batteries smoking.

    If you all have any idea why that would be or what I should do to correct my project, I would really appreciate it! I apologize for what is probably a very simple problem, I would just love to learn from this experience and continue perusing this amazing craft. Thank you so much!
  2. jcsd
  3. Oct 6, 2013 #2


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    Science Advisor

    Your switch has 3 terminals, but you only need the center one and one of the outside ones. Leave the other terminal alone.

    If you don't already have a multimeter, now might be a good time to get one.
    You can get a digital multimeter for around $10 and it will save you having to guess a lot of the time.
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