Step 2: Testing LEDs from a string of Christmas Tree lights

Looking at the LEGO base-plate, it became obvious to me that one of the lights just needed to have an advance turn indicator. So for this project, a total of 10-LEDs will be needed:
  • 4-green
  • 3-yellow
  • 3-red
All the LEDs in this project are T-1 size, which is 3mm in diameter that fit perfectly in the round hole of a head light brick. I happened to have a broken string of LED Christmas Tree lights in which only half the string lit. This became a perfect supply of very bright LEDs.

You can opt to purchase LEDs if you wish. You'll want LEDs that are rated at 20,000mcd (millicandela). That's bright enough to see them in sunlight. If you buy LEDs or have some on hand, you can skip straight ahead to step 7.

This, up to step 6, are all about extracting an LED from an individual Christmas tree bulb.

First cut an LED from the string of lights, strip the ends of the wire with a #14AWG (American Wire Gauge) wire-stripper and test the LED. Do this for each LED. You don't want to bother breaking into a light only to find out later it was burnt out. LEDs last a long time, but they can burn out.

I like to fiddle with electronic circuits from time to time, so long ago I built myself a dual-voltage, dual-polarity power supply and incorporated some other features into it, such as some fixed rate frequencies, a variable-rate frequency generator, and an LED tester. That's what you're looking at in the image.

The LED tester is simply nothing more than a 1KΩ (kilo-ohm) resistor connected to the +5-volt portion of the power supply. The LED is then connected to the other end of the resistor resistor and the ground of the power supply.

You can make your own LED tester from a 9V battery and a 1KΩ resistor. Tape one lead of the resistor to the positive (+) terminal of the battery. Then briefly touch one lead of the LED to the other lead of the resistor and touch the second lead of the LED to the ground (-) terminal of the battery.

LEDs light in only one direction. If it doesn't light, swap the leads around and try again. If it still doesn't light, toss it out and try another LED.
We are REALLY enjoying this instructable!! We are having one issue. We can't get the yellow LEDs to run on the program. We have checked everything back to the Adruino board and everything works (all lights will light up when we check from the board to the LEDs). Would it be possible for you to check the code again to see if there is anything in there that might be keeping the yellow LEDs from working? It is all we can think of. Thanks!
Thank you all for the compliments.<br><br>I've just uploaded the cross-intersection code in step 25, for anyone considering building that type of intersection.
Hello, thanks for this awesome instructable. My son and I are trying to build the cross intersection. We are trying to understand the wiring to the micro-controller. I am trying to understand your wiring diagram. I don't have all the headers and would like to know what wires I could solder together prior to the micro controller. I have 2 2x16 female headers, 2 1x4 male headers and 2 1x5 male headers. thanks!
the dumpster was a great idea
Hi..<br><br>It's possible do this, with an arduino Duemilanove?<br><br>Can i put the led's togeher with a wire?<br><br>Thanks,<br>Pedro Peregrina
in my micro-controller class we had to make a 4 way intersection with the main traffic lights, turn lane lights and a push button for walking. if you felt froggy you could toss in the other 2 parts. ours was based off how Phoenix Az had their system back in the day it has since changed alot due to more roads and all that.
nice job! <br>one thing you could do to hide those wires on the back is take a 1x4 smooth piece like you have on the top and glue it on the back
Great minds think alike! I was planning to do exactly that. I'm just currently out of yellow and grey tiles. It would be the only part of the build that is not authentic LEGO construction, but it would definitely finish it off.
it is a wonderful world of lego
Nice, the video is cute!
Just another 10 months until Christmas! This will go under the tree with my trains!
That is so awesome!
If this was only about ten years ago I would be bouncing off the walls right now. Great ideal and Instructable.
Now THAT is a great first Instructable!!!<br><br>Be welcome!

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